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Environmental MicrobiologyTalaro Chapter 26

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• Environmental Microbiology – Study of microbes in their natural habitats– Microbial Diversity – study of the different types

of microbes in an environment

• Microbial Ecology– Studies the interactions between microbes & their

environments– Involving biotic & abiotic components– Distribution– Abundance – numbers of bacteria

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Microbes comprise approximately half of all the biomass on Earth

Prokaryotes exist in all of the habitats on Earth Extreme cold Extreme heat Low O2

Extreme pressure – “barophiles” now called piezophiles High salt (low aw)

Prokaryotes exits in environments that are too extreme or inhospitable for eukaryotic cells – Extremophiles!!

Limits of life on Earth are defined by the presence of prokaryotes which tells us what to look for when looking for life on

extraterrestrial bodies

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The primary role of microorganisms is to serve as catalysts of biogeochemical cycles

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Microbial catalysts interact on a much smaller spatial scale, but affect the biosphere over a long period of time

Nanometers to micrometersBacteria on the tip of a plant rootBacteria living in specialized organs of invertebrates

Geologic TimeProduction of O2

Millions to billions of years

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Microorganism have a greater metabolic versatility than do macroorganisms

PhotoautotrophsChemoautrophsPhotoheterotrophChemoheterotrophs

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Only a small number of bacteria are pathogenic!

Plant and animals are dependent upon the actions of prokaryotes

Archaea and Bacteria participate in mutualistic relationships that benefit both organisms

And there are bacteria that are pathogens of animals and plants

Prokaryotes do not Exist in Isolation

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Examples of Mutualism• Sheep and cattle (ruminants) live off grass

• Lack the digestive enzymes to break down cellulose

• Bacteria in intestinal tract break down cellulose• Products of cellulose degradation are converted to carbonsources that the ruminants can use • CH4 is also produced in high amounts (belching!)

• Sugars absorbed by animal and used for energy

• Plants unable to fix atmospheric N2

• Symbiotic bacteria infect roots

• Plant requires nitrogen for proteins

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Biofilms• Complex aggregation

– Bacteria, archaea, protozoa, algae– Microbial Mat

• Free floating organism

• Attached organism

– Highly structured

• Extracellular polysaccharide– Protective & adhesive matrix

• Protection from the environment

• Protection from protozoans

• Protection from antibiotics & chemicals

Antarctica glaciersHot springs

Antarctic Sun February 12, 2006

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• Grows by cell division & recruitment• Industrial biofilms

– Pipe corrosion– Ship corrosion

• Infections– Dental plaque– Contact lenses– Heart valves– Artificial hip joints

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• Physiologically Integrated– Each group performs a specialized metabolic

function

• Lateral gene transfer– Conjugation between different species– Transduction between different species

• Cell to cell communication– Quorum sensing

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1. Initial attachment

2. Production of EPS 5. Dispersion

4. Maturation of Biofilm Architecture

3. Early Biofilm Architecture

13www.microbes.org/labs.asp

Microbial matCyanobacteria & purple bacteriaLake Cadagno, SwitzerlandWhite area is precipitated sulfur

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Cyanobacterial mat in run-off froma hot springs at Yellowstone National Park

www.mit.edu/people/janelle/homepage.html

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Winogradsky Column • A glass column

that simulates the complex interactions of microbial biofilms in an aqueous environment– Upper aerobic

zone– Microaerophilic

zone– Lower anaerobic

zone

Environmental Technology Consortium at Clark Atlanta University and Northern Arizona University 

Nutrient Cycling

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• Algae, cyanobacteria, aerobic heterotrophs

– CO2 + H2O CH2O + O2

• Oxygenic photosynthesis

• H2O is a source of electrons

– CH2O + O2 CO2 + H2O

• Aerobic respiration

• H2S oxidizers

– CO2 + H2S CH2O + S + H2O

• Anoxygenic photosynthesis

• H2S is a source of electrons

More on anoxygenic and oxygenic photosynthesis is few moments

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• Purple nonsulfur photoheterotrophs– May exist as photoheterotrophs, photoautotrophs or

chemoheterotrophs – Freely alternate between these metabolic modes

depending on environmental conditions • Degree of anaerobiosis• Availability and types of carbon sources

– CO2 for autotrophic growth – Organic compounds for heterotrophic growth

• Availability of light for phototrophic growth• The “non-sulfur” label was used since it was

originally thought that these bacteria could not use H2S as an electron donor

• Can use H2S in low concentrations

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• Purple non-sulfur bacteria– CH2O + O2 CO2 + H2O (Chemoheterotrophs)

– CH2O + O2 CO2 + H2O (Photoheterotrophs)

– CO2 + H2O CH2O + O2 (Photoautotrophs)

• Purple & Green sulfur bacteria– Anoxygenic photosynthesis

– H2, H2S or So SO42-

• Sulfate reducers– SO4

2- S2- compound (H2S or FeS)

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Quorum Sensing• Cell-cell communication in bacteria • Coordinate behavior/activities between bacterial cells of the

same species• Autoinducers trigger a change when cells are in high

concentration– Specific receptor for the inducer– Extracellular concentration of autoinducer increases with

population – Threshold is reached– The population responds with an alteration in gene expression

• Bioluminescence• Secretion of virulence factors• Biofilm formation• Sporulation• Competence

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Energy & Nutrient Flow

 

It is likely that most of the Earth's atmospheric oxygen was produced by bacterial cells.

Plant cell chloroplast and oxygenic photosynthesis are originated in prokaryotes.

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Photosynthesis developed 3 bya

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Anoxygenic Photosynthesis – Anaerobic bacterial photosynthesis that does not produce O2

– CO2 + H2S (CH2O)n + S + H2O• H2, H2S or So or organic compounds serves as a source of electrons

– Need electrons to make fix C and make ATP

– Purple and green photosynthetic sulfur bacteria• Aquatic & anaerobic• Pigments that absorb different • Bacteriochlorophyll (800 - 1000 nm [far red]) • Carotenoids (400 - 550 nm)

– Phycobilins are not present • Only 1 photosystem

– Rhodobacter • Oxidize succinate or butyrate during CO2 fixation • Hypothesized to be have become an endosymbiont of eucaryotes • Mitochondrion 16S rRNA sequences

24www.microbes.org/labs.asp

Cyanobacteria & purple bacteriaLake Cadagno, Switzerland

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• Start here next time

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CyanobacteriaTremendous ecological importance in the C, O and N cycles

Evolutionary relationship to plants

Cyanobacteria have chlorophyll a, carotenoids and phycobilins

Same chlorophyll a in plants and algaeChlorophyll a absorbs light at 450 nm & 650 - 750 nm

Pycobilins absorb at 550 and 650 nm

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Some cyanobacteria fix nitrogen in specialized cells HETEROCYSTS.

Provide anaerobic environment required for nitrogenase.

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Cyanobacteria have membranes that resemble photosynthetic thylakoids in plant chloroplasts.

Hypothesized that cyanobacteria were the progenitors of eucaryotic chloroplasts via endosymbiosis.

Cyanobacteria are very similar to the chloroplasts of red algae (Rhodophyta).

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Several species of cyanobacteria are symbionts of liverworts, ferns, cycads, flagellated protozoa, and algae.

The photosynthetic partners of lichens are commonly cyanobacteria.

There is also an example of a cyanobacterium as endosymbionts of plant cells.

A cyanobacterial endophyte (Anabaena spp.) fixes nitrogen that becomes available to the water fern, Azolla.

www.csupomona.edu

www.botany.wisc.edu/.../AnabaenaAzolla2.jpg

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Several thousand cyanobacteria species. Many are symbionts.

200 species are free-living, nonsymbiotic procaryotes.

Cyanobacteria often are isolated from extreme environments.

Hot springs of the Yellowstone National Park Antarctica lakes

Copious mats 2 to 4 cm thick in water beneath more than 5 m of permanent ice.

Cyanobacteria are not found in acidic waters where algae (euckaryotic) predominate.

www.resa.net/nasa/antarctica.htm

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Figure 17. The distribution of photosynthetic pigments among

photosynthetic microorganisms.

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Green alga

Red alga

cyanobacterium

Green bacterium

Purple bacterium

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Anoxygenic bacterial photosynthesis Photosystem ICyclic PhotophosphorylationCyanobacteria, algae and plants, also have Photosystem II

bacterial chlorophyll

iron sulfur protein

ATP is generated during photophosphorylation

cyclic photophosphorylation

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CO2 + H2S (CH2O)n + S + H2OOxidation of H2S is linked to PS1

Anoxygenic bacterial photosynthesis Photosystem I

Electrons from H2S are passed to ferredoxinNADP is reduced

Autotrophic CO2 fixationCO2 (CH2O)n

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Anoxygenic photosynthesis

Limitations on the amount of C that can be fixed

Need more electrons to fix more C

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Oxygenic Photosynthesis

Plants, algae and cyanobacteria

PS2 ensures a constant supply of electrons

Electrons lost here must be replenished

H2O is source of electrons

CO2 (CH2O)nCalvin Cycle

ATP is generate by noncyclic

photophosphorylation Electrons from PS1 reduce ferredoxin Ferredoxin passes the electrons to NADP

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Table 6. Differences between plant and bacterial photosynthesis

Plant Photosynthesis Bacterial Photosynthesis

Organismsplants, algae, cyanobacteria

purple and green bacteria

Type of chlorophyllchlorophyll a  absorbs 650-750 nm

bacteriochlorophyll  absorbs 800-1000 nm

Photosystem I (cyclic photophosphorylation)

present present

Photosystem II(noncyclic photophosphorylation)

present absent

Produces O2 yes no

Photosynthetic electron donor H2OH2S, other sulfur compounds

or  certain organic compounds

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