A LysR-Type Transcriptional Regulator in Burkholderia cenocepacia Influences Colony Morphology and Virulence

Abstract

Burkholderia cenocepacia strain K56-2 typically has rough colony morphology on agar medium; however, shiny colony variants (shv) can appear spontaneously. These shv all had a minimum of 50% reduction in biomass formation and were generally avirulent in an alfalfa seedling infection model. Three shv-K56-2 S15, K56-2 S76, and K56-2 S86-were analyzed for virulence in a chronic agar bead model of respiratory infection and, although all shv were able to establish chronic infection, they produced significantly less lung histopathology than the rough K56-2. Transmission electron microscopy revealed that an extracellular matrix surrounding bacterial cells was absent or reduced in the shv compared to the rough wild type. Transposon mutagenesis was performed on the rough wild-type strain and a mutant with an insertion upstream of ORF BCAS0225, coding for a putative LysR-type regulator, exhibited shiny colony morphology, reduced biofilm production, increased N-acyl homoserine lactone production, and avirulence in alfalfa. The rough parental colony morphotype, biofilm formation, and virulence in alfalfa were restored by providing BCAS0225 in trans in the BCAS0225::pGSVTp-luxCDABF mutant. Introduction of BCAS0225 restored the rough morphotype in several shv which were determined to have spontaneous mutations in this gene. In the present study, we show that the conversion from rough wild type to shv in B. cenocepacia correlates with reduced biofilm formation and virulence, and we determined that BCAS0225 is one gene involved in the regulation of these phenotypes.