Biodegradation and bioaugmentation of tetracycline by Providencia stuartii TX2: Performance, degradation pathway, genetic background, key enzymes, and application risk assessment.

The antibiotic tetracycline (TC) is an emerging pollutant frequently detected in various environments. Biodegradation is a crucial approach for eliminating TC contamination. However, only a few efficient TC-degrading bacteria have been isolated, and the molecular mechanisms of TC degradation, as well as their application potential, remain poorly understood. This study isolated a novel TC-degrading bacterium, Providencia stuartii TX2, from the intestine of black soldier fly larvae. TX2 exhibited remarkable performance, degrading 72.17 % of 400 mg/L TC within 48 h. Genomic analysis of TX2 unveiled the presence of antibiotic resistance genes and TC degradation enzymes. Transcriptomic analysis highlighted the roles of proteins related to efflux pumps, enzymatic transformation, adversity resistance, and unknown functions. Three TC degradation pathways were proposed, with TC being transformed into 27 metabolites through epimerization, hydroxylation, oxygenation, ring opening, and de-grouping, reducing TC toxicity. Additionally, TX2 significantly enhanced TC biodegradation in four TC-contaminated environmental samples and reduced antibiotic resistance genes and mobile genetic elements in chicken manure. This research provides insights into the survival and biodegradation mechanisms of Providencia stuartii TX2 and evaluates its potential for environmental bioremediation.

Comparative Metagenomic and Metatranscriptomic Analyses Reveal the Response of Black Soldier Fly (Hermetia illucens) Larvae Intestinal Microbes and Reduction Mechanisms to High Concentrations of Tetracycline.

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.