From petroleum-contaminated soils to remediation candidates: multi-assay screening of microbial isolates for bulk...

Twelve indigenous hydrocarbon-tolerant microbial isolates, including eleven bacterial isolates and one filamentous fungal isolate, were recovered from petroleum-contaminated soils and petroleum-derived products collected in Algeria and functionally screened for hydrocarbon-associated growth, surface-active phenotypes, and operational bulk hydrocarbon removal in soil microcosms. The isolates were identified using 16S rRNA gene sequencing for bacteria and ITS sequencing for the fungal isolate, supported by phylogenetic analysis. All isolates grew in mineral salt medium supplemented with diesel or gasoline as the sole added organic carbon source, with strongly strain- and substrate-dependent responses. Bacillus sp. strain K2 showed the highest diesel-associated biomass accumulation (OD₆₀₀ ≈ 1.9), whereas Micrococcus sp. strain K8 and Aspergillus sp. strain K12 showed the strongest gasoline-associated growth (OD₆₀₀ ≥ 1.3). Nine isolates displayed measurable emulsification activity, with Enterococcus sp. strain K1 reaching approximately 29% with diesel and Kocuria sp. strain K3 approximately 39% with gasoline. MATH-derived cell surface hydrophobicity ranged from 18 to 79% with diesel and from 4 to 65% with gasoline, with Pseudomonas sp. strain K4 and Streptomyces sp. strain K9 showing the highest diesel- and gasoline-associated hydrophobicity, respectively. All isolates showed positive drop-collapse responses, indicating extracellular surface-active behavior under the assay conditions. In sterilized-soil microcosms, operational bulk hydrocarbon removal measured by UV-Vis after solvent extraction was highest for Aneurinibacillus sp. strain K7 with diesel (76.08%) and for Lysinibacillus sp. strain K10 with gasoline (91.32%). Taken together, these findings identify locally derived microbial candidates with hydrocarbon-removal and surface-interaction potential. However, compound-specific hydrocarbon profiling, chemical characterization of surface-active metabolites, and biosafety assessment are required before field-oriented application.