Metagenomic Insights into the Adaptive Responses of the Microbiome of a Spent Engine Oil-Perturbed Agricultural Soil to Iron Stress

Abstract

In hydrocarbon-impacted matrices, accessibility to iron, an essential micronutrient poses a significant challenge to microorganisms due to its complexation with hydrocarbon pollutants. This necessitates the elicitation of diverse adaptive responses to counteract the iron stress and achieve cellular iron homeostasis. In this study, putative genes responsible for iron acquisition, iron regulation, and iron storage in agricultural soil (1S) and agricultural soil amended with spent engine oil (AB1) were evaluated through functional annotation of their open reading frames (ORFs). Functional annotation was done using KEGG KofamKOALA and BacMet. Annotation revealed 110 genes in AB1 of which 96 (87.3%) were annotated for iron acquisition. The iron acquisition genes were responsible for Fe2+/Fe3+ transport and efflux, heme transport, vitamin B12/cobalamin transport, siderophore transport and biosynthesis. In IS metagenome, 28 genes were detected, of which 20 (71.4%) were annotated for iron acquisition. More genes involved in iron regulation and oxidative stress protection were detected in AB1 metagenome while significant differences observed in the iron metabolism genes recovered from 1S and AB1 metagenomes were statistically validated (p < 0.05). The study revealed that spent engine oil contamination of the agricultural soil imposed significant iron stress on the AB1 microbiome necessitating the expression of several genes encoding high affinity iron uptake systems (siderophores, ABC iron transporters), global iron regulators, and iron-induced oxidative stress protection proteins.