Module 9: Lakes

• why are lakes nutrient limited?

  less organic material, phosphorus and nitrogen limit growth
• oligotrophic: low nutrients and primary productivity, clear water
• mesotrophic: intermediate level of productivity
• eutrophic: excessive nutrients, high biological activity
• why is lake mendota eutrophic?

  human activity
• when does lake mixing occur?

  in the fall when surface water is colder/more dense, brings up nutrients from the bottom
• when is there the highest microbial activity in lakes?

  summer when water is warmest, most metabolic activity
• primary producers create organic carbon
• degraders mineralize organic compounds
• what are the major phyla in lakes?

  1. proteobacteria: photosynthetic
  2. bacteriodetes
  3. cyanobacteria: primary producers
  4. actinobacteria: dominant phyla
• actinobacteria is found in 50% of lake environments, has very small genome
• acl-b1: actinobacteria that encodes bacteriorhodopsin and uses it to make ATP
• acl-b1 is chemohetertroph (organic energy and carbon source)
• acl-b1 is chitinase (grows on chitin)
• bacteriorhodopsin: expressed under oxygen limiting conditions in acl-b1
• how are protons pumped through bacteriorhodopsin?

  1. trans retinal is formed by proton donation in acidic environment
  2. light causes conformation shift to cis retinal
  3. basic environment deprotonates, creates gradient
• cyanobacteria: plant-like photosynthesis
• cyanobacteria bloom in eutrophic lakes in the spring and generate cyanotoxins
• what happens when a cyanobacteria bloom crashes?

  other groups increase population to degrade (ex. flavobacteria)