Anhydrobiotic engineering for the endophyte bacterium Kosakonia radicincitans by osmoadaptation and providing exogenously hydroxyectoine.

ABSTRACT

This study presents an anhydrobiotic engineering approach aiming at conferring a high degree of desiccation tolerance to the Gram-negative endophyte Kosakonia radicincitans. In particular, pre-conditioning of bacteria under high salinities provides a remarkable positive influence on drying survival. The endophytic bacteria accumulate exogenous hydroxyectoine > 500 µmol g-1 dry weight cells exerted by osmotic stress at 4% NaCl. Microfermentation research demonstrated that hydroxyectoine provides positive effects on reducing the lag phase duration and alleviates the dissolved oxygen consumption under high salinity conditions. Beyond the amassing of hydroxyectoine, this work provides evidence supporting the notion that hydroxyectoine can produce significant changes in the endogenous bacterial metabolome during the exponential growth phase at high-osmolarity. Metabolome changes include alterations on tricarboxylic acid cycle, novo-synthesis of specific intracellular metabolites such as mannitol, myo-inositol and trehalose, and fold changes on amino acids such as L-leucine, L-asparagine, L-serine, L-methionine and L-proline. The significant fold change of L-aspartate suggests a potential acidic proteome at high-osmolarity environments, extending the knowledge of salt-stressed bacterial endophytes. Thus, these findings place the metabolic salt stress response and the hydroxyectoine accumulation by K. radicincitans into a physiological context, paving the way into the interaction between cellular phenotype associated with salt stress tolerance and drying survival capacity of Gram-negative endophytes.