Protein phosphatase SppA regulates apical growth and dephosphorylates cell polarity determinant DivIVA in Streptomyces coelicolor

Abstract

Members of the Actinobacteria, including mycobacteria and streptomycetes, exhibit a distinctive mode of polar growth, with cell wall synthesis occurring in zones at cell poles and directed by the essential cell polarity determinant DivIVA. Streptomyces coelicolor modulates polar growth via the Ser/Thr protein kinase AfsK, which phosphorylates DivIVA. Here, we show that the phosphoprotein phosphatase SppA has strong effects on polar growth and cell shape and that it reverses the AfsK-mediated phosphorylation of DivIVA. SppA affects hyphal branching and the rate of tip extension. The sppA mutant hyphae also exhibit a high frequency of spontaneous growth arrests, indicating problems with maintenance of tip extension. The phenotypic effects are partially suppressed in an afsK sppA double mutant, indicating that AfsK and SppA to some extent share target proteins. Strains with a nonphosphorylatable mutant DivIVA confirm that the effect of afsK on hyphal branching during normal growth is mediated by DivIVA phosphorylation. However, the phenotypic effects of sppA deletion are independent of DivIVA phosphorylation and must be mediated via other substrates. This study adds a PPP-family protein phosphatase to the proteins involved in the control of polar growth and cell shape determination in S. coelicolor.