Mesocosm-based simulations to optimize a bioremediation strategy for the effective restoration of wildfire-impacted soils contaminated with high-molecular-weight hydrocarbons

Characterization of trehalolipid biosurfactant produced by the novel marine strain Rhodococcus sp. SP1d and its potential for environmental applications

BACKGROUND

Biosurfactants are surface-active compounds with environmental and industrial applications. These molecules show higher biocompatibility, stability and efficiency compared to synthetic surfactants. On the other hand, biosurfactants are not cost-competitive to their chemical counterparts. Cost effective technology such as the use of low-cost substrates is a promising approach aimed at reducing the production cost. This study aimed to evaluate the biosurfactant production and activity by the novel strain Rhodococcus sp. SP1d by using different growth substrates. Therefore, to exploit the biosurfactant synthesized by SP1d for environmental applications, the effect of this compound on the bacteria biofilm formation was evaluated. Eventually, for a possible bioremediation application, the biosurfactant properties and its chemical characteristics were investigated using diesel as source of carbon.

RESULTS

Rhodococcus sp. SP1d evidence the highest similarity to Rhodococcus globerulus DSM 43954^T and the ability to biosynthesize surfactants using a wide range of substrates such as exhausted vegetable oil, mineral oil, butter, n-hexadecane, and diesel. The maximum production of crude biosurfactant after 10 days of incubation was reached on n-hexadecane and diesel with a final yield of 2.38 ± 0.51 and 1.86 ± 0.31 g L^- 1 respectively. Biosurfactants produced by SP1d enhanced the biofilm production of P. protegens MP12. Moreover, the results showed the ability of SP1d to produce biosurfactants on diesel even when grown at 10 and 18 °C. The biosurfactant activity was maintained over a wide range of NaCl concentration, pH, and temperature. A concentration of 1000 mg L^- 1 of the crude biosurfactant showed an emulsification activity of 55% towards both xylene and olive oil and a reduction of 25.0 mN m^- 1 of surface tension of water. Eventually, nuclear magnetic resonance spectroscopy indicated that the biosurfactant is formed by trehalolipids.

CONCLUSIONS

The use of low-cost substrates such as exhausted oils and waste butter reduce both the costs of biosurfactant synthesis and the environmental pollution due to the inappropriate disposal of these residues. High production yields, stability and emulsification properties using diesel and n-hexadecane as substrates, make the biosurfactant produced by SP1d a sustainable biocompound for bioremediation purpose. Eventually, the purified biosurfactant improved the biofilm formation of the fungal antagonistic strain P. protegens MP12, and thus seem to be exploitable to increase the adherence and colonization of plant surfaces by this antagonistic strain and possibly enhance antifungal activity.

Unravelling the sponge microbiome as a promising source of biosurfactants

Microbial surfactants are particularly useful in bioremediation and heavy metal removal from soil and aquatic environments, amongst other highly valued uses in different economic and biomedical sectors. Marine sponge-associated bacteria are well-known producers of bioactive compounds with a wide array of potential applications. However, little progress has been made on investigating biosurfactants produced by these bacteria, especially when compared with other groups of biologically active molecules harnessed from the sponge microbiome. Using a thorough literature search in eight databases, the purpose of the review was to compile the current knowledge on biosurfactants from sponge-associated bacteria, with a focus on their relevant biotechnological applications. From the publications between the years 1995 and 2021, lipopeptides and glycolipids were the most identified chemical classes of biosurfactants. Firmicutes was the dominant phylum of biosurfactant-producing strains, followed by Actinobacteria and Proteobacteria. Bioremediation led as the most promising application field for the studied surface-active molecules in sponge-derived bacteria, despite the reports endorsed their use as antimicrobial and antibiofilm agents. Finally, we appoint some key strategies to instigate the research appetite on the isolation and characterization of novel biosurfactants from the poriferan microbiome.