Desert soil bacteria deposit atmospheric carbon dioxide in carbonate precipitates

Carbonate precipitation by soil microbes has generated major concern recently because of the potential for mitigating the challenge of increasing CO2 level; however, while desert soil microbes have the capacity of carbonate formation, it is unknown if they can deposit atmospheric carbon dioxide. We isolated soil bacteria from the Mu Us Desert in northern China to perform an experiment of carbonate formation by bacteria isolated from the soil. We detected the precipitates produced by the bacteria, and identified the carbon source of the carbonate precipitates using stable carbon isotopic tracing. Six bacterial strains, designated as strains 1-6, were isolated from the desert soil, including Arthrobacter sp., Rhodococcus sp., Planococcus sp., Streptomyces sp., Arthrobacter sp., and Microbacterium sp. We confirmed that all six species precipitated carbonate (vaterite and calcite) using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray. 13CO2 labeling showed that the abundance of 13C was significantly higher in carbonate precipitates, of which 1.03% was represented by atmospheric carbon; that is, the atmospheric CO2 participates in the formation of carbonate by desert soil bacteria. To our knowledge, this is the first study to demonstrate the occurrence of carbonate precipitation by these desert soil bacterial strains (strains 1, 2, 4, 5, and 6), which expands the current knowledge on carbonate-depositing bacteria in drylands. The carbon transformation process, from atmospheric CO2 to carbonate precipitates by soil bacteria, indicates a process of atmospheric CO2 deposition through microbial carbonate precipitation. Although under controlled conditions, this study provided an important insight supporting that drylands probably contribute strongly to global carbon processes via soil microbial activity.