Effectiveness of biodegradation of petroleum products by mixed bacterial populations in liquid medium at different pH values.

The possibility of using mineral oils as a carbon source by bacteria adapted to high oil concentrations was tested in liquid media with different pH values (pH = 5, 7 and 9). Two types of inocula were tested: inoculum I consisted of selected strains used in the bioremediation of oil-contaminated soils and inoculum II contained bacteria isolated from soil samples previously bioremediated at pH = 5, 7 and 9. Biodegradation was observed in all the investigated media independently of initial pH value and type of inoculum used. After 21 days of cultivation the reduction of oil content reached 60-70% in medium with pH = 5 and 80-90% in medium with pH = 7 and 9, respectively. Inoculum I consisted of strains of Arthrobacter, Pseudomonas, Agrobacter, Xanthomonas spp. After 21 days of incubation the elimination of some strains was observed. In cultures conducted at pH = 5 Agrobacter strain was no longer found, at pH 9 - the Pseudomonas strain was lost. In cultures maintained at pH = 7 all the introduced strains survived. Prolonged incubation in liquid medium at pH = 5 of strains isolated from bioremediated soils (type II inoculum) leads to the elimination of Bacillus from initial consortium of Arthrobacter, Bacillus and Pseudomonas. In cultures containing bacteria of type II inoculum (Arthrobacter, Bacillus, Achromobacter, Agrobacter, Alcaligenes, Pseudomonas, Xanthomonas, Micrococcus) conducted in liquid media at pH = 9 the Micrococcus strain was no longer present. In liquid cultures incubated at pH = 7 all introduced strains were recovered (Arthrobacter, Bacillus, Achromobacter).