Chicken manure application alters microbial community structure and the distribution of antibiotic-resistance genes in rhizosphere soil of Cinnamomum camphora forests

The distribution of antibiotic-resistance genes (ARGs) in environmental soil is greatly affected by livestock and poultry manure fertilization, the application of manure will lead to antibiotic residues and ARGs pollution, and increase the risk of environmental pollution and human health. Cinnamomum camphora is an economically significant tree species in Fujian Province, China. Here, through high-throughput sequencing analysis, significant differences in the composition of the bacterial community and ARGs were observed between fertilized and unfertilized rhizosphere soil. The application of chicken manure organic fertilizer significantly increased the relative abundance and alpha diversity of the bacterial community and ARGs. The content of organic matter, soluble organic nitrogen, available phosphorus, nitrate reductase, hydroxylamine reductase, urease, acid protease, β-glucosidase, oxytetracycline, and tetracycline in the soil of C. camphora forests have significant effects on bacterial community and ARGs. Significant correlations between environmental factors, bacterial communities, and ARGs were observed in the rhizosphere soil of C. camphora forests according to Mantel tests. Overall, the findings of this study revealed that chicken manure organic fertilizer application has a significant effect on the bacterial community and ARGs in the rhizosphere soil of C. camphora forests, and several environmental factors that affect the bacterial community and ARGs were identified.

Isolation and characterization of gut bacteria associated with the degradation of host-specific terpenoids in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae

Insect intestinal bacteria play an important role in resisting defensive substances of host plants. Pagiophloeus tsushimanus (Coleoptera: Curculionidae) feeds exclusively on camphor trees (Cinnamomum camphora, Laurales: Lauraceae) in China, causing substantial economic and ecological losses. It is unclear how the larvae of P. tsushimanus outcome the main secondary metabolites of C. camphora such as D-camphor, eucalyptol, and linalool. In this study, we isolated terpenoid-degrading bacteria from the gut of P. tsushimanus larvae by using selective culture medium. Maximum likelihood phylogenetic analyses were performed with 16S rDNA sequences to identify the bacteria, and results showed ten strains belonged to four genera, including Pseudomonas, Enterobacter, Serratia, and Corynebacterium. Then, gas chromatography was employed to determine the degradability of D-camphor, eucalyptol, and linalool by the isolated strains, results showed that Z5 strain (i.e., Corynebacterium variabile, Actinomycetales: Corynebacteriaceae), F1 strain (i.e., Pseudomonas aeruginosa, Pseudomonadales: Pseudomonaceae), and A3 strain (i.e., Serratia marcescens, Enterobacterales: Enterobacteriaceae) had the highest degradation rates of D-camphor, linalool, and eucalyptol, respectively. The intestinal bacteria were capable of terpenoid degradation in vitro, which suggested that these gut bacteria associated with P. tsushimanus play an important role in overcoming host plant secondary metabolite defense, thereby facilitating the host specialization of this pest.