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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 – 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 Microbial ammonification Amino acids (–NH2) Ammonium ion (NH4 Nitrite ion (NO2 -) Nitrate ion (NO3 -) Microbial decomposition +) Nitrosomonas Nitrobacter Pseudmonas Ammonia (NH3) Nitrite ion (NO2- ) Nitrate ion (NO3- ) N2 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 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 • 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 (–SH) Thiobacillus H2S SO4 2– SO42– Microbial decomposition Microbial dissimilation H2S SO42– (for energy) Microbial & plant assimilation Desulfovibrio Amino acids H2S (reduced) Amino acids 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
