Lipopolysaccharide (LPS) and lipooligosaccharide (LOS) are important virulence determinants found in gram-negative bacteria. LOS differs from LPS in that it lacks the O-repeat characteristic of LPS. While the genetic basis of LOS production in the pathogenic Neisseria has been extensively studied, little research has focused on the genetics underlying LOS production and resulting diversity in commensal Neisseria. A commensal strain that caused a fatal case of bacterial endocarditis, Neisseria sicca 4320, was found to produce a unique polysaccharide similar to the O-repeat of LPS in addition to typical Neisseria LOS. N. sicca 4320 was analyzed by bioinformatic and molecular biological gene-finding screens to identify putative O-repeat biosynthesis genes. Twenty-one open reading frames (ORFs) with similarity to other polysaccharide biosynthesis genes were located in the screens of N. sicca 4320. Two open reading frames with similarity to glycosyltransferases were found to be unique to N. sicca 4320.