Bacterial Roles in the Precipitation of Carbonate Minerals

Abstract

Bacterial carbonate formation includes autotrophic pathways that induce local C02 depletion of the medium and heterotro-phic pathways that can lead to active or passive precipitation. In active precipitation, solid carbonate is localised by ionic exchange through the cell membrane. In passive precipitation, processes such as ammonification, dissimilatory nitrate reduction, degradation of urea or uric acid, and sulphate reduction lead to carbonate and bicarbonate production and a pH increase, processes which induce solid carbonate precipitation. In heterotrophic bacterial communities, pathways of carbonate precipitation always appear to be responses to enrichment by organic matter, and the precise nutritional conditions play a major role in the relationships between bacteria and the developing crystals. Heterotrophic bacterial pre-cipitation, evaluated by laboratory experiments, appears to be the most probable process in the formation of apparently abiotic lime-stones. Bacterial carbonate formation has applications for stone-work preservation and restoration.