Effects of Salinity on the Biodegradation of Polycyclic Aromatic Hydrocarbons in Oilfield Soils Emphasizing Degradation Genes and Soil Enzymes

The biodegradation of organic pollutants is the main pathway for the natural dissipation and anthropogenic remediation of polycyclic aromatic hydrocarbons (PAHs) in the environment. However, in the saline soils, the PAH biodegradation could be influenced by soil salts through altering the structures of microbial communities and physiological metabolism of degradation bacteria. In the worldwide, soils from oilfields are commonly threated by both soil salinity and PAH contamination, while the influence mechanism of soil salinity on PAH biodegradation were still unclear, especially the shifts of degradation genes and soil enzyme activities. In order to explain the responses of soils and bacterial communities, analysis was conducted including soil properties, structures of bacterial community, PAH degradation genes and soil enzyme activities during a biodegradation process of PAHs in oilfield soils. The results showed that, though low soil salinity (1% NaCl, w/w) could slightly increase PAH degradation rate, the biodegradation in high salt condition (3% NaCl, w/w) were restrained significantly. The higher the soil salinity, the lower the bacterial community diversity, copy number of degradation gene and soil enzyme activity, which could be the reason for reductions of degradation rates in saline soils. Analysis of bacterial community structure showed that, the additions of NaCl increase the abundance of salt-tolerant and halophilic genera, especially in high salt treatments where the halophilic genera dominant, such as Acinetobacter and Halomonas. Picrust2 and redundancy analysis (RDA) both revealed suppression of PAH degradation genes by soil salts, which meant the decrease of degradation microbes and should be the primary cause of reduction of PAH removal. The soil enzyme activities could be indicators for microorganisms when they are facing adverse environmental conditions.

Differences In The Properties of Extracellular Polymeric Substances Responsible For PAH Degradation Isolated From Mycobacterium Gilvum SN12 Grown On Pyrene And Benzo[a]pyrenee

To evaluate the differences in the characteristics of extracellular polymeric substances (EPS) secreted by Mycobacterium gilvum SN12 (M.g. SN12) cultured on pyrene (Pyr) and benzo[a]pyrene (BaP) , heating method was used to extract EPS from M.g. SN12, and the composition, emulsifying activity and morphology of EPS extracts were investigated in this study. It was indicated that EPS extracts varied significantly with the addition of Pyr or BaP to the bacterial cultures. Concentration of proteins and carbohydrates, the main components of the EPS extracts, first increased and then decreased, with an increase in the concentration of Pyr (0–120 mg L-1) and BaP (0–120 mg L-1). A similar trend was observed for the emulsifying activity of the EPS extracts. EPS extracted from all cultures exhibited a compact structure with smooth surface, except EPS extracted from BaP-grown M.g. SN12, which exhibited a more fragile and softer surface. These findings suggest that Pyr and BaP had different influence on the properties of isolated EPS, providing insights into the mechanism underlying PAH biodegradation by some bacteria secreting EPS. To the best of our knowledge, this is the first report on the texture profile of EPS samples extracted from M.g. SN12 grown on PAHs.