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The role of iron in Mycobacterium smegmatis biofilm formation: the exochelin siderophore is essential in limiting iron conditions for biofilm formation but not for planktonic growth.

Ojha A, Hatfull GF - Mol. Microbiol. (2007)

Bottom Line: 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 microM) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.

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 microM 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 microM 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 microM) 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.

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Related in: MedlinePlus

Requirements of supplemental iron for biofilm formation and synthesis of C56–C68 fatty acids. M. smegmatis biofilms were grown for 4 days, with supplemental ferric iron induced in the following concentrations: none (A), 0.5 μM (B), 1 μM (C), 2 μM (D) and 5 μM (E). Samples were harvested, mycolic acids extracted, and analysed by MALDI-TOF as shown in the right. The position of the series of C56–C68 fatty acids is indicated above.
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fig06: Requirements of supplemental iron for biofilm formation and synthesis of C56–C68 fatty acids. M. smegmatis biofilms were grown for 4 days, with supplemental ferric iron induced in the following concentrations: none (A), 0.5 μM (B), 1 μM (C), 2 μM (D) and 5 μM (E). Samples were harvested, mycolic acids extracted, and analysed by MALDI-TOF as shown in the right. The position of the series of C56–C68 fatty acids is indicated above.

Mentions: The microarray and mutant data described above suggest a specific role of iron in biofilm development distinct from that for planktonic growth. To further define this role for iron, we evaluated biofilm formation at intervals of iron concentration between those that do (2 μM) and do not (0 μM) support biofilms (Fig. 6). Because M. smegmatis biofilms characteristically contain a novel series of C56–C68 fatty acids (Ojha et al., 2005), we also examined the correlation between iron dependence and the synthesis of these fatty acids (Fig. 6). Visual examination of the dishes shows that addition of supplemental iron at 0.5 μM is sufficient to support only very limited biofilm maturation, and the textured appearance of the biofilms increase as iron concentration increases (Fig. 6); measurements of the accumulated biomass confirm this observation. The synthesis of the C56–C68 fatty acids closely mirrors this, and they are absent or at low levels in the absence of iron and at 0.5 μM, but are the most prominent fatty acid components at 1 μM and higher iron concentrations (Fig. 6). There is clearly a strong association between supplemental iron concentration and this fatty acid synthesis.


The role of iron in Mycobacterium smegmatis biofilm formation: the exochelin siderophore is essential in limiting iron conditions for biofilm formation but not for planktonic growth.

Ojha A, Hatfull GF - Mol. Microbiol. (2007)

Requirements of supplemental iron for biofilm formation and synthesis of C56–C68 fatty acids. M. smegmatis biofilms were grown for 4 days, with supplemental ferric iron induced in the following concentrations: none (A), 0.5 μM (B), 1 μM (C), 2 μM (D) and 5 μM (E). Samples were harvested, mycolic acids extracted, and analysed by MALDI-TOF as shown in the right. The position of the series of C56–C68 fatty acids is indicated above.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2170428&req=5

fig06: Requirements of supplemental iron for biofilm formation and synthesis of C56–C68 fatty acids. M. smegmatis biofilms were grown for 4 days, with supplemental ferric iron induced in the following concentrations: none (A), 0.5 μM (B), 1 μM (C), 2 μM (D) and 5 μM (E). Samples were harvested, mycolic acids extracted, and analysed by MALDI-TOF as shown in the right. The position of the series of C56–C68 fatty acids is indicated above.
Mentions: The microarray and mutant data described above suggest a specific role of iron in biofilm development distinct from that for planktonic growth. To further define this role for iron, we evaluated biofilm formation at intervals of iron concentration between those that do (2 μM) and do not (0 μM) support biofilms (Fig. 6). Because M. smegmatis biofilms characteristically contain a novel series of C56–C68 fatty acids (Ojha et al., 2005), we also examined the correlation between iron dependence and the synthesis of these fatty acids (Fig. 6). Visual examination of the dishes shows that addition of supplemental iron at 0.5 μM is sufficient to support only very limited biofilm maturation, and the textured appearance of the biofilms increase as iron concentration increases (Fig. 6); measurements of the accumulated biomass confirm this observation. The synthesis of the C56–C68 fatty acids closely mirrors this, and they are absent or at low levels in the absence of iron and at 0.5 μM, but are the most prominent fatty acid components at 1 μM and higher iron concentrations (Fig. 6). There is clearly a strong association between supplemental iron concentration and this fatty acid synthesis.

Bottom Line: 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 microM) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.

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 microM 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 microM 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 microM) 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.

Show MeSH
Related in: MedlinePlus