The respiratory chains of four strains of the alkaliphilic Bacillus clausii

• It is important to understand how alkaliphilic prokaryotes thrive at high pH.
• An interesting issue is their ability to cope with bioenergetics at high pH.
• We show that four genetically similar strains adopt different biochemical behaviors.
• Two of the strains show a functional redundancy of the terminal part of the respiratory chain.
• Biochemical data correlate with the expression of cytochrome c oxidase and quinol oxidase genes (heme-copper types).

A comparative analysis of terminal respiratory enzymes has been performed on four strains of Bacillus clausii used for preparation of a European probiotic. These four strains originated most probably from a common ancestor through early selection of stable clones for industrial propagation. They exhibit a low level of intra-specific diversity and a high degree of genomic conservation, making them an attractive model to study the different bioenergetics behaviors of alkaliphilic bacilli. The analysis of the different bioenergetics responses has been carried out revealing striking differences among the strains. Two out of the four strains have shown a functional redundancy of the terminal part of the respiratory chain. The biochemical data correlate with the expression level of the mRNA of cytochrome c oxidase and quinol oxidase genes (heme-copper type). The consequences of these different bioenergetics behaviors are also discussed.