Recovery of competence in calcium-limited Azotobacter vinelandii

Abstract

A. vinelandii cells required 0.5 mM Ca in the Fe-limited competence induction medium. This requirement also was fulfilled by Sr, but not by Mg. Cells pregrown in competence medium lacking Ca rapidly recovered competence with the addition of 0.5 mM Ca, provided they were suspended in the growth supernatant. A 60,000 dalton glycoprotein (pI (isoelectric point) 5.10) present in competent or noncompetent culture supernatants participated in Ca-mediated competence recovery. Cells grown in Ca-limited medium appeared to have leaky cell envelopes and released a diverse array of proteins into the culture supernatant and into distilled water washes of the cells, 7 of which appeared to be more dominant in competent cells. Two distilled water washes of cells grown in Ca-limited medium did not prevent Ca-mediated recovery of competence in the culture supernatant. Four to 6 distilled water washes removed a competence-specific protein (pI 5.19) and prevented Ca-mediated recovery of competence in the culture supernatant.