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Bacteria from the genus Burkholderia are widespread in nature, with strains being isolated from rhizosphere, aquatic environments, man-made environments and in association with hosts causing disease or beneficial interactions. One common feature across the genus is the ability to produce an exopolysaccharide (EPS) termed cepacian. This ability is confirmed by the presence of the bce biosynthetic genes in all Burkholderia sequenced genomes with the exception for Burkholderia mallei (Ferreira et al., 2010). Cepacian is composed of a branched acetylated heptasaccharide repeat-unit with D-glucose, D-rhamnose, D-mannose, D-galactose and D-glucuronic acid in the ratio of 1:1:1:3:1 (Cescutti et al., 2000). Cepacian biosynthesis starts with the synthesis of the nucleotide sugar precursors, catalyzed by isomerases, mutases, epimerases, among other enzymes (Ferreira et al., 2010). This step is followed by the assembly of the repeat-units by the sequential addition of sugars to an isoprenoid lipid by dedicated glycosyltransferases. The last step of cepacian biosynthesis comprises polymerization and export of the polysaccharide to the extracellular environment. A multienzyme complex including a repeat-unit translocase, a polysaccharide polymerase, an outer membrane protein, among others are involved in this process (Ferreira et al., 2010; Moreira et al., 2003). Insights into the biosynthetic steps will be covered in this chapter. Within the genus Burkholderia, a particular group of strains belonging to the so called Burkholderia cepacia complex (Bcc) have been isolated from the lungs of patients suffering of cystic fibrosis (CF). The analysis of sequential isolates from the same patient revealed that during the bacterial process of lung infection and colonization, a transition between mucoid to nonmucoid phenotype occurs (Zlosnik et al., 2008). This phenotypic conversion is predominantly from mucoid to nonmucoid and the relevance of it in disease progression is still under debate. It is therefore of importance not only to understand the factors triggering the mucoid phenotype conversion, but also the molecular mechanisms involved in cepacian biosynthesis regulation. Concerning EPS biosynthesis regulation, the present knowledge includes regulation at transcriptional level, namely through quorum sensing mechanisms. Indeed, it is known that exopolysaccharide production in plant-associated Burkholderia is regulated by N-acyl homoserine lactones (Suarez-Moreno et al., 2010). Another Burkholderia gene recently characterized and implicated in cepacian production is hfq encoding a RNA chaperone involved in the riboregulation of target mRNAs by small regulatory non-coding

Mechanisms Controlling the Expression of the Exopolysaccharide of Burkholderia and Role in Niche Adaptation