Effect of variation in physicochemical parameters on the growth of Pseudomonas aeruginosa and Escherichia coli isolated from marine water sample

Marine microorganisms play vital roles in global nutrient cycling, ecological balance, and environmental health. However, variations in physicochemical conditions resulting from natural processes and human activities can have a significant impact on bacterial growth, survival, and ecological adaptation. Thus, knowledge of how environmental factors affect bacterial physiology is crucial for predicting microbial responses in marine environments and for informing environmental management and public health strategies. This study examined the effects of selected physicochemical parameters on the growth of Escherichia coli and Pseudomonas aeruginosa isolated from marine water samples. Bacterial isolates were characterized and identified using morphological and biochemical techniques. The two bacterial isolates were subjected to controlled variations in pH (2.5–8.5), temperature (25–60 °C), salt concentration (0–5.0 mg/mL), metallic ions (Ca²⁺, Mg²⁺, and K⁺), and incubation periods up to 24 h. The bacterial growth response was determined at an optical density (OD) of 600 nm. Statistical analysis was performed using SPSS version 27, and statistical significance was set at p ≤ 0.05. Both isolates showed optimum growth at pH 6.5, with an ODs of 1.045 ± 0.023 for P. aureginosa and 1.030 ± 0.020 for E. coli , whereas growth was severely inhibited under highly acidic conditions. The optimum growth temperature was 37 °C for P. aeruginosa (OD = 0.730 ± 0.020) and 45 °C for E. coli (OD = 0.855 ± 0.023). Both organisms were strongly and significantly inhibited by salt concentration ( p < 0.001); however, P. aeruginosa was more tolerant to high salt concentrations. Calcium ions showed a significant positive effect on E. coli growth ( r = 0.897, p = 0.006), while magnesium and potassium ions induced species-specific responses. Potassium ions had a variable effect on both species. Incubation time showed a strong positive relationship with growth in both isolates ( p < 0.001), with optimal growth at 24 h for P. aeruginosa (OD = 0.425 ± 0.025) and 22–24 h for E. coli. ( OD = 0.380 ± 0.030). The study demonstrated that variation in physicochemical parameters has a distinct effect on the growth of both organisms, which indicates species-specific adaptive responses. Notably, P. aeruginosa showed broader tolerance to higher salt concentrations and lower temperature thresholds than E. coli . These results improve our understanding of their possible ecological adaptations and may initiate further study and targeted biotechnological applications, environmental management strategies, and microbial risk assessment in marine ecosystems.