Physiology of the yeast Kluyveromyces marxianus during batch and chemostat cultures with glucose as the sole carbon source

Growth, substrate consumption, metabolite formation, biomass composition and respiratory parameters of Kluyveromyces marxianus ATCC 26548 were determined during aerobic batch and chemostat cultivations, using mineral medium with glucose as the sole carbon source, at 30 degrees C and pH 5.0. Carbon balances closed within 95-101% in all experiments. A maximum specific growth rate of 0.56 h(-1), a biomass yield on glucose of 0.51 g g(-1), and a maximum specific consumption of oxygen of 11.1 mmol g(-1) h(-1) were obtained during batch cultures. The concentration of excreted metabolites was very low at the culture conditions applied, representing 6% of the consumed carbon at most. Acetate and pyruvate were excreted to a larger extent than ethanol under the batch conditions, and the protein content accounted for 54.6% of the biomass dry weight. Steady states were obtained during chemostats at dilution rates of 0.1, 0.25 and 0.5 h(-1). At the two former dilution rates, cells grew at carbon limitation and the biomass yield on glucose was similar to that obtained under the batch conditions. Metabolite formation was rather low, accounting for a total of 0.005 C-mol C-mol(-1) substrate. At 0.5 h(-1), although the biomass yield on glucose was similar to the value obtained under the above-mentioned conditions, the cultivation was not under carbon limitation. Under this condition, 2-oxoglutarate, acetate, pyruvate and ethanol were the prevalent metabolites excreted. Total metabolite formation only accounted to 0.056 C-mol C-mol(-1) of substrate. A very high protein and a low carbohydrate content (71.9% and 9.6% of biomass dry weight, respectively) were measured in cells under this condition. It is concluded that K. marxianus aligns with the so-called aerobic-respiring or Crabtree-negative yeasts. Furthermore, it has one of the highest growth rates among yeasts, and a high capacity of converting sugar into biomass, even when carbon is not the limiting nutrient. These results provide useful data regarding the future application of K. marxianus in processes aimed at the production of biomass-linked compounds, with high yields and productivities.     

Proteomic,metabolic and immunological changes in Biomphalaria glabrata infected with Schistosoma mansoni

Mansonic schistosomiasis is a neglected disease transmitted by Biomphalaria spp. snails. Understanding what happens inside the intermediate host is important to develop more efficient ways of reducing schistosomiasis prevalence. Our purpose was to characterize metabolic and immunological changes in Biomphalaria glabrata 24 h after exposure to Schistosoma mansoni. For this purpose, proteins were extracted from snails’ whole tissue with Tris-Urea buffer and digested with tripsin. Mass spectrometry was performed and analyzed with MaxQuant and Perseus software. Also, the hemolymph of five snails 24 h post exposure was collected, and the numbers of hemocytes, levels of urea, uric acid, nitric oxide, calcium, glycogen and alanine and aspartate aminotransferases activities were assessed. Snails were also dissected for measurement of glycogen content in the cephalopodal region and gonoda-digestive gland complex. Globin domain proteins were found to be up-regulated; also the number of circulating hemocytes was significantly higher after 24 h of exposure to the parasite. NO levels were higher 24 h post exposure. Several proteins associated with energy metabolism were found to be up-regulated. Glycogen analysis showed a significant decrease in the gonad-digestive gland complex glycogen content. We found several proteins which seem to be associated with the host immune response, most of which were up-regulated, however some were down-regulated, which may represent an important clue in understanding B. glabrata – S. mansoni compatibility.     

Programmed T-cell death in experimental chagas disease

In mature T cells, programmed cell death is thought to serve a regulatory function by limiting both the duration and amplitude of immune responses. Programmed cell death might also be involved in immuno-pathogenesis of certain infectious diseases: recent evidence suggests that programmed T-cell death plays an important role in immune suppression during viral infections. In this article, George DosReis, Maria Evangelina Fonseca and Marcela Lopes review their findings on programmed T-cell death in experimental infection induced by the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. They also discuss the differential behavior of CD4(+) and CD8(+) T-cell subsets regarding programmed cell death, and same possible pathogenic aspects of host-parasite interaction, where abnormal or exaggerated programmed T-cell death could be involved.     

Vascular redox imbalance in rats submitted to chronic exercise

Exercise training has been used for treatment/prevention of many cardiovascular diseases, but the mechanisms need to be clarified. Thus, our aim was to compare oxidative stress parameters between rats submitted to a swimming training and sedentary rats (control). Twelve male rats were divided into two groups: control and exercise training. The exercise training had daily 1 h swimming sessions for 8 weeks and a load (5% of its body mass) was placed in rat's tail. Thereafter the animals were killed, aorta and heart were surgically removed and blood was collected. Body mass gain, thiobarbituric acid reactive species (TBARS), carbonyl content, total reactive antioxidant potential (TRAP), total antioxidant reactivity (TAR), superoxide dismutase (SOD) activity and catalase (CAT) activity were evaluted. The trained rats showed a lower body mass gain and no modifications on heart. An increased SOD activity was observed on aorta after the training, but no changes were seen for CAT activity, which led to an increased SOD/CAT ratio. The arterial TBARS was also increased for trained rats. The decrease in TRAP in exercise training was the single modification on plasma. Our findings suggest that the increased SOD activity could play a role in vascular adaptations to exercise training. Copyright © 2010 John Wiley & Sons, Ltd.     

Beta-glucosidase activity from the thermophilic fungus Scytalidium thermophilum is stimulated by glucose and xylose

An inducible mycelial beta-glucosidase from Scytalidum thermophilum was characterized. The enzyme exhibited a pI of 6.5, a carbohydrate content of 15%, and an apparent molecular mass of about 40 kDa. Optima of temperature and pH were 60 degrees C and 6.5, respectively. The enzyme was stable up to 1 h at 50 degrees C and exhibited a half-life of 20 min at 55 degrees C. The enzyme hydrolyzed p-nitrophenyl-beta-d-glucopyranoside, p-nitrophenyl-beta-d-xylopyranoside, o-nitrophenyl-beta-d-galactopyranoside, p-nitrophenyl-alpha-arabinopyranoside, cellobiose, laminaribiose and lactose. Kinetic studies indicated that the same enzyme hydrolyzed these substrates. Beta-Glucosidase was activated by glucose or xylose at concentration varying from 50 to 200 mM. The apparent affinity constants (K0.5) for glucose and xylose were 36.69 and 43.24 mM, respectively. The stimulatory effect of glucose and xylose on the S. thermophilum beta-glucosidase is a novel characteristic which distinguish this enzyme from all other beta-glucosidases so far described.     

Reactive phenotypes after acute and chronic NK-cell activation

Several phenotypic changes have been shown to occur after NK-cell stimulation, involving molecules that have been proved to regulate NK-cell migration into tissues and NK-cell activation and proliferation as well as target cell recognition and killing. Here, we review the reactive phenotypes observed in vivo after acute and chronic NK-cell activation.     

Reinstatement of Rhodotorula colostri (Castelli) Lodder and Rhodotorula crocea Shifrine & Phaff, former synonyms of Rhodotorula aurantiaca (Saito) Lodder

Rhodotorula aurantiaca (Saito) Lodder is an anamorphic basidiomycetous yeast species that belongs to the so-called "Erythrobasidium lineage" of the Urediniomycetes, according to molecular phylogenetic studies based on nucleotide sequence analyses of different ribosomal DNA regions. In the most recent editions of the yeast taxonomy treatises the species Rhodotorula colostri (Castelli) Lodder and Rhodotorula crocea Shifrine & Phaff were listed as synonyms of R. aurantiaca. Taxonomic heterogeneity within R. aurantiaca was demonstrated in a study based on whole-cell protein profiles and is also hinted at by the observed differences in physiological and biochemical characteristics among the different strains under that species name. We determined partial nucleotide sequences of the 26S rRNA gene (D1/D2 domains) of strains maintained in the CBS culture collection under R. aurantiaca, including the type strains of its synonyms. The results showed that R. colostri and R. crocea are clearly distinct from R. aurantiaca and from any other currently recognised basidiomycetous yeast species. Furthermore, phylogenetic analysis of the sequence data placed the former two species in separate lineages of the Microbotryomycetidae: R. colostri in the "ruineniae clade" (Sporidiobolus lineage or Sporidiobolales) and R. crocea loosely linked to Rhodotorula javanica (Microbotryum lineage).