Enhanced Degradation of Petroleum and Chlorinated Hydrocarbons by a Dual-Bacteria System

In this study, the gradient pressure enrichment method was first used to screen out an environmental bacterium with the degradation ability of typical petroleum hydrocarbons such as phenanthrene and n-hexadecane, identified as Pseudomonas and named TB-1, from soil samples collected from 9 crude oil-contaminated sites; then, enhanced degradation of mixed organic pollutants, including petroleum and chlorinated hydrocarbons which are commonly coexistent, was achieved by a dual-bacteria system, with the addition of a laboratory storage strain Pseudomonas BL5. The degradation rate of phenanthrene and n-hexadecane by the dual-bacteria system was lower compared with the single bacterium Pseudomonas TB-1 under the tested conditions: phenanthrene degradation decreased from 44.2% to 23.1%, and n-hexadecane degradation decreased from 77.9% to 54.7% at a pollutant concentration of 100 mg/L after 7 days of cultivation. In contrast, the degradation ability of the dual-bacteria system against the mixed pollutants composed of petroleum and chlorinated hydrocarbons was good, with a degradation rate of 82.2% for phenanthrene, 89.2% for n-hexadecane, 73.1% for p-chlorobenzene, and 95.7% for dichloroethane with each concentration of 100 mg/L after 7 days. These results indicate that, although the dual-bacteria system does not enhance degradation under single-hydrocarbon conditions, its performance under chemically complex co-contamination suggests a potential cooperative or complementary interaction between the two strains. Such interactions are proposed here as a working hypothesis rather than a confirmed mechanism. Overall, the defined dual-Pseudomonas system shows promising potential for the treatment of environments co-contaminated with petroleum and chlorinated hydrocarbons.