Environmental
Microbiology
Talaro
Chapter 26
1
• 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
2
Microbes comprise approximately half
of all the biomass on Earth
Prokaryotes exist in all of the habitats on Earth
Extreme cold
Prokaryotes exits in
Extreme heat
Low O2
environments that are too
Extreme pressure – “barophiles” extreme or inhospitable for
now called piezophiles
eukaryotic cells –
High salt (low aw)
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
3
The primary role of microorganisms is to
serve as catalysts of biogeochemical cycles
4
textbookofbacteriology.net
Microbial catalysts interact on a much smaller
spatial scale, but affect the biosphere over a
long period of time
Nanometers to micrometers
Bacteria on the tip of a plant root
Bacteria living in specialized
organs of invertebrates
Geologic Time
Production of O2
Millions to billions of years
5
Microorganism have a greater metabolic
versatility than do macroorganisms
Photoautotrophs
Chemoautrophs
Photoheterotroph
Chemoheterotrophs
6
Prokaryotes do not Exist in Isolation
Plant and animals are dependent upon the actions of
prokaryotes
Archaea and Bacteria participate in mutualistic
relationships that benefit both organisms
Only a small number of bacteria are pathogenic!
And there are bacteria that are pathogens
of animals and plants
7
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 carbon
sources 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
8
Biofilms
• Complex aggregation
Antarctica glaciers
Hot springs
– Bacteria, archaea, protozoa, algae
– Microbial Mat
• Free floating organism
• Attached organism
– Highly structured
• Extracellular polysaccharide
– Protective & adhesive matrix
Antarctic Sun February 12, 2006
• Protection from the environment
• Protection from protozoans
• Protection from antibiotics & chemicals
9
• Grows by cell division & recruitment
• Industrial biofilms
– Pipe corrosion
– Ship corrosion
• Infections
–
–
–
–
Dental plaque
Contact lenses
Heart valves
Artificial hip joints
10
• 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
11
1. Initial attachment
4. Maturation of Biofilm Architecture
2. Production of EPS
5. Dispersion
3. Early Biofilm Architecture
12
www.microbes.org/labs.asp
Microbial mat
Cyanobacteria & purple bacteria
Lake Cadagno, Switzerland
White area is precipitated sulfur
13
Cyanobacterial mat in run-off from
a hot springs at Yellowstone National Park
www.mit.edu/people/janelle/homepage.html
14
Winogradsky Column
Nutrient Cycling
• 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
15
• Algae, cyanobacteria, aerobic heterotrophs
– CO2 + H2O  CH2O + O2
• Oxygenic photosynthesis
More on
• H2O is a source of electrons anoxygenic and
oxygenic
– CH2O + O2  CO2 + H2O
photosynthesis
• Aerobic respiration
is few moments
• H2S oxidizers
– CO2 + H2S  CH2O + S + H2O
• Anoxygenic photosynthesis
• H2S is a source of electrons
16
• 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
17
• 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
– SO42-  S2- compound (H2S or FeS)
18
19
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
20
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.
21
Photosynthesis developed  3 bya
22
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 l
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
23
Cyanobacteria & purple bacteria
Lake Cadagno, Switzerland
www.microbes.org/labs.asp
24
• Start here next time
25
Cyanobacteria
Tremendous 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 algae
Chlorophyll a absorbs light at 450 nm
& 650 - 750 nm
Pycobilins absorb at 550 and 650 nm
26
Some cyanobacteria fix
nitrogen in specialized cells
HETEROCYSTS.
Provide anaerobic environment
required for nitrogenase.
27
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).
28
Several species of cyanobacteria are
symbionts of liverworts, ferns,
cycads, flagellated protozoa, and
algae.
The photosynthetic partners of
lichens are commonly cyanobacteria.
www.botany.wisc.edu/.../AnabaenaAzolla2.jpg
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
29
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
www.resa.net/nasa/antarctica.htm
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.
30
Green alga
Figure 17. The distribution of
photosynthetic pigments among
photosynthetic microorganisms.
Red alga
cyanobacterium
Green bacterium
Purple bacterium
textbookofbacteriology.net 31
Anoxygenic bacterial photosynthesis
iron sulfur protein
Photosystem I
Cyclic Photophosphorylation
Cyanobacteria, algae and plants, also have Photosystem II
ATP is generated
during
photophosphorylation
bacterial chlorophyll
cyclic photophosphorylation
32
Anoxygenic bacterial photosynthesis
Photosystem I
Electrons from
H2S are passed to
ferredoxin
NADP is reduced
Autotrophic CO2 fixation
CO2  (CH2O)n
CO2 + H2S  (CH2O)n + S + H2O
Oxidation of H2S is linked to PS1
textbookofbacteriology.net
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Anoxygenic photosynthesis
Limitations on the amount of C that can be fixed
Need more electrons to fix more C
34
Electrons lost
here must be
replenished
CO2  (CH2O)n
Calvin Cycle
Electrons
from PS1
reduce
ferredoxin
Ferredoxin
passes the
electrons
to NADP
Oxygenic Photosynthesis
Plants, algae and cyanobacteria
PS2 ensures a
ATP is generate by
constant supply of
noncyclic
photophosphorylation electrons
H2O is source
of electrons
35
textbookofbacteriology.net
Table 6. Differences between plant and bacterial photosynthesis
Plant Photosynthesis
Bacterial Photosynthesis
Organisms
plants, algae,
cyanobacteria
purple and green bacteria
Type of chlorophyll
chlorophyll a
absorbs 650-750 nm
bacteriochlorophyll
absorbs 800-1000 nm
Photosystem I
(cyclic photophosphorylation)
present
present
present
absent
yes
no
H2O
H2S, other sulfur compounds
or
certain organic compounds
Photosystem II
(noncyclic photophosphorylation)
Produces O2
Photosynthetic electron donor
textbookofbacteriology.net
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