Rhodobacter sphaeroides adaptation to high concentrations of cobalt ions requires energetic metabolism changes

AbstractRhodobacter sphaeroides has for a long time been investigated for its adaptivecapacities to different environmental and nutritional conditions, includingpresence of heavy metals, which make it a valuable model organism for under-standing bacterial adaptation to metal stress conditions and future environ-mental applications, such as bioremediation of polluted sites. To furthercharacterize the capability of R. sphaeroides to cope with high cobalt ion con-centrations, we combined the selection of adaptive defective mutants, carriedout by negative selection of transposon insertional libraries on 5 mM Co 2+ -enriched solid medium, with the analysis of growing capacities and transcrip-tome profiling of a selected mutant (R95). A comparative analysis of resultsfrom the mutant and wild-type strains clearly indicated that the adaptive abilityof R. sphaeroides strongly relies on its ability to exploit any available energy-supplying metabolisms, being able to behave as photo- or chemotrophic micro-organism. The selected R95 mutant, indeed, exhibits a severe down-expressionof an ABC sugar transporter, which results nonpermissive for its growth incobalt-enriched media under aerobic conditions. Interestingly, the defectiveexpression of the transporter does not have dramatic effects on the growthability of the mutant when cultivated under photosynthetic conditions.