Abstract
Biotechnology processes rely on the efficiency of microbial cell factories. The budding yeast Saccharomyces cerevisiae is an important cell factory but shows a limited native substrate-product spectrum. Non-conventional yeasts with diverse origins can potentially broaden this spectrum. Here, we benchmarked non-conventional yeasts Kluyveromyces marxianus (KM) and Rhodotorula toruloides (RT) against S. cerevisiae CEN.PK and W303 strains. We developed a computational method for quantification of cellular/organellar volumes and applied it for evaluating K+ and Na+ cations impact on yeasts. We observed an inverse relationship between the maximal growth rate and cell volume that was responsive to K+/Na+ cationic interventions. We found that the addition of certain K+ concentration to CEN.PK cultures containing 1.0 M of Na+ increased the specific growth rate by four–fold with a parabolic shift in cell and vacuole volumes. An impairment of ethanol and acetate utilization in CEN.PK, acetate in W303, at increased cation concentrations implied that K+-Na+ interactions interceded over the metabolic pathways required for consumption of respiratory substrates. The addition of cations induced trade-off in glucose utilization but alleviated cellular aggregates formation in RT and K+-Na+ interactions increased beta-carotene yield by 60% compared with the reference. Comparison of cell and vacuole volumes in the exponential phase showed that volumes decreased the most for KM and least for RT in response to K+/Na+ cations. Noteworthy for the implication in aging research using yeasts, vacuole to cell volume ratio increased with the increase in cell volume for W303 and KM, but not for CEN.PK and RT strains.
Importance For designing efficient bioprocesses an understanding of responses by microbial cell factories to changes in the culture environment is essential. The control of cell volume is one of such relevant responses that affects productivity of microbial cell factories. For determining cell volume, we developed a computational method based on optical microscopy images and applied it for evaluating impact of the most common salts (potassium and sodium) on K. marxianus and R. toruloides. We benchmarked responses of these unicellular eukaryotes against extensively characterized strains of S. cerevisiae, CEN.PK and W303. We found distinct cellular and vacuolar heterogeneity in response to the increased cationic concentrations in exponentially growing yeasts. Our results showed that potassium and sodium cationic interactions could be applied for improving the cellular fitness of CEN.PK and increasing the productivity of beta-carotene in R. toruloides, which is a commercially important antioxidant and a valuable additive in foods.
Competing Interest Statement
The authors have declared no competing interest.