Insights into bacterial associations catabolizing atrazine by culture-dependent and molecular approaches

Abstract

With the specific selection pressures of four atrazine concentrations (10–33 mg l⁻¹) and two pH values (5.5 and 7.5), eight atrazine-catabolizing microbial associations were enriched and isolated from pesticide-contaminated South African loamy soil. Community-level physiological profiling of Environmental Biolog analysis data identified species complement differences in response to both pH and atrazine concentration and these were confirmed by polymerase chain reaction-based denaturing gradient gel electrophoresis (PCR-DGGE). These differences were not detected by conventional plate cultures and light and scanning electron microscopy. To probe atrazine catabolism under a range of environmental conditions, the two (pH 5.5, KRA02; pH 7.5, KRA06) associations catabolizing 30 mg atrazine l⁻¹ were combined (KRA30). The highest specific growth rate was recorded at pH 4, while at pH 8 little growth resulted. With pH 4-poised cultures, the specific growth rates at 15 and 20 °C were comparable but more than doubled for the next 10° increment. These differences reflected species complement changes. Direct comparison of KRA30 with a reference strain, Pseudomonassp. strain ADP, identified comparable specific growth and atrazine catabolic rates. To probe catabolism further, nitrogen-limited batch cultures were made in the presence of supplemental carbon (citrate) but the catabolic rate did not change. The results are discussed with reference to in situ bioaugmentation remediation programmes.