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Recombination is one of the most important molecular mechanisms of prokaryotic genome evolution, but its exact roles are still in debate. Here we try to infer genome-wide recombination within a species, utilizing a dataset of 149 complete genomes of Escherichia coli from diverse animal hosts and geographic origins, including 45 in-house sequenced with the single-molecular real-time platform. Two major clades identified based on physiological, clinical and ecological characteristics form distinct genetic lineages based on scarcity of interclade gene exchanges. By defining gene-based syntenies for genomic segments within and between the two clades, we build a fine-scale recombination map for this representative global E. coli population. The map suggests extensive within-clade recombination that often breaks physical linkages among individual genes but seldom interrupts the structure of genome organizational frameworks as well as primary metabolic portfolios supported by the framework integrity, possibly due to strong natural selection for both physiological compatibility and ecological fitness. In contrast, the between-clade recombination declines drastically when phylogenetic distance increases to the extent where a 10-fold reduction can be observed, establishing a firm genetic barrier between clades. Our empirical data suggest a critical role for such recombination events in the early stage of speciation where recombination rate is associated with phylogenetic distance in addition to sequence and gene variations. The extensive intraclade recombination binds sister strains into a quasisexual group and optimizes genes or alleles to streamline physiological activities, whereas the sharply declined interclade recombination split the population into clades adaptive to divergent ecological niches., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Staphylococcus aureus is a common human bacterium that sometimes becomes pathogenic, causing serious infections. A key feature of S. aureus is its ability to acquire resistance to antibiotics. The presence of the staphylococcal cassette chromosome (SCC) element in serotypes of S. aureus has been confirmed using multiplex PCR assays. The SCC element is the only vector known to carry the mecA gene, which encodes methicillin resistance in S. aureus infections. Here, we report the genome sequence of a novel methicillin-sensitive S. aureus (MSSA) strain: SCC-like MSSA463. This strain was originally erroneously serotyped as methicillin-resistant S. aureus in a clinical laboratory using multiplex PCR methods. We sequenced the genome of SCC-like MSSA463 using pyrosequencing techniques and compared it with known genome sequences of other S. aureus isolates. An open reading frame (CZ049; AB037671) was identified downstream of attL and attR inverted repeat sequences. Our results suggest that a lateral gene transfer occurred between S. aureus and other organisms, partially changing S. aureus infectivity. We propose that attL and attR inverted repeats in S. aureus serve as frequent insertion sites for exogenous genes.

Using a pyrosequencing-based custom-made sequencer BIGIS-4, we sequenced a Gram-negative bacterium Glaciecola mesophila sp. nov. (Gmn) isolated from marine invertebrate specimens. We generated 152043 sequencing reads with a mean high-quality length of 406 bp, and assembled them using the BIGIS-4 post-processing module. No systematic low-quality data was detected beyond expected homopolymer-derived errors. The assembled Gmn genome is 5144318 bp in length and harbors 4303 annotated genes. A large number of metabolic genes correspond to various nutrients from surface marine invertebrates. Its abundant cold-tolerant and cellular signaling and related genes reveal a fundamental adaptation to low-temperature marine environment.