A catecholic siderophore produced by the thermoresistant Bacillus licheniformis VK21 strain

Thermophilic and thermoresistant strains of bacilli were screened on a medium containing Chrome Azurol S for the producers of siderophores. It was found that the Bacillus licheniformis VK21 strain dramatically increases secretion of the metabolite, a chelator of Fe3+, in response to addition of manganese(II) salts. The growth of the producer on a minimal medium containing MnSO4 under the conditions of iron deficiency is accompanied by the accumulation of a catecholic product, the content of which reaches maximum at the beginning of the stationary growth phase of culture. In the presence of FeCl3, the amount of the catecholic product in the medium considerably decreases. The siderophore, called S-VK21, was isolated from the cultural medium and purified by reversed phase HPLC, and its siderophore function was confirmed by the test for the restoration of growth of producer cells in a medium containing EDTA. The UV spectrum of the siderophore has absorption maxima at 248 and 315 nm. According to the amino acid analysis and NMR spectrometry, the metabolite S-VK21 is 2,3-dihydroxybenzoyl-glycyl-threonine.