Microbiology Sem -V Paper-5, Unit-1 - PowerPoint Presentation

1. Microbiology Sem-VPaper-5, Unit-1Microbial BioDiversityDr. Rita MahapatraAssistant ProfessorNeotech College of applied Science and Research, Virod, Vadodara

2. Microbial biodiversity is defined as the variability among microorganisms. Microbial biodiversity is all about how different kinds of microorganisms arose and why ; how exactly are microorganisms either similar to or different from each other; and evolution of microbial cells, The diversity of microorganisms we see today is the result of nearly 4 billion years of evolution. Microbial diversity can be seen in many ways besides phylogeny, including cell size and morphology (shape), physiology, motility, mechanism of cell division, pathogenicity, developmental biology, adaptation to environmental extremes and so on. With the laws of chemistry and physics. This enormous metabolic versatility has allowed prokaryotes to thrive in every potential habitat on Earth suitable for life.The diversity is measured by various perspective such as Morphology, structural, metabolic, ecology , behavioral and evolution.1: What is Microbial Biodiversity?

3. 1.1: Morphological diversityIndividual cells of whatever shape can be found in a variety of multicellular arrangements, from simple pairs and tetrads to multicellular filaments, sheets, rosettes, and true multicellular organisms. Many species form highly structured multispecies mats that resemble the tissues of animals and plants that carry out complex biochemical transformationsMost bacteria and archaea measure 1 to 5 μm, but they range from 0.1 μm in thickness to over a millimeter. At the low end, it is hard to understand how everything that is needed for life could fit into the cell. At the high end, they can be easily seen without a microscope.Microbes are often divided by shape into rods, cocci, and spirals (fig-1). Although these are the most common cell shapes, bacterial and archaeal cells also come in a wide range of other shapes: filaments (branched or unbranched), irregular, pleomorphic (different shapes under different conditions or even in the same culture), star-shaped, stalked, and many, many others. i.e Haloquadratum is a flat, square organism.Figure. 1: Categories of bacteria based on the shape of their cells.

4. 1.2: Structural diversityMany bacteria have “typical” gram-positive (single membrane, thick cell wall) or gram-negative (double embrane, thin cell wall) cell envelopes. However, there is wide variation even within these two major types. Many gram-positive bacteria have an outer membrane, made of mycolic acids rather than glycerol-phosphate esters. Many gram-negative bacteria lack the lipopolysaccharide layer. Many archaea and bacteria (both gram positive and gram negative) have an orderly protein coat, the S-layer .In bacteria, cell walls are composed of peptidoglycan, but there is a surprising range of chemical variations within this type of material. Archaea do not have peptidoglycan cell walls, although some archaeal cell walls contain a related material, pseudomurein.Microbes have a wide range of external structures: flagella, pili, fibrils, holdfasts, stalks, buds, capsules, sheaths, and so on.They also have a wide variety of internal structures such as spores, daughter cells, thylakoids, mesosomes, and the nucleoid.In reality, microbial cells are just as structurally organized, and diverse, as are eukaryotic cells.

5. 1.3: Metabolic diversityAll cells require an energy source and a metabolic strategy for conserving energy from it to drive energy-consuming life processes. As far as is known, energy can be tapped from three sources in nature: organic chemicals, inorganic chemicals and light.Organisms that conserve energy from chemicals are called chemotrophs, and those that use organic chemicals are called chemoorganotrophs.Energy is conserved from the oxidation of the compound and is stored in the cell in the energy-rich bonds of the compound adenosine triphosphate (ATP).Some microorganisms can obtain energy from an organic compound only in the presence of oxygen; these organisms are called aerobes. Others can obtain energy only in the absence of oxygen are called anaerobes.Macroscopic eukaryotes are not metabolically diverse; they are either chemoheterotrophic (e.g., animals) or photoautotrophic (e.g., plants). Bacteria and archaea have a much broader range of energy and carbon sources, which can be generally divided into four broad types, chemoheterotrophs, chemoautotrophs, photoheterotrophs, and photoautotrophs.

6. 1.3: Cont.Chemoheterotrophs obtain both carbon and energy from organic compounds. Some organisms can use a wide range of organic compounds and can either oxidize or ferment them. Others can use only a very narrow range of organic compounds and process them in a specific way. Saprophytes and pathogenic microbes are examples of this group.Chemoautotrophs obtain cell carbon by fixing CO2. Energy is obtained from inorganic chemical reactions such as the oxidation or reduction of sulfur or nitrogen compounds, iron, hydrogen, etc. These organisms do not need organic compounds for either energy or cell carbon. Sulfur-oxidizing bacteria and methane-producing archaea are examples of this group.Photoheterotrophs obtain cell carbon from organic compounds, but energy is harvested from light. Halophilic archaea and most purple photosynthetic bacteria are examples of this group. Photoautotrophs (photosynthetic) obtain cell carbon by fixing CO2. Energy is obtained from light. These organisms do not need organic compounds for either energy or cell carbon. Most cyanobacteria and some purple photosynthetic bacteria are examples of this group.

7. 1.4: Ecological diversityMicrobes live in an amazing range of habitats, from laboratory distilled-water carboys, through freshwater and marine environments, to saturated brines like the Great Salt Lake or the Dead Sea. They grow at temperatures of −5°C to over 118°C; Pyrodictium cultures are sometimes incubated in autoclaves! Organisms are known to grow at pH 0 (0.5 M sulfuric acid) and at pH 11 (Drano). Very often, these extremes are combined: Acidianus grows in 0.1 M sulfuric acid at 80°C! Some bacteria live in the water droplets that make up the clouds, and others live in deep-underground aquifers or deep-sea sediments. Many microbes live in intimate symbiosis with other creatures, in complex communities, or as permanent intracellular “guests.” In fact, if you are on or around Earth and find liquid water, there is almost certainly something living in it.

8. 1.5: Behavioral diversityIt may seem odd to consider the behavior of microscopic organisms, but they do have behavior.Motility and taxis are one form of behavior, both of which come in a variety of forms, from the phototactic Chlorobium bacteria that use gas vacuoles and symbiosis with motile bacteria to adjust their place in the water column. to the chemotactic Rhizobium bacteria that sense and swim (via flagella) toward chemical signals sent by receptive plant roots.Magnetotactic bacteria have a built-in magnetic compass that allows them to use Earth’s magnetic field for orientation.All organisms have developmental cycles; at the very least they can switch between active-growth (i.e., log phase) to resting or slow-growth (i.e., stationary phase) stages. Other developmental cycles include sporulation; the production of swarmer cells, cysts, or akinetes; and even terminal differentiation and development into distinct germ and somatic cell types, such as heterocysts in filaments of cyanobacteria, “slugs” in myxobacteria, and the very complex life cycles of Streptomyces species.

9. 1.5: Cont.Microbes also respond to their environments metabolically, by expressing the genes needed to compete for the resources available at the time. An example of this would be converting metabolism from oxidative to fermentative when oxygen is exhausted in a culture or from glucose to galactose use when the glucose is used up in a mixed-sugar medium.In addition, microbes act communally. Organisms communicate by sending and receiving chemical signals or by direct contact. For example, Myxococcus, swarming begins with a chemical signal propagated through the community, which brings the cells into proximity. Direct contact between cells then directs aggregation and formation of fruiting bodies. Microbes also form specific symbioses with other microbes or with macroscopic creatures. Complex communities of microbes associate into “mats” that process and recycle resources throughout the community.

10. 1.6: Evolutionary diversityUnderlying all of these different aspects of diversity is genetic diversity, perhaps more specifically viewed as evolutionary diversity. Microbes are far more evolutionarily diverse than are macroscopic creatures; Even most plants and animals are microscopic! So microbial diversity is actually the same as biological diversity, with just a few of the more macro organisms overlooked.Evolutionary diversity is usually expressed in terms of trees: branched graphs that trace the genealogies of organisms. When these trees are based on genetic diversity (gene sequences), they can be both quantitative and objective.

11. 2: Origin of life, Evolution and origin of biodiversityEarth is thought to have formed about 4.5 billion years ago, based on analyses of slowly decaying radioactive isotopes. Earth cooled much earlier than previously believed, with solid crust forming and water condensing into oceans perhaps as early as 4.3 billion years ago. The presence of liquid water implies that conditions could have been compatible with life within a couple of hundred million years after Earth was formed.Fossilized remains of procaryotic cells around 3.5 to 3.8 billion years old have been discovered in stromatolites (microbialmats consisting of layers of filamentous prokaryotes and trapped mineral materials) and sedimentary rocks.Microfossil evidence strongly suggests that microbial life was present within at least 1 billion years of the formation of Earth and probably somewhat earlier, and by that time, microorganisms had already attained an impressive diversity of morphological forms.

12. One hypothesis for the origin of life holds that the first membrane- enclosed, self-replicating cells arose out of a primordial soup rich in organic and inorganic compounds in a “warm little pond,” as Charles Darwin suggested in On the Origin of Species— in other words, life arose on Earth’s surface. Although there is experimental evidence that organic precursors to living cells can form spontaneously under certain conditions, surface conditions on early Earth are thought to have been hostile to both life and its inorganic and organic precursors. The dramatic temperature fluctuations and mixing resulting from meteor impacts, dust clouds, and storms, along with intense ultraviolet radiation, make a surface origin for life unlikely.2.1: Surface Origin Hypothesis

13. A more likely hypothesis is that life originated at hydrothermal springs on the ocean floor, well below Earth’s surface, where conditions would have been much less hostile and much more stable.A steady and abundant supply of energy in the form of reduced inorganic compounds, for example, hydrogen (H2) and hydrogen sulfide (H2S), would have been available at these spring sites.When the very warm (90–100°C) hydrothermal water flowed up through the crust and mixed with cooler, iron-containing and more oxidized oceanic waters, precipitates of colloidal pyrite (FeS), silicates, carbonates, and magnesium-containing montmorillonite clays formed. These precipitates built up into structured mounds with gel-like adsorptive surfaces, semipermeable enclosures, and pores. Serpentinization, the abiotic process by which Fe/Mg silicates (serpentines) react with other minerals and H2, was a likely source of the first organic compounds, such as hydrocarbons and fatty acids. These could then have reacted with iron and nickel sulfide minerals to eventually form amino acids, simple peptides, sugars, and nitrogenous bases. 2.2: Subsurface Origin Hypothesis

14. 2.2: cont.With phosphate from seawater, nucleotides such as AMP and ATP could have been formed and polymerized into RNA by montmorillonite clay, a material known to catalyze such reactions.The flow of H2 and H2S from the crust provided steady sources of electrons for this prebiotic chemistry, and the process was perhaps powered by redox and pH gradients developed across semipermeable FeS membrane-like surfaces, providing a prebiotic proton motive force.An important point to keep in mind here is that before life appeared on Earth, organic precursors of life would not have been consumed by organisms, as they would be today. So the possibility that millions of years ago organic matter accumulated to levels where self-replicating entities emerged, is not an unreasonable hypothesis (fig-2) .

15. Fig. 2: Submarine mounds and their possible link to the origin of life. Model of the interior of a hydrothermal mound with hypothesized transitions from prebiotic chemistry to cellular life depicted. Key milestones are self-replicating RNA, enzymatic ctivity of proteins, and DNA taking on a genetic coding function, leading to early cellular life. This was followed by diversification of molecular biology and biochemistry, eventually giving rise to early Bacteria and archaea. LUCA, last universal common ancestor. Inset: photo of an actual hydrothermal mound. Hot mineral-rich hydrothermal fluid mixes with cooler, more oxidized, ocean water, forming recipitates. The mound is composed of precipitates of Fe and S compounds, clays, silicates, and carbonates.

16. Another important step in the emergence of cellular life was the synthesis of phospholipid membrane vesicles that could enclose the evolving biochemical and replication machinery. Proteins embedded in the lipids would have made the vesicles semipermeable and thus able to shuttle nutrients and wastes across the membrane, setting the stage for the evolution of energy-conserving processes and ATP synthesis. By entrapping RNA and DNA, these lipoprotein vesicles, which may have been similar to montmorillonite clay vesicles that can be synthesized in the laboratory, may have enclosed the first self-replicating entities, partitioning the biochemical machinery in a unit not unlike the cells we know today.From this population of structurally very simple early cells, referred to as the last universal common ancestor (LUCA), cellular life began to evolve in two distinct directions, possibly in response to physiochemical differences in their most successful niches (Fig.-2).2.3: Lipid Membranes and Cellular Life

17. 2.4: An RNA World and Protein SynthesisLife may have first arisen at submerged hydrothermal springs, and the first self-replicating life forms may have been RNAs.Eventually, DNA evolved and the DNA plus RNA plus protein model for cellular life was fixed.Early microbial metabolism was anaerobic and likely chemolithotrophic, exploiting abundant abiotic sources of H2, FeS, and H2S. The earliest carbon metabolism may have been autotrophic.Early Bacteria and Archaea diverged from a common ancestor as long as 4 billion years ago. Microbial metabolism diversified on early Earth with the evolution of methanogenesis and anoxygenic photosynthesis (fig. 3). Oxygenic photosynthesis eventually led to anoxic Earth, banded iron formations, and great bursts in metabolic and cellular evolution.

18. Fig. 3: Major landmarks in biological evolution, Earth’s changing geochemistry, and microbial metabolic diversification. The maximum time for the origin of life is fixed by the time of the origin of Earth, and the minimum time for the origin of oxygenic photosynthesis is fixed by the Great Oxidation Event, about 2.4 billion years ago (BYA). Note how the oxygenation of the atmosphere from cyanobacterial metabolism was a gradual process, occurring over a period of about 2 billion years. Bacteria respiring at low O2 levels likely dominated Earth for a billion years or so before Earth’s atmosphere reached current levels of oxygen.2.5: Early Metabolism

19. Over time, organic materials would have accumulated and could have provided the environment needed for the appearance of new chemoorganotrophic bacteria with diverse metabolic strategies to conserve energy from organic compounds. Suggested that the first oxygen-utilizing prokaryotes were Amphiaerobic, that is, they retained the ability to live anaerobically although they had acquired the ability to metabolize aerobically (Present-day amphiaerobes are called facultative organisms). From them, according to Schopf et al. (1983), obligate aerobes evolved more than 2 billion years ago.With the appearance of oxygen-producing cyanobacteria and aerobic heterotrophs, the stage wasset for extensive cellular compartmentalization of such vital processes as photosynthesis and respiration.New types of photosynthetic cells evolved, where photosynthesis was carried on in specialCont.

20. Cont. Organelles, the chloroplasts, and new types of respiring cells evolved in which respiration was carried on in other special organelles, the mitochondria. it is now generally accepted that these organelles arose by endosymbiosis (see next slide).The accumulation of oxygen in the atmosphere led to the buildup of an ozone (O3) shield thatscreened out UV components of sunlight. The ozone results from the action of short-wavelengthUV on O2: 3O2 → 2O3 The ozone screen would have stopped any abiotic synthesis dependent on UV irradiation and at the same time would have allowed the emergence of life forms onto land surfaces of the Earth, where they were directly exposed to sunlight. This emergence would have been impossible earlier because of the lethality of UV radiation (Schopf et al., 1983).

21. Up to about 2 billion years ago, all cells apparently lacked a membrane- enclosed nucleus and organelles, the key characteristics of eukaryotic cells (domain Eukarya). Here we consider the origin of the Eukarya and show how eukaryotes are genetic chimeras containing genes from at least two different phylogenetic domains. The eukaryotic cell developed from endosymbiotic events. In the most likely scenario, a H2-producing species of Bacteria was incorporated as an endosymbiont into a H2-consuming species of Archaea (the host). The modern eukaryotic cell is a chimera with genes and characteristics from both Bacteria and Archaea (Fig. 4).A well-supported explanation for the origin of the eukaryotic cell is the endosymbiotic hypothesis. The hypothesis says that the mitochondria of modern-day eukaryotes arose from the stable incorporation of a respiring bacterium into other cells, and that chloroplasts similarly arose from the incorporation of a cyanobacterium-like organism that carried out oxygenic photosynthesis.2.6: Endosymbiotic Origin of Eukaryotes

22. Oxygen was almost certainly a driving force in endosymbiosis through its consumption in energy metabolism by the ancestor of the mitochondrion and its production in photosynthesis by the ancestor of the chloroplast. The greater amounts of energy released by aerobic respiration undoubtedly contributed to rapid evolution of eukaryotes, as did the ability to exploit sunlight for energy.The overall physiology and metabolism of mitochondria and chloroplasts and the sequence and structures of their genomes support the endosymbiosis hypothesis. For example, both mitochondria and chloroplasts contain ribosomes of prokaryotic size (70S) and have 16S ribosomal RNA gene sequences characteristic of certain Bacteria. Mitochondria and chloroplasts also contain small amounts of DNA arranged in a covalently closed, circular form, typical of Bacteria.Indeed, these and many other revealing signs of Bacteria are present in organelles from modern eukaryotic cells. Moreover, the same antibiotics that inhibit ribosome function in free-living Bacteria inhibit ribosome function in these organelles. It took about 2 billion years to the present for the rise and diversification of unicellular eukaryotic microorganisms, the origin of multicellularity, and the appearance of structurally complex plant, animal, and fungal life.2.6: cont.

23. Figure. 4: Endosymbiotic models for the origin of the eukaryotic cell. (a) The nucleated line divergedfrom the archaeal line and later acquired by endosymbiosis the bacterial ancestor of the mitochondrionand then the cyanobacterial ancestor of the chloroplast, at which point the nucleated line diverged intothe lineages giving rise to plants and animals. (b) The hydrogen hypothesis. The bacterial ancestor of themitochondrion was taken up endosymbiotically by a species of Archaea and the nucleus developed later followed by the endosymbiotic acquisition of the cyanobacterial ancestor of the chloroplast.

24. 3: Microbial EvolutionEvolution, the process by which organisms undergo descent with modification, is driven by mutation and selection. In this Darwinian view of life, all organisms are related through descent from an ancestor that lived in the past. Since the time of LUCA (last universal common ancestor), life has undergone an extensive process of change as new kinds of organisms arose from other kinds existing in the past. Evolution has also led to the loss of life forms, with organisms due to survival of the fittest i.e those organisms are less able to compete becoming extinct over time.The modern organisms evolved by evolution under the pressure of natural selection and are well adapted to their ecological niches.

25. 3.1: Genomic ChangesEvolution of cells with RNA genome than modern cells with DNA genome (fig. 5).DNA sequence variation can arise in the genome of an organism from mutations including the loss or gain of whole genes. Mutations, which arise from errors in replication and from certain external factors such as ultraviolet radiation, are essential for life to evolve through natural selection. Adaptive mutations are those that improve the fitness of an organism.Genetic mutation such as; Gene duplication, gene deletion and horizontal gene transfer lead to microbial evolution.Figure. 5: Summary of evolution

26. 3.2: Selection and the Rapidityof Evolution in ProkaryotesAs environmental changes create new habitats, cells are presented with new conditions under which they may either survive and successfully compete for nutrients or become extinct. The heritable variation present in a population of cells provides the raw material for natural selection.Natural selection probably resulted in rapid diversificationModern DNA has enzymes that reduce the rate of mutationsRNA is more likely to have copying errors Higher mutation rate in early evolution than now

27. 3.3: Evolutionary tree of microorganismsThe evolutionary history of a group of organisms is called its phylogeny, and a major goal of evolutionary analysis is to understand phylogenetic relationships.Phylogenetic Trees- Reconstructing evolutionary history from observed nucleotide sequence differences includes construction of a phylogenetictree, which is a graphic depiction of the relationships among sequences of the organisms under study, much like a family tree.A phylogenetic tree is composed of nodes and branches (fig. 6).The tips of the branches represent species that exist now and from which the sequence data were obtained. The nodes are points in evolution where an ancestor diverged into two new organisms, each of which then began to evolve along its separate pathway. The branches define both the order of descent and the ancestry of the nodes, whereas the branch length represents the number of changes that have occurred along that branch.

28. Figure. 6: : Phylogenetic trees. Unrooted (a) and rooted (b, c) forms of a phylogenetic tree are shown. The tips of the branches are species (or strains) and the nodes are ancestors. Ancestral relationships are revealed by the branching order in rooted trees.In its most basic form, a phylogenetic tree is a depiction of lines of descent, and the relationship between two organisms. therefore should be read in terms of common ancestry. That is, the more recently two species shared a common ancestor, the more closely related they are. The rooted trees in Fig.- 6 b and c illustrate this point. Species 2 is more closely related to species 3 than it is to species 1 because 2 and 3 share a more recent common ancestor than do 2 and 1.3.3: cont.

29. 3.4: Tree ConstructionModern evolutionary analysis uses character-state methods, also called cladistics, for tree construction. Character-state methods define phylogenetic relationships by examining changes in nucleotides at particular positions in the sequence, using those characters that are phylogenetically informative. 16S ribosomal RNA (16S rRNA), a molecule used for phylogenetic analyses, has both highly conserved and highly variable regions, primers specific for the 16S rRNA gene from various taxonomic groups can be synthesized. These may be used to survey different groups of organisms in any specific habitat. This technique is in widespread use in microbial ecology and has revealed the enormous diversity of the microbial world The characters that define a monophyletic group; that is, a group that has descended from one ancestor (fig. 8) describes how phylogenetically informative characters are recognized in aligned sequences. Computer-based analysis of these changes generates a phylogenetic tree, or cladogram.A widely used cladistic method is parsimony, which is based on the assumption that evolution is most likely to have proceeded by the path requiring fewest changes.

30. 3.4: Cont.Computer algorithms based on parsimony provide a way of identifying the tree with the smallest number of character changes.Other methods, maximum likelihood and Bayesian analysis, proceed ike parsimony, but they differ by assuming a model of evolution, for example, that certain kinds of nucleotide changes occur more often than others. Inexpensive computer applications, such as PAUP (Phylogenetic Analysis Under Parsimony, and Other Methods), guidebooks, and web-accessible tutorials are available for learning the basic procedures of cladistic analysis and tree construction.Biologists previously grouped living organisms into five kingdoms: plants, animals, fungi, protists, and bacteria (fig. 7).DNA sequence-based phylogenetic analysis, on the other hand, has revealed that the five kingdoms do not represent five primary evolutionary lines. Life on Earth has evolved along three primary lineages, called domains. Two of these domains, the Bacteria and the Archaea, are exclusively composed of prokaryotic cells. The Eukarya contains the eukaryotes including the plants, animals, fungi, and protists (Table. 1).

31. Figure 7: The five-kingdom classification by Whittaker ( Whittaker RH, Science 163:150–160, 1969. doi:10.1128/9781555818517.ch2.

32. Figure. 8: Universal phylogenetic tree as determined from comparative SSU rRNA genesequence analysis. Only a few key organisms or lineages are shown in each domain. At least 80 lineages of Bacteria have now been identified although many of these have not yet been cultured. LUCA, last universal common ancestor.

33. Table 1: Major characteristics of Bacteria, Archaea, and Eukarya

34. 4.: Value of microbial biodiversityMicrobial activity and diversity are both a part of and inseparable from pond ecosystem function, and that concepts such as redundancy of microbial species and the 'value' of conserving biodiversity at the microbial level have little meaning. Carbon fixation and nutrient cycling appeared to be regulated by 'complex reciprocal' physical, chemical and microbial interactions.Molecular methods have changed the way we classify and examine microorganisms in their ecosystems and the way we screen for novel products and processes. The molecular perspective gives us more than just a glimpse of the evolutionary past; it also brings a new future to the discipline of microbial ecology. Since the molecular-phylogenetic identifications are based on sequences, as opposed to metabolic properties, microbes can be identified without being cultivated. Consequently, all the sequence-based techniques of molecular biology can be applied to the study of natural microbial ecosystems.

35. The biotechnology and industrial microbiology potential for new products and processes from examining microbial diversity at both the molecular and organism functional level will increase as more knowledge is deciphered from sequences to assess targets and function.In recent years, with the need for additional compounds for use in medicine, marine microorganisms are receiving increased attention.Some of the newer chemicals that have been discovered are microalgal metabolites. There also is an interest in the culture of symbiotic marine microorganisms, including Prochloron, which are associated with macroscopic hosts.The term “microbial ecology” is now used in a general way to describe the presence and contributions of microorganisms, through their activities, to the places where they are found.Thomas D. Brock, the discoverer of Thermus aquaticus, which is known the world over as the source of Taq polymerase for the polymerase chain reaction (PCR), has given a definition of microbial ecology that may be useful: “Microbial ecology is the study of the behavior and activities of microorganisms in their natural environments.4. : Cont.

36. 4.: Cont.“The important operator in this sentence is their environment instead of the environment. To emphasize this point, Brock has noted that “microbes are small; their environments also are small.” In these small environments or “microenvironments,” other kinds of microorganisms (and macroorganisms) often also are present, a critical point that was emphasized by Sergei Winogradsky in 1947.Environmental microbiology, in comparison, relates primarily to all-over microbial processes that occur in a soil, water, or food, as examples. It is not concerned with the particular “microenvironment” where the microorganisms actually are functioning, but with the broader-scale effects of microbial presence and activities. One can study these microbial mediated processes and their possible global impacts at the scale of “environmental microbiology” without knowing about the specific microenvironment (and the organisms functioning there) where these processes actually take place.

37. 4.: Cont.However, it is critical to be aware that microbes function in their localized environments and affect ecosystems at greater scales, including causing global-level effects. Microbial diversity in natural environments is extensive. Methods for studying diversity vary and diversity can be studied at different levels, i.e. at global, community and population levels. These methods characterize the microbial processes and thereby can be used to reach a better understanding of microbial diversity. In future, these techniques can be used to quantitatively analyze microbial diversity and expand our understanding of their ecological processes. Microorganisms, in the course of their growth and metabolism, interact with each other in the cycling of nutrients, including carbon,Sulfur, nitrogen, phosphorus, iron, and manganese. This nutrient cycling, called biogeochemical cycling when applied to the environment, involves both biological and chemical processes.

38. 4.2: Microbial biodiversity as index of environmental changeMicroorganisms affect climate change. Methanogens produce methane in natural and artificial anaerobic environments (sediments, water- saturated soils such as rice paddies, gastrointestinal tracts of animals (particularly ruminants), wastewater facilities and biogas facilities), in addition to the anthropogenic methane production associated with fossil fuels. The main sinks for CH4 are atmospheric oxidation and microbial oxidation in soils, sediments and water. Atmospheric CH4 levels have risen sharply in recent years but the reasons are unclear so far, although they involve increased emissions from methanogens and/or fossil fuel industries and/or reduced atmospheric CH4 oxidation, thereby posing a major threat to controlling climate warming.

39. Rice feeds half of the global population and rice paddies contribute ~20% of agricultural CH4 emissions despite covering only ~10% of land.Anthropogenic climate change is predicted to double CH4 emissions from rice production by the end of the century. Ruminant animals are the largest single source of anthropogenic CH4 emissions, with a 19–48 times larger carbon footprint for ruminant meat production than plant- based high- protein foods.Even the production of meat from non- ruminant animals (such as pigs,poultry and fish) produces 3–10 times more CH4 than high- protein plant foods.The combustion of fossil fuels and the use of fertilizers has greatly increased the environmental availability of nitrogen, perturbing global biogeochemical processes and threatening ecosystem sustainability.Agriculture is the largest emitter of the potent greenhouse gas N2O, which is released by microbial oxidation and reduction of nitrogen.4.2.: Cont.

40. 4.2.: Cont.The enzyme N2O reductase in Rhizobacteria (in root nodules) and other soil microorganisms can also convert N2O to N2 (not a greenhouse gas). Climate change perturbs the rate at which microbial nitrogen transformations occur (decomposition, mineralization, nitrification, denitrification and fixation) and release N2O. There is an urgent need to learn about the effects of climate change and other human activities on microbial transformations of nitrogen compounds Infectious diseases.Climate change affects the occurrence and spread of diseases in marine and terrestrial biota, depending on diverse socioeconomic, environmental and host–pathogen- specific factors. Understanding the spread of disease and designing effective control strategies requires knowledge of the ecology of pathogens, their vectors and their hosts, and the influence of dispersal and environmental factors

41. ReferencesBrock Biology Of Microorganisms, 14th Edition. Medigan Mt And Martinko Jm (2014), Parker J. Prentice Hall International Inc.Prescott’s Microbiology, Eighth Edition Reviewed By Joanne J. Dobbins Joanne M. Willey , Linda M. Sherwood , And Christopher J. Woolverton . 2011. Mcgraw-Hill Higher Education, New York, Ny. General Microbiology , Roger Y. Stanier Macmillan, 1987.Geomicrobiology, Fifth Edition, H. L. Ehrlich, D. K. Newman. CRC Press is an imprint of Taylor & Francis Group.Principles of microbial diversity , James W. Brown, Department of Biological Sciences, North Carolina State University, Raleigh, North Carolina.