Bacteria are a key component of the critical zone, because of their role in the nutrient availability for the vegetation. There is still little knowledge on the direct role of bacteria on Ca storage/leaching in soils while it is an essential macronutrient for vegetation growth. In recent years, Ca stable isotopes have shown their potential in understanding the Ca biogeochemical cycle. Preliminary studies highlighted that in the presence of soil bacteria, the plant uptake of nutrients is increased due to the mineral bioweathering. Moreover, Ca isotope signatures of nutrient media also showed differences between growth experiments in batch in the presence and absence of bacteria. In this study, the focus is to verify if Ca adsorption and incorporation into/onto bacterial strains induce such isotopic fractionation. Batch experiments were carried out on Pseudomonas aeruginosa (a Gram-negative bacterium) and on the vegetative and sporulated forms of Bacillus subtilis (a Gram-positive bacterium). These experimentations showed that: (i) no observable isotopic fractionations were induced during calcium/bacteria contact for all experimental parameters (pH, kinetic, bacterial cell number, interaction time, dead/alive bacteria); (ii) Ca was mainly stored in the bacterial cell wall compartments. On the other hand, significant Ca isotopic differences between the spores and the sporulation medium (Δ^44/40Ca_{spores–sporulation medium} ranging from − 0.53 to − 1.15‰), suggest isotopic fractionation during the sporulation process, likely occurring during the attachment of Ca to carboxyl acid groups as calcium chelates with dipicolinic acid. The absence of Ca isotope fractionation during Ca sorption on vegetative and sporulated bacteria via passive channels indicates that the tested bacteria’s contribution to the Ca biogeochemical cycle is indirect primary enhancing bioweathering and Ca bioavailability for vegetation. If confirmed by further studies, only the sporulation mechanisms itself may directly impact the Ca biogeochemical cycle.

细菌是关键区的关键组成部分，因为它们在植被的养分可用性中发挥着作用。关于细菌对土壤中钙储存/浸出的直接作用，人们仍然知之甚少，而钙是植被生长所必需的常量营养素。近年来，Ca 稳定同位素在理解 Ca 生物地球化学循环方面显示出其潜力。初步研究强调，在土壤细菌存在的情况下，由于矿物生物风化，植物对养分的吸收增加。此外，营养培养基的 Ca 同位素特征也显示，在存在和不存在细菌的情况下，分批生长实验之间存在差异。在本研究中，重点是验证 Ca 吸附和掺入细菌菌株/掺入细菌菌株是否诱导这种同位素分级。对铜绿假单胞菌（一种革兰氏阴性细菌）和枯草芽孢杆菌（一种革兰氏阳性细菌）的营养和孢子形式进行了批量实验。这些实验表明：（i） 对于所有实验参数（pH 值、动力学、细菌细胞数量、相互作用时间、死/活细菌），在钙/细菌接触期间没有诱导可观察到的同位素分馏;（ii） Ca 主要储存在细菌细胞壁隔室中。另一方面，孢子和孢子形成培养基之间的显着 Ca 同位素差异（Δ^44/40Ca_{孢子 - 孢子形成培养基}范围为 − 0.53 至 − 1.15‰），表明孢子形成过程中存在同位素分馏，可能发生在钙与二羧酸螯合时 Ca 与羧酸结合期间。 在通过被动通道对营养细菌和孢子细菌进行 Ca 吸附过程中不存在 Ca 同位素分馏，这表明测试细菌对 Ca 生物地球化学循环的贡献是间接初级增强植被的生物风化和 Ca 生物利用度。如果通过进一步的研究得到证实，只有孢子形成机制本身可能直接影响 Ca 的生物地球化学循环。