Molecular and Biochemical Characterization of Salt-Tolerant Trehalose-6-Phosphate Hydrolases Identified by Screening and Sequencing Salt-Tolerant Clones From the Metagenomic Library of the Gastrointestinal Tract

Gut microbiota and metabolic functions in herbivorous fish from Xisha coral reefs, China

Herbivorous fishes are the major consumers of macroalgae on coral reefs. Macroalgae are then degraded by fish gut microbiota. Despite the importance of this process, there remains a lack of information about the gut bacterial community of herbivorous fishes in coral reefs. This study examined the composition and potential metabolic functions of gut microbiota through full-length 16S rRNA amplicon sequencing for coral reef fish species from the Xisha islands of China, including five herbivorous species (Naso unicornis, N. lituratus, N. brevirostris, Ctenochaetus striatus, and Siganus argenteus) and one carnivorous species (Myripristis kuntee). The composition of the gut bacterial community and potential functional genes were observed and significant differences were identified between herbivorous and carnivorous fish species. The bacterial diversity (Shannon and Simpson indexes) in herbivorous fish was significantly higher than in carnivorous fish. Clostridium was significantly more abundant in carnivorous fish than herbivorous fish (p < 0.05). Conversely, Niameybacter, Alistipes, Desulfovibrio, and Akkermansia were more abundant in herbivorous fish (p < 0.05). These bacterial genera, which are shared among herbivorous fish, are believed to play crucial roles in macroalgae metabolism. A principal coordinate analysis further revealed that the gut bacterial composition of the five herbivorous fish species could be divided into two distinct clusters, which was influenced by selective feeding behaviors on different macroalgae types. Functional analysis of gut bacteria in herbivorous fishes showed a high abundance of carbohydrate metabolism pathways. Through comparison with the carbohydrate-active enzyme (CAZy) database, eight glycoside hydrolases (GHs) and one glycosyltransferase (GT) were identified in herbivorous fishes, providing further insights into the roles of gut microbiota in macroalgae metabolism. This study provides valuable insights into the roles of the gut microbiota in herbivorous fishes with regard to metabolizing various types of macroalgae.

Salt tolerance evolution facilitates antibiotic resistome in soil microbiota: Evidences from dissemination evaluation, hosts identification and co-occurrence exploration

Salinity is considered as one of the vital factors affecting the profiles of antibiotic resistance genes (ARGs) in soils, whereby its roles in shaping the antibiotic resistome were still poorly understood. Here, metagenomic analysis was conducted to track the ARGs distributions and dissemination in soils during salt accumulation and desalinization processes. Neutral-salt accumulation for 45 and 90 days significantly increased the relative abundances of ARGs and mobile genetic elements (MGEs) carrying antibiotic resistance contigs (ARCs). The ARGs within antibiotic efflux and target protection families primarily carried by Streptomyces, Nocardioides, Rhodanobacter and Monashia were largely enriched by salinity. The ARGs subtypes of the resistance-nodulation-division (RND) family, ATP-binding cassette (ABC) family, rRNA methyltransferase and other efflux were closely associated with MGEs, contributing to the enrichment of ARGs. Moreover, the ARGs subtypes and transposons were genetically linked with the salt-tolerance mechanisms of organic osmolyte transporters and K⁺ uptake proteins on the same ARC, demonstrating the coselection of ARGs and halotolerant genes. Furthermore, the antibiotic resistome could recover to a normal state after the prolonged incubation by alleviating salt stress. Nevertheless, the acquisition of ARGs by opportunistic pathogens after salt treatment was increased, serving to prioritize further efforts on the health risks correlated with resistance propagation and human exposure in saline soils.

Purification and characterization of cold-adapted and salt-tolerant dextranase from Cellulosimicrobium sp. THN1 and its potential application for treatment of dental plaque

The cold-adapted and/or salt-tolerant enzymes from marine microorganisms were confirmed to be meritorious tools to enhance the efficiency of biocatalysis in industrial biotechnology. We purified and characterized a dextranase CeDex from the marine bacterium Cellulosimicrobium sp. THN1. CeDex acted in alkaline pHs (7.5-8.5) and a broad temperature range (10-50°C) with sufficient pH stability and thermostability. Remarkably, CeDex retained approximately 40% of its maximal activities at 4°C and increased its activity to 150% in 4 M NaCl, displaying prominently cold adaptation and salt tolerance. Moreover, CeDex was greatly stimulated by Mg2+, Na+, Ba2+, Ca2+ and Sr2+, and sugarcane juice always contains K+, Ca2+, Mg2+ and Na+, so CeDex will be suitable for removing dextran in the sugar industry. The main hydrolysate of CeDex was isomaltotriose, accompanied by isomaltotetraose, long-chain IOMs, and a small amount of isomaltose. The amino acid sequence of CeDex was identified from the THN1 genomic sequence by Nano LC-MS/MS and classified into the GH49 family. Notably, CeDex could prevent the formation of Streptococcus mutans biofilm and disassemble existing biofilms at 10 U/ml concentration and would have great potential to defeat biofilm-related dental caries.