Project description:Alkaliphilic microorganisms are similar to mesophilic counterparts with exception to membrane proteins. Detection of membrane proteins is difficult due to hydrophobicity and low absolute abundance. Caldalkalibacillus thermarum TA2.A1 is of interest due to growth from pH 7.5 to pH 10. Combination of whole cell lysate proteomics and membrane extracts solubilized with either SDS or FOS-choline-12 detected 158 membrane proteins, including a complete electron transport chain. Additionally, transporters for osmolytes ectoine and glycine betaine were observed.
Project description:Caldalkalibacillus thermarum possesses a highly branched respiratory chain. Branched electron transport chains (ETC) in model organisms such as Escherichia coli primarily facilitate growth at a wide range of dissolved oxygen levels. The aim of this study was to investigate whether a polyextremophile such as C. thermarum is regulated in a similar fashion. With this in mind, the organism was cultivated in chemostat bioreactors with a range of oxygen levels in the inlet gas (0.25% O2 – 4.2% O2). Proteomic analysis unexpectedly showed both the type I and the type II NADH dehydrogenases present in all conditions. Moreover, also two different terminal oxidases were present. The cytochrome c:oxygen aa3 complex abundance was highest at 4.2% O2, while the cytochrome c:oxygen ba3 complex exhibited higher abundance at the lowest O2 concentration 0.25% O2. The abundance of the cytochrome c:oxygen ba3 complex started to decline below 0.42% O2. Often this would result in emergence of the cytochrome c:oxygen bb3 complex or the menaquinol:oxygen bd complex, the other two terminal oxidases of C. thermarum; but neither was detected. Besides changes in the respiratory chain, 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, introducing a novel perspective to the field of alkaliphiles. contact: s.i.dejong@tudelft.nl or d.g.g.mcmillan@tudelft.nl
