This study investigates the capability of the microbially induced calcite precipitation (MICP) method to enhance the shear strength parameters of soil-steel interfaces. A set of modified direct shear tests, designed based on the Taguchi design of experiments method, are conducted on poorly-graded loose sand samples, which are bio-treated and prepared against a rough steel surface. Data analysis is performed using the analysis of means (ANOM). The direct shear tests show that introducing the bio-cementation process effectively improves the interface properties, leading to a significant increase in the shear strength of the sand-steel interface. Scanning electron microscopy (SEM) analyses of the bio-treated samples demonstrate the successful precipitation of calcium carbonate between the soil particles and the interface. Moreover, this research introduces a cost-effective approach by utilizing a novel culture medium for the bacteria, incorporating waste materials. These findings contribute to the advancement of the MICP method for improving soil-structure interfaces, offering potential benefits for large-scale geotechnical engineering projects.