Calcium signalling in Bacillus subtilis

Few systematic studies have been devoted to investigating the role of Ca2as an intracellular messenger in prokaryotes. Here we report an investigati on on the potential involvement of Ca2+ in signalling in Bacillus subtilis, a Gram-positive bacterium. Using aequorin, it is shown that B. subtilis ce lls tightly regulate intracellular Ca2+ levels. This homeostasis can be cha nged by an external stimulus such as hydrogen peroxide, pointing to a relat ionship between oxidative stress and Ca2+ signalling. Also, B. subtilis gro wth appears to be intimately linked to the presence of Ca2+, as normal grow th can be immediately restored by adding Ca2+ to an almost non-growing cult ure in EGTA containing Luria broth medium. Addition of Fe2+ or Mn2+ also re stores growth, but with 5-6 h delay, whereas Mg2+ did not have any effect. In addition, the expression of alkyl hydroperoxide reductase C (AhpC), whic h is strongly enhanced in bacteria grown in the presence of EGTA, also appe ars to be regulated by Ca2+. Finally, using Ca-45(2+) overlay on membrane e lectrotransferred two-dimensional gels of B. subtilis, four putative Ca2+ b inding proteins were found, including AhpC. Our results provide strong evid ence for a regulatory role for Ca2+ in bacterial cells. (C) 1998 Elsevier S cience B.V. All rights reserved.