The catE gene of Bacillus licheniformis M2-7 is essential for growth in benzopyrene, and its expression is regulated by the Csr system.

Benzopyrene is a high-molecular-weight polycyclic aromatic hydrocarbon that is highly recalcitrant and induces carcinogenic effects. CsrA is a conserved regulatory protein that controls the translation and stability of its target transcripts, having negative or positive effects depending on the target mRNAs. It is known that Bacillus licheniformis M2-7 has the ability to grow and survive in certain concentrations of hydrocarbons such as benzopyrene, prompted in part by CsrA, as is present in gasoline. However, there are a few studies that reveal the genes involved in that process. To identify the genes involved in the Bacillus licheniformis M2-7 degradation pathway, the plasmid pCAT-sp containing a mutation in the catE gene was constructed and used to transform B. licheniformis M2-7 and generate a CAT1 strain. We determined the capacity of the mutant B. licheniformis (CAT1) to grow in the presence of glucose or benzopyrene as a carbon source. We observed that the CAT1 strain presented increased growth in the presence of glucose but a statistically considerable decrease in the presence of benzopyrene compared with the wild-type parental strain. Additionally, we demonstrated that the Csr system positively regulates its expression since it was observed that the expression of the gene in the mutant strain LYA12 (M2-7 csrA:: Sp, SpR) was considerably lower than that in the wild-type strain. We were thus able to propose a putative regulation model for catE gene in B. licheniformis M2-7 strain by CsrA regulator in the presence of benzopyrene.

Posttranscriptional regulation of PhbR, the transcriptional activator of polyhydroxybutyrate synthesis, by iron and the sRNA ArrF in Azotobacter vinelandii.

Azotobacter vinelandii is a Gram-negative bacterium able to synthesize poly-ß-hydroxybutyrate (PHB), a biodegradable plastic of industrial interest. The phbBAC operon encodes the enzymes of PHB synthesis and is activated by the transcriptional regulator PhbR and the sigma factor RpoS. Iron limitation has been previously reported to increase PHB accumulation in A. vinelandii; however, the mechanism by which iron controls PHB synthesis is unknown. Under iron starvation in Escherichia coli, the RyhB sRNA modulates the translation of genes involved in iron homeostasis. ArrF is the RyhB analogue in A. vinelandii and similarly increases in quantity during Fe(2+) depletion. In this study, we evaluate the effect of iron and ArrF on PHB accumulation, and on phbR and phbBAC expression in A. vinelandii strain UW136. Using transcriptional and translational fusions of phbR and phbB with gusA reporter gene, we found that iron limitation increased the expression of phbBAC at the transcriptional level and posttranscriptionally increased the expression of phbR. We also found that the ArrF sRNA is a positive regulator of phbR expression at the posttranscriptional level. Collectively, these data suggest that iron limitation increases the translation of phbR through ArrF.