RESUMEN
A thorough understanding of microbial communities in the gut of lower termites is needed to develop target-specific and environmentally benign wood protection systems. In this study, the bacterial community from Reticulitermes virginicus was examined by Illumina sequencing of 16S ribosomal RNA (rRNA) spanning the V3 and V4 regions. Prior to library preparation, the termites were subjected to five treatments over an 18-day period: three groups were fed on wood treated with 0.5% chitosan, 25% acetic acid, or water, the fourth group was taken directly from the original collection log, and the fifth group was starved. Metagenomic sequences were analyzed using QIIME 2 to understand the treatments' effects on the dynamics of the gut bacteria. Four dominant phyla were detected: Bacteroidetes (34.4% of reads), Firmicutes (20.6%), Elusimicrobia (15.7%), and Proteobacteria (12.9%). A significant effect of chitosan treatment was observed in two phyla; Firmicutes abundance was significantly lower with chitosan treatment when compared to other groups, while Actinobacteria was lower in unexposed and starved termites. The results suggest that chitosan treatment not only affects the structure of the microbial community in the gut, but other treatments such as starving also cause shifts in termite gut communities.
RESUMEN
BACKGROUND: Chitosan is a derivative form of chitin, which is the major component of exoskeletons of arthropods and the cell walls of fungi. The antimicrobial activity of chitosan against lepidopterans, aphids, fungi and bacteria has been extensively investigated, but only one report on the termiticidal effect of chitosan on termites has been published. In this study, we examined the termiticidal activity of chitosan by exposing single colonies of Reticulitermes flavipes (Kollar) and Reticulitermes virginicus Banks to wood treated with six different concentrations of chitosan solutions. Termite mortality and percent mass loss of wood samples after exposure to termites for 4 weeks were calculated. RESULTS: High termite mortality (≥ 94%) occurred during exposure of R. flavipes termites to chitosan-treated wood with ≥38 mg g-1 treatment concentrations (≥ 2% chitosan), while <50% termite mortality was observed at lower treatment concentrations (11-15 mg g-1 ; 0.5% and 1% chitosan). For R. virginicus, 100% mortality was observed at all levels of treatment concentrations. A decrease in the percent mass loss of the wood sample was apparent in samples treated with solutions with an increasing chitosan concentration, with a significant difference (P < 0.05) between lower and higher treatment concentrations. Treatment retention in wood samples upon leaching was also determined and showed retention levels of between 0 and 30 mg g-1 chitosan retention. CONCLUSION: This study investigated the exposure of subterranean termites to chitosan as a wood preservative. The results show that chitosan treatments at sufficiently high loadings could protect wood against termites, preferably under non-leaching conditions. © 2018 Society of Chemical Industry.
