Metabolic and physiological perturbations of Escherichia coli W3100 by bacterial small RNA RyhB.

RyhB is a key regulator of iron level in Escherichia coli (E. coli), which assists in conserving iron for life-sustaining cellular functions when cytoplasmic levels of the ferrous form of iron is limited. RyhB affects glucose metabolism. Seventy percent of the genes that are regulated by RyhB are related to metabolism. We demonstrated for the first time that the activity of the pentose phosphate pathway increased upon ryhB activation using a¹³C stable isotope-based technique called METAFoR (Metabolic flux ratio analysis). U-¹³C glucose-based studies showed that the reversible exchange activity of serine and glycine was enhanced by flux redistribution, which further favors NADPH formation. In addition, Entner-Doudoroff (ED) pathway activity was inhibited in the ryhB-defective cells. Quantitative physiology-based experiments highlighted a significant increase in the levels of reactive oxygen species in ryhB-induced W3100 E. coli cells in batch culture. A simultaneous decrease in NADH/NAD⁺ and NADPH/NADP⁺ ratios outlined the potentially direct roles of NADH and NADPH in antagonizing the excess formed after ryhB activation. Our observations offer a new perspective regarding the roles of RyhB and highlight that this small RNA can significantly affect cell metabolism in addition to its role as a regulator of gene expression.

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