A functional interplay of hns genes governs the control of the motile-to-biofilm lifestyle switch in Burkholderia cenocepacia

The onset of the chronic stage of infection by bacteria in the Burkholderia cepacia complex depends on the controlled transition to the biofilm-associated lifestyle. In this study, we systematically investigated the effect of all five hns genes of Burkholderia cenocepacia H111 on the motile-to-biofilm lifestyle switch and pathogenicity. The hns genes are distributed across the three replicons ( hns 1.1 and hns 1.2 on chromosome 1, hns 2 on chromosome 2, and hns 3.1 and hns 3.2 on the megaplasmid pC3). We showed that deletion of either hns 1.1 or hns 1.2 affects cell growth and promotes the cell transition to the biofilm, with the major impact observed in cells lacking hns 1.2 . According to a comparative transcriptome analysis, the motile-to-biofilm switch linked to the absence of hns 1.2 is supported by downregulation of flagellar and chemotaxis genes and upregulation of several genes involved in biofilm formation. In contrast, biofilm-related genes were downregulated; biofilm formation was reduced; and motility was increased in cells lacking hns 3.1 . An opposite impact of hns 1.2 and hns 3.1 on the motile-to-biofilm transition was also supported by using cells expressing these hns genes at high levels. Furthermore, hns 3.1 and hns 1.1 were shown to play a role in bacterial virulence in the Galleria mellonella infection model. Therefore, this study uncovers hns genes as new players of the motile-to-biofilm transition in B. cenocepacia . IMPORTANCE Several opportunistic pathogenic bacteria can thrive as motile, free-living cells in soil and water, as well as in biofilm in their hosts. This includes the closely related species comprising the Burkholderia cepacia complex, which chronically colonize the airway in individuals with cystic fibrosis. Over the last two decades, the number of genes involved in the control of the motile-to-biofilm lifestyle switch has increased in this bacterial group, particularly in Burkholderia cenocepacia . In the present study, we uncover three hns genes that participate in the motile-to-biofilm lifestyle switch in B. cenocepacia H111 under the conditions tested. While two chromosomally encoded hns genes work to maintain cells at the motile stage, a megaplasmid-encoded hns gene facilitates the cell transition to biofilm. By systematically investigating all five hns genes, we considerably expand our understanding of the control of the motile-to-biofilm lifestyle switch in the Burkholderia cepacia complex.