Abstract

This study investigated the inhibitory impact of leaf/stem extract of Ocimum gratissimum on microbial communities responsible for microbiologically influenced corrosion (MIC) of steel. Steel coupons preconditioned with the plant extract as corrosion inhibition treatment were buried in simulated soil and incubated anaerobically for 28 days. Metagenomic DNA was extracted from the soil samples, sequenced and analyzed to characterize shifts in microbial community structure after 28 days compared to untreated baseline and control samples. Results showed that Proteobacteria was the most dominant phylum, increasing in relative abundance from 53.27% at baseline at day 0 (E0) to 96.58% in the untreated control sample at day 28 (E28), while sample treated with O. gratissimum (B) resulted in a slightly lower relative abundance of 89.91%. The family Pseudomonadaceae followed a similar trend, increasing from 5.72% (E0) to 24.76% in E28 as compared to a lower abundance of 11.50% in B. At the genus level, Pseudomonas rose in abundance from 5.72% (E0) to 24.76% (E28) with a marked variation of 5.18% in treated sample (B). Likewise, Sphingomonas increased in abundance to 3.11% in E28 from 0.20% at baseline, while lower (0.42%) in treated sample B. Notably, Pseudomonas balearica, a bacterial specie known to form biofilms on metal surfaces and cause corrosion, varied between 1.91% in E28 to 0.22% in B, indicating microbial inhibition by the extract. These findings indicate that O. gratissimum leaf/stem extract effectively inhibited several key corrosion-associated bacteria, highlighting their potential as eco-friendly alternatives for managing MIC on buried steel infrastructures.