Growth of Pseudomonas protegens Pf-5 in M9 minimal salts medium

Growth in minimal salts medium meant that a microorganism has the full repertoire of biosynthetic machinery for surviving in habitats lacking in vitamins and growth factors. This significantly expands the types of habitats suitable for colonization by the microbe. Such evolutionary selected and endowed survival advantage provided a critical growth advantage and colonization potential to particular microbes. Pseudomonas protegens Pf-5 (ATCC BAA-477) potential for growth in minimal salts medium was evaluated by aerobic growth experiments at 25 and 30 oC in M9 medium. Experiment results revealed that the bacterium could grow in M9 medium without nutrient and yeast extract supplementation, but with a long lag phase of 18 hours and a small optical density of 0.7 and 1.0 at 25 and 30 oC, respectively after 45 hours of incubation. Variation in pH, on the other hand, revealed similar pH profiles of net secretion of acidic metabolites during growth in M9 medium, that stabilized prior to attainment of maximal optical density in the cultures at the two temperatures. Supplementation of M9 medium with 1 g/L yeast extract at 25 oC resulted in a shorter lag phase of 3 hours in P. protegens Pf-5 and a maximal optical density of 3.1, which indicated the importance of vitamins and growth factors in yeast extract in supplying necessary building blocks for biomass formation. Similarly, net secretion of acidic metabolites was observed in pH profile prior to exponential phase growth in P. protegens Pf-5, which was followed by a gradual rise in culture broth’s pH. Collectively, P. protegens Pf-5 could grow in minimal salts medium without supplementation of vitamins and growth factors at 25 and 30 oC; thereby, pointing to a significant competitive advantage in survival and colonization of new habitats in the face of nutritional and environmental stressors.