Investigation into effects of transgenic glufosinate-resistant Zoysia grasses with herbicide application on bacterial communities under field conditions

Zoysia grass (Zoysia japonica Steud.) is a commercially valuable turfgrass that is popularly cultivated for use in sports and recreational environments. A field study was conducted in 2013 to evaluate the effects of transgenic herbicide-resistant Zoysia grasses in combination with the herbicide glufosinate on microbial communities. We investigated population changes in cultivable total bacteria and glufosinateresistant bacteria using the traditional plate-count method. The results showed that total and glufosinate-resistant bacteria counts decreased in September. Significant differences in the abundance of cultivable bacteria were observed between Zoysia grass lines as well as between March and September samples in both glufosinate-treated and nontreated plots. However, there was no significant difference in the abundance of total cultivable bacteria between Zoysia grass lines in March or between Basta-treated and untreated plots in September. To assess the possible horizontal gene transfer (HGT) of the bar gene across microorganisms, total soil DNAs and genomic DNAs of glufosinate-resistant bacteria isolated from soils and water were analyzed by PCR. No positive DNA bands were found, indicating that HGT did not occur during this experimental period. We also investigated changes in taxonomic distribution of the bacterial community using 16S rRNA gene clone libraries constructed from soil samples. Although bacterial diversities increased in September, there were no significant differences in species richness between genetically modified (GM) and non-GM Zoysia grasses as well as between glufosinatetreated and untreated soils.