# Influence of Bacillus subtilis on the corrosion resistance of B30 copper–nickel alloy and the biomass-regulated mineralization mechanism

## TL;DR

This study shows how Bacillus subtilis can protect copper-nickel alloys in seawater by forming a mineral layer that reduces corrosion.

## Contribution

The study identifies how different bacterial components influence biomineralization for corrosion protection.

## Key findings

- B. subtilis created a protective biofilm and mineral layer, reducing corrosion current and pit depth.
- EPS from B. subtilis formed stable Mg-calcite, offering the most durable protection.
- SMPs promoted calcite formation but with lower protective efficacy compared to EPS.

## Abstract

This study investigates the corrosion inhibition behavior of Bacillus subtilis on B30 copper–nickel alloy in seawater, focusing on its biomass components in regulating biomineralization. Results show that B. subtilis formed a protective biofilm and induced the precipitation of a uniform biomineral layer, mainly composed of Ca-Mg carbonates. This layer acted as a physical barrier, resulting in a low corrosion current of (5.85 ± 0.08) × 10⁻⁷ A/cm² and reducing the maximum pit depth from 44.74 to 18.54 µm. Furthermore, the roles of different biomass components, such as bacterial cells, extracellular polymeric substances (EPS), and soluble microbial products (SMPs), were also investigated. It was found that all components could initiate mineralization, but with distinct outcomes: bacterial cells primarily served as structural templates; EPS facilitated the formation of highly crystalline and stable Mg-calcite, providing the most durable protection, while SMPs promoted the formation of well-crystallized calcite with comparatively lower protective efficacy.

Corrosion is a critical issue prevalent across various industries, where traditional corrosion control technologies are often limited by high costs, complex implementation, and potential environmental hazards. Biomineralization, as an emerging green anti-corrosion strategy, is not only environmentally friendly but also enables long-term effective protection, reducing reliance on toxic chemical agents and lowering economic costs. However, due to the complexity of microbial systems, the mechanisms underlying biomineralization are not yet fully understood. In this study, different biomass components—including bacterial cells, extracellular polymeric substances, and secreted metabolites—were isolated from Bacillus subtilis cultures using a series of separation techniques, and their impacts on the mineralization process were systematically evaluated. This work elucidates the corrosion inhibition mechanism of biomineralization and provides valuable insights into the relationship between specific microbial components and biomineral formation, which holds significant implications for developing eco-friendly corrosion inhibition technologies.