SlyB is a small lipoprotein of 158 amino acids which is conserved in different Gram-negative bacteria. In contrast to other bacteria, where slyB is monocistronic, in Burkholderia multivorans and in B. cenocepacia, slyB is the last gene of an operon comprising three open reading frames encoding a putative thiol peroxidase, a putative sugar kinase and SlyB. B. multivorans slyB mutants produced elongated cells and filaments which were never observed in cultures of wild-type or slyB-complemented cells. The slyB mutant also showed increased sensitivity to EDTA and SDS, and decreased siderophore production. Proteome analysis of a fraction enriched for membrane proteins suggested that SlyB, like the peptidoglycan-associated protein OpcL, is a major protein of the outer membrane. Taken together, these phenotypes suggest that SlyB contributes to the integrity of the cell envelope. By PCR amplification we were also able to demonstrate the conservation of slyB in all B. cepacia complex species tested.