Microbacterium Sulfonylureivorans Sp. Nov., Isolated From A Sulfonylurea Herbicides Degrading Consortium

A novel Gram-stain positive, aerobic, motile, rod-shaped bacterium, designated strain LAM7116T, was isolated from a sulfonylurea herbicides degrading consortium enriched with the birch forest soil from Xinjiang. The optimal temperature and pH for the growth of strain LAM7116T were 35 °C and 7.0, respectively. Strain LAM7116T could grow in the presence of NaCl up to 4% (w/v). Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain LAM7116T was closely related to the members of the genus Microbacterium, with the highest similarity to Microbacterium flavescens DSM 20643T (98.1%) and Microbacterium kitamiense Kitami C2T (98.1 %). Strain LAM7116T formed a distinct subclade with M. flavescens DSM 20643T within the genus Microbacterium in the 16S rRNA gene phylogenetic trees. The genomic DNA G+C content of LAM7116T was 69.9 mol%. The DNA-DNA hybridization (DDH) value between strain LAM7116T and M. flavescens DSM 20643T was 27.20 %. The average nucleotide identity (ANI) value was 83.96 % by comparing the draft genome sequences of strain LAM7116T and M. flavescens DSM 20643T. The major fatty acids were anteiso-C15:0, anteiso-C17:0, iso-C17:0 and iso-C16:0. The respiratory quinones of strain LAM7116T were MK-13 and MK-14. The main polar lipids were diphosphatidylglycerol, phosphatidylglycerol, an unidentified lipid and an unidentified glycolipid. Based on the phenotypic characteristics and genotypic analyses, we propose that strain LAM7116T represents a novel species, for which the name Microbacterium sulfonylureivorans sp. nov. was proposed. The type strain is LAM7116T (=CGMCC 1.16620T =JCM 32823T). Strain LAM7116T secreted auxin IAA and grew well in Ashby nitrogen-free culture medium. Genomic results showed that strain LAM7116T carried the nitrogenase iron protein (nifU and nifR3) gene, which indicated that strain LAM7116T has the potential to fix nitrogen and promote plant growth. At the same time, the strain LAM7116T can degrade nicosulfuron (a kind of sulfonylurea herbicides) by using glucose as carbon source, microbial degradation of nicosulfuron is the primary process of removing nicosulfuron from environments, and biodegradation is the most effective and environmentally friendly. Microbacterium sulfonylureivorans sp. nov. LAM7116T is a potential candidate for the biofertilizers of organic agriculture areas, having broad prospects for using, and may possess potential to be used in bioremediation of nicosulfuron-contaminated environments.

Effect of Repeated Application of Sulfonylurea Herbicides on Sulfosulfuron Dissipation Rate in Soil

Accelerated microbial degradation following previous repeated applications of the same pesticide, or another pesticide of a similar chemical structure, is a known phenomenon. Currently there is limited information regarding accelerated degradation of sulfonylurea (SU) herbicides. This study is aimed to evaluate the effect of repeated SU applications on the degradation rate of the SU herbicide sulfosulfuron in soil. The effect of repeated applications of sulfosulfuron on its degradation was assessed in two soils, using a sorghum root elongation bioassay. The effect of consecutive applications of sulfonylurea herbicides over the course of three to four seasons was further examined in controlled environment and a field study. Degradation of sulfosulfuron was determined following its application to soil samples from the field or a controlled environment, by measuring sulfosulfuron residues using liquid chromatography-tandem mass spectrometry. Following the repeated application of sulfosulfuron in the bioassay, the time to reduce sorghum root growth by 50% was shortened by up to 31.6%. However, consecutive application of SUs in the controlled environment had no effect on sulfosulfuron degradation rate constant. Yet, sulfosulfuron degradation rate was enhanced by a factor of 1.35 following consecutive application of SUs in the field, compared to untreated control soil. The data confirm that sulfosulfuron degradation could be enhanced due to repeated sulfosulfuron applications, thus potentially reducing its herbicidal efficacy.