Impact of carbon starvation on stress resistance, survival in soil habitats and biocontrol ability of Pseudomonas putida strain 2C8

Exposure to carbon-limited growth conditions has been shown to induce resistance to a variety of environmental stresses in bacteria. Adaptation to nutrient-limited conditions by repeated culture on soil agar media was found to induce resistance to osmotic tension, oxidative stress and carbon limited culture conditions in Pseudomonas putida strain 2C8. Rifampicin resistant derivatives of strain 2C8 adapted to nutrient-limited conditions (strains 2C8-26Arif and 2C8-28Crif) did not exhibit enhanced survival in bulk soil relative to the parental strain. However, colonization of the apple rhizosphere by 2C8-26Arif and 2C8-28Crif was superior to that of the parental strain, 2C8rif. Improved colonization of the apple rhizosphere was not the result of an elevated ability to utilize apple root exudates as a sole carbon source. Enhanced colonization of the rhizosphere by carbon starved derivatives of 2C8rif was associated with improved biological control of Rhizoctonia root rot of apple caused by an introduced strain of Rhizoctonia solani AG 5. These findings demonstrate that inoculum production conditions can significantly alter the survival and efficacy of strain 2C8, and should be carefully considered in optimizing the use of this biocontrol rhizobacterium.