Low-temperature chemotaxis, halotaxis and chemohalotaxis by the psychrophilic marine bacterium Colwellia psychrerythraea 34H.

A variety of ecologically important processes are driven by bacterial motility and taxis, yet these basic bacterial behaviours remain understudied in cold habitats. Here, we present a series of experiments designed to test the chemotactic ability of the model marine psychrophilic bacterium Colwellia psychrerythraea 34H, when grown at optimal temperature and salinity (8°C, 35 ppt) or its original isolation conditions (-1°C, 35 ppt), towards serine and mannose at temperatures from -8°C to 27°C (above its upper growth temperature of 18°C), and at salinities of 15, 35 and 55 ppt (at 8°C and -1°C). Results indicate that C. psychrerythraea 34H is capable of chemotaxis at all temperatures tested, with strongest chemotaxis at the temperature at which it was first grown, whether 8°C or -1°C. This model marine psychrophile also showed significant halotaxis towards 15 and 55 ppt solutions, as well as strong substrate-specific chemohalotaxis. We suggest that such patterns of taxis may enable bacteria to colonize sea ice, position themselves optimally within its extremely cold, hypersaline and temporally fluctuating microenvironments, and respond to various chemical signals therein.