Microbial community structure changes during Aroclor 1242 degradation in the rhizosphere of ryegrass (Lolium multiflorum L.)

Polychlorinated biphenyls in a commercial mixture (Aroclor 1242) were added to soil at 8.0 mg kg−1 with and without ryegrass (Lolium multiflorum L.) planted in a specially designed rhizobox. At the end of 90 days, the presence of plants significantly increased Aroclor 1242 degradation compared with soils without ryegrass. Phospholipid fatty acids (PLFAs) profiles were affected by the distance from the rhizosphere, indicating a distance-dependent selective enrichment of competent species that may be responsible for efficient Aroclor 1242 degradation. The highest concentration of total PLFAs also occurred at 3 mm from the root zone in planted soils. The numbers of bacteria (cy17:0, 16:0), gram-positive bacteria (a15:0, i16:1, a17:0) and actinomycete (18:2ω6,9c) were significantly higher in planted soils than in unplanted soils. Furthermore, individual PLFAs [i16:0, 16:0 N alcohol, 18:0(10Me), i16:1, a15:0, i14:1, 14:0 2OH, 18:1ω9c, a17:0, 14:0 3OH, i14:0, a16:0, 16:1ω5c] were strongly correlated with the Aroclor 1242 degradation rates (%) (P<0.05) in planted treatments, whereas individual PLFAs of i16:1, 12:0 3OH, 15:0, a15:0 had significant correlations with the Aroclor 1242 degradation rates (%) (P<0.05) in unplanted soils. In particular, individual PLFAs i16:1 had strong correlations with Aroclor 1242 degradation in treatments both with and without ryegrass.