Diversity of Expressed vlhA Adhesin Sequences and Intermediate Hemagglutination Phenotypes in Mycoplasma synoviae

Abstract

A reservoir of pseudogene alleles encoding the primary adhesin VlhA occurs in the avian pathogen Mycoplasma synoviae. Recombination between this reservoir and its single expression site was predicted to result in lineages of M. synoviae that each express a different vlhA allele as a consequence of host immune responses to those antigens. Such interstrain diversity at the vlhA expression site, including major differences in the predicted secondary structures of their expressed adhesins, was confirmed in 14 specimens of M. synoviae. Corresponding functional differences in the extent to which they agglutinated erythrocytes, a quantitative proxy for VlhA-mediated cytadherence, were also evident. There was a >20-fold difference between the highest-and lowest-agglutinating strains and a rheostatic distribution of intermediate phenotypes among the others (Tukey-Kramer honestly significant difference [HSD], P < 0.001). Coincubation with the sialic acid analog 2-deoxy-2,3-didehydro-N-acetylneuraminate inhibited hemagglutination in a pattern correlated with endogenous sialidase activity (r ‫؍‬ 0.91, P < 0.001), although not consistently to the same extent that erythrocyte pretreatment with sialidase purified from Clostridium perfringens did (P < 0.05). The striking correlation between the ranked hemagglutination and endogenous sialidase activities of these strains (Spearman's r ‫؍‬ 0.874, P < 0.001) is evidence that host-induced vlhA allele switching indirectly drives sequence diversity in the passenger sialidase gene of M. synoviae.Mycoplasma synoviae is a pathogen associated with osteoarthritis, synovitis, and respiratory tract lesions of poultry (15,19,20). Cytadherence mediated by its primary adhesin VlhA is a precursor to virulence (30). Posttranslational cleavage of full-length VlhA produces the peptides MSPA (carboxy-terminal portion of VlhA) and MSPB (amino-terminal portion) (Fig. 1A). Receptor binding and cytadherence are attributed to MSPA, while the function of MSPB remains undefined (30). Interrupted expression of the vlhA gene or pretreatment with antisera against MSPA resulted in the inability of M. synoviae colonies to adsorb erythrocytes, a proxy for VlhA-mediated in vivo cytadherence. Strains able to agglutinate erythrocytes in vitro caused synovitis at a significantly higher frequency than did variants incapable of hemagglutination (29).Transcription of vlhA occurs at a single promoter next to a large assemblage of promoterless vlhA pseudogenes constituting a 69-kb locus in the M. synoviae genome. VlhA variants result from unidirectional site-specific recombination of pseudogenes into one of five specific residues at the expression site. Sequential integration of different pseudogene sequences can further result in the formation of chimeric alleles. The selective pressure of anti-VlhA antibodies in vivo is proposed to perpetuate lineages of M. synoviae that each express a different allele of vlhA as an antigen-diversifying mechanism to evade the adaptive immune system of the host (1,30,31,32).Although th...

Mycoplasmalipoproteins are major determinants of neutrophil extracellular trap formation

“…Lipoproteins play a central role in the pathogenesis of mycoplasmosis (Browning et al, 2011). Surface lipoproteins of mycoplasmas interact with the host during infection and influence strain virulence (Szczepanek et al, 2010) by promoting cytoadhesion (Sachse et al, 2000;Boesen et al, 2001;Thomas et al, 2005;May and Brown, 2011;Xiong et al, 2016), apoptosis (Ni et al, 2015), host DNA digestion and trafficking of nutrients and metabolites (Schmidt et al, 2007;Cacciotto et al, 2013). Furthermore, Mycoplasma lipoproteins play a pivotal role both in inducing adaptive host immune responses to infection and promoting evasion of this response, particularly by generating dramatic levels of antigenic variation on the bacterial cell surface (Cacciotto et al, 2010;Nouvel et al, 2010;Browning et al, 2011).…”

Molecular identification of Mycoplasma synoviae from seroprevalent commercial breeder farms at Chittagong district, Bangladesh

“…In the present study, sera samples were collected from the different breeder farms of Chittagong district where the birds were not vaccinated against MS. After collection of the samples, SPA test was done followed by PCR as a confirmatory test for identification of the organism as the culturing of MS is costly, time-consuming, and inconclusive [24,26]. Details of the seroprevalenceof MS with different risk factors are shown in Table-2.…”

“…On the other hand, PCR is comparatively easy, less time-consuming, and most reliable diagnostic tool. Therefore, PCR was adopted in this study for confirmation of the presence of MS in the infection [26,48]. …”

A Sialoreceptor Binding Motif in the Mycoplasma synoviae Adhesin VlhA

“…The predicted full-length VlhA sequences adjacent to the single transcription promoter of nine lineages of M. synoviae varying in avidity of cytadherence (F10-2AS, FMT, K4907, K5016, K5395, MS117, MS173, MS178, and a>30X-passaged Florida lineage of strain WVU1853 T ) [14] were aligned with that of the reference strain MS53 [8] and with a 60-a.a. hemagglutinating VlhA C-terminal fragment from a ca. 12X-passaged Tunisian lineage of strain WVU1853 T [15] by using ClustalΩ [17] .…”

“…The selective pressure of specific host immune responses to these antigens is thought to drive diversity in vlhA allele expression [10] – [13] . Despite the critical importance of cytadherence to the establishment and maintenance of infection, discrete VlhA types were demonstrated to have significantly different avidities for host cell binding, which can be quantified by agglutination of erythrocytes [14] . M. synoviae 's capacity for cytadherence maps surprisingly to a hypervariable C-terminal domain of VlhA called MSPA [15] – [16] .…”