The periodontal pathogen Aggregatibacter actinomycetemcomitans has an irregular outer membrane. A gene (omp67) was identified to be associated with the biogenesis of this morphology. This gene is part of a 3-gene operon and codes for a 141-kDa protein designated morphogenesis protein C (morC), which is conserved in several Gram-negative bacteria, including Haemophilus influenzae and Pasteurella multocida. Insertional inactivation of this gene resulted in the conversion of an irregularly shaped membrane to a flat membrane. Associated with this morphological change were the autoaggregation of bacteria during planktonic growth and a concomitant increase in the surface hydrophobicity of the bacterium. The absence of morC also resulted in the loss of secretion of leukotoxin but not the ltxA transcription. Omp67 is an outer membrane protein with yet unknown structure but prediction methods suggest the presence of a rather large ß-barrel.