Physiological activity and growth dynamics of isolates capable of biodegradation of petroleum products under conditions of changing pH, temperature and salinity of the environment

Recently, biological approaches using microbial biodegraders have become increasingly common in the cleanup of oil spills as an environmentally friendly and cost-effective alternative to physical and chemical methods. The aim of this work was to determine the physiological activity and growth dynamics of 12 isolates obtained from natural sources by measuring their optical density under various conditions (pH, temperature, NaCl concentration).

The most promising biodegraders were identified using liquid mineral medium with 2% diesel fuel (DF). Growth was monitored by optical density at 600 nm: over 14 days on DF and over 24 h in the stress tests (10–40°C, pH 5–8, 0.5–10% NaCl), with standard LB (0.5% NaCl, 30°C) as the control and the most active strain Les V 5 as the reference in the DF experiment. All measurements were performed in three biological replicates and are presented as mean ± confidence interval (Student's t-test); the relative error was mainly below 3% (considered insignificant), and inter-group differences were assessed by the Student criterion selected according to the sample distribution.

Morphological and biochemical profiling revealed diverse isolates, all capable of using glucose, sucrose and lactose. Based on 14-day cultivation with DF, five promising strains were selected (Lug III 1b, Lug VII 5, Lug IV 5z, Lug IV 5cor, Les V 5), the best specific growth increment exceeding the reference by 19% (1.453 vs. 1.221). The isolates tolerated 15–40°C, pH 5–8 and up to 7% NaCl, with the highest growth at 1–3% NaCl. 16S rRNA sequencing identified Brevundimonas diminuta (100% similarity, Lug IV 5cor) and Bacillus sp. (99.38%, Les V 5), presumably a novel strain.

Thus, the selected strains exhibit pronounced resistance to abiotic stressors and hydrocarbon-degradation potential, making them promising candidates for the bioremediation of oil-contaminated areas.