Abstract
The bacterium Pseudoalteromonas tunicata is a common surface colonizer of marine eukaryotes, including the macroalga Ulva australis.Genomic analysis of P. tunicata identified genes potentially involved in surface colonization, including genes with homology to bacterial virulence factors that mediate attachment. Of particular interest is the presence of a gene, designated ptlL32, encoding an ortholog to the Leptospira lipoprotein LipL32, which has been shown to facilitate the interaction of Leptospira sp. with host extracellular matrix (ECM) structures and is thought to be an important virulence trait for pathogenic Leptospira. To investigate the role of PtlL32 in the colonization by P. tunicata we constructed and characterized a ΔptlL32 mutant strain. Whilst P. tunicata ΔptlL32 bound to an abiotic surface with the same capacity as the wild type strain, it had a marked effect on the ability of P. tunicata to bind to ECM, suggesting a specific role in attachment to biological surfaces. Loss of PtlL32 also significantly reduced the capacity for P. tunciata to colonize the host algal surface demonstrating a clear role for this protein as a host-colonization factor. PtlL32 appears to have a patchy distribution across specific groups of environmental bacteria and phylogenetic analysis of PtlL32 orthologous proteins from non-Leptospira species suggests it may have been acquired via horizontal gene transfer between distantly related lineages. This study provides the first evidence for an attachment function for a LipL32-like protein outside the Leptospira and thereby contributes to the understanding of host colonization in ecologically distinct bacterial species.
Highlights
Macroalgae, or seaweeds, are important ecosystem engineers in temperate marine environments and are a rich source of biologically active compounds (Egan et al, 2008, 2013b)
This study provides the first experimental evidence for a function of LipL32-like proteins outside of the Leptospira genus and builds upon our current understanding of the traits that drive host colonization in marine bacteria
Attachment of the P. tunicata ptlL32 strain to extracellular matrix (ECM) structures was compared to wild type (WT) and C ptlL32, at times that have been characterized as early (2 h) and late (6 h) stages of irreversible attachment in other bacterial species (Hinsa et al, 2003; Palmer et al, 2007; Li et al, 2012)
Summary
Macroalgae, or seaweeds, are important ecosystem engineers in temperate marine environments and are a rich source of biologically active compounds (Egan et al, 2008, 2013b). The SAMC can influence the health of the host alga and members of this community have the potential to function as opportunistic pathogens (Gachon et al, 2010; Egan et al, 2013a). There remains a paucity of knowledge regarding the specific mechanisms that facilitate interaction of the SAMC with the host alga (Egan et al, 2013a). With the exception of a MSHA-like pili that has been demonstrated to play a role in the attachment of the bacterium to both abiotic and host surfaces (Dalisay et al, 2006), there is a lack of experimental data on the specific factors that mediate host colonization in this bacterium. Genome analysis of P. tunicata has identified genes with homology to putative colonization factors, lipoproteins, pili and outer membrane proteins www.frontiersin.org
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