Gene sequences of the pil operon reveal relationships between symbiotic strains of Vibrio fischeri

Abstract

Symbiosis between the bobtail squid Euprymna scolopes (Mollusca: Cephalopoda) and Vibrio fischeri bacteria has been a well-studied model for understanding the molecular mechanisms of colonization and adherence to host cells. For example, pilin expression has been observed to cause subtle variation in colonization for a number of Gram-negative bacteria with eukaryotic hosts. To investigate variation amongst pil genes of closely related strains of vibrios, we amplified pil genes A, B, C and D to determine orientation and sequence similarity to other symbiotic vibrios. The pilA gene was found to be upstream from all other pil genes, and not contiguous with the rest of the operon. The pilB, pilC and pilD loci were flanked at the 39 end by yacE, followed by a conserved hypothetical gene. DNA sequences of each pil gene were aligned and analysed phylogenetically using parsimony for both individual and combined gene trees. Results demonstrate that certain pil loci (pilB and pilD) are conserved among strains of V. fischeri, but pilC differs in sequence between symbiotic and free-living strains. Phylogenetic analysis of all pil genes gives better resolution of Indo-west Pacific V. fischeri symbionts compared with analysis of the 16S rRNA gene. Hawaiian and Australian symbiotic strains form one monophyletic tree, supporting the hypothesis that V. fischeri strain specificity is selected by the geographical location of their hosts and is not related to specific squid species.

Microbial experimental evolution as a novel research approach in the Vibrionaceae and squid-Vibrio symbiosis

“…Interestingly, V. cholerae colonization factors (e.g., genes responsible for pili formation) primarily reside on Chromosome I. Consequently, different V. fischeri ecotypes could be the result of evolution at loci involved in metabolism as opposed to those involved in tissue colonization ( Browne-Silva and Nishiguchi, 2007 ; Soto et al, 2014 ). Experimental evolution studies with E. coli have demonstrated that resource partitioning and alternative substrate specialization is sufficient for ecological polymorphisms to arise in prokaryotes ( Rosenzweig et al, 1994 ).…”

Vibrio casei sp. nov., isolated from the surfaces of two French red smear soft cheeses

“…The clearly separated rumoiensis clade consists of Vibrio rumoiensis (Yumoto et al, 1999) and Vibrio litoralis (Nam et al, 2007) and forms a distant lineage within the genus. Micro-organisms belonging to the genus Vibrio are known to live either freely or associated as symbionts with aquatic animals in marine or estuarine waters (Browne-Silva & Nishiguchi, 2008) or as parasites of fish, crustaceans and molluscs (Thompson et al, 2004). Vibrio species have been reported less frequently as members of microbial consortia on cheese surfaces (Feurer et al, 2004), but some studies have suggested that they play a role in the ripening process (ElBaradei et al, 2007).…”

Gene-Swapping Mediates Host Specificity among Symbiotic Bacteria in a Beneficial Symbiosis

“…In V. fischeri , pilus subunits are synthesized by the pilABCD operon, where pilA contributes to colonization effectiveness and encodes a protein similar to type IV-A pilins (where mshA is a close relative [25], [26]. Phylogenetic and molecular differences have also been observed in pilB and pilD loci among multiple V. fischeri strains isolated from different squid hosts [27]. Our study demonstrates that V. fischeri ETJB1C pilC complemented with non-native Hawaiian V. fischeri ES114 pilC (- pilC ETJB1H:: pilC ES114) is dominant in E. scolopes , but loses in E. tasmanica , since there is a competitive dominance for the native pilC locus (Fig.…”