chapter 27 environmental microbiology. microbes live in the most widely varied habitats on earth...
TRANSCRIPT
Chapter 27
Environmental Microbiology
• Microbes live in the most widely varied habitats on Earth
– due to metabolic diversity – dynamic associations occur between microbes and
ecosystem
• Extremophiles– Most are Archaea – Produce specialized enzymes (extremozymes) that
allow them to tolerate extreme conditions
Metabolic Diversity
• Microbes live in an intensely competitive environment– High biodiversity
– Competitive exclusion
– Live in symbiotic relationships • Ruminants• Mycorhizae
Endomycorrhiza
Ectomycorrhiza
• Soil Microbiology• Billions of organisms in soil
– Over 80 % are bacteria• Millions in each gram of soil
– Most are in the top few centimeters of soil – Biomining – Many antibiotics come from Actinomycetes
• Streptomycin, tetracycline – Bacterial populations estimated by plate count
– Biogeochemical cycles for carbon, nitrogen, sulfur and phosphorus are vital for life
• Elements oxidized and reduced by microbes to meet their metabolic need
• Recycles elements into the environment– Production
– Consumption
– Decomposition
The Carbon Cycle
• All organisms contain large amounts of carbon
• Autotrophs fix CO2 into organics– 1st step of carbon cycle
• Heterotrophs consume autotrophs– 2nd step of carbon cycle
• Carbon reenters the environment as CO2
– due to respiration; decomposition by microbes; burning fossil fuels
• Global warming
The Nitrogen Cycle
• Nitrogen is needed for synthesis of proteins and nucleic acids
• Deamination– amino groups are removed and converted to
ammonia
• Ammonification– release of ammonia
• Nitrification – oxidation of ammonium into nitrate– nitrate can be fully oxidized and used as an electron
acceptor
• Denitrification – leads to loss of nitrogen back to the atmosphere as
nitrogen gas – Pseudomonas species are the most important soil
denitrifying bacteria– Occurs in waterlogged soils where little oxygen is
available
Nitrogen Cycle
Nitrate ion (NO3-)
PseudmonasN2
Nitrite ion (NO2-)
NitrobacterNitrate ion (NO3
- )
Ammonium ion (NH4+)
NitrosomonasNitrite ion (NO2
- )
Amino acids (–NH2)Microbial ammonification
Ammonia (NH3)
Proteins and waste productsMicrobial decomposition
Amino acids
• Nitrogen makes up ~ 80% of the Earth’s atmosphere– Exists as nitrogen gas (N2)
• Must be fixed into usable form – Specific microbes important in this conversion– Nitrogen fixation requires nitrogenase– Deactivated by oxygen
N2
Nitrogen - fixation
Ammonia (NH3)
• Two types of nitrogen fixers:– Free-living
• found in rhizosophere• Aerobic species - Azotobacter and Beijerinckia• Cyanobacteria –heterocysts• Anaerobic species - Clostridium
– Symbiotic
• Rhizobia form root nodules on legume plants • Frankia associated with alder trees• Lichens when containing a cyanobacteria • Cyanobacteria & Azolla in rice patty water
The Sulfur Cycle
• Involves numerous oxidation states
• Most reduced forms are sulfides like H2S gas– Generally forms under anaerobic conditions
• Source of energy for some autotrophic bacteria– Convert reduced sulfur in H2S into elemental sulfur
and oxidized sulfates – Thiobacillus– Endoliths
• Winogradsky studied filamentous aquatic bacteria Beggiatoa alba– Revealed much about bacterial sulfur
recycling and chemoautotrophy
• Primary producers in deep ocean and endolithic communities are chemoautotrophic bacteria
• Several photo-autotrophic bacteria use light for energy and use H2S to reduce CO2
• Sulfates are incorporated into plants, animals and bacteria as disulfide bonds in proteins
• Proteins decompose; sulfur released as H2S– Dissimilation
Sulfur Cycle
Proteins and waste products Amino acidsMicrobial decomposition
Amino acids (–SH)Microbial dissimilation
H2S
H2SThiobacillus
SO42– (for energy)
SO42–
Microbial & plant assimilationAmino acids
SO42– Desulfovibrio H2S (reduced)
The Phosphorus Cycle
• Limiting factor for plant and animal growth
• Exists primarily as phosphate ion (PO43-)
• Little change during oxidation – soluble to insoluble; organic to inorganic – Often related to pH – Can be solubilized in rock by acids produced by
bacteria like Thiobacillus
• There is no product to return it to atmosphere
• Accumulates in sea; certain islands are mined for phosphate deposits
• Used in detergents and fertilizers– Runoff may lead to eutrophication
The Phosphorous Cycle