In situresponse of the linuron degradation potential to linuron application in an agricultural field

Abstract

To assess the involvement of the genus Variovorax and the linuron hydrolase gene libA in in situ linuron degradation in agricultural fields, changes in Variovorax community size and composition, in libA abundance and in linuron mineralization capacity were monitored in field soil plots either treated or not with a linuron‐containing herbicide mixture. Changes in Variovorax community composition, due to the proliferation of a hereto unknown Variovorax phylotype D, and increases in libA numbers occurred concomitant to increases in linuron mineralization capacity in the plot treated with the herbicide mixture. The observations suggest that Variovorax and libA proliferated as a response to linuron and hence their contribution to in situ linuron degradation. The involvement of Variovorax phylotype D and libA in linuron degradation in the examined soil was supported by laboratory soil microcosm experiments. Attempts to enrich in suspended cultures and isolate the organism corresponding to phylotype D from the soil were unsuccessful as the enrichment resulted in replacement of Variovorax phylotype D by other Variovorax phylotypes. This illustrates that linuron‐degrading strains isolated by liquid enrichment cultures are not always representatives of those responsive to linuron in the field, although the genus specificity of linuron degradation was retained.

Functional Redundancy of Linuron Degradation in Microbial Communities in Agricultural Soil and Biopurification Systems

“…DNA concentrations of the purified DNA fragments were determined with the NanoDrop 1000 spectrophotometer (Thermo Scientific). The (9,16,17). hylA, dcaQ I , and dcaQ II gene copy numbers were determined on the same DNA extracts that were previously used to determine libA and 16S rRNA gene copy numbers (9,16,17).…”

“…The agricultural soil DNA extracts used originated from a field experiment and a concomitant SM experiment which assessed the responses of the Variovorax community, libA gene copy number, and linuron mineralization potential to linuron application. A detailed description of those experiments is found in the work of Bers et al (9). Briefly, two adjacent potato field plots either were not treated with any herbicide (plot P0) or, at day 0, were treated with 450 g linuron ha Ϫ1 (plot PF).…”

“…Until recently, libA was the only linuron hydrolysis gene linked with linuron mineralization. In several environments such as agricultural soil and on-farm biopurification systems (BPS) used for the treatment of agricultural pesticide-contaminated wastewater, the abundance of libA increased in parallel with increasing linuron mineralization capacity as a response to linuron application, indicating a prominent role for libA in linuron mineralization in environmental settings (8,9). However, in addition to LibA, other linuron hydrolases were proposed to contribute to linuron mineralization in Variovorax and in the environment, as some linuron-degrading Variovorax isolates lack a libA homologue and libA did not proliferate in all environments that developed linuron mineralization activity upon exposure to linuron (7).…”

“…Moreover, we examined whether commensalism in linuron metabolism as observed for hylA-carrying WDL1 and hence multispecies food webs are involved in linuron biodegradation in the environment. For those purposes, gene copy numbers of hylA as well as dcaQ were determined in available DNA extracts from two different ecosystems for which the responses of the resident Variovorax community, of the libA gene copy number, and of the intrinsic capacity to mineralize linuron to the application of linuron were studied previously (9,16,17). The gene dcaQ encodes the glutamine-aminotransferase-like component of the multicomponent enzyme 3,4-dioxygenase converting 3,4-DCA into chlorocatechol and functions as a marker for linuron biodegradation beyond 3,4-DCA (18,19).…”

“…The gene dcaQ encodes the glutamine-aminotransferase-like component of the multicomponent enzyme 3,4-dioxygenase converting 3,4-DCA into chlorocatechol and functions as a marker for linuron biodegradation beyond 3,4-DCA (18,19). The first ecosystem is an agricultural soil with a history of linuron treatment and was studied as a field experiment followed by a lab-scale soil microcosm (SM) experiment that was initiated to verify results of the field experiment in a controlled way (9). The second ecosystem mimicked the environment of an on-farm BPS.…”