A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants.

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Effect of sialic acid loss on dendritic cell maturation.

Sialic acids are key structural determinants and contribute to the functionality of a number of immune cell receptors. Previously, we demonstrated that differentiation of human dendritic cells (DCs) is accompanied by an increased expression of sialylated cell surface structures, putatively through the activity of the ST3Gal.I and ST6Gal.I sialyltransferases. Furthermore, DC endocytosis was reduced upon removal of the cell surface sialic acid residues by neuraminidase. In the present work, we evaluate the contribution of the sialic acid modifications in DC maturation. We demonstrate that neuraminidase-treated human DCs have increased expression of major histocompatibility complex (MHC) and costimulatory molecules, increased gene expression of specific cytokines and induce a higher proliferative response of T lymphocytes. Together, the data suggest that clearance of cell surface sialic acids contributes to the development of a T helper type 1 proinflammatory response. This postulate is supported by mouse models, where elevated MHC class II and increased maturation of specific DC subsets were observed in DCs harvested from ST3Gal.I(-/-) and ST6Gal.I(-/-) mice. Moreover, important qualitative differences, particularly in the extent of reduced endocytosis and in the peripheral distribution of DC subsets, existed between the ST3Gal.I(-/-) and ST6Gal.I(-/-) strains. Together, the data strongly suggest not only a role of cell surface sialic acid modifications in maturation and functionality of DCs, but also that the sialic acid linkages created by different sialyltransferases are functionally distinct. Consequently, with particular relevance to DC-based therapies, cell surface sialylation, mediated by individual sialyltransferases, can influence the immunogenicity of DCs upon antigen loading.

Influence of the carbon source on Gordonia alkanivorans strain 1B resistance to 2-hydroxybiphenyl toxicity.

The viability of bacteria plays a critical role in the enhancement of fossil fuels biodesulfurization efficiency since cells are exposed to toxic compounds such as 2-hydroxybiphenyl (2-HBP), the end product of dibenzothiophene (DBT) biodesulfurization. The goal of this work was to study the influence of the carbon source on the resistance of Gordonia alkanivorans strain 1B to 2-HBP. The physiological response of this bacterium, pre-grown in glucose or fructose, to 2-HBP was evaluated using two approaches: a growth inhibition toxicity test and flow cytometry. The results obtained from the growth inhibition bioassays showed that the carbon source has an influence on the sensitivity of strain 1B growing cells to 2-HBP. The highest IC50 value was obtained for the assay using fructose as carbon source in both inoculum growth and test medium (IC50-48 h = 0.464 mM). Relatively to the evaluation of 2-HBP effect on the physiological state of resting cells by flow cytometry, the results showed that concentrations of 2-HBP >1 mM generated significant loss of cell viability. The higher the 2-HBP concentration, the higher the toxicity effect on cells and the faster the loss of cell viability. In overall, the flow cytometry results highlighted that strain 1B resting cells grown in glucose-SO4 or glucose-DBT are physiologically less resistant to 2-HBP than resting cells grown in fructose-SO4 or fructose-DBT, respectively.

Screening of novel yeast inulinases and further application to bioprocesses.

Inulin is a carbohydrate composed of linear chains of ß-2,1-linked D-fructofuranose molecules terminated by a glucose residue through a sucrose-type linkage at the reducing end. Jerusalem artichoke (JA) is one of the most interesting materials among unconventional and renewable raw materials, with levels of inulin reaching 50-80% of dry matter. Inulin or inulin-rich materials can be actively hydrolyzed by microbial inulinases to produce glucose and fructose syrups that can be used in bioprocesses. In this study, several microbial strains were isolated and their ability to inulinase biosynthesis was evaluated. The novel yeast strain Talf1, identified as Zygosaccharomyces bailii, was the best inulinase producer, attaining 8.67 U/ml of inulinase activity when JA juice was used as the inducer substrate. Z. bailii strain Talf1 and/or its enzymatic crude extract were further applied for bioethanol production and biodesulfurization (BDS) processes, using inulin and JA juice as carbon source. In a consolidated bioprocessing for ethanol production from 200 g/l inulin, Z. bailii strain Talf1 was able to produce 67 g/l of ethanol. This ethanol yield was improved in a simultaneous saccharification and fermentation (SSF) process, with the ethanologenic yeast Saccharomyces cerevisiae CCMI 885 and the Talf1 inulinases, achieving a production of 78 g/l ethanol. However, the highest ethanol yield (∼48%) was obtained in a SSF process from JA juice (∼130 g/l fermentable sugars), where the S. cerevisiae produced 63 g/l ethanol. Relatively to the dibenzothiophene BDS tests, the Gordonia alkanivorans strain 1B achieved a desulfurization rate of 4.8 µM/h within a SSF process using Talf1 inulinases and JA juice, highlighting the potential of JA as a less expensive alternative carbon source. These results showed the high potential of Z. bailii strain Talf1 inulinases as a versatile tool for bioprocesses using inulin-rich materials.