Asmus Kalckar Olesen:
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Mobile genetic elements such as plasmids facilities horizontal transfer of genetic material, which impact bacterial adaption greatly. Plasmids are in general extrachromosomal self-replicating circular DNA which can be horizontally transferred across bacterial cell lineages by conjugation. The phylogenetic ranges of hosts in which the plasmid can transfer to, i.e., the plasmid host range, do however vary for different plasmid groups. Plasmids encode genes that gives beneficial traits to its host under certain environmental conditions. Additionally, can plasmids exchange
genetic material with the hosts chromosome or other plasmids in the host cell e.g., via transposons, or homologous recombination. Thus, do plasmids facilitate a horizontal flow of genes across the tree of life. Conjugation, which is encoded by genes on the conjugative element such as the conjugative plasmid, is the transfer of DNA through a mating pair formation between bacterial cells. Conjugative plasmids can facilitate their own transfer whereas, plasmids that are not capable of facilitating their own transfer but can transfer by utilizing the mating pair formation of such as a conjugative plasmid, are determined as mobilizable plasmids.
Conjugation is believed to be a very efficient evolutionary mechanism in microbial communities of many environments. Since plasmids often is found carrying antibiotic resistance genes, such as β-lactamases, plasmids are regarded as a key source of dissemination of antibiotic resistance
genes. Conversely, can the spread of plasmids in microbial communities also be utilized to propagate beneficial traits, such as genes encoding enzymes that breakdown pesticides in drinking water. The work in manuscript I, II and III seek to decipher the transfer of plasmids in microbial communities originating from, sewage, human feces (as proxy for the human gut) and groundwater fed biological rapid sand filters (sand filters). The transfer efficiency and host ranges of several plasmid archetypes in the microbial communities were investigated using fluorescent reporter gene systems, combined with flow cytometric enumeration and fluorescence activated cell sorting (FACS) and subsequently 16S rRNA gene amplicon sequencing.
In manuscript I we investigate the transfer and host range of the clinically relevant IncHI1A plasmid R27 in comparison to the IncP1 plasmid pB10, in the microbial communities extracted from urban residential sewage entering full-scale wastewater treatment plants. In manuscript II we investigated the transfer of mobilizable and conjugative plasmids simultaneously in microbial communities, originating from sewage and the human gut, by implementing a novel tri fluorescent reporter gene system. Specifically, we tracked the transfer of the mobilizable IncQ1 plasmid RSF1010 and the conjugative IncP1, IncW and IncI1 plasmids, pKJK5, R388, and p6222, respectively. In manuscript III we tracked the transfer of the IncP1 plasmids RP4 and pKJK5, the IncP9 and IncQ1 plasmids pTOL and RSF1010 respectively. We did so in microbial communities extracted from sand filters to determine the potential of plasmids as vectors for the dissemination of bioremediation factors.
β-lactamases, are an important resistance mechanism of especially Gram-negative bacteria towards β-lactam antibiotics such as penicillin. β-lactamases can be found on the chromosome but are often found located on plasmids as well. The extracellular excretion of β-lactamases by the producing bacteria can also protect non-producing sensitive bacteria within proximity. In manuscript IV we studied the effect of β-lactamase production during amoxicillin treatment in the gut microbiota of Wistar rats, and the ecological impact of gene location and copy number.