Efficient Biosynthesis of Acidic/Lactonic Sophorolipids and Their Application in the Remediation of Cyanobacterial Harmful Algal Blooms

Abstract

Cyanobacterial harmful algal blooms (CyanoHABs) pose significant threats to human health and natural ecosystems worldwide, primarily caused by water eutrophication, increased surface water temperature, and co-occurring microorganisms. Urgent action is needed to develop an eco-friendly solution to effectively curb the proliferation of CyanoHABs. Sophorolipids (SLs) are fully biodegradable biosurfactants synthesized by Starmerella bombicola. They can be classified into lactone and acid types. The lactone type displays strong antimicrobial activity, while the acid type exhibits good solubility, which make them ideal agents for mitigating CyanoHABs. Nevertheless, the broad utilization of SLs are hindered by their expensive production costs and the absence of effective genetic editing tools in the native host. In this study, we constructed recombinant strains capable of producing either acidic or lactonic SLs using the CRISPR-Cas9 gene editing system. The yields of acidic and lactonic SLs reached 53.64 g/L and 45.32 g/L in a shaking flask, respectively. In a 5 L fermenter, acidic SLs reached 129.7 g/L using low-cost glucose and rapeseed oil as substrates. The addition of 5 mg/L lactonic SLs effectively degraded cyanobacteria within 30 min, and a ratio of 8.25:1.75 of lactonic to acidic SLs showed the highest degradation efficiency. This study offers a safe and promising solution for CyanoHABs treatment.

CRISPR-Cas Technology for Bioengineering Conventional and Non-Conventional Yeasts: Progress and New Challenges

“…Starmerella bombicola is known to produce sophorolipids which are carbohydrate-based, amphiphilic biosurfactants [98,99]. Due to the initial lack of effective gene editing tools, the screening of high-yield sophorolipid-producing strains relied on directed evolution using physical mutation, chemical mutation, and compound mutagenesis methods [100,101].…”