Production of acidic xylo-oligosaccharides by a family 10 endoxylanase from Thermoascus aurantiacus and use as plant growth regulators

Neutral and acidic oligosaccharides were obtained from birchwood xylan by treatment with an endoxylanase, family 10 class, from Thermoascus aurantiacus. The main acidic xylooligosaccharide (aldotetrauronic acid) was separated from the hydrolysate by anion-exchange and size-exclusion chromatography and the primary structure was determined by ¹³C NMR spectroscopy. The aldotetrauronic yield was 15% (w/w) of the total solubilised sugars. The addition of purified aldoterauronic acid at 1.6–16 mg l^–1 growth medium, induced callus and somatic embryogenesis in culture explants of common mallow (Malva silvestris L.) and cotton (Gosssypium hirsutum).     

Co-evolution with lytic phage selects for the mucoid phenotype of Pseudomonas fluorescens SBW25

The effects of co-evolution with lytic phage on bacterial virulence-related traits are largely unknown. In this study we investigate the incidence of the mucoid phenotype of the bacterium Pseudomonas fluorescens SBW25 in response to co-evolution with the lytic phage phi2 (φ2). The mucoid phenotype of Pseudomonas spp. is due to overproduction of alginate and is a considerable virulence factor contributing to the intractability of infections most notably in cystic fibrosis (CF) lung, but also in pathogenic infections of plants. Our data show that this phenotype can evolve as an adaptive response to phage predation and is favoured under specific abiotic conditions, in particular a homogenous spatial structure and a high rate of nutrient replacement. The mucoid phenotype remains partially sensitive to phage infection, which facilitates ‘apparent competition'' with phage-sensitive competitors, partially offsetting the costs of alginate production. Although P. fluorescens SBW25 is not a pathogen, several key characteristics typical of Pseudomonas aeruginosa clinical isolates from CF lung were noted, including loss of motility on mucoid conversion and a high rate of spontaneous reversion to the wild-type phenotype. Although the genetic mechanisms of this phenotype remain unknown, they do not include mutations at many of the commonly reported loci implicated in mucoid conversion, including mucA and algU. These data not only further our understanding of the potential role phage have in the ecology and evolution of bacteria virulence in both natural and clinical settings, but also highlight the need to consider both biotic and abiotic variables if bacteriophages are to be used therapeutically.     

Synthesis of compounds having antimicrobial activity from alginate

Compounds having antimicrobial activity were synthesized from sodium alginate, the main constituent of brown algae. Sodium alginate was oxidized with sodium periodate to get alginate dialdehyde (ADA). FTIR spectrum of the ADA gave very small peak characteristic for aldehyde groups at 1720 cm⁻¹, indicating that the aldehyde group is masked somehow. It may be hydrated, involving at hemiacetal formation or hemialdol, similar to cellulose dialdehyde. Two methods were used for the condensation of ADA with o-phenylenediamine analogs to obtain the final products. The first method was stirring at room temperature and the second method was heating in microwave. The microwave method gave higher yield and shorter reaction time than the other method. The condensation reaction is considered as a shiff-base formation and the proposed mechanism was suggested. The condensation products were characterized by FTIR and UV spectra. The antimicrobial potency for five of these products in addition to the used alginate and to the precursor amines was evaluated against four pathogenic fungi and six pathogenic bacteria species.     

Host-derived glycans serve as selected nutrients for the gut microbe: human milk oligosaccharides and bifidobacteria

Lactation is a common feeding strategy of eutherian mammals, but its functions go beyond feeding the neonates. Ever since Tissier isolated bifidobacteria from the stool of breast-fed infants, human milk has been postulated to contain compounds that selectively stimulate the growth of bifidobacteria in intestines. However, until relatively recently, there have been no reports to link human milk compound(s) with bifidobacterial physiology. Over the past decade, successive studies have demonstrated that infant-gut-associated bifidobacteria are equipped with genetic and enzymatic toolsets dedicated to assimilation of host-derived glycans, especially human milk oligosaccharides (HMOs). Among gut microbes, the presence of enzymes required for degrading HMOs with type-1 chains is essentially limited to infant-gut-associated bifidobacteria, suggesting HMOs serve as selected nutrients for the bacteria. In this study, I shortly discuss the research on bifidobacteria and HMOs from a historical perspective and summarize the roles of bifidobacterial enzymes in the assimilation of HMOs with type-1 chains. Based on this overview, I suggest the co-evolution between bifidobacteria and human beings mediated by HMOs.     

Alginate gel biochip for real-time monitoring of intracellular processes in bacterial and yeast cells

A method was developed for producing cell biochips on the basis of calcium alginate. Cell immobilization in microvolumes of nontoxic alginate gel under mild conditions extended the range of testable micro-organisms. The possibility of studying the intracellular processes with alginate gel biochips was demonstrated in model experiments with Escherichia coli, Bordetella bronchiseptica, and Saccharomyces cerevisiae. Cell biochips proved to be suitable for simultaneous monitoring of nucleic acid and protein syntheses with two fluorescent dyes. The effect of chloramphenicol on nucleic acid synthesis was studied with five bacterial strains. Inducible synthesis of the green fluorescence protein (EGFP) in E. coli cells was monitored with the use of biochips. The level of EGFP synthesis correlated with the inductor concentration in the medium.Translated from Molekulyarnaya Biologiya, Vol. 39, No. 1, 2005, pp. 96–102.Original Russian Text Copyright © 2005 by Fesenko, Nasedkina, Chudinov, Prokopenko, Yurasov, Zasedatelev.     

Influence of encapsulation on the survival of probiotics in food matrix under simulated stress conditions

The main objective of the present study was to evaluate the influence of encapsulation by extrusion technique using two hydrogels, namely; sodium alginate (Na-ALG) and whey protein isolate (WPI) on Bifidobacterium bifidium viability and stability of yoghurt under simulated gastrointestinal conditions. Probiotic bacteria (free or encapsulated) were added to yogurt for four weeks to test their viability and stability. Physicochemical and sensory analysis of yoghurt were conducted. Viability of B. bifidium in the simulated gastrointestinal conditions pH 2 and pH 7.5 was determined. Also, the efficiency of encapsulated final yield of the microcapsules was determined. With storage time, the pH of yoghurt containing encapsulated bacteria increased more than that of yoghurt containing free probiotic bacteria, resulting in a decrease in acidity. When compared to yoghurt containing encapsulated bacteria, the lactose level of yoghurt containing free probiotic bacteria decreased over time. The viscosity of yoghurt containing encapsulated WPI remained stable over the storage period, with syneresis remaining stable. The sensory properties of yoghurt containing free probiotics deteriorated over time. Cell viability was significantly reduced in yoghurt-containing free probiotics compared to other treated yoghurts. Cell viability in free probiotics yoghurt was lower than in encapsulated ones when exposed to simulated gastric and intestinal juice. In conclusion, WPI- encapsulated probiotics showed better stability over 28 days of storage in both yoghurt and gastrointestinal conditions, followed by sodium alginate.     

Enzymatically Depolymerized Alginate Oligomers That Cause Cytotoxic Cytokine Production in Human Mononuclear Cells

Enzymatically depolymerized guluronate and mannuronate oligomers were prepared from polyuronates with an alginate lyase from a Pseudoalteromonas sp., and their effects on mononuclear cells from human peripheral blood were examined. Conditioned medium prepared by the incubation of cells with an untreated polyuronate had little effect on growth of human leukemic U937 cells, but a medium prepared with depolymerized uronate oligomers inhibited their growth. Inhibition was greater in a medium prepared with guluronate oligomer than one prepared with mannuronate oligomer. The cytotoxic activity of the medium was heat-labile and nondialyzable. Apoptotic nuclear morphological changes and increased caspase-3-like activity were found in U937 cells treated with a medium prepared with depolymerized uronates. The medium prepared with purified tetra-guluronate and tetra-mannuronate also was cytotoxic; these effects were inhibited by antibodies to tumor necrosis factor-α. Our results suggested that enzymatically depolymerized guluronate and mannuronate oligomers induced the production of cytotoxic cytokines in human mononuclear cells, although the uronate polymers before depolymerization had no such activity.