AUTHOR=de Jong Samuel I. , Wissink Martijn , Yildirim Kadir , Pabst Martin , van Loosdrecht Mark C. M. , McMillan Duncan G. G. 

TITLE=Quantitative proteomics reveals oxygen-induced adaptations in Caldalkalibacillus thermarum TA2.A1 microaerobic chemostat cultures

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1468929

DOI=10.3389/fmicb.2024.1468929

ISSN=1664-302X

ABSTRACT=<p>The thermoalkaliphile <italic>Caldalkalibacillus thermarum</italic> possesses a highly branched respiratory chain. These primarily facilitate growth at a wide range of dissolved oxygen levels. The aim of this study was to investigate the regulation of <italic>C. thermarum</italic> respiratory chain. <italic>C. thermarum</italic> was cultivated in chemostat bioreactors with a range of oxygen levels (0.25% O<sub>2</sub>–4.2% O<sub>2</sub>). Proteomic analysis unexpectedly showed that both the type I and the type II NADH dehydrogenase present are constitutive. The two terminal oxidases detected were the cytochrome <italic>c</italic>:oxygen <italic>aa</italic><sub>3</sub> oxidase, whose abundance was highest at 4.2% O<sub>2</sub>. The cytochrome <italic>c</italic>:oxygen <italic>ba</italic><sub>3</sub> oxidase was more abundant at most other O<sub>2</sub> levels, but its abundance started to decline below 0.42% O<sub>2</sub>. We expected this would result in the emergence of the cytochrome <italic>c</italic>:oxygen <italic>bb</italic><sub>3</sub> complex or the menaquinol:oxygen <italic>bd</italic> complex, the other two terminal oxidases of <italic>C. thermarum</italic>; but neither was detected. Furthermore, the sodium-proton antiporter complex Mrp was downregulated under the lower oxygen levels. Normally, in alkaliphiles, this enzyme is considered crucial for sodium homeostasis. We propose that the existence of a sodium:acetate exporter decreases the requirement for Mrp under strong oxygen limitation.</p>