We recently isolated multiple diverse plasmids from a complex groundwater microbial community. These native plasmids constitute a major category of mobile extrachromosomal DNA elements responsible for harboring and transferring genes important for survival and fitness. A model system developed to optimize plasmid DNA isolation procedures was targeted to samples which are characterized by low cell density and high complexity. The approach resulted in successful identification of several hundred circular plasmids, including some of the largest plasmids reported and spanned seven plasmid incompatibility groups. Natively these plasmids encoded traits such as metal, antibiotic, and phage resistance along with toxin-antitoxin systems are encoded on abundant circular plasmids, all of which could confer novel and advantageous traits to their hosts. I will present the work we did to experimentally validate the functions of genes on one of the most abundant plasmids we found in these samples. I will also present some of our most recent results for using these plasmids in the natural transformation of both gram negative and gram positive bacteria. From an ecological perspective, this study highlights the role of the “plasmidome” in maintaining the latent capacity of a microbiome, enabling rapid adaptation to environmental stresses. These natural genetic elements also provide parts for a genetic tool kit to modify and examine novel environmental strains and communities.
Discovery of large native plasmids and the implications for
understanding and manipulating microbial communities
Senior Scientist, Biological Systems & Engineering
Lawrence Berkeley National Lab
Vice President for Biofuels & Bioproducts, Director of Host Engineering
Joint BioEnergy Institute