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Abstract
Peanut (Arachis hypogaea L.) is an important commercial crop for the state of Georgia, which produces about 50% of the total U.S. peanut crop. However, compared to other commodity crops, peanut production has one of the highest costs due to the extensive usages of fungicides and fertilizers. One of those fertilizers is calcium, in the form of gypsum or lime. Insufficient calcium during flowering and fruiting may lead to significant reduction in yield and increased disease severity. To explore the function of soil microbes in calcium cycling, we conducted experiments to isolate calcite dissolving bacteria (CDB) from Georgia peanut-producing fields and characterized their potential to elevate soluble calcium in soil. CDB refers to a functional group of bacteria that can solubilize calcite, the mineral form of calcium, and release soluble calcium making it available to plants. A total of 65 CDB were isolated representing 15 unique strains belonging to 10 different genera from peanut fields at the Black Shank farm, Tifton, GA. A subset of the CDB, named as “Top mix” due to their high capacity to dissolve calcite, increased soluble calcium level in soil. CDB abundance in soil was negatively corelated with calcium level. We further conducted a survey of CDB in 15 peanut-producing fields belonging to three regions with distinct soil characters in southern Georgia. We found that three genera of “core” CDB, namely Paenibacillus, Niallia and Rossellomorea, were present in all regions. CDB belonging to Staphylococcus, Mesobacillus, Pseudarthobacer, and Schouchella were unique to a single field of the three regions surveyed. The core and unique CDB showed comparable capacity to dissolve calcite on plate. To explore the impact of CDB on peanut pod development, we developed an “In-Tube growth” (ITG) system that allows roots and pods on the same peanut plant to grow in differently controlled soil. We demonstrated that peanuts grown in ITG tubes were comparable to those in soil in terms of their normal development and responses to calcium deficiency. Future research is needed to determine the molecular mechanisms of CDB-mediated calcite solubilization. CDB may one day be used as a bio-fertilizer to replace or complement the current usage of mineral fertilizers in peanut production.