Effect of temperature on growth of Pseudomonas protegens Pf-5 and Pseudomonas aeruginosa PRD-10 in LB Lennox medium

Temperature affects growth of bacteria by influencing enzyme and growth kinetics. Specifically, evolution selects for specific temperature range in which a microbe could thrive, and thus fix the temperature range in which biomolecule structure and function are finely tuned for coping with the thermal conditions prevailing within a cell at a particular temperature. Using aerobic culture in LB Lennox medium in shake flasks, this study aimed to understand the growth of Pseudomonas protegens Pf-5 (ATCC BAA-477) and Pseudomonas aeruginosa PRD-10 (ATCC 15442) at 25, 30 and 37 ^oC. Experiment results revealed that P. protegens Pf-5 grew very poorly at 37 ^oC (with maximal optical density of 0.66), while better growth was observed at 25 and 30 ^oC. Specifically, P. protegens Pf-5 appeared to be better adapted to growth at 25 ^oC, where the maximal optical density obtained was 5.3 compared to 4.6 at 30 ^oC. More importantly, two phase growth behaviour was observed during growth at 30 ^oC where a faster initial phase of growth was followed by a slower one. Growth at 25 and 30 ^oC exhibited similar pH trend, which suggested similar metabolic processes was activated during growth. On the other hand, P. aeruginosa PRD-10 demonstrated a more efficient conversion of LB Lennox medium into biomass where the maximal optical density obtained at all three growth temperatures were higher than those of P. protegens Pf-5. More importantly, growth of P. aeruginosa PRD-10 exhibited a clear adaptation to growth at 25 and 37 ^oC, while growth at 30 ^oC resulted in a lower biomass yield compared to that of 25 and 37 ^oC. On the other hand, pH variation during culture revealed that P. aeruginosa PRD-10 likely activated similar metabolic processes at all three growth temperatures, where a higher growth temperature would result in the net secretion of more alkaline metabolites. Collectively, P. protegens Pf-5 and P. aeruginosa PRD-10 demonstrated clear temperature adaptation at an evolutionary level. In addition, experiment data suggested that P. aeruginosa PRD-10 might have co-evolved with humans on a substantial time scale resulting in a temperature preference of 37 ^oC over 30 ^oC.