This review discusses the various types of bacterial genomic islands that can be transferable by conjugation, their intra- and intercellular mobility, and the m

Summary: We identified a genetic context encoding a transcriptional regulator of the Rgg family and a small hydrophobic peptide (SHP) in nearly all streptococci and suggested that it may be involved in a new quorum‐sensing mechanism, with SHP playing the role of a pheromone. Here, we provide further support for this hypothesis by constructing a phylogenetic tree of the Rgg and Rgg‐like proteins from Gram‐positive bacteria and by studying the shp/rgg1358 locus of Streptococcus thermophilus LMD‐9. We identified the shp1358 gene as a target of Rgg1358, and used it to confirm the existence of the steps of a quorum‐sensing mechanism including secretion, maturation and reimportation of the pheromone into the cell. We used surface plasmon resonance to demonstrate interaction between the pheromone and the regulatory protein and performed electrophoretic mobility shift assays to assess binding of the transcriptional regulator to the promoter regions of its target genes. The active form of the pheromone was identified by mass spectrometry. Our findings demonstrate that the shp/rgg1358 locus encodes two components of a novel quorum‐sensing mechanism involving a transcriptional regulator of the Rgg family and a SHP pheromone that is detected and reimported into the cell by the Ami oligopeptide transporter.

In the last few years many attempts have been made to differentiate more than 20 Bifidobacterium species. It has been recognized that identification of bifidobacterial species is problematic because of phenetic and genetic heterogeneities. In order to contribute to our understanding of Bifidobacterium taxonomy, we studied Bifidobacterium phylogeny by performing both 16S rRNA and 16S to 23S (16S-23S) internally transcribed spacer (ITS) sequence analyses. In this study, we determined 16S rRNA sequences of five Bifidobacterium strains representing four species, and compared them with the sequences available in the GenBank database, and used them to construct a distance tree and for a bootstrap analysis. Moreover, we determined the ITS sequences of 29 bifidobacterial strains representing 18 species and compared these sequences with each other. We constructed a phylogenetic tree based on these sequence data and compared this tree with the tree based on 16S rRNA sequence data. We found that the two trees were similar topologically, suggesting that the two types of molecules provided the same kind of phylogenetic information. However, while 16S rRNA sequences are a good tool to infer interspecific links, the 16S-23S rDNA spacer data allowed us to determine intraspecific relationships. Each of the strains was characterized by its own ITS sequence; hence, 16S-23S rRNA sequences are a good tool for strain identification. Moreover, a comparison of the ITS sequences allowed us to estimate that the maximum level of ITS divergence between strains belonging to the same species was 13%. Our data allowed us to confirm the validity of most of the Bifidobacterium species which we studied and to identify some classification errors. Finally, our results showed that Bifidobacterium strains have no tRNA genes in the 16S-23S spacer region.

Conjugation is a key mechanism of bacterial evolution that involves mobile genetic elements. Recent findings indicated that the main actors of conjugative transfer are not the well-known conjugative or mobilizable plasmids but are the integrated elements. This paper reviews current knowledge on “integrative and mobilizable elements” (IMEs) that have recently been shown to be highly diverse and highly widespread but are still rarely described. IMEs encode their own excision and integration and use the conjugation machinery of unrelated co-resident conjugative element for their own transfer. Recent studies revealed a much more complex and much more diverse lifecycle than initially thought. Besides their main transmission as integrated elements, IMEs probably use plasmid-like strategies to ensure their maintenance after excision. Their interaction with conjugative elements reveals not only harmless hitchhikers but also hunters that use conjugative elements as target for their integration or harmful parasites that subvert the conjugative apparatus of incoming elements to invade cells that harbor them. IMEs carry genes conferring various functions, such as resistance to antibiotics, that can enhance the fitness of their hosts and that contribute to their maintenance in bacterial populations. Taken as a whole, IMEs are probably major contributors to bacterial evolution.