Hyper-Exg1 Export Promotes the Biotransformation of Mogrosides in Saccharomyces Cerevisiae kre6Δ Mutants

Fungi are able to secrete extracellular enzymes to convert macromolecules into smaller units for growth and adaptation. Studies has been reported that hyper-production of extracellular enzymes and proteins is sometimes associated with cell wall alterations in fungus. Previously, we identified that Saccharomyces cerevisiae kre6Δ mutant can efficiently convert mogroside V into anti-diabetic bioactive compound mogroside IIIE. However, the underlying mechanism is unidentified, we therefore hypothesized the facilitative conversion of kre6Δ mutant might be cause by changes in cell wall structures and enzyme secretion behavior. In the current study, we examined the extracellular enzyme secretion in relation to mogrosides bioconversion efficiency of several cell wall mutants; while analyzing their cell walls differences by transmission electron microscopy (TEM), zymolyase sensitivity test, and mannoprotein release assays. We found only mutants, including kre1Δ, las21Δ, gas1Δ, and kre6Δ, defective in mannoprotein anchorage at outer cell wall layer, had an efficient mogrosides conversion property; such mannoprotein defects suggests with increased cell wall porosity in relation to increased Exg1 enzyme release responsible for mogrosides conversion. Wild-type cells, or cwh41Δ or cwh43Δ mutants without mannoprotein defects, however, had average enzyme release and mogrosides conversion rates. Moreover, the discovery of extra mannoprotein and enzyme present in the medium of kre6Δ mutants and other mutants may further used for increasing the color stability and aroma respectively in wine making industry and promote the bioactive compounds synthesis efficiency.