Abstract
The RNA chaperone Hfq fulfills important roles in small regulatory RNA (sRNA) function in many bacteria. Loss of Hfq in the dissimilatory metal reducing bacterium Shewanella oneidensis strain MR-1 results in slow exponential phase growth and a reduced terminal cell density at stationary phase. We have found that the exponential phase growth defect of the hfq mutant in LB is the result of reduced heme levels. Both heme levels and exponential phase growth of the hfq mutant can be completely restored by supplementing LB medium with 5-aminolevulinic acid (5-ALA), the first committed intermediate synthesized during heme synthesis. Increasing expression of gtrA, which encodes the enzyme that catalyzes the first step in heme biosynthesis, also restores heme levels and exponential phase growth of the hfq mutant. Taken together, our data indicate that reduced heme levels are responsible for the exponential growth defect of the S. oneidensis hfq mutant in LB medium and suggest that the S. oneidensis hfq mutant is deficient in heme production at the 5-ALA synthesis step.
Highlights
The RNA chaperone Hfq is a highly conserved protein that mediates interactions between many regulatory small regulatory RNA (sRNA) molecules and their mRNA targets in bacteria
Heme or 5-aminolevulinic acid substantially rescues the small colony phenotype of the S. oneidensis hfq mutant Because most bacteria have the capacity to scavenge iron from hemoglobin to support vital cellular functions [27], we determined whether the addition of iron to the medium at concentrations approximating those found in trypticase soy agar plates containing 5% sheep blood could rescue the growth defect of the hfq mutant
We report that the exponential growth defect of the S. oneidensis hfq mutant in LB medium is due to reduced levels of heme during exponential phase growth
Summary
The RNA chaperone Hfq is a highly conserved protein that mediates interactions between many regulatory sRNA molecules and their mRNA targets in bacteria (for reviews see [1,2,3,4]). Hfq protein monomers form a homohexameric ring capable of binding both regulatory small, noncoding RNAs (sRNAs) and their target mRNAs [5,6]. These Hfq-RNA interactions stabilize sRNAs and help the sRNAs locate and interact with their mRNA targets. Consistent with a role in a multitude of cellular processes, loss of Hfq is typically pleiotropic, and hfq mutants exhibit a diverse array of bacteriumspecific phenotypes. This suggests that, despite its high level of conservation, Hfq has evolved distinct roles in closely related bacteria. Though reduced sRNA function likely contributes to many hfq mutant phenotypes, the mechanisms by which loss of Hfq results in particular mutant phenotypes often remain obscure
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