Mechanisms of oxygen inhibition of nirK expression in Rhodobacter sphaeroides

Author:

Hartsock Angela1,Shapleigh James P.1

Affiliation:

1. Department of Microbiology, Wing Hall, Cornell University, Ithaca, NY 14853, USA

Abstract

R. sphaeroidesstrain 2.4.3, when lacking thecbb3oxidase, is unable to transition from aerobic respiration to denitrification using cellular respiration as a means of reducing oxygen levels. This is due to an inability to expressnirK, the gene encoding nitrite reductase. Under certain photosynthetic conditions this strain can transition from aerobic to nitrate respiration, demonstrating thatnirKexpression can occur in the absence of a functionalcbb3oxidase. If oxygen levels are reduced under non-photosynthetic conditions using low-oxygen gas mixes, nitrite reductase activity is detected at wild-type levels in the strain lacking the oxidase. In addition, co-culture experiments show that incubation of thecbb3deficient strain 2.4.3 withR. sphaeroides2.4.1, which isnirKdeficient but has the high-affinitycbb3oxidase, restores denitrification in sealed-vessel experiments. Taken together these results indicate that high end-point O2levels are the reason why the strain lacking thecbb3oxidase cannot transition from aerobic respiration to denitrification under certain conditions. The protein probably being affected by these O2levels is the transcriptional regulator NnrR.

Publisher

Microbiology Society

Subject

Microbiology

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