Disruption of the polyhydroxyalkanoate synthase gene in Aeromonas hydrophila reduces its survival ability under stress conditions.

Aeromonas hydrophila 4AK4 produces PHBHHx copolyesters consisting of 3-hydroxybutyrate and 3-hydroxyhexanoate. In this paper, the physiological functions of PHBHHx on the bacterial survival ability were systematically studied using a PHBHHx synthase PhaC-disrupted mutant termed A. hydrophila CQ4 and its wild type A. hydrophila 4AK4. It was found that PHBHHx synthesis in A. hydrophila 4AK4 provided improved resistance against environmental stress factors including heat and cold treatments, hydrogen peroxide, UV irradiation, ethanol and high osmotic pressure compared with its PHBHHx synthase negative mutant A. hydrophila CQ4. The above resistant abilities were further confirmed by the different expression levels of sigma factor sigma(S) encoded by rpoS via real-time PCR study. The results suggested that rpoS played an important role in the enhanced resistance of host strain to stresses conferred by PHBHHx.