Hongyuhang Ni

Salmonella is an important foodborne pathogen which comprises strains that exhibit varied virulence phenotypes and the capability of causing invasive human infection. In this study, the gene expression profile of foodborne and clinical Salmonella strains that exhibit high- and low-level virulence was investigated, with results showing that the expression level of a number of genes, including the rnc gene which encodes the RNase III ribonuclease, were exceptionally high in the high virulence strains. Investigation of the role of rnc in mediating expression of virulence phenotypes in Salmonella showed that the product of this gene could enhance expression of the superoxide dismutase SodA, which is an essential determinant of survival fitness of Salmonella under the oxidative stress elicited by the host immunity. On the other hand, we also discovered that the double-stranded RNA (dsRNA) released from Salmonella could trigger immune response of the host, and that the high-level expression of the rnc gene enabled Salmonella to evade the host immunity by reducing the amount of dsRNA accumulated in the bacterial cell. These findings provide insightful understanding of the regulation of Salmonella virulence and facilitate development of novel antimicrobial treatments through suppression of virulence expression and survival fitness of this important pathogen.

Salmonella is an important foodborne pathogen which comprises strains that exhibit varied virulence phenotypes and the capability of causing invasive human infection. In this study, the gene expression profile of foodborne and clinical Salmonella strains that exhibit high- and low-level virulence was investigated, with results showing that the expression level of a number of genes, including the rnc gene which encodes the RNase III ribonuclease, were exceptionally high in the high virulence strains. Investigation of the role of rnc in mediating expression of virulence phenotypes in Salmonella showed that the product of this gene could enhance expression of the superoxide dismutase SodA, which is an essential determinant of survival fitness of Salmonella under the oxidative stress elicited by the host immunity. On the other hand, we also discovered that the double-stranded RNA (dsRNA) released from Salmonella could trigger immune response of the host, and that the high-level expression of the rnc gene enabled Salmonella to evade the host immunity by reducing the amount of dsRNA accumulated in the bacterial cell. These findings provide insightful understanding of the regulation of Salmonella virulence and facilitate development of novel antimicrobial treatments through suppression of virulence expression and survival fitness of this important pathogen.

Black soldier fly (Hermetia illucens L) larvae (BSFL) possess remarkable antibiotic degradation abilities due to their robust intestinal microbiota. However, the response mechanism of BSFL intestinal microbes to the high concentration of antibiotic stress remains unclear. In this study, we investigated the shift in BSFL gut microbiome and the functional genes that respond to 1250 mg/kg of tetracycline via metagenomic and metatranscriptomic analysis, respectively. The bio-physiological phenotypes showed that the survival rate of BSFL was not affected by tetracycline, while the biomass and substrate consumption of BSFL was slightly reduced. Natural BSFL achieved a 20% higher tetracycline degradation rate than the germ-free BSFL after 8 days of rearing. Metagenomic and metatranscriptomic sequencing results revealed the differences between the entire and active microbiome. Metatranscriptomic analysis indicated that Enterococcus, Vagococcus, Providencia, and Paenalcaligenes were the active genera that responded to tetracycline. Furthermore, based on the active functional genes that responded to tetracycline pressure, the response mechanisms of BSFL intestinal microbes were speculated as follows: the Tet family that mediates the expression of efflux pumps expel tetracycline out of the microbes, while tetM and tetW release it from the ribosome. Eventually, tetracycline was degraded by deacetylases and novel enzymes. Overall, this study provides novel insights about the active intestinal microbes and their functional genes in insects responding to the high concentration of antibiotics.