Single amino acid substitution in homogentisate 1,2‐dioxygenase is responsible for pigmentation in a subset of B urkholderia cepacia complex isolates

Summary The B urkholderia cepacia complex ( B cc) is a group of Gram‐negative bacilli that are ubiquitous in the environment and have emerged over the past 30 years as opportunistic pathogens in immunocompromised populations, specifically individuals with cystic fibrosis ( CF ) and chronic granulomatous disease. This complex of at least 18 distinct species is phenotypically and genetically diverse. One phenotype observed in a subset of B urkholderia cenocepacia (a prominent B cc pathogen) isolates is the ability to produce a melanin‐like pigment. Melanins have antioxidant properties and have been shown to act as virulence factors allowing pathogens to resist killing by the host immune system. The melanin‐like pigment expressed by B . cenocepacia is produced through tyrosine catabolism, specifically through the autoxidation and polymerization of homogentisate. B urkholderia cenocepacia   J 2315 is a CF clinical isolate that displays a pigmented phenotype when grown under normal laboratory conditions. We examined the amino acid sequences of critical enzymes in the melanin synthesis pathway in pigmented and non‐pigmented B cc isolates, and found that an amino acid substitution of glycine for arginine at amino acid 378 in homogentisate 1,2‐dioxygenase correlated with pigment production; we identify this as one mechanism for expression of pigment in B cc isolates.