The first world swimming championships of roseobacters—Phylogenomic insights into an exceptional motility phenotype

Abstract

Many marine Alphaproteobacteria of the Roseobacter group show a characteristic swim-or-stick lifestyle, for which motility is a crucial trait. Three phylogenetically distinct flagellar gene clusters (FGCs) have been identified in Rhodobacteraceae that have been named fla1, fla2 and fla3 according to their relative abundance. In addition to the flagellar-dependent swimming and swarming motility, pilus-dependent twitching mediates bacterial locomotion. Furthermore, filament independent modes of motility, namely gliding and sliding, have been described for various microorganisms. However, no mode of motility other than swimming has so far been described for roseobacters. In the present study, we investigated motility, distribution of flagellar systems and the phylogeny of 120 genome-sequenced Rhodobacteraceae. The phylogenetically broad taxon sampling that included 114 type strains revealed the presence of at least ten distinct clades that were statistically well supported. The investigation of the actual physiological capacity for swimming motility on soft agar plates showed that only about half of the 120 tested strains were motile under the tested conditions. Seven strains developed a conspicuous dendritic motility phenotype that was reminiscent of the swarming motility in Pseudomonas aeruginosa. The observed dendritic motility in two strains (i.e. Sulfitobacter pseudonitzschiae DSM 26842 and Roseovarius pacificus DSM 29589) was particularly surprising because they did not harbor any genes of the FGC. Accordingly, it was concluded that this form of dendritic motility was independent of a flagellum. A comparative genomics approach allowed a remarkable number of pilus-related candidate genes to be identified for this novel type of motility in Rhodobacteraceae.

Quorum sensing regulates ‘swim‐or‐stick’ lifestyle in the phycosphere

“…The second luxI gene in S. pseudonitzschiae F5 likely produces one or more other AHL molecules that we were not able to characterize due to the limitation of AHL mass spectrometry standards. As mentioned before, S. pseudonitzschiae F5 displayed a dendritic motility phenotype, which is absent in most roseobacters (Bartling et al ., 2018). It is not clear what ecological advantage dendritic motility have on bacteria like S. pseudonitzschiae .…”

Quorum Sensing Regulates ‘swim-or-stick’ Lifestyle in the Phycosphere

“…pseudonitzschiae F5 likely produces one or more other AHL molecules that we were not able to characterize due to the limitation of AHL mass spectrometry standards. As mentioned before, S. pseudonitzschiae F5 displayed a dendritic motility phenotype, which is absent in most roseobacters (Bartling et al, 2018 Interestingly, two additional S. pseudonitzschiae strains displayed this phenotype previously (Bartling et al, 2018), indicating this phenotype is common in this species for unknown reasons.…”

Mycobacterium smegmatisexpands across surfaces using hydraulic sliding

“…To the authors' knowledge fluid-filled colony protrusions have not been reported previously for any mycobacteria or gram positive bacteria. The closest examples in the literature are some strains of Roseobacters (gram negative), which can form liquid channels, but the mechanism for this phenomenon has not been analysed (Bartling et al, 2018).…”

“…Additionally water put onto an agar surface dissipates, even without the action of surfactant, so fluid must be being trapped within the protrusions to prevent it dissipating (Jain et al, 1991). Liquid channels have been seen in several motile Rhodobacteraceae strains (aquatic α-Proteobacteria) but the mechanism for their formation has not been investigated (Bartling et al, 2018). The structure of the colony with a liquid core enclosed by biofilm appears to be unique.…”