Investigation of the role of hxn genes in the nicotinic acid catabolic process of Aspergillus nidulans

Although many microorganisms can utilize nicotinic acid as a sole nitrogen source in nature, the nicotinate catabolic process was studied only in a limited number of prokaryotes. The eukaryotic utilization routes are completely unknown. In our laboratory we started to reveal the nicotinate utilization process in A. nidulans. Since the 1970s we know that conversion of nicotinate to 6-hydroxynicotinate (common first step of catabolism from prokaryotes to eukaryotes) by Purine hydroxylase II depends on a regulator hxnR and the induction by nicotinate or 6-hydroxynicotinate. We identified 11 co-regulated genes involved in nicotinate utilization and organized in three clusters (hxnP/S/T/Y/R/Z, hxnX/W/V and hxnM/N). In order to study their function we systematically deleted each of the hxn genes and the nicotinate utilization properties of the deletion mutants were screened by growth tests.

Here we present the expression profile of hxn genes and nicotinate utilization properties of the deletion strains. According to the transcript profile, the hxn genes are inducible by nicotinate, are non-inducible in strains carrying hxnR∆ mutation and show strong constitutive expression in hxnR^c (hxnR constitutive allele) background. The growth tests indicated that HxnS, HxnT and HxnY are involved in the initial steps of the catabolism and the pathway splits up to alternative routes after the first step. HxnV, HxnX, HxnW, HxnM and HxnN act downstream to the step in which the compounds of the alternative routes are converted into a common intermediate. Identification of the intermediate metabolites was aided by GC-MS analysis. Here we outline the preliminary scheme of the nicotinate catabolism in A. nidulans.

Acknowledgement: This research was supported byNKFI-K16 119516, by GINOP-2.3.2-15-2016-00035 and by GINOP-2.3.3-15-2016-00006.