Abstract
Shewanella oneidensis MR-1 is a heterotrophic facultative anaerobe that respires using various organic and inorganic compounds. This organism has served as a model to study bacterial metabolic and regulatory systems that facilitate their survival in redox-stratified environments. The expression of many anaerobic respiratory genes in MR-1, including those for the reduction of fumarate, dimethyl sulfoxide, and metal oxides, is regulated by cyclic AMP receptor protein (CRP). However, relatively little is known about how this organism regulates the expression of catabolic enzymes catalyzing the oxidation of organic compounds, including lactate. Here, we investigated transcriptional mechanisms for the lldP (SO_1522) and dld (SO_1521) genes, which encode putative lactate permease and D-lactate dehydrogenase, respectively, and demonstrate that CRP regulates their expression in MR-1. We found that a crp-deletion mutant of MR-1 (Δcrp) showed impaired growth on D-lactate. Complementary expression of dld in Δcrp restored the ability to grow on D-lactate, indicating that the deficient growth of Δcrp on D-lactate is attributable to decreased expression of dld. In vivo transcription and in vitro electrophoretic mobility shift assays reveal that CRP positively regulates the expression of the lldP and dld genes by directly binding to an upstream region of lldP. Taken together, these results indicate that CRP is a global transcriptional regulator that coordinately regulates the expression of catabolic and respiratory pathways in MR-1, including D-lactate dehydrogenase and anaerobic terminal reductases.
Highlights
The genus Shewanella belongs to the class Gammaproteobacteria and is widely distributed in nature, including marine, freshwater, sedimentary, and soil environments (Venkateswaran et al, 1999; Hau and Gralnick, 2007; Fredrickson et al, 2008; Rodionov et al, 2011)
These results suggest that crp has a decreased capacity for metabolizing D-lactate
These results suggest that cyclic AMP receptor protein (CRP) is required for the expression of gene(s) involved in D-lactate utilization, such as the dld gene encoding D-lactate dehydrogenase (LDH) in MR-1, this regulator is not essential for the expression of genes involved in L-lactate and pyruvate utilization
Summary
The genus Shewanella belongs to the class Gammaproteobacteria and is widely distributed in nature, including marine, freshwater, sedimentary, and soil environments (Venkateswaran et al, 1999; Hau and Gralnick, 2007; Fredrickson et al, 2008; Rodionov et al, 2011) Members of this genus are able to utilize a variety of electron acceptors for respiration, such as insoluble solid compounds (e.g., iron and manganese oxides) and soluble organic and inorganic compounds [e.g., oxygen, fumarate, nitrate, nitrite, dimethyl sulfoxide, and trimethylamine N-oxide (TMAO)] (Myers and Nealson, 1988; Fredrickson et al, 2008). Further studies to identify the physiological functions of the cAMP/CRP regulatory system in Shewanella are needed
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