Environmental Microbiology Chapter 27 Environmental Microbiology

Metabolic Diversity 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

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 Denitrification 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 Proteins and waste products Amino acids Microbial decomposition Proteins and waste products Amino acids Microbial ammonification Amino acids (–NH2) Ammonia (NH3) Nitrosomonas Ammonium ion (NH4+) Nitrite ion (NO2- ) Nitrobacter Nitrite ion (NO2-) Nitrate ion (NO3- ) Pseudmonas Nitrate ion (NO3-) N2

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 Nitrogen - fixation N2 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

Proteins decompose; sulfur released as H2S 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 acids Amino acids (–SH) Microbial decomposition Proteins and waste products Amino acids Microbial dissimilation Amino acids (–SH) H2S Thiobacillus H2S SO42– (for energy) Microbial & plant assimilation SO42– Amino acids Desulfovibrio SO42– 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