Studies on the respiratory system in alkaliphilic Bacillus; a proposed new respiratory mechanism

Respiratory electron transfer systems in two alkaliphilic Bacillus species, YN-1 and YN-2000, were investigated In the cyanide-sensitive pathway of the obligate alkaliphilic Bacillus YN-1, the terminal enzyme was a caa3-type cytochrome c oxidase constituting up to just 10% of the total oxygen-reducing activity, while 90% of the respiratory activity was due to cyanide-insensitive, nonproteinaceous material with a molecular weight of 662. These results were consistent with the cyanide-tolerant growth of the bacterium. The molecular and catalytic properties of the nonproteinaceous material were not identical with those of menaquinones extracted from the bacterium. Furthermore, the nonproteinaceous material was also found in the facultative alkaliphilic Bacillus YN-2000, when that bacterium was cultivated in alkaline conditions. A new respiratory oxygen-reducing mechanism comprising a nonproteinaceous component and a catalase is proposed for these alkaliphilic Bacillus species.