Abstract
Within the Haloferax genus, both the surface (S)-layer protein, and the glycans that can decorate it, vary between species, which can potentially result in many different surface types, analogous to bacterial serotypes. This variation may mediate phenotypes, such as sensitivity to different viruses and mating preferences. Here, we describe S-layer glycoproteins found in multiple Haloferax strains and perform comparative genomics analyses of major and alternative glycosylation clusters of isolates from two coastal sites. We analyze the phylogeny of individual glycosylation genes and demonstrate that while the major glycosylation cluster tends to be conserved among closely related strains, the alternative cluster is highly variable. Thus, geographically- and genetically-related strains may exhibit diverse surface structures to such an extent that no two isolates present an identical surface profile.
Highlights
The prokaryotic cell envelope provides archaeal and bacterial cells with a protective coat that resists environmental stressors both abiotic and biotic—namely viruses and toxins secreted by competing cells
H. volcanii contains two N-glycosylation pathways—a major pathway which is functional at all concentrations of salt tested and an alternative glycosylation pathway which is only recruited at lower salinity—with each pathway generating its own distinct glycan modification [6]
The 16S rRNA gene of all these isolates had over 99% identity to that of the H. volcanii type strain and was deemed too conserved for resolving relatedness between isolates
Summary
The prokaryotic cell envelope provides archaeal and bacterial cells with a protective coat that resists environmental stressors both abiotic and biotic—namely viruses and toxins secreted by competing cells. The surface layer (S-layer) is generally composed of a single protein that is always glycosylated [1]. N-glycosylation—the covalent attachment of glycans to select target asparagine residues in proteins—is thought to be one of the most common post-translational modifications of archaeal cell surface proteins, including S-layer glycoproteins, as well as flagelins [2]. Archaeal N-linked glycans are richly diverse in composition and structure [4,5] and archaeal N-glycosylation gene pathways show considerable variation in gene content, sharing only a few common components. H. volcanii contains two N-glycosylation pathways—a major pathway which is functional at all concentrations of salt tested and an alternative glycosylation pathway which is only recruited at lower salinity—with each pathway generating its own distinct glycan modification [6]. When relying on the general N-glycosylation pathway, the H. volcanii
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