Roles of different peptide transporters in nutrient acquisition in Candida albicans.

Fungi possess two distinct proton-coupled peptide transport systems, the dipeptide/tripeptide transporters (PTR) and the oligopeptide transporters (OPT), which enable them to utilize peptides as nutrients. In the pathogenic yeast Candida albicans, peptide transporters are encoded by gene families consisting of two PTR genes and eight OPT genes. To gain insight into the functions and importance of specific peptide transporters, we generated mutants lacking the two dipeptide/tripeptide transporters Ptr2 and Ptr22, as well as the five major oligopeptide transporters Opt1 to Opt5. These mutants were unable to grow in media containing peptides as the sole nitrogen source. Forced expression of individual peptide transporters in the septuple mutants showed that Ptr2 and Ptr22 could utilize all tested dipeptides as substrates but differed in their abilities to transport specific tripeptides. Interestingly, several oligopeptide transporters, which are thought to transport peptides consisting of more than three amino acids, also mediated the uptake of tripeptides. Opt1 especially turned out to be a highly flexible transporter that enabled growth on all tripeptides tested and could even utilize a dipeptide, a function that has never been ascribed to this family of peptide transporters. Despite their inability to grow on proteins or peptides, the opt1Δ opt2Δ opt3Δ opt4Δ opt5Δ ptr2Δ ptr22Δ septuple mutants had no in vivo fitness defect in a mouse model of gastrointestinal colonization. Therefore, the nutritional versatility of C. albicans enables it to utilize alternative nitrogen sources in this host niche, which probably contributes to its success as a commensal and pathogen in mammalian hosts.

Environmental induction of white-opaque switching in Candida albicans.

Candida albicans strains that are homozygous at the mating type locus (MTLa or MTLalpha) can spontaneously switch at a low frequency from the normal yeast cell morphology (white) to an elongated cell type (opaque), which is the mating-competent form of the fungus. The ability to switch reversibly between these two cell types also contributes to the pathogenicity of C. albicans, as white and opaque cells are differently adapted to specific host niches. We found that in strain WO-1, a strain in which genomic alterations have occurred, but not in other tested strains, switching from the white to the opaque phase can also be induced by environmental conditions. Transient incubation of white cells under anaerobic conditions programmed the cells to switch en masse to the opaque phase. The anaerobic induction of white-opaque switching was controlled by the transcription factor CZF1, which in heterozygous MTLa/alpha cells regulates filamentous growth under embedded, hypoxic conditions. Intriguingly, passage of white cells of strain WO-1 through the mouse intestine, a host niche in which the cells are likely to be exposed to anaerobic conditions, resulted in a strongly increased frequency of switching to the opaque phase. These results demonstrate that white-opaque switching is not only a spontaneous process but, in combination with genomic alterations, can also be induced by environmental signals, suggesting that switching and mating of C. albicans may occur with high efficiency in appropriate niches within its human host.

Efficacy of the Telemedical Lifestyle intervention Program TeLiPro in Advanced Stages of Type 2 Diabetes: A Randomized Controlled Trial.

OBJECTIVE: Lifestyle interventions are the foundation of treatment in newly diagnosed type 2 diabetes. However, their therapeutic potential in advanced disease stages is unknown. We evaluated the efficacy of the Telemedical Lifestyle intervention Program (TeLiPro) in improving metabolic control in advanced-stage type 2 diabetes. RESEARCH DESIGN AND METHODS: In this single-blind, active comparator, intervention study, patients with type 2 diabetes (with glycated hemoglobin [HbA1c] ≥7.5% [58.5 mmol/mol]), and BMI ≥27 kg/m2 and on ≥2 antidiabetes medications) were recruited in Germany and randomized 1:1 using an electronically generated random list and sealed envelopes into two parallel groups. The data analyst was blinded after assignment. The control group (n = 100) got weighing scales and step counters and remained in routine care. The TeLiPro group (n = 102) additionally received telemedical coaching including medical-mental motivation, a formula diet, and self-monitored blood glucose for 12 weeks. The primary end point was the estimated treatment difference in HbA1c reduction after 12 weeks. All available values per patient (n = 202) were analyzed. Analyses were also performed at 26 and 52 weeks of follow-up. RESULTS: HbA1c reduction was significantly higher in the TeLiPro group (mean ± SD -1.1 ± 1.2% vs. -0.2 ± 0.8%; P < 0.0001). The estimated treatment difference in the fully adjusted model was 0.8% (95% CI 1.1; 0.5) (P < 0.0001). Treatment superiority of TeLiPro was maintained during follow-up (week 26: 0.6% [95% CI 1.0; 0.3], P = 0.0001; week 52: 0.6% [0.9; 0.2], P < 0.001). The same applies for secondary outcomes: weight (TeLiPro -6.2 ± 4.6 kg vs. control -1.0 ± 3.4 kg), BMI (-2.1 ± 1.5 kg/m2 vs. -0.3 ± 1.1 kg/m2), systolic blood pressure (-5.7 ± 15.3 mmHg vs. -1.6 ± 13.8 mmHg), 10-year cardiovascular disease risk, antidiabetes medication, and quality of life and eating behavior (P < 0.01 for all). The effects were maintained long-term. No adverse events were reported. CONCLUSIONS: In advanced-stage type 2 diabetes, TeLiPro can improve glycemic control and may offer new options to avoid pharmacological intensification.

The SAT1 flipper, an optimized tool for gene disruption in Candida albicans.

The construction of Candida albicans mutants by targeted gene disruption usually depends on the use of nutritional markers for the selection of prototrophic transformants from auxotrophic host strains, but it is becoming increasingly evident that this strategy may cause difficulties in the interpretation of mutant phenotypes. Here, we describe a new method for inactivating both alleles of a target gene in C. albicans wild-type strains to obtain homozygous null mutants. The SAT1 flipping method relies on the use of a cassette that contains a dominant nourseothricin resistance marker (caSAT1) for the selection of integrative transformants and a C. albicans-adapted FLP gene that allows the subsequent excision of the cassette, which is flanked by FLP target sequences, from the genome. Two rounds of integration/excision generate homozygous mutants that differ from the wild-type parent strain only by the absence of the target gene, and reintegration of an intact gene copy for complementation of mutant phenotypes is performed in the same way. Transformants are obtained after only 1 day of growth on a selective medium, and integration into the target locus occurs with high specificity after adding homologous flanking sequences on both sides of the cassette. FLP-mediated excision of the SAT1 flipper cassette is achieved by simply growing the transformants for a few hours in medium without selective pressure, and nourseothricin-sensitive (NouS) derivatives can easily be identified by their slower growth on indicator plates containing a low concentration of nourseothricin. We demonstrate the use of the system by deleting the OPT1 gene, which encodes an oligopeptide transporter, in the C. albicans model strain SC5314. The null mutants became resistant to the toxic peptide KLLEth, and reintroduction of an intact OPT1 copy restored susceptibility. The SAT1 flipping method provides a highly efficient method for gene disruption in C. albicans wild-type strains, which eliminates currently encountered problems in the genetic analysis of this important human fungal pathogen.

A family of oligopeptide transporters is required for growth of Candida albicans on proteins.

The human fungal pathogen Candida albicans can use proteins as the sole source of nitrogen for growth. The secretion of aspartic proteinases, which have been shown to contribute to virulence of C. albicans, allows the fungus to digest host proteins to produce peptides that must be taken up into the cell by specific transporters. To understand in more detail how C. albicans utilizes proteins as a nitrogen source, we undertook a comprehensive analysis of oligopeptide transporters encoded in the C. albicans genome. We identified eight OPT genes encoding putative oligopeptide transporters, almost all of which are represented by polymorphic alleles in strain SC5314. Expression of these genes was differentially induced when C. albicans was grown in YCB-BSA medium, which contains bovine serum albumin as the sole nitrogen source. Whereas deletion of single OPT genes in strain SC5314 did not affect its ability to utilize proteins as a nitrogen source, opt123delta triple mutants had a severe growth defect in YCB-BSA which was rescued by reintroduction of a single copy of OPT1, OPT2 or OPT3. In addition, forced expression of OPT4 or OPT5 under control of the ADH1 promoter also restored growth of an opt123delta mutant, demonstrating that at least OPT1-OPT5 encode functional peptide transporters. The various oligopeptide transporters differ in their substrate preferences, as shown by the ability of strains expressing specific OPT genes to grow on peptides of defined length and sequence. We present evidence that in addition to the known role of oligopeptide transporters in the uptake of tetra- and pentapeptides these proteins can also transport longer peptides up to at least eight amino acids in length, ensuring an efficient utilization of the various peptides produced via endoproteolytic digestion of proteins by the secreted aspartic proteinases. As even transporters encoded by polymorphic alleles of a single gene exhibited differences in their efficiency to take up specific peptides, the oligopeptide transporters represent an example for how the evolution of gene families containing differentially expressed and functionally optimized members increases the nutritional versatility and, presumably, the adaptation of C. albicans to different host niches.