| The transformation of alachlor in aquatic systems was examined in a series of outdoor mesocosm (11.3-m3) and microcosm (250-mL) experiments. In addition to using conventional microbiological analyses, small subunit (ssu) rRNA levels were quantified using domain-level oligonucleotide probes to assess microbial community conditions. Water column alachlor levels and other parameters including total phosphorus, total nitrogen, pH, dissolved oxygen, chlorophyll a, and total and dissolved organic carbon were also monitored over time.; The first experiment assessed four nutrient-based treatments (ranging from oligotrophic to hypereutrophic conditions) to assess alachlor transformation rate as a function of aquatic fertility conditions. The second study assessed the effects of different light treatments (full exposure, partial exposure, or very limited exposure to sunlight) on alachlor transformation. It was generally found that alachlor transformation rate correlated with the levels of eubacterial and universal microbial ssu-rRNA activity. The active biotransformation of alachlor was verified in a smaller-scaled microcosm study where selective biological inhibitors (cycloheximide and/or antibacterial agents) were used to reduce domain-level activities; microbial activities and rates of alachlor transformation were significantly reduced when microbial inhibitors were present.; Ultimately, it was found that the ssu-rRNA data corresponded well with direct microscopic determinations of biomass. However, it was discovered that the conventional 16S-gene probes designed to detect eubacterial ssu rRNA also appeared to bind to ssu rRNA from algal communities. This was verified in an experiment that showed that non-specific binding occurred to ssu rRNA from pure algal cultures. This interference, which might pose a problem in assessing the ecology of aquatic systems using molecular techniques, can be overcome with an additional probe to the 785 region of ssu rRNA with sequences that selectively hybridize to the rRNA from cyanobacteria and plastids. |
