The research team, led by Ahmeed Olalekan Ashade of Lagos State University of Science and Technology together with colleagues at Lagos State University and Elizade University, set out to isolate bacteria capable of degrading hydrocarbons while tolerating heavy metals and producing surface-active biomolecules. Such a combination of traits has been sparsely reported in the literature, particularly for West African freshwater systems, even though co-contamination by petroleum and metals is the norm rather than the exception in polluted industrial waterways. The work builds on the group’s earlier metagenomic surveys, which showed that Ologe Lagoon harbors a diverse array of prokaryotic phylotypes with potential biotechnological value.

To capture these hardy microbes, the researchers identified three sampling points reflecting different levels of human disturbance: an industrial-contaminated site, a human-activities site, and a presumed-undisturbed reference site. Surface water was collected in sterile flasks and sediments were retrieved from the lagoon floor using an Ekman grab, yielding composites of 1,500 milliliters of water and 600 grams of sediment. Physicochemical profiling of the samples confirmed measurable burdens of nickel, cadmium, lead, mercury, and cobalt in both water and sediment, with sediment nickel reaching 5.21 milligrams per kilogram at the reference site and water nickel peaking at 1.18 milligrams per kilogram at the industrial site.

The isolation strategy relied on continuous enrichment, a technique that applies strong selective pressure to favor organisms with the desired traits. Samples were incubated aerobically for 30 days in mineral salt medium containing 1 percent Escravos light crude oil as the sole carbon and energy source, fortified with filter-sterilized solutions of nickel chloride, cadmium chloride, and lead acetate at concentrations of 0.5, 0.1, and 1.0 millimolar respectively. Flasks were shaken at 150 revolutions per minute in the dark at 27 degrees Celsius, and after three consecutive transfers onto fresh medium, pure bacterial colonies were obtained. Control flasks containing heat-killed cells confirmed that the observed changes were biological rather than abiotic.

Molecular identification using 16S rDNA Sanger sequencing and phylogenetic analysis with the Neighbor Joining algorithm revealed three standout strains. Strain OLW3 was identified as Alcaligenes aquatilis with 99.86 percent sequence similarity, strain OLW6 as Alcaligenes faecalis with 99.45 percent similarity, and strain OLW15 as Rossellomorea marisflavi with 98.28 percent similarity. The 16S rRNA sequences were deposited in GenBank under accession numbers OP626095, OP626097, and OP626099. The genus Alcaligenes, belonging to the phylum Pseudomonadota, is renowned for its metabolic versatility, with members documented in impacted sediments from Charleston Harbor in the United States to Quintero Bay in Chile, where they degrade hydrocarbons, synthetic dyes, and pharmaceutical compounds. Rossellomorea marisflavi, a Gram-positive, spore-forming, moderately halophilic bacterium formerly classified among the bacilli, contributes to organic matter decomposition and nutrient cycling in sediments.

When the three strains were grown on crude oil-heavy metal mineral salt medium over a 30-day time course, their degradation performance was striking. Strain OLW3, after a six-day lag phase likely reflecting the time needed to induce catabolic enzymes such as dioxygenases for these complex hydrophobic substrates, achieved a degradation rate of 0.056 milligrams per liter per day, a degradation rate constant of 6.43 per day, a half-life of 12.49 days, and an overall percentage degradation of 81.06 percent. Strain OLW15 proved the most efficient, with a degradation rate of 0.065 milligrams per liter per day, a rate constant of 7.16 per day, a half-life of 10.58 days, and 85.67 percent degradation. Strain OLW6, after a seven-day acclimatization period, degraded 54.27 percent of the hydrocarbons, a figure the authors suggest could be improved through optimization of growth conditions.

Gas chromatography with flame ionization detection provided molecular-level confirmation of biodegradation. Chromatograms taken at day 0, day 15, and day 30 showed progressive reductions in the peak areas of hydrocarbon fractions across all three enrichment systems. Strain OLW3 completely removed nC5 pentane and nC6 hexane by day 30 and reduced nC4 isobutane from 43.66 to 10.04 milligrams per kilogram, consistent with aerobic oxidation of straight-chain alkanes into alcohols and organic acids that feed into central metabolic pathways and beta-oxidation. Strain OLW6 cut m,p-xylene from 175.11 to 32.78 milligrams per kilogram and nC13 tridecane from 128.16 to 47.64 milligrams per kilogram, while strain OLW15 halved anthraquinone and reduced propyl-benzene from 125.47 to 36.27 milligrams per kilogram. Declining ratios of nC17 to pristane and nC18 to phytane, classic biomarkers of biodegradation, further documented preferential consumption of readily degradable aliphatics over recalcitrant isoprenoids.

Equally important was the demonstration that these bacteria tolerated the metals present in their enrichment medium. In tolerance assays on Luria Bertani media fortified with metal concentrations ranging from 0.5 to 20 millimolar, strain OLW3 tolerated up to 2.5 millimolar lead, strain OLW6 resisted cadmium concentrations in the same range, and strain OLW15 withstood 1.5 millimolar nickel. The authors note that bacteria deploy diverse detoxification strategies, including efflux pumps that expel metal ions, extracellular sequestration via exopolysaccharides, biosorption and bioprecipitation, and intracellular binding by metallothioneins. Exopolysaccharide production carries a double benefit, decreasing cell surface hydrophobicity to aid adhesion to hydrophobic hydrocarbons while simultaneously binding lead outside the cell, thereby reducing metal bioavailability and protecting the wider food web from uptake.

The biosurfactant credentials of the isolates were assessed through hemolytic, oil spread, and cetyltrimethylammonium bromide blue agar assays, along with measurements of the emulsification index after 24 hours. Strains OLW3 and OLW6 showed complete beta-hemolysis on blood agar, a presumptive indicator of biosurfactant production, while OLW15 tested positive on the blue agar plate assay used to detect anionic biosurfactants such as rhamnolipids. Emulsification indices reached 50 to 58.9 percent on crude oil and kerosene for OLW3, and 58.3 and 50 percent on crude oil for OLW6 and OLW15 respectively, with all isolates emulsifying vegetable oil at 36 to 58 percent. Statistical analysis using one-way analysis of variance with Friedman multiple test comparison confirmed significant differences among the emulsification datasets, with post-hoc Dunn’s testing showing the greatest divergence between OLW6 and OLW15.

Perhaps most compelling from an applied perspective is the robustness of the biosurfactants under harsh conditions. Near-neutral pH favored production for all isolates, but OLW3 and OLW6 remained active at pH 10, and OLW6 continued producing biosurfactant at 80 degrees Celsius while OLW3 and OLW15 functioned at 50 degrees Celsius. All three tolerated 10 percent sodium chloride, suggesting utility in coastal and saline environments where salt stress often undermines bioremediation. These properties point toward applications ranging from in-situ cleanup in hot climates to microbial enhanced oil recovery, where biosurfactants reduce oil viscosity and improve mobility, and to refinery and petrochemical wastewater treatment. The authors propose that whole-genome sequencing, characterization of metal resistance mechanisms, and high-performance liquid chromatography profiling of the biosurfactants represent the next steps. For now, the message from Ologe Lagoon is clear: even ecosystems degraded by unchecked pollution can yield microbial resources capable of healing environments like their own home.

Subject of Research: Hydrocarbon-degrading, heavy metal-tolerant, biosurfactant-producing bacteria isolated from Ologe Lagoon water and sediments in Lagos State, Nigeria

Article Title: Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments

Article References: Ashade, A. O., Obayori, O. S., Fashola, M. O., Salam, L. B., & Oso, S. O. (2026). Hydrocarbon degradation and heavy metal tolerance of bacterial isolates from Ologe lagoon water and sediments. BMC Environmental Science, 3(1), Article 8. https://doi.org/10.1186/s44329-026-00051-z

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00051-z

Keywords: bioremediation, hydrocarbon degradation, heavy metal tolerance, biosurfactant, Ologe Lagoon, Alcaligenes, Rossellomorea marisflavi, crude oil pollution, 16S rRNA sequencing, gas chromatography, freshwater pollution, Nigeria