Question

The questions are related to microbiology

In the absence of oxygen, two different cultures of E. Coli are growing in a minimal medium- both with the same basic composition of standard salts, and both containing ammonium chloride as the nitrogen source, and glucose as the carbon source. Only the first culture contains sodium nitrate in addition.

1) Describe the two metabolic pathways in the two different cultures and put them in to a global perspective. To what nutrients cycles do they contribute, and how?

2) what are some of the major groups of environmental bacteria that use these pathways? Describe them briefly. What are typical habits where these pathways play an important role?

Answer 1

1) The nitrate reduction is associated with the bateriums ability to breath in the absence of oxygen and having two different metabolic pathways: respiratory nitrate reductase and dissimilatory nitrate reduction.

In the first pathway, the denirtification process take place where the nitrate is reduced to nitric, nitric oxide, nitrous oxide and to dinitrogen.

In the second pathway, nitrate is directly converted to ammonia. This can be performed by cells with nrf gene. Among Actinobacteria, respiratory nitrate reductase (Nar) is observed. This class of enzyme is mostly membrane bounded and is having different subunit. One of the subunit is nitrate reductase Z from E.coli.

E.coli has three native glycolytic pathways. EMPP, EDP and OPPP. The EMPP employs the ezymatic steps to yield 2 pyruvates, two ATP, two NADH per glucose while OPPP serve as an oxidation route for NADPH synthesis. In E.coli glucose metabolism mainly relies on the EMPP and OPPP while the EDP primarly remains inactive except during growth with gluconate.

2) Other bwcterias that use this pathway include pseudomonas stutzeri, staphylococus cannosus, B.subtilis .