L24 Microbiomes and Microbial Ecology

what does the human microbiome do for us?

1. helps w digestion

2. trains our immune system

3. competes against pathogens → uses up nutrients, space, etc

4. linked to “healthy state”

hygiene hypothesis

theory that a lack of early exposure to microorganisms can lead to overactive immune systems and an increased susceptibility to autoimmune disorders

skin microbiome

• environment → dry, slightly salty, acidic, prevents growth of many microbes

• mainly gram positive

• microflora of skin influenced by weather, age, host factors

oral microbiome

• complex habitat w large diversity

• saliva contains antimicrobial enzymes

• bacteria colonize tooth surfaces by attaching to acidic glycoprotein organic layer deposited by saliva

GI microbiome

10^13 microbial cells

• accounts for most of your microbiota

• influenced by diet and physical conditions

urogenital tract microflora - vagina

• glycogen-rich environment

• lactic acid bacteria produce weakly acidic environment by fermenting glucose

you inherit your mother’s microbes

• this is a good thing

• significant differences between natural and C-section births

the carbon cycle

microbes (euk algae and prok cyanobacteria) consume CO2 and produce O2 → photosynthesis

• microbes are key decomposers

nitrogen cycle

NO3- → NO2- → N2 (nitrate reduction)

• bacteria are the only organisms that can fix nitrogen N2 → NH3

Sergei Winogradsky

• discovered process of nitrogen fixation by isolated anaerobic Clostridium

• discovered chemolithotrophy

• studied biofilm communities

microhabitats

microbes have habitats and populations

• ex soil particle

species richness

number of individual species in a community

relative abundance

proportional representation of a species in a community