Abstract
The effect of amino acids (glutamine, asparagine, and serine) and organic acids (citrate, malate, and pyruvate) on plasmid transfer was investigated on agar plates using Pseudomonas strains differing in physiological status. Counts by culture-dependent and culture-independent methods showed that the presence of organic compounds as the sole nutrient source increased the absolute number of transconjugants. Morevover, the presence of glutamine and pyruvate as the sole nutrient source resulted in a higher transfer frequency. This stimulatory effect of pyruvate was also investigated in short-term conjugation experiments under nutrient-amended conditions with glucose. Compared with glutamine, the presence of pyruvate resulted in a higher transfer frequency after 5 h of conjugation with active cells. The present study confirmed the importance of organic compounds and the physiological status of bacteria to plasmid transfer, and provided evidence that certain organic compounds (glutamine and pyruvate) can stimulate the growth of transconjugants and/or conjugal gene exchange between Pseudomonas spp.
