1. Chapter 21 Lecture Outline Microbial Ecology

2. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 2 Microbes in Ecosystems Microbes are ubiquitous  Found in every habitable environment  Fill every potential niche Every living cell component can be used by a microbe Genome + environment  Determines ability of microbe to fill a niche

3. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 3 Microbes in Ecosystems Microbes assimilate minerals  CO 2, N 2 Microbes absorb energy  Producers: Algae, Phytoplankton, Bacteria Microbes at all levels of food web  Consumers: Bacteria, Archaea, Eukaryotes  Decomposers: Fungi, Viruses  Importance varies in different habitats E.g., all marine producers are microbes

4. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 4 Microbes in Ecosystems Environmental factors determine growth  Oxygen level Electron acceptor critical for cells to grow  Growth slower in anaerobic environment  Requires presence of mineral electron acceptors  Availability of other nutrients Nitrogen, phosphorus, sulfur, minerals  Temperature Microbes classified by temperature range  Salinity  pH

5. Extremophiles Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 5

6. 6 Symbiotic Interactions: Interaction of Microbe with Another Species Mutualism  Both partners benefit from species-specific association and may fail to grow independently Synergism = syntrophy  Both partners benefit, but partners can be easily separated and grow independently; non-specific association Commensalism  One species benefits, while the partner species neither benefits or is harmed Amensalism  One partner is harmed by non-specific association Parasitism  One partner harmed by specific association

7. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 7 Microbe-Plant Symbiosis: Mutualism Rhizobium-legume mutualistic interaction  Legumes secrete flavonoid attractants  Rhizobium binds with NOD protein to the root hair the plant  Root hair is induced to curl around Rhizobium  Infection thread is formed and Rhizobium enters cortical cells  Rhizobium differentiates into bacteroids No cell wall Surrounded by plant derived membrane known as symbiosome Bacteroid is anaerobic and fixes nitrogen Plant produces leghemoglobin to bind off oxygen and provides ATP and nutrients

8. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 8 Microbe-Plant Symbiosis: Parasitism Agrobacterium induces plant galls  Ti plasmid induces tumor growth Fungi grow haustorium into plant cell  Doesn’t break plasma membrane  Absorbs nutrients from host  Fungal diseases Anthracnose