Characterisation of the Paenarthrobacter nicotinovorans ATCC 49919 genome and identification of several strains harbouring a highly syntenic nic-genes cluster.

BACKGROUND: Paenarthrobacter nicotinovorans ATCC 49919 uses the pyridine-pathway to degrade nicotine and could provide a renewable source of precursors from nicotine-containing waste as well as a model for studying the molecular evolution of catabolic pathways and their spread by horizontal gene transfer via soil bacterial plasmids. RESULTS: In the present study, the strain was sequenced using the Illumina NovaSeq 6000 and Oxford Nanopore Technology (ONT) MinION platforms. Following hybrid assembly with Unicycler, the complete genome sequence of the strain was obtained and used as reference for whole-genome-based phylogeny analyses. A total of 64 related genomes were analysed; five Arthrobacter strains showed both digital DNA-DNA hybridization and average nucleotide identity values over the species threshold when compared to P. nicotinovorans ATCC 49919. Five plasmids and two contigs belonging to Arthrobacter and Paenarthrobacter strains were shown to be virtually identical with the pAO1 plasmid of Paenarthrobacter nicotinovorans ATCC 49919. Moreover, a highly syntenic nic-genes cluster was identified on five plasmids, one contig and three chromosomes. The nic-genes cluster contains two major locally collinear blocks that appear to form a putative catabolic transposon. Although the origins of the nic-genes cluster and the putative transposon still elude us, we hypothesise here that the ATCC 49919 strain most probably evolved from Paenarthrobacter sp. YJN-D or a very closely related strain by acquiring the pAO1 megaplasmid and the nicotine degradation pathway. CONCLUSIONS: The data presented here offers another snapshot into the evolution of plasmids harboured by Arthrobacter and Paenarthrobacter species and their role in the spread of metabolic traits by horizontal gene transfer among related soil bacteria.

The contribution of mRNA targeting to spatial protein localization in bacteria.

About 30% of all bacterial proteins execute their function outside of the cytosol and must be inserted into or translocated across the cytoplasmic membrane. This requires efficient targeting systems that recognize N-terminal signal sequences in client proteins and deliver them to protein transport complexes in the membrane. While the importance of these protein transport machineries for the spatial organization of the bacterial cell is well documented in multiple studies, the contribution of mRNA targeting and localized translation to protein transport is only beginning to emerge. mRNAs can exhibit diverse subcellular localizations in the bacterial cell and can accumulate at sites where new protein is required. This is frequently observed for mRNAs encoding membrane proteins, but the physiological importance of membrane enrichment of mRNAs and the consequences it has for the insertion of the encoded protein have not been explored in detail. Here, we briefly highlight some basic concepts of signal sequence-based protein targeting and describe in more detail strategies that enable the monitoring of mRNA localization in bacterial cells and potential mechanisms that route mRNAs to particular positions within the cell. Finally, we summarize some recent developments that demonstrate that mRNA targeting and localized translation can sustain membrane protein insertion under stress conditions when the protein-targeting machinery is compromised. Thus, mRNA targeting likely acts as a back-up strategy and complements the canonical signal sequence-based protein targeting.