Effect of water activity on stress tolerance and biocontrol activity in antagonistic yeast Rhodosporidium paludigenum

The aims of this study were to optimize the salt-adaptation conditions of the marine antagonistic yeast Rhodosporidium paludigenum and investigate the biocontrol activity of salt-induced cell suspensions of R. paludigenum on postharvest pathogens in fruits. Low water activity (a_w=0.98, 0.97, 0.96, and 0.95) inhibited the growth of R paludigenum in nutrient yeast dextrose broth, but the yeast grew better in the medium modified with NaCl solute than other nonionic solutes. R paludigenum grown in 6.6% NaCl-modified medium had higher viabilities (92.1%) at low water activity (a_w=0.95) than control (81.1%) after 48h incubation. The salt-adapted R. paludigenum also showed better viability than the un-adapted cells after being frozen, which may be related to the accumulation of intracellular trehalose. Moreover, the best biocontrol inhibition in pears and Chinese winter jujubes was obtained when R. paludigenum was grown in NaCl-modified medium. Therefore, this study implies that improving physiological inducement methods may be a promising strategy for accelerating commercialization of biocontrol agents.