Isolation of a selected microbial consortium from a pesticide-contaminated mix-load site soil capable of degrading the herbicides atrazine and alachlor

Contaminated soil from a 100-year-old mix-load site located in Reading, PA was evaluated for its potential to provide indigenous microorganisms capable of degrading two widely utilized herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine; AT) and alachlor (2-chloro-2′,6′-diethyl-N-[methoxymethyl]-acetanilide; AL). Three different locations from the site were chosen for experimentation based on herbicide handling activities. Standard enrichment techniques were used to isolate a selective microbial consortium (SCM) with the desirable degrading capabilities. Three enrichment treatment schemes were evaluated; AT and AL, AL alone, and only AT. Degradative organisms were isolated from only one of the sample locations. Considerable differences in the soil parameters of the three sample locations were found that might have had an effect on the ability of the indigenous microbial populations within the soil to degrade AT and AL. In the initial cultures from this location, degradation occurred in the AT and AL treatment only. Because the AT and AL were the only sources of carbon and nitrogen (N) for the microbes, these results suggest that AL alone was not a sufficient N source. In general, the ability to degrade AL by the SMC was dependent on AT degradation. Alachlor degradation did not begin until approximately 15% of the AT was transformed. Once all of the AT was removed very little further AL degradation occurred. The average half-life (t1/2) of AT was 7.5 d, while average t1/2 for AL degradation was 11 d. Individual colonies from the SMC were identified by fatty acids methyl ester (FAME) analysis. Five strains were identified with similarity indexes above 70%. These isolates included the following: Alcaligenes xylosoxydans subsp. denitrificans, Alcaligenes xylosoxydans subsp. xylosoxydans, Pseudomonas putida, Pseudomonas marginalis, and Providencia rustigianii.