Chondroitinase AC: A host-associated genetic feature of Helicobacter bizzozeronii

- A polysaccharide lyase was identified in gastric Helicobacter bizzozeroni and homologues were detected only in other canine- and feline-associated Helicobacter species.
- The substrate specificity of the enzyme was investigated and identified as specific for chondroitin sulphate but not dermatan sulphate, with an optimal pH of activity between 4 and 5.5.
- Chondroitin sulphate is a unique feature of gastric mucosa of dogs secreted by chief cells, and the presence of this gene in H. bizzozeronii is a likely consequence of host-parasite coevolution as result of adaptation to the canine host.

Investigating mechanisms involved in host adaptation is crucial to understand pathogen evolution. Helicobacter species appear to have a host species-specific tropism, coevolving with their natural hosts, and to develop several strategies allowing the colonization of the stomach throughout lifetime of their hosts. However, little is known about genetic features associated with the adaptation to a specific animal host. In this study we discovered a polysaccharide lyase that is expressed by the canine-associated species H. bizzozeronii and acts as chondroitinase AC-type lyase of broad specificity. Except for its low pH-optimum between pH 4.0 and pH 5.5, the properties of the H. bizzozeronii chondroitin lyase AC resemble the ones from Arthrobacter aurescens. However, homologues of this gene have been detected only in Helicobacter species colonizing the canine and feline gastric mucosa. Since a unique feature of the canine stomach is the secretion of chondroitin-4-sulphate in the gastric juice of the fundus mucosa by chief cells, the expression of chondroitinase AC by H. bizzozeronii is likely the consequence of adaptation of this bacterium to its host and a potential link to gastric disorders in dogs.