Calcite precipitation by the nitrogen-fixing cyanobacterium Anabaena sp. ATCC 33047.

Microbiologically induced calcium carbonate precipitation (MICP) is an ecologically vital process where the metabolic activity of microorganisms causes the precipitation of calcium carbonate. In cyanobacteria, MICP is thought to occur primarily due to photosynthesis. During this process, cyanobacteria consume carbon dioxide, raising the local pH, which leads to conditions favorable to calcium carbonate precipitation. However, how individual cells contribute to MICP is poorly understood. Here, we use quantitative microscopy to obtain direct evidence of MICP caused by the filamentous cyanobacterium Anabaena sp. ATCC 33047 (hereafter Anabaena) in nitrogen fixing conditions. Anabaena cells differentiate into photosynthetic vegetative cells and nitrogen-fixing heterocysts. Our results show that MICP occurs due to two distinct interactions: Firstly, mechanical stress on vegetative cells can cause leakage and/or lysis, releasing sequestered bicarbonate into the environment, resulting in the formation of new crystals. Secondly, close contact between a heterocyst and a calcite crystal seed appears to cause rapid crystal growth. To our knowledge, the latter interaction has not been reported previously. By providing greater insight into MICP caused by Anabaena, these results increase our understanding of the interplay between cyanobacteria and calcium carbonate precipitation, which plays a role in oceanic buffering and mineral formation around the globe.