Question

5. The KEGG and NCBI databases contain a wealth of information obtained from sequencing and analyzing the complete genome of Acinetobacter baumannii 1656-2, which is a medically important oxidase negative (cytochrome c oxidase- negative) bacterium that is multidrug resistant. For this microorganism, which statement regarding oxidative phosphorylation is correct?

This microbe possesses subunits of cytochrome c oxidase and therefore displays cytochrome c oxidase activity

The formation of ATP depends directly on the oxidation of cytochrome c.

The cytochrome bd complex allows oxygen to be reduced by the quinone pool

Subunit a of the F-type ATPase has 876 amino acids

Answer 1

Acinetobacter baumannii is a well known pathogenic organism, which is negative for cytochrome c oxidase. Hence the first 2 options of this question can be ruled out.

As per the full genome sequencing data of Acinetobacter baumannii 1656-2 (GenBank: CP001921.1), the genome contains cytochrome bd-type oxidase. Presence of this gene in this organism support the bioenegetics through this protein. This gene is also expressed in a number of pathogenic bacteria. Cytochrome bd consists of 2 subunits - a CydA and CydB and a small protein called CydX. The enzyme acts as a catalyst to reduce oxygen to water. During this process, quinol acts as the reducing substance. During the entire process, electrons are generated, which causes the generation of a proton motive force, thereby resulting in synthesis of ATP using ATP synthase. But, since this process is not linked to proton pump, it has lower energy efficiency.

Cytochrome bd also plays other role in bacterial life cycle, like helping the bacteria in tolerating stress including the oxidative and nitrosative stress. It also has a role to play in bacterial virulence. Hence, many pathogenic bacteria contain this gene.