Extracellular Ca2+ transients affect poly-(R)-3-hydroxybutyrate regulation by the AtoS-AtoC system in E. coli

Overview & Synopsis

Escherichia coli is exposed to wide extracellular concentrations of Ca2+, while the cytosolic levels of the ion are subject to stringent control and are implicated in many physiological functions. This study shows that extracellular Ca2+ controls complexed poly-(R)-3-hydroxybutyrate (cPHB) biosynthesis through the AtoS-AtoC two component system. Maximal cPHB accumulation was observed at higher [Ca2+]e in AtoS-AtoC expressing E. coli compared to their ΔatoSC counterparts, in both cytosolic and membrane fractions. The reversal of EGTA-mediated down-regulation of cPHB biosynthesis by the addition of Ca2+ and Mg2+ was under the control of the AtoS-AtoC system. Moreover, the Ca2+ channel blocker verapamil reduced total and membrane-bound cPHB levels, the inhibitory effect being circumvented by Ca2+ addition only in atoSC+ bacteria. Histamine and compound 48/80 affected cPHB accumulation in a [Ca2+]e-dependent manner directed by the AtoS-AtoC system. In conclusion, these data provide evidence for the involvement of external Ca2+ on cPHB synthesis regulated by the AtoS-AtoC two-component system, thus linking Ca2+ with a signal transduction system, most probably through a transporter.