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Zusammenfassung:
One of the current goals of human gut microbiome research is to develop genetic systems for non-model organisms found in the human gastrointestinal tract to obtain a better understanding of community dynamics and function. Currently, prokaryotic defence systems represent one of the most significant barriers to the establishment such genetic systems for intractable microbes. The majority of these defence systems employ various strategies to recognise and eliminate foreign DNA, whether derived from phages/viruses, plasmids, or other mobile genetic elements. One such system is the Bacteriophage Exclusion (BREX) system, which methylates the microbe"s own DNA at a non-palindromic 6 bp sequence and prevents viral replication via an undetermined mechanism. In addition to viral defense, BREX has also been shown to negatively impact plasmid uptake efficiency. We identified a novel BREX anti-defence systems in the major archaeon associated with the human gut, Methanobrevibacter smithii and have characterised its in vitro role as an anti-viral and anti-plasmid system. We show that the M. smithii type strain contains an atypical type I BREX system that methylates the chromosome at two distinct nucleotide motifs. This methylation activity is carried out by the pglX methyltransferase, but its activity is dependent on BREX genes pglX, brxA, brxB, brxC, and pglZ. Additionally, we report the role of M. smithii BREX in modulating viral infection in an E. coli host and its effect on plasmid transformation. This represents the first characterisation of a BREX system in an archaeal host and paves the way for future genetic manipulation of this non-model organism.
