Metabolic Diversity Overall, the chemical reactions that take place within microbial cells are highly diverse There are 2 key “ingredients” in this diverse collection of recipes Carbon-for precursors and building blocks Energy-to make things work

Introduction-Overview and Definitions Carbon and Metabolic Diversity Energy Pathways: Electron Transfers, ATP Production Other Catabolic Diversity

Introduction-Overview and Definitions Metabolism The sum total of all of the chemical reactions that occur in a cell Catabolic reactions (catabolism) Energy-releasing metabolic reactions, typically break down large molecules to precursors and building blocks Anabolic reactions (anabolism) Biosynthetic metabolic reactions that use the precursors and the building blocks

Broad Overview of Metabolism There are only a few key precursor molecules (but lots of ways to get them or make them) Energy sources vary: light, chemical bonds etc.

Carbon dioxide etc. But prokaryotes will not make something by de novo synthesis if they can import it instead

Classification based on Energy/Carbon Source Microorganisms have a variety of ways to conduct their metabolism Grouped into energy source classes Chemotrophs use chemical energy Lithotrophs use inorganic compounds Organotrophs use carbon compounds Phototrophs use light energy Oxygenic release oxygen as waste product Anoxygenic release some other waste product

Classification based on Energy/Carbon Source Microorganisms have a variety of ways to conduct their metabolism Grouped into carbon source classes Heterotrophs rely on reduced carbon in the environment Autotrophs reduce aka “fix” their own CO2

Phototrophic autotrophs (photoautotrophs) are familiar Autotrophs fix carbon but they may be chemotrophs or phototrophs with respect to energy source Phototrophic autotrophs (photoautotrophs) are familiar Cyanobacteria (Sec.14.3) Photosynthesize using chlorophyll a Fix CO2 to carbohydrate using Calvin Cycle Chemotrophic autotrophs (chemoautotrophs) are less familiar Methanogens (Sec.13.20) = Archaea; sediments, animals Convert CO2 to CH4 with unusual enzymes for energy Utilize methanol or acetate from CH4 for carbon

Chemotrophic heterotrophs (chemoheterotrophs) are very common Heterotrophs acquire reduced carbon from the environment but may be chemotrophs or phototrophs with respect to energy source Chemotrophic heterotrophs (chemoheterotrophs) are very common Phototrophic heterotrophs (photoheterotrophs) also exist Heliobacter (Sec. 14.8) a gram + rod Carries out photosynthesis using bacteriochlorophyll g Relies on pyruvate, lactate, butyrate, acetate for carbon