RESPONSE OF A MARINE SEDIMENT MICROBIAL COMMUNITY EXPOSED TO 2,4-DICHLOROPHENOXYACETIC ACID

Acclimation of a marine sediment microbial community to the herbicide 2, 4-dichlorophenoxyacetic acid (2, 4-D) was examined by comparing its ability to metabolize 2, 4-D before and after exposure to the herbici de. The experimental treatments (control: 2-week exposure, seawater on ly; test: 2-week exposure, seawater plus 100 ppm 2, 4-D) took place un der simulated in situ conditions, in an incubation chamber, which main tained the physical and chemical gradient structure of the sediment co mmunity. The surface of the sediment was exposed to recirculating seaw ater on a tidal cycle. 2, 4-D (100 ppm) was added to the seawater so t hat its availability to the sediment microbes mimicked the natural sit uation. Before and after treatment, bacterial abundance, productivity, and transformation of 2, 4-D were determined. After 2 weeks, bacteria l populations were similar in the 2, 4-D treatment and the initial sed iment sample, but higher in the seawater-only treatment. Bacterial pro ductivity was higher in both 2-week treatments, compared to productivi ty measured before treatment, but rates were the same in 2, 4-D and se awater treatments. In contrast, 2, 4-D transformation rates increased 28% in the 2-week 100-ppm 2, 4-D treatment, compared to the average of the sea,vater control and the initial sample. This increased transfor mation rate indicates that the sediment community acclimated to the se lective pressure of 2, 4-D treatment by increasing its ability to util ize this compound as a substrate.