Robust Linuron Degradation in On-Farm Biopurification Systems Exposed to Sequential Environmental Changes

Abstract

On-farm biopurification systems (BPS) treat pesticide-contaminated wastewater of farms through biodegradation. Adding pesticide-primed soil has been shown to be beneficial for the establishment of pesticidedegrading populations in BPS. However, no data exist on the response of pesticide-degrading microbiota, either endogenous or introduced with pesticide-primed soil, when BPS are exposed to expected less favorable environmental conditions like cold periods, drought periods, and periods without a pesticide supply. Therefore, the response of microbiota mineralizing the herbicide linuron in BPS microcosm setups inoculated either with a linuron-primed soil or a nonprimed soil to a sequence of such less favorable conditions was examined. A period without linuron supply or a drought period reduced the size of the linuron-mineralizing community in both setups. The most severe effect was recorded for the setup containing nonprimed soil, in which stopping the linuron supply decreased the linuron degradation capacity to nondetectable levels. In both systems, linuron mineralization rapidly reestablished after conventional operation conditions were restored. A cold period and feeding with a pesticide mixture did not affect linuron mineralization. The changes in the linuron-mineralizing capacity in microcosms containing primed soil were associated with the dynamics of a particular Variovorax phylotype that previously had been associated with linuron mineralization. This study suggests that the pesticide-mineralizing community in BPS is robust in stress situations imposed by changes in environmental conditions expected to occur on farms. Moreover, it suggests that, in cases where effects do occur, recovery is rapid after restoring conventional operation conditions.The treatment of pesticide-contaminated wastewater in onfarm biopurification systems (BPS) is a low-cost and effortless solution for farmers to minimize the direct losses of pesticides to surface water (6). On-farm BPS operate as biofilters in which the pesticides are removed from the wastewater by biodegradation and sorption processes occurring in the biofilter matrix. The matrix in a BPS, designated a biomix, is composed of a mixture of soil, peat, and straw or other organic waste materials (6, 9). The addition of pesticide-primed soil to BPS has been proposed as an alternative for bioaugmentation with axenic cultures of specialized pesticide-degrading bacteria to accelerate pesticide degradation and avoid the production of toxic metabolites (7, 18). Sniegowski et al. (18) showed that bioaugmentation with a linuron-primed soil containing linuron-mineralizing microorganisms immediately resulted in the establishment of a linuron mineralization capacity in BPS microcosms. The size of the linuron-mineralizing populations in the system further increased when the microcosms were fed linuron. BPS microcosms inoculated with nonprimed soils also developed a linuron mineralization capacity but only after a much longer period of linuron supply. In the BPS microcosms contain...

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).…”

“…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 second ecosystem mimicked the environment of an on-farm BPS. Microcosms (BMs) containing BPS material were treated with linuron (7,16), and different stress events were imposed to study their effects on linuron mineralization (20,21).…”

Quantification of IncP-1 Plasmid Prevalence in Environmental Samples

“…The korB assay was used to analyze the abundance and dynamics of IncP-1 plasmids in a large pesticide-degrading biofilter operated on a farm near Kortrijk, Belgium, which was previously characterized (23). Four spatially separated plots in the biofilter were sampled three times over a season with continuing applications of pesticide wastes, before start-up (March), during processing (July), and after closedown (September).…”

“…Four spatially separated plots in the biofilter were sampled three times over a season with continuing applications of pesticide wastes, before start-up (March), during processing (July), and after closedown (September). The biofilter, composed of coco chips, straw, and soil, received 37 different active compounds, including 16 halogenated aromatics (23). Total DNA was extracted from 0.5 g of 2-mm-sieved biofilter samples by using the FastPrep FP120 bead beating system for cell lysis and the FastDNA SPIN Kit for Soil (MP Biomedicals, Santa Ana, CA) and purified by using the GENECLEAN Spin Kit (MP Biomedicals).…”