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β(1-6)glucan homopolymer in mycoplasma capsules

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Vastel, Manon | Ferre, Séverine | Tocqueville, Véronique | Ambroset, Chloé | Gautier-Bouchardon, Anne, V. | Tardy, Florence | Gaurivaud, Patrice

Edité par CCSD -

International audience. β(1-6)glucopyranose (β(1-6)glucan) polysaccharidic capsules have been previously described in three ruminant mycoplasma species (Mycoplasma (M.) agalactiae, M. feriruminatoris and M. mycoides subsp. capri serovar capri) and associated to pro-inflammatory properties (Rubin-Bejerano et al., 2007). The aim of this study was to determine if other Mycoplasma species from different animal hosts (ruminants but also poultry, swine and primates) were also able to secrete capsular β(1-6)glucan. A first in vitro screening conducted using the non-specific Dubois’ method for polysaccharides quantification evidenced a polysaccharidic capsule in various mycoplasmas infecting ruminants, primates and poultry but not swine. Amongst them, only M. iowae strain I695 was shown by dot blot to produce a capsule containing β(1-6)glucan.Genome comparisons evidenced in M. iowae strain I695 (accession number of the genome: CP033512.2) a β(1-6)glucan biosynthesis pathway similar to that previously described in M. agalactiae strain L14628 (Gaurivaud et al., 2016). Furthermore, an antigenic variation resulting in sectored colonies using immunoblotting assays was observed in both strains. In M. agalactiae L14628 this variation is due to a nine-G repetition at the beginning of the gene coding the glycosyltransferase responsible for the secretion of the β(1-6)glucan (Gaurivaud et al., 2016). In M. iowae I695 the presence of a nine-TA repetition at the beginning of the glycosyltransferase gene might similarly be responsible for the antigenic variation.The potential secretion of a β(1-6)glucan capsule was screened in vitro by colony blotting and by a PCR assay targeting the gene coding the glycosyltransferase in different M. iowae isolates.Preliminary results indicate that out of 21 isolates only the strain I695 produces a β(1-6)glucan capsule in vitro and is equipped with the gene coding the glycosyltransferase. The absence of a glycosyltransferase gene has so far been confirmed by WGS of three isolates (with available genome in Genbank for one of them). This suggests that the β(1-6)glucan capsule production is not a characteristic of the M. iowae species, in contrast to what was observed in M. agalactiae. The role of the capsule in serum-killing susceptibility of the isolates will be further ssessed.

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