Carbon fixation performance and the stability surroundings of Serratia sp. isolated from karst

Carbon exists in many forms in nature, among which carbonate and carbon dioxide (CO₂) are the most important forms and play an important role in the global carbon cycle. Microorganisms play an important role in the material and energy cycles in karst systems. Lots of CO₂-fixing bacterial existed in the karst region due to its special ecological environment. However, very limited attention has been given to the karst region with natural advantage, as a possible source for isolation of carbonic anhydrase (CA) bacteria. In this work, we found that the karst region was pregnant with bacteria belonging to different genera able to induce CaCO₃ precipitation. 15 strains of high yield of CA enzyme activity (> 200 U/L) were isolated from karst soil, and Serratia sp. identified by 16 S rDNA sequencing was the highest enzyme production. The optimal culture conditions of Serratia sp. growth were 20°C and pH 9, and the CA activity was 2795.84 U/L. Ca²⁺, Mg²⁺, Fe²⁺ and Cl^- showed the promoted effect on the growth and the CA activity of Serratia sp., however, Fe²⁺ and OH^- had inhibited the growth and the CA activity on high concentrations. The carbon conversion of Serratia sp. was 39.51 mmol/L on 20°C and pH 9, and produced 3.518 g/L CaCO₃, indicating that it showed a good CO₂ chelation capacity than other strains. This study clarified the application environment of Serratia sp, indicating that the CA bacteria from karst region have broad application prospects in CO₂ capture, utilization and storage.