Calcite dissolving bacteria: Promising approach as biofertilizer, a review

CHRISTINA LEMSON HAMBO^1*MAWAZO JAMSON SHITINDI²KALLUNDE PILLY SIBUGA²YASINTA BEDA NZOGELA²

• ¹Dar es Salaam University College of Education, Dar es Salaam, Tanzania
• ²Sokoine University of Agriculture, Morogoro, Tanzania

Calcium (Ca) is an essential macronutrient and a secondary messenger important for proper growth and functioning of plants. It’s important for membrane stability, cell integrity, cell division and elongation. In the soils Ca exists in inorganic and organic forms. Inorganic fraction constitutes soil-Ca solution which is readily available for plant uptake, exchangeable Ca which replenishes solution pool and fixed Ca which replenishes exchangeable Ca slowly upon weathering to release Ca2+. Similarly, organic forms of Ca are inactive and un-available for plant uptake until decomposed, mineralized and dissolved into Ca2+. Calcium deficiency in the soil reduces plant growth, development and yields and it’s corrected by application of Ca fertilizers and Ca-rich soil amendments. Unfortunately, many smallholder farmers have limited access to Ca fertilizers, thus cannot purchase optimal amounts required for enhancing plant growth and crop yields. This calls for alternative technologies that enhance the dissolution of unavailable forms of Ca in the soil. Calcite dissolving bacteria (CDBs) are a functional group of bacteria that have the capacity to dissolve poorly soluble calcite minerals into Ca2+ thus increasing the % Ca2+ saturation on the soil exchange sites, making it available for plants uptake. CDB offers an economically viable and environmentally friendly option to overcome Ca deficiency in the soil. Longly, CDBs have been a subject of research interest especially on their ability to precipitate calcite for soil stabilization and soil strength enhancement. However, studies on the use of CDBs to improve Ca2+ supply power of the soils and its resultant effects on plant growth and crop productivity especially under field conditions are limited. For effective formulation of CDB based biofertilizers, one should understand the chemistry of calcite, calcium availability in the soil, diversity of CDBs, mechanisms of calcite dissolution by CDBs, mechanisms by which CDBs promote plant growth and the potentials of CDBs as biofertilizer in crop production. This review is among the first to provide detailed information on these aspects of CDBs. We employed a Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) method to explore and expand the understanding on the potential of CDBs as biofertilizers in crop production.