In this study, we demonstrate that sulphate-reducing bacteria induce anoxic low-temperature Ca-dolomite formation both in situ in Lagoa Vermelha and Brejo do Espinho, two neighbouring, dolomite-precipitating hypersaline lagoons in Brazil, and in laboratory culture experiments. The metabolic activity of sulphate-reducing bacteria facilitates dolomite formation under anoxic conditions, as demonstrated with experiments using dialysis bags. Overall changes in the chemical conditions of the medium exclusively, without the presence of bacteria, did not result in carbonate precipitation. Only pure cultures of metabolizing sulphate-reducing bacteria induced Ca-dolomite and high Mg-calcite precipitates, indicating that the carbonate nucleation takes place in the locally changed microenvironment around the sulphate-reducing bacterial cells. Not all pure strains, however, produced Ca-dolomite under similar conditions, suggesting that the bacterial metabolism, activity and the rate of mineral precipitation have an influence on the type of carbonate formed.