Isolation and identification of hexazinone-degrading bacterium from sugarcane-cultivated soil in Kenya.

The s-triazine herbicide hexazinone [3-cyclohexyl-6-dimethylamino-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], is widely used in agriculture for weed control. Laboratory biodegradation experiments for hexazinone in liquid cultures were carried out using sugarcane-cultivated soils in Kenya. Liquid culture experiments with hexazinone as the only carbon source led to the isolation of a bacterial strain capable of its degradation. Through morphological, biochemical and molecular characterization by 16S rRNA, the isolate was identified as Enterobacter cloacae. The isolate degraded hexazinone up to 27.3% of the initially applied concentration of 40 µg mL(-1) after 37 days of incubation in a liquid culture medium. The study reports the degradation of hexazinone and characterization of the isolated bacterial strain.

Effects of carbon amendment on in situ atrazine degradation and total microbial biomass.

This study elucidates the effects of carbon amendment on metabolic degradation of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine) and total microbial biomass in soil. Degradation of (14)C-ring-labelled atrazine was monitored in laboratory incubations of soils supplemented with 0, 10, 100 and 1000 µg g(-1) sucrose concentrations. An experiment to determine the effect of carbon amendment on total microbial biomass and soil respiration was carried out with different concentrations of sucrose and non-labelled atrazine. The soils were incubated at a constant temperature and constant soil moisture at water potential of -15 kPa and a soil density of 1.3 g cm(-3). Mineralization of (14)C-ring-labelled atrazine was monitored continuously over a period of 59 d in the first experiment. The CO(2) production was monitored for 62 d in the second experiment and microbial biomass determined at the end of the incubation period. The addition of 1000 µg g(-1) sucrose reduced atrazine mineralization to 43.5% compared to 51.7% of the applied amount for the treatment without sucrose. The addition of 1000 µg g(-1) sucrose modified the transformation products to 1.08 µg g(-1) deisopropylatrazine (DIA), 0.32 µg g(-1) desethylatrazine (DEA) and 0.18 µg g(-1) deisopropyl-2-hydroxyatrazine (OH-DIA). Treatment without sucrose resulted in formation of 0.64 µg g(-1) hydroxyatrazine (HA), 0.28 µg g(-1) DIA and 0.20 µg g(-1) OH-DIA. Atrazine dealkylation was enhanced in treatments with 100 and 1000 µg g(-1) of sucrose added. HA metabolite was formed in the control (no sucrose) and in the presence of 10 µg g(-1) of sucrose, whereas DEA was only detected in treatment with 1000 µg g(-1) sucrose. Results indicate that total microbial biomass increased significantly (P < 0.001) with the addition of 1000 µg g(-1) sucrose.

Biodegradation of s-triazine herbicide atrazine by Enterobacter cloacae and Burkholderia cepacia sp. from long-term treated sugarcane-cultivated soils in Kenya.

In this study soils from sugarcane-cultivated fields were screened for bacterial species capable of atrazine (6-chloro-N²-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) degradation due to long exposure of the soils to this herbicide. To enrich for atrazine degraders, Minimal Salt Medium containing atrazine as the sole N source and glucose as the C source was inoculated with soils impacted with this herbicide and incubated. Bacterial growth was monitored by measuring optical density. The degradation of atrazine was followed by measuring residual atrazine in liquid cultures over a given time period by high performance liquid chromatography. Bacterial strains isolated from the enrichment cultures were characterized by biochemical tests and identified by 16S rRNA gene sequencing. Two bacterial strains coded ISL 8 and ISL 15 isolated from two different fields were shown to have 94 and 96% 16S rRNA gene sequence similarity to Burkholderia cepacia respectively. Another bacterial sp., ISL 14 was closely related to Enterobacter cloacae with a 96% 16S rRNA gene sequence similarity. There was not much difference between the extents of atrazine degradation by the enrichment cultures with communities (79-82% applied amount) from which pure strains were isolated and the pure strains themselves in liquid cultures that showed a degradation of 53-83% of applied amount. The study showed existence of bacterial strains in different sugarcane-cultivated fields which can use atrazine as a nitrogen source. The bacterial strains isolated can be used to enhance the degradation of atrazine in contaminated soils where atrazine is still considered to be recalcitrant.

(13)C NMR characterization of triacylglycerols of Moringa oleifera seed oil: an "oleic-vaccenic acid" oil.

The composition of acyl chains and their positions in the triacylglycerols of the oil extracted from seeds of Moringa oleifera were studied by (13)C NMR spectroscopy. The unsaturated chains of M. oleifera seed oil were found to comprise only mono-unsaturated fatty acids and, in particular, two omega-9 mono-unsaturated acids, (cis-9-octadecenoic (oleic acid) and cis-11-eicosenoic acids) and one omega-7 mono-unsaturated acid (cis-11-octadecenoic acid (vaccenic acid)). The mono-unsaturated fatty acids were detected as separated resonances in the spectral regions where the carbonyl and olefinic carbons resonate according to the 1,3- and 2-positions on the glycerol backbone. The unambiguous detection of vaccenic acid was also achieved through the resonance of the omega-3 carbon. The (13)C NMR methodology enabled the simultaneous detection of oleate, vaccenate, and eicosenoate chains according to their positions on the glycerol backbone (1,3- and 2-positions) through the carboxyl, olefinic, and methylene envelope carbons of the triacylglycerol acyl chains.