Abstract
Many species of mycobacteria form structured biofilm communities at liquid–air interfaces and on solid surfaces. Full development of Mycobacterium smegmatis biofilms requires addition of supplemental iron above 1 μM ferrous sulphate, although addition of iron is not needed for planktonic growth. Microarray analysis of the M. smegmatis transcriptome shows that iron-responsive genes – especially those involved in siderophore synthesis and iron uptake – are strongly induced during biofilm formation reflecting a response to iron deprivation, even when 2 μM iron is present. The acquisition of iron under these conditions is specifically dependent on the exochelin synthesis and uptake pathways, and the strong defect of an iron–exochelin uptake mutant suggests a regulatory role of iron in the transition to biofilm growth. In contrast, although the expression of mycobactin and iron ABC transport operons is highly upregulated during biofilm formation, mutants in these systems form normal biofilms in low-iron (2 μM) conditions. A close correlation between iron availability and matrix-associated fatty acids implies a possible metabolic role in the late stages of biofilm maturation, in addition to the early regulatory role. M. smegmatis surface motility is similarly dependent on iron availability, requiring both supplemental iron and the exochelin pathway to acquire it.
Highlights
IntroductionThe formation of bacterial biofilms involves a developmental process that begins with surface attachment, followed by spreading, maturation and matrix synthesis (O’Toole et al, 2000)
Most bacteria are found in the environment not as isolated cells growing planktonically, but as biofilms – organizedThe formation of bacterial biofilms involves a developmental process that begins with surface attachment, followed by spreading, maturation and matrix synthesis (O’Toole et al, 2000)
Full development of Mycobacterium smegmatis biofilms requires addition of supplemental iron above 1 mM ferrous sulphate, addition of iron is not needed for planktonic growth
Summary
The formation of bacterial biofilms involves a developmental process that begins with surface attachment, followed by spreading, maturation and matrix synthesis (O’Toole et al, 2000) This process is accompanied by changes in gene expression profiles, and these have been described for several prokaryotes, including Escherichia coli (Schembri et al, 2003; Beloin et al, 2004; Ren et al, 2004a; Pruss et al, 2006), Pseudomonas aeruginosa (Whiteley et al, 2001; Waite et al, 2005; 2006), Bacillus subtilis (Stanley et al, 2003; Ren et al, 2004b), Vibrio cholerae (Moorthy and Watnick, 2005), Xylella fastidiosa (de Souza et al, 2004; 2005), Thermatoga maritima (Pysz et al, 2004), Staphylococcus aureus (Beenken et al, 2004), Campylobacter jejuni (Sampathkumar et al, 2006) and Streptococcus pyogenes (Cho and Caparon, 2005). Different sets of genes are expressed at different stages throughout the course of biofilm development (Waite et al, 2005; Domka et al, 2007)
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