Alleviation of the toxicity of oily wastewater to canola plants by the N 2-fixing, aromatic hydrocarbon biodegrading bacterium Stenotrophomonas maltophilia-SR1

Soils may be contaminated by oily wastewater during both upstream and downstream oil and gas production processes such as extraction, transportation, and refining. Oil-contaminated sites could nonetheless be used for agricultural purposes in arid regions provided they are managed appropriately. The present study introduces the successful application of a novel nitrogen-fixing, aromatic hydrocarbon-degrading bacterial isolate for the bioremediation of agricultural soils contaminated by oily wastewater. The isolate was recovered from uncontaminated soil and identified by 16S rRNA gene sequencing as Stenotrophomonas maltophilia-SR1 (MH634684). It successfully utilized various aromatic hydrocarbons such as benzene, toluene, and xylene as its sole carbon source and presented with plant growth promoting (PGP) properties such as indoleacetic acid and ammonia production and phosphate solubilization. The efficacy of this novel S. maltophilia-SR1-N2 fixing bacterial isolate at reducing aromatic hydrocarbon toxicity of oily wastewater was validated by its ability to promote the growth of canola (Brassica napus L.) cultivated in soils contaminated with oily wastewater. Inoculating S. maltophilia-SR1 on canola growing in soil amended with different concentrations of oily wastewater significantly increased chlorophyll content and soluble carbohydrates, proteins, and amino acids compared with uninoculated plants. Oily wastewater contamination induced the accumulation of high levels of hydroxyl radical, superoxide anion, hydrogen peroxide, and nitric oxide and caused plasma membrane degradation in uninoculated canola plants. In contrast, the presence of S. maltophilia-SR1 in soil contaminated with various oily wastewater concentrations upregulated nitrate, total nitrogen, nitrate reductase, and nonenzymatic and enzymatic antioxidants in the plants. It also markedly suppressed oxidative and nitrosative stress induced by oily wastewater. The findings of the present study lay theoretical and empirical foundations for the optimization of canola cultivation on agricultural soils contaminated by oily wastewater.