Aerotaxis in Halobacterium salinarium is methylation-dependent

The behavioural response to a gradient of oxygen (aerotaxis) has been characterized in the archaeon, Halobacterium salinarium. When the gas surrounding a drop of H. salinarium strain S9-P culture was changed abruptly from 10% (v/v) O₂ to 100% N₂, the bacteria transiently increased the frequency of reversing before they adapted and resumed random swimming. When the gas was returned to 10% O₂ the bacteria responded by swimming smoothly for approximately 45 s. Aerotaxis was strongest when respiration in H. salinarium was highest and when bacteriorhodopsin and halorhodopsin were not contributing to the proton motive force. Starvation for methionine of the auxotrophic H. salinarium essentially abolished the step-down aerotactic response. Methanol production from demethylation of methyl-accepting chemotaxis proteins was transiently increased in H. salinarium S9-P by a step down or step up in oxygen concentration, as observed in methylation-dependent chemotaxis in H. salinarium. The taxis-negative and methyltransferase-deficient mutant, H. salinarium strain Pho72 did not exhibit changes in methanol release in response to aerotaxis or chemotaxis stimuli. This is the first report of an aerotactic response that is dependent on methylation of methyl-accepting chemotaxis proteins. Aerotaxis in Escherichia coli and Salmonella typhimurium is independent of transducer methylation.