Polar Flagella Glycosylation in Aeromonas: Genomic Characterization and Involvement of a Specific Glycosyltransferase (Fgi-1) in Heterogeneous Flagella Glycosylation.

Gabriel Forn-Cuní,Susan M Twine,Kelly M Fulton,Susana Merino,Jeffrey C Smith,Elena Mendoza-Barberà,Juan M Tomás

doi:10.3389/fmicb.2020.595697

Gabriel Forn-Cuní, Susan M Twine + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2020.595697

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Abstract

Polar flagella from mesophilic Aeromonas strains have previously been shown to be modified with a range of glycans. Mass spectrometry studies of purified polar flagellins suggested the glycan typically includes a putative pseudaminic acid like derivative; while some strains are modified with this single monosaccharide, others modified with a heterologous glycan. In the current study, we demonstrate that genes involved in polar flagella glycosylation are clustered in highly polymorphic genomic islands flanked by pseudaminic acid biosynthetic genes (pse). Bioinformatic analysis of mesophilic Aeromonas genomes identified three types of polar flagella glycosylation islands (FGIs), denoted Group I, II and III. FGI Groups I and III are small genomic islands present in Aeromonas strains with flagellins modified with a single monosaccharide pseudaminic acid derivative. Group II were large genomic islands, present in strains found to modify polar flagellins with heterogeneous glycan moieties. Group II, in addition to pse genes, contained numerous glycosyltransferases and other biosynthetic enzymes. All Group II strains shared a common glycosyltransferase downstream of luxC that we named flagella glycosylation island 1, fgi-1, in A. piscicola AH-3. We demonstrate that Fgi-1 transfers the first sugar of the heterogeneous glycan to the pseudaminic acid derivative linked to polar flagellins and could be used as marker for polysaccharidic glycosylation of Aeromonas polar flagella.

Highlights

Protein glycosylation is a common post-translational modification in bacteria and has been described in both gram-negative and gram-positive bacteria (De Maayer and Cowan, 2016; Schäffer and Messner, 2017)
In order to establish whether genes within this fragment are involved in the biosynthesis of the heptasaccharide that modifies the polar flagellin of A. piscicola AH-3, an in frame deletion of all the genes between the gene downstream of pseC and the gene downstream of the acyl-CoA reductase was generated
Mesophilic Aeromonas possess a constitutive and Oglycosylated polar flagellum, whose glycan composition ranges from a single pseudaminic acid derivative to a heteropolysaccharide (Canals et al, 2007; Tabei et al, 2009)

Summary

Introduction

Protein glycosylation is a common post-translational modification in bacteria and has been described in both gram-negative and gram-positive bacteria (De Maayer and Cowan, 2016; Schäffer and Messner, 2017). This post-translational modification has been identified in many target proteins, including surface proteins such as pili, flagella, adhesins and surface layer. Aeromonads are rod-shaped, Gram-negative bacteria, ubiquitous in the environment, and frequently associated with fresh or estuarine water They are emerging as the causative agents of gastrointestinal and extraintestinal disease in a vast evolutionary range of animals (Janda and Abbott, 2010). The pathogenicity of Aeromonads is multifactorial, and depends on specific strain characteristics, but common pathogenic factors across Aeromonadaceae are toxins and secretion systems, outermembrane proteins, capsules, polysaccharides, cell-wall proteins and flagella (Tomás, 2012)

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