A quinol oxidase, encoded by cyoABCD, is utilized to adapt to lower O2 concentrations in Rhizobium etli CFN42.

Zachary R Lunak,K Dale Noel

doi:10.1099/mic.0.083386-0

Abstract

Bacteria have branched aerobic respiratory chains that terminate at different terminal oxidases. These terminal oxidases have varying properties such as their affinity for oxygen, transcriptional regulation and proton pumping ability. The focus of this study was a quinol oxidase encoded by cyoABCD. Although this oxidase (Cyo) is widespread among bacteria, not much is known about its role in the cell, particularly in bacteria that contain both cytochrome c oxidases and quinol oxidases. Using Rhizobium etli CFN42 as a model organism, a cyo mutant was analysed for its ability to grow in batch cultures at high (21 % O2) and low (1 and 0.1 % O2) ambient oxygen concentrations. In comparison with other oxidase mutants, the cyo mutant had a significantly longer lag phase under low-oxygen conditions. Using a cyo :: lacZ transcriptional fusion, it was shown that cyo expression in the wild type peaks between 1 and 2.5 % O2. In addition, it was shown with quantitative reverse transcriptase PCR that cyoB is upregulated approximately fivefold in 1 % O2 compared with fully aerobic (21 % O2) conditions. Analysis of the cyo mutant during symbiosis with Phaseolous vulgaris indicated that Cyo is utilized during early development of the symbiosis. Although it is commonly thought that Cyo is utilized only at higher oxygen concentrations, the results from this study indicate that Cyo is important for adaptation to and sustained growth under low oxygen.

Highlights

Bacteria have remarkable adaptability to environmental changes, such as fluctuations in oxygen concentration
In this study we sought to determine the oxygen conditions in which cyoABCD. Although this oxidase (Cyo) is utilized in an ubiquinol–cytochrome c oxidoreductase (Fbc)-containing organism such as R. etli CFN42
This strain is useful for studying Cyo, as inspection of the genome indicated that Cyo is the only terminal oxidase independent of the Fbc pathway

Summary

Introduction

Bacteria have remarkable adaptability to environmental changes, such as fluctuations in oxygen concentration. Terminal oxidases are the enzymes that catalyse oxygen reduction during aerobic respiration. In many bacteria this step is achieved by cytochrome c oxidases, which catalyse electron transfer from cytochrome c to oxygen. Prior to this reaction, cytochrome c is reduced by quinol through the action of ubiquinol–cytochrome c oxidoreductase (Fbc), known as the bc complex (Fig. 1). Electrons from quinol flow either through the aforementioned Fbc or directly to oxygen via terminal oxidases known as quinol oxidases (Fig. 1). Because oxygen is a substrate for both quinol and cytochrome c oxidases, oxygen is expected to be a major factor in how each of these oxidases is regulated and utilized within bacteria

Methods

Results

Conclusion