This study investigates the corrosion of 90/10 copper-nickel (Cu-Ni) alloy caused by sulfate-reducing bacteria (SRB) in the presence of aluminum anodes, with particular emphasis on the role of electron supply in microbial corrosion and the resulting local corrosion failures. The study reveals that the electron supply from the anode supports SRB growth on the Cu-Ni alloy through an “Electrons-siphoning” mechanism. However, the supply is insufficient to sustain the SRB population, resulting in ineffective cathodic protection (i = 2.34 × 10 A cm). The addition of 20 ppm riboflavin (RF) to the SRB biofilm enhances electrical activity and increases the electron donor density, thereby restoring the anode's protective effect. As a result, the i of the 90/10 Cu-Ni alloy decreases by an order of magnitude (to 3.5 × 10 A cm). These findings provide valuable new insights into the mechanisms of microbial corrosion.