pSRD191, a new member of RepL replicating plasmid family from Selenomonas ruminantium

Development of the First Shuttle Vector System and Optimization of Transformation in Selenomonas sputigena

Selenomonas sputigena, an anaerobic bacterium found in the human respiratory tract, has recently gained significant attention due to its dual role in human health - as both a periodontal pathogen and a protective agent against severe asthma. However, the absence of genetic tools for this organism has severely limited our understanding of its molecular mechanisms and therapeutic potential. Here, we report the first successful development of a genetic modification system for S. sputigena ATCC 35185. We constructed a shuttle vector carrying the Rep191 replication protein from Selenomonas ruminantium and systematically optimized transformation conditions. Through careful optimization of key parameters including DNA quantity, bacterial growth phase, membrane permeabilization, and post-pulse recovery time, we achieved a 22.5-fold improvement in transformation efficiency (from ~2,000 to ~45,000 CFU/μg DNA). The broad applicability of our system was demonstrated through successful transformation of multiple Selenomonas species, establishing the first standardized genetic modification system for this genus. We further validated the system's functionality by achieving stable GFP expression in S. sputigena, representing the first demonstration of ectopic protein expression in this organism. This work provides essential tools for investigating the molecular basis of S. sputigena's therapeutic effects and pathogenic capabilities, potentially accelerating the development of novel microbiome-based treatments for both respiratory and oral diseases.

Promiscuous plasmid replication in thermophiles: Use of a novel hyperthermophilic replicon for genetic manipulation of Clostridium thermocellum at its optimum growth temperature

Clostridium thermocellum is a leading candidate for the consolidated bioprocessing of lignocellulosic biomass for the production of fuels and chemicals. A limitation to the engineering of this strain is the availability of stable replicating plasmid vectors for homologous and heterologous expression of genes that provide improved and/or novel pathways for fuel production. Current vectors relay on replicons from mesophilic bacteria and are not stable at the optimum growth temperature of C. thermocellum. To develop more thermostable genetic tools for C. thermocellum, we constructed vectors based on the hyperthermophilic Caldicellulosiruptor bescii replicon pBAS2. Autonomously replicating shuttle vectors based on pBAS2 reproducibly transformed C. thermocellum at 60 °C and were maintained in multiple copy. Promoters, selectable markers and plasmid replication proteins from C. bescii were functional in C. thermocellum. Phylogenetic analyses of the proteins contained on pBAS2 revealed that the replication initiation protein RepL is unique among thermophiles. These results suggest that pBAS2 may be a broadly useful replicon for other thermophilic Firmicutes.

A novel erythromycin resistance plasmid from Bacillus sp. strain HS24, isolated from the marine sponge Haliclona simulans

A better understanding of the origin and natural reservoirs of resistance determinants is fundamental to efficiently tackle antibiotic resistance. This paper reports the identification of a novel 5.8 kb erythromycin resistance plasmid, from Bacillus sp. HS24 isolated from the marine sponge Haliclona simulans. pBHS24B has a mosaic structure and carries the erythromycin resistance gene erm(T). This is the first report of an erythromycin resistance plasmid from a sponge associated bacteria and of the Erm(T) determinant in the genus Bacillus.

Spreading and mutability of Selenomonas ruminantium plasmids

Two small plasmids from Selenomonas ruminantium strain 19D were cloned in Escherichia coli and completely characterized. Sequence comparison indicated that the plasmids are similar to those reported in genetically vaguely related S. ruminantium strain S20. Small 1.4-kb plasmids pSRD191 and pONE430 are only distantly related (approximately 30 % for deduced Rep protein amino acid sequence) but possess a short highly conserved region outside rep gene. Larger plasmids pSRD192 and pONE429 possess large identical DNA regions in an otherwise dissimilar background. Recombination is proposed as an important mechanism of evolution and spreading of S. ruminantium plasmids.