1. Bacterial Physiology (Micr430) Lecture 6 Lipids and Nitrogen Metabolism (Text Chapters: 9, 12) IN CASE OF EMERGENCY WHEN I CANNOT UPLOAD SLIDES, PLEASE USE THE FOLLOWING SHARE SITE: GO TO: skydrive.live.com Type: hxu3@live.comhxu3@live.com Password: micr430 Look for new Powerpoint slide files for the next lecture within a folder named Bacterial Physiology Slides and download it.

2. Lipids A common feature of all lipids is their insolubility in water. All lipids in bacteria are in membranes Membrane lipids are amphipathic, with hydrophilic and hydrophobic regions that cause them to orient into bilayers This characteristic provides a solubility barrier to polar solutes in an aqueous environment

3. Lipids The major membrane lipids are phospholipids consisting of fatty acids esterized (in bacteria) to glycerol phosphate derivatives. Fatty acids are chains of methylene carbons with a carboxyl group at one end. Phospholipids comprise the bimolecular leaflet structure of the cytoplasmic membrane, which is both flexible and self-sealing.

4. Fatty Acids Straight-chain fatty acids are the major constituents of membrane phospholipids Saturated fatty acids Unsaturated fatty acids branched-chain fatty acids have been found in Bacillus, Staphylococcus, Corynebacterium, Mycobacterium, Pseumodonas and Spirochaeta Ring-containing fatty acids (lactobacillic acid) Mono-unsaturated and ring-containing fatty acids contribute to the flexibility and fluidity that enable membranes to undergo changes in shape that accompany cell growth or movement.

5.  -Oxidation of Fatty Acids Many bacteria grow on fatty acids If fatty acids with even number of carbons, all fatty acids turn to acetyl- CoA. If fatty acids with odd carbons, most carbons turn into acetate with the last one being proprionyl CoA.

6. Reactions in fatty acid catabolism Fig. 9.1

7. Biosynthesis of Fatty Acids Acetyl-CoA is the ultimate precursor of fatty acid carbons Acetyl-CoA carboxylase catalyzes the first committed reaction in the pathway Fatty acid biosynthesis in bacteria is conducted by a soluble, disassociated system designated as type II. At least eight individual enzyme components are readily separated and purified from E. coli and P. shermanii

8. Biosynthesis of Fatty Acids Biosynthesis of fatty acids differs from oxidation process: Reductant used is NADPH (vs NADH) Biosynthesis needs CO, a carboxylation step The acyl carrier differs, biosynthesis uses ACP (acyl carrier protein) while oxidation uses CoASH.

9. Reactions in Fatty acid Biosynthesis Fig. 9.4

10. Common Phosphoglycerides Fig. 9.5

11. Biosynthesis of Phospholipids The first committed steps in phosphoglyceride biosynthesis involve coupling two molecules of fatty acids to glycerol-3-phosphate This reaction is catalyzed by two acyl transferases

12. Phospho- glyceride synthesis Fig. 9.6

13. NITROGEN METABOLISM Nitrogen fixation Inorganic nitrogen assimilation

14. Nitrogen Fixation Microorganisms play a major role in the nitrogen cycle A unique group of bacteria fix atmospheric nitrogen into ammonia and assimilate ammonia into amino acids Certain nitrogen fixing bacteria have established a symbiotic relationship with plants where they fix atmospheric nitrogen into forms that can be readily utilized by host plants

15. Nitrogen Fixation Process Nitrogen fixation is accomplished by a variety of bacteria and cyanobacteria using a multicomponent nitrogenase system Nitrogenase consists of two oxygen-sensitive proteins Component I (dinitrogenase) Component II (dinitrogenase reductase) N 2 + 6 H + + 6 e - + 12 ATP + 12 H 2 O --  2 NH 3 + 12 ADP + 12 Pi

16. Nitrogenase Reaction Fig. 12.4

17. Heterocysts Filamentous cyanobacteria protect their nitrogenase by differentiating 5 to 10% of vegetative cells into special nitrogen-fixing cells called heterocysts: Heterocysts possess nitrogenase enzymes They have only photosystem I, not producing O 2 They do not fix CO 2 They are surrounded by a thick cell wall that is a permeability barrier to O 2. They are not dividing.

18. Heterocysts Fig. 12.5

19. Nitrate Assimilation Nitrate can serve as the source of cellular nitrogen for plants, fungi and many bacteria Nitrate reductase and nitrite reductase are both cytoplasmic enzymes that reduce nitrate to ammonia Electron donors for nitrate reductase can be NADH, ferredoxin or flavodoxin. Electron donors for major nitrite reductase in E. coli is NADH.

20. Nitrate Assimilation Nitrate nitrite nitroxyl hydroxylamine ammonia Fig. 12.1