Overproduction of poly-β-hydroxybutyrate in the Azotobacter vinelandii mutant that does not express small RNA ArrF
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Azotobacter vinelandii contains an iron-regulatory small RNA ArrF whose expression is dependent upon the levels of iron and ferric uptake regulator. The deletion of this ArrF-encoding gene resulted in a 300-fold increase in the production of poly-β-hydroxybutyrate (PHB), a polymer of industrial importance. This ∆arrF mutant exhibited wild-type growth and growth-associated PHB production. Limited iron and aeration elevated the PHB production in the mutant as well as wild type. Real-time RT-PCR revealed that phbB, phbA, and phbC were upregulated ∼61-, 18-, and eightfold, respectively, in the mutant. The phbR transcript of the activator PhbR for this operon was also ∼11 times more abundant. The analysis of phbR transcript predicted a region of complementarity near its Shine–Dalgarno sequence that could potentially basepair with the conserved region of ArrF. These results suggest that ArrF represses the expression of PhbR in an antisense manner and derepression of this activator in the mutant elevates the expression of phbB, phbA, and phbC, resulting in the PHB overproduction.
KeywordsPolyhydroxybutyrate Azotobacter vinelandii Small RNA ArrF Iron Aeration
The authors would like to thank Professors Scott Willard, Din-Pow Ma, and Ken Willeford for reviewing the paper. The authors thank Professor Jeff Wilkinson for allowing us to use LightcyclerR 2.0. This work was supported in part by a grant from Robert M Hearing Foundation, by the Mississippi Agricultural and Forestry Experiment Station (MAFES) Project Number MIS-401030, and by a grant of MAFES SRI. This paper was approved for publication as Journal Article No. J-11447 of the Mississippi Agricultural and Forestry Experiment Station, Mississippi State University.
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