Sulphate transport in Candida utilis

Expanding the Knowledge on the Skillful Yeast Cyberlindnera jadinii

Cyberlindnera jadinii is widely used as a source of single-cell protein and is known for its ability to synthesize a great variety of valuable compounds for the food and pharmaceutical industries. Its capacity to produce compounds such as food additives, supplements, and organic acids, among other fine chemicals, has turned it into an attractive microorganism in the biotechnology field. In this review, we performed a robust phylogenetic analysis using the core proteome of C. jadinii and other fungal species, from Asco- to Basidiomycota, to elucidate the evolutionary roots of this species. In addition, we report the evolution of this species nomenclature over-time and the existence of a teleomorph (C. jadinii) and anamorph state (Candida utilis) and summarize the current nomenclature of most common strains. Finally, we highlight relevant traits of its physiology, the solute membrane transporters so far characterized, as well as the molecular tools currently available for its genomic manipulation. The emerging applications of this yeast reinforce its potential in the white biotechnology sector. Nonetheless, it is necessary to expand the knowledge on its metabolism, regulatory networks, and transport mechanisms, as well as to develop more robust genetic manipulation systems and synthetic biology tools to promote the full exploitation of C. jadinii.

Ultradian metabolic oscillation of Saccharomyces cerevisiae during aerobic continuous culture: hydrogen sulphide, a population synchronizer, is produced by sulphite reductase

We have reported that the consecutive cyclic production of H(2)S resulted in population synchrony of ultradian metabolic oscillation (Sohn et al., 2000). In order to understand the origin of H(2)S and its nature of periodic production, changes of sulphur compounds concentration and responsible enzymes were investigated. The concentrations of extracellular sulphate, intracellular glutathione and cysteine oscillated during metabolic oscillation but only the oscillation of sulphate concentration was out of phase with H(2)S production. The sulphate concentration in culture directly affected the amplitude and the period of metabolic oscillation: (a) the period of metabolic oscillation shortened from 50 min to 30 min when sulphate concentration in the medium was reduced from 46 mM to 2.5 mM; (b) the metabolic oscillation disappeared under sulphate-depletion conditions and arose again by the addition of sulphate. Pulse injection of sulphite (10 microM) perturbed metabolic oscillation with a burst production of H(2)S, while thiosulphate (up to 500 microM) was without apparent effect. Furthermore, addition of S-adenosyl methionine (100 microM) or azoxybacilin (3 mg/kg) decreased H(2)S production with perturbation of metabolic oscillation. The results presented here suggest that H(2)S, a population synchronizer, is produced by sulphite reductase in the sulphate assimilation pathway, and dynamic regulation of sulphate uptake plays an important role in ultradian metabolic oscillation.

Single transporter for sulfate, selenate, and selenite in Escherichia coli K-12

A Michaelis-Menten kinetic analysis of the transport of sulfate, selenate, and selenite into Escherichia coli K-12 showed that the three dianions were transported by the same carrier. Km values, used as a measure of the affinity of each ligand for the carrier, showed that sulfate was bound 5 times more tightly than selenate and 37 times more tightly than selenite. The specificity ratio, Vmax/Km, also indicated that sulfate was the preferred ligand. There was little difference in the ratios for selenate and selenite.

A sulfate, sulfite and thiosulfate incorporating system in Candida utilis

Sulfate, sulfite and thiosulfate incorporation in the yeast Candida utilis is inhibited by extracellular sulfate, sulfite and thiosulfate and by sulfate analogues selenate, chromate and molybdate. The three processes are blocked if sulfate, sulfite, thiosulfate, cysteine and homocysteine are allowed to accumulate endogenously. Incorporation of the three inorganic sulfur oxy anions is inactivated by heat at the same rate. Mutants previously shown to be defective in sulfate incorporation are also affected in sulfite and thiosulfate uptake. Revertants of these mutants selected by plating in ethionine-supplemented minimal medium recovered the capacity to incorporate sulfate, sulfite and thiosulfate. These results taken together with previous evidence demonstrate the existence of a common sulfate, sulfite and thiosulfate incorporating system in this yeast.

Isolation of sulphate transport defective mutants of Candida utilis: further evidence for a common transport system for sulphate, sulphite and thiosulphate

Selenate-resistant mutants of Candida utilis were isolated. They did not take up sulphate while incorporation of an organic sulphur source, such as L-methionine, was similar to the wild-type strain. They grew poorly on sulphate, sulphite and thiosulphate and, as expected, grew well on methionine. Sulphite reductase activities of the mutants were similar to the wild type strain. The properties of these mutants support the view of a common transport system for sulphate, sulphite and thiosulphate.

Sulphate transport in Candida utilis

Sulphate uptake by Candida utilis follows Michaelis-Menten type kinetics characterized by a Km of 1.43 mM for sulphate. The process is unidirectional, pH, temperature and energy dependent. Molybdate, selenate, thiosulphate, chromate and sulphite are competitive inhibitors. Dithionite is a mixed-type inhibitor of sulphate uptake. If cells are pre-incubated with sulphate, sulphite, thiosulphate, dithionite or sulphide, sulphate uptake is severely blocked. Inhibition by endogenous sulphate, sulphite and thiosulphate was specific for sulphate uptake. Thus, incorporation of extracellular sulphate seems to be under the control of a heterogeneous pool of sulphur compounds. These results are discussed in connection with the regulation of sulphur amino acid biosynthesis in C. utilis.