Abstract-The effect of aging of the herbicides atrazine, terbuthylazine, 2,4-D, and mecoprop on their bioavailability to degrading microorganisms was studied in soil and aquifer sediment. 14 C-ring-labeled herbicide (2.5 mg/kg) was added to sterilized soil or aquifer sediment and stored at 10ЊC for up to 103 d before inoculation with either the atrazine and terbuthylazine-degrading Pseudomonas sp. strain ADP (atrazine-degrading Pseudomonas) or an enriched culture able to mineralize 2,4-D and mecoprop. The initial mineralization rate and recovery of 14 CO 2 after 62 to 113 d of incubation were used as measures of the availability of the compounds to the microorganisms. Aging in soil reduced the initial mineralization of atrazine. Thus, only 17% of the added 14 C-atrazine had been mineralized after 21 h of incubation when aged for 88 d as compared with 33% when the atrazine had been aged for 1 d. 14 CO 2 recovery was only 58% after 88 d of aging as compared with 81% when aged for 1 d. A similar effect of aging was seen with terbuthylazine. With 2,4-D, the effect of aging in soil on mineralization by the enriched culture was much smaller. Aging had no effect on mineralization of mecoprop in soil or on mineralization of any of the herbicides in aquifer sediment.

The aim of the study was to determine the effect of aging of the herbicide isoproturon and its metabolites monodesmethyl-isoproturon and 4-isopropyl-aniline in agricultural soil on their availability to the degrading bacterium Sphingomonas sp. strain SRS2. The 14C-ring-labeled isoproturon, monodesmethyl-isoproturon, and 4-isopropyl-aniline were added to sterilized soil and stored for 1, 49, 71, or 131 d before inoculation with strain SRS2. The availability of the compounds was estimated from the initial mineralization and the amount of 14CO2 recovered after 120 d of incubation. Aging in soil for 131 d reduced the initial mineralization of isoproturon and monodesmethyl-isoproturon and, in the case of isoproturon, also reduced the recovery of 14CO2. Initial mineralization and recovery of 14CO2 from aged 4-isopropyl-aniline were slightly reduced, but less 14CO2 was generally produced than with isoproturon or monodesmethyl-isoproturon. Thus, recovery of 14CO2 from 14C-isoproturon and 14C-monodesmethyl-isoproturon was 50.7 to 64.4% of the initially added 14C, while recovery from 14C-4-isopropyl-aniline was only 11.7 to 17.0%. Sorption measurements revealed similar Freundlich constants (K(f)) for isoproturon and monodesmethyl-isoproturon, whereas K(f) for 4-isopropyl-aniline was more than fivefold greater. The findings imply that in soil, partial degradation of isoproturon to 4-isopropyl-aniline may lead to reduced mineralization of the herbicide due to sorption of the aniline moiety.

Drinking water resources, such as groundwater, are threatened by pollution. The pesticide metabolite 2,6-dichlorobenzamide (BAM) is one of the compounds frequently found in groundwater. Studies have attempted to add specific BAM-degrading bacteria to sand filters at drinking water treatment facilities. This biotechnology has shown great potential in removing BAM from contaminated water. However, the degradation potential was formerly lost after ~2–3 weeks due to a decrease of the degrader population over time. The aim of the present study was to overcome the constraints leading to loss of degraders from inoculated filters. Our approach was threefold: (1) Development of a novel inoculation strategy, (2) lowering the flowrate to reduce washout of cells, and (3) increasing the concentration of nutrients hereunder the pollutant in a smaller inlet water stream. The two latter were achieved via modifications of the inlet water by applying membrane treatment which, besides producing an ultra-pure water fraction, produced a residual water stream with nutrients including BAM concentrated in ~ten-fold reduced volume. This was done to alleviate starvation of degrader bacteria in the otherwise oligotrophic sand filters and to enable a decreased flowrate. By this approach, we achieved 100% BAM removal over a period of 40 days in sand filter columns inoculated with the BAM-degrader Aminobacter sp. MSH1. Molecular targeting of the degrader strain showed that the population of degrader bacteria persisted at high numbers throughout the sand filter columns and over the entire timespan of the experiment. 16S rRNA gene amplicon sequencing confirmed that MSH1 dominated the bacterial communities of the inoculated sand filter columns at experimental termination. The community composition of the indigenous prokaryotes, based on beta diversity, in the sand filter columns was governed by the feed water type i.e., membrane retentate or untreated water.

The widely used herbicide atrazine and some of its degradation products are among the most commonly found xenobiotics in groundwater in Europe as well as in the USA. The bacterium Pseudomonas sp. strain ADP (P. ADP) possesses genes encoding atrazine mineralization on the self-transmissible plasmid pADP-1. In the present study, this ability of the strain to mineralize atrazine in aquifer sediment under both aerobic and denitrifying conditions at 10 degrees C was studied. P. ADP was able to mineralize more than 50% of 2.8 muM atrazine within 14 days under both growth conditions. Counts of degraders as colony forming units (CFU) on atrazine plates and counts of atzA gene copies as determined by quantitative competitive polymerase chain reaction (cPCR) were performed. The atzA gene encodes the enzyme which catalyzes the first step of atrazine mineralization by the strain. Quantification of the atzA gene gave rise to higher numbers than did counts of CFU. High nitrate concentrations inhibited atrazine mineralization and culturability on agar plates, but atzA copy numbers remained stable throughout the experiment. The results show a potential for bioaugmentation using P. ADP at both aerobic and denitrifying conditions and the use of cPCR as a tool for monitoring the bacteria independent of culturability.

The role of gene expression during acclimation of aquatic microbial communities was examined by relating transcription of tfdA to the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The tfdA gene encodes for a 2,4-D/2-oxoglutarate dioxygenase that transforms 2,4-D to 2,4-dichlorophenol. Transcription of tfdA, the abundance of tfdA genes and 2,4-D degrading populations, and the rate of 2,4-D disappearance were followed in laboratory incubations of two pond water samples that were exposed to 0.11 mM 2,4-D. Both communities responded to 2,4-D exposure by induction of tfdA transcription but the dynamics of transcript abundance and the homology to the tfdA riboprobe suggested different populations of 2,4-D degraders in the two ponds. In one community, where tfdA transcripts were highly homologous to the tfdA gene of Ralstonia eutropha JMP134, transcription of tfdA was transient and dropped while 2,4-D degradation continued. In the other freshwater community, where tfdA genes with a lower similarity to the tfdA gene of strain JMP134 were transcribed, transcript levels remained high although 2,4-D degradation had ceased. Restriction fragment length polymorphism analysis of tfdA amplicons similarly demonstrated the presence of different tfdA loci in the two freshwater communities, and this difference in populations of tfdA genes probably explains the observed difference in dynamics of catabolic gene transcription.