Levans production by Gluconacetobacter diazotrophicus

Background: Growth of Gluconacetobacter diazotrophicus with glucose as carbon an energy source has been extensively studied. However, there are no reports in the literature describing growth of G. diazotrophicus in cultures containing sucrose as carbon source. The first step in sucrose pathway and production of levans was investigated. Biomass, levans, gluconic acid and keto gluconic acids production and levansucrase activity were determined in cultures with different sucrose concentration and nitrogen sources. Results: The biomass production was maximal in cultures containing 100 g x L-1 sucrose and inorganic nitrogen. Gluconic acid production was observed under all conditions tested, at levels up to 9 g x L-1 in cultures with sucrose excess and biological N2-fixation (BNF). Keto gluconic acids were detectable only in cultures with sucrose excess and supplemented with organic nitrogen sources. Levans production, although observed in all cultures, was maximal in batch culture with 100 g x L-1 of sucrose and BNF, concomitant with a significant expression of extracellular levansucrase. Conclusions: Ours results not only describe some unknown aspects of G. diazotrophicus physiology, but open up the possibility of developing a technology of levans production by this organism using culture media with sucrose (or some cheaper substitute, like molasses) and without the addition of any N-source because of its ability of fixing atmospheric N2.

Efeito da suplementação de frutanos e cálcio no metabolismo ósseo de meninas com baixa ingestão de cálcio / Effect of oligofructose-enriched inulin on bone metabolism of girls with low calcium intakes

A aquisição de massa óssea ocorre até a terceira década de vida e a mineralização óssea constitui-se na melhor estratégia para prevenção de osteoporose na idade adulta. A única fonte de cálcio é alimentar e sua ingestão pode ser melhorada com um maior consumo de alimentos fontes, fortificação de alimentos e uso de prebióticos. No presente ensaio clínico foi estudado o efeito do consumo de bebida láctea suplementada com frutanos (inulina e oligofrutose) e cálcio sobre o metabolismo ósseo de meninas de 9 a 12 anos com baixa ingestão de cálcio. Foi elaborada uma formulação de bebida láctea padrão, adicionada de 200mg de cálcio, e outro teste, adicionada de 200mg de cálcio e 8,8g de frutano (BENEO TM Synergy 1). Ambas foram avaliadas quanto aos aspectos químicos, microbiológicos e sensoriais. Para o estudo foram selecionadas 60 participantes entre as alunas matriculadas nas escolas públicas de Umuarama, PR. As voluntárias, pré-puberes com consumo de cálcio < 75% da ingestão adequada (aproximadamente 500mg/dia) foram submetidas à triagem por meio de avaliação antropométrica, de estilo de vida, de consumo alimentar e estádio puberal de Tanner, e foram divididas de forma aleatória em três grupos. Os grupos 1 e 2 participaram de experimento duplo cego tipo crossover e receberam suplementação de uma porção diária de bebida láctea com cálcio ou bebida láctea com cálcio e frutano, por onze semanas cada e com intervalo de 3 semanas (washout). O grupo 3 não recebeu nenhuma suplementação e foi considerado como grupo controle. As participantes foram submetidas a oito avaliações bioquímicas que incluíram análises de cálcio, paratormônio intacto (PTHi), fosfatase alcalina fração específica óssea (FAO) e osteocalcina (OC)...

Sugar signalling and gene expression in relation to carbohydrate metabolism under abiotic stresses in plants.

Sucrose is required for plant growth and development. The sugar status of plant cells is sensed by sensor proteins. The signal generated by signal transduction cascades, which could involve mitogen-activated protein kinases, protein phosphatases, Ca 2+ and calmodulins, results in appropriate gene expression. A variety of genes are either induced or repressed depending upon the status of soluble sugars. Abiotic stresses to plants result in major alterations in sugar status and hence affect the expression of various genes by down- and up-regulating their expression. Hexokinase-dependent and hexokinase-independent pathways are involved in sugar sensing. Sucrose also acts as a signal molecule as it affects the activity of a proton-sucrose symporter. The sucrose trans-porter acts as a sucrose sensor and is involved in phloem loading. Fructokinase may represent an additional sensor that bypasses hexokinase phosphorylation especially when sucrose synthase is dominant. Mutants isolated on the basis of response of germination and seedling growth to sugars and reporter-based screening protocols are being used to study the response of altered sugar status on gene expression. Common cis-acting elements in sugar signalling pathways have been identified. Transgenic plants with elevated levels of sugars/sugar alcohols like fructans, raffinose series oligosaccharides, trehalose and mannitol are tolerant to different stresses but have usually impaired growth. Efforts need to be made to have transgenic plants in which abiotic stress responsive genes are expressed only at the time of adverse environmental conditions instead of being constitutively synthesized.