Effect of nutrient amendments and sterilization on mineralization and/or biodegradation of 14C-labeled MCPP by soil bacteria under aerobic conditions

Mineralization and/or degradation of the phenoxy herbicide mecoprop (MCPP) by a group of soil bacteria under the effects of nutrient amendments and sterilization were investigated. Five different species of Pseudomonas (P. paucimobilis, P. aeruginosa, P. mallei, P. pseudomallei, and P. pickettii) were isolated from sediments of Lake Mariut, a freshwater lake in south Alexandria, Egypt. MCPP mineralization and/or removal were tested by the selected Pseudomonas species as active and dead masses in minimal and nutrient-rich media supplemented with 14C-MCPP at a final concentration of 10 μg l−1 for 6 successive weeks. Results revealed significant variations in the removal percentages of MCPP by either mineralization or biodegradation. Pseudomonas spp. exhibited high selectivity toward MCPP. Considering the short duration of the experiment (45 days) Pseudomonas spp. investigated in this study provide an effective and selective potential for MCPP decontamination. As a general trend, all of the investigated species exhibited higher biodegradation and removal efficiency of MCPP (1.3–89.5%) compared to their mineralization abilities (0.10–9.28%) under the experimental conditions. Also the highest MCPP mineralization and degradation by the selected Pseudomonas spp. were achieved by their inactive (dead) followed by active-rich cultures (both were inoculated in nutrient-rich medium), confirming the positive effects of nutrient amendments and sterilization on MCPP decontamination. Efficiency of Pseudomonas spp. was positively correlated with time up to the 3rd week for biodegradation and up to the 6th week for mineralization, indicating high mineralization efficiency provided enough time. Finally, Pseudomonas spp. showed selective preferences among them toward MCPP with the highest mineralization efficiency achieved by P. aeruginosa (1SB) and P. mallei (2SA), while the highest biodegradation efficiency was achieved by P. pickettii (5SB) and P. pseudomallei (3S). They seemed very promising but require longer exposure and higher MCPP concentration to stimulate and enhance their metabolic and mineralization capabilities. Results of this study can be manipulated efficiently to select the most promising Pseudomonas species for decontaminating polluted systems providing the optimum degradation conditions.