Effect of emulsifying bacteria on phytotoxicity attenuation of soils contaminated with weathered petroleum hydrocarbons

Introduction: Plants and microorganisms have been used as bioindicators to evaluate the toxicity of hydrocarbons in soils. Objective: This study evaluates the toxicity of a chronically-contaminated Gleysol with several concentrations of weathered petrolewn hydrocarbons (WPH), collected from La Venta, Tabasco (Mexico), on the growth of Clitoria ternatea and the phytoxicity attenuation due to inoculation of emulsifying bacteria. Methods: Soils with 50 and 150 g WPH kg(-1), and control soil with 0.15 g WPH kg(-1) (biogenic origin) were utilized, as well as the inoculation of six emulsifying bacteria and their combination (consortium). The WPH-phytotoxicity was evaluated by considering plant height, dry biomass production (root, shoot, and total), leaf area, specific leaf area, and the efficiency of photosystem II (EPSII), after 30 days. Results: WPH did not affect plant height, but soil with 50 g WPH kg(-1) diminished root and total dry weight, and leaf area, when compared to both control soil and soil with 150 g WPH kg(-1). The strain Sml (Stenotrophomonas maltophilia C1OS1) significantly increased shoot and total dry weight, while the strain Ro (Raoultella ornithinolytica C5S3) produced higher specific leaf area relative to uninoculated plants. In control soil, the bacterial consortium stimulated plant height. The strains Sm (Serratia marcescens C11S1) and Sm2 (S. marcescens C7S3) improved plant height and specific leaf area when compared to uninoculated plants in soil with 50 g WPH kg(-1). In soil with 150 g WPH kg(-1) strains Spa (Stenotrophomonas pavanii C5S3F) and Cfr (Citrobacter freundii C4S3) enhanced root and shoot dry weight, respectively. The EPSII was unaffected by soil contamination. Emulsifying bacteria reduced the phytotoxic effects of WP, but depending on the content of WPH in soils. Conclusions: Soil with 50 g WPH kg(-1) showed the greatest phytotoxic effects on plant growth. Bacterial inoculation favored growth, biomass production and leaf area in soil with 150 g WPH kg(-1). The EPSII was not affected by WPH in soils.