Succinic acid production from pulp and paper industry waste - A transcriptomic approach

The utilization of renewable resources for the production of bio-based products is essential in order to develop sustainable bioprocesses and biorefineries. Xylose-rich hydrolysates produced from hemicelluloses contained in lignocellulosic resources could be used for the production of succinic acid, one of the most important platform chemicals in the bio-economy era. Exploitation of spent sulphite liquor (SSL), a xylose rich by-product from pulp and paper industry has been previously investigated for succinic acid production by Actinobacillus succinogenes, one of the most efficient natural succinic acid producers. In this study, the metabolic potential of this strain was evaluated through the RNA expression of the metabolic pathways involved in succinic acid production utilizing glucose, xylose or SSL as carbon sources. A transcriptomic approach of the key enzymes of glucose and xylose catabolism, carboxylic acid production as well as oxidative phosphorylation led to an improved understanding on the energy consuming metabolic pathways. The transcriptomic analysis was carried out in batch cultures. A cDNA library was constructed at different phases of the fermentation where major metabolic changes in extracellular metabolites or biomass production were observed. Real time PCR was used to determine the expression levels of the genes of interest throughout the fermentation. The bottlenecks of the fermentative production of succinic acid by A. succinogenes were addressed with particular focus on the effect of glucose and xylose catabolism on pathways that involve ATP consumption and NADH oxidation. All subunits of ATP synthase were highly expressed in all substrates. In particular ATP synthase F0 (ATP SYN F0) was higher expressed when glucose was the only carbon source. Phosphoenol-pyruvate carboxykinase (PEPCK) expression was delayed when xylose was present in the medium. Despite the fact that extracellular lactic acid was not detected, low expression levels of lactic acid dehydrogenase (

A solid state fungal fermentation-based strategy for the hydrolysis of wheat straw

This paper reports a solid-state fungal fermentation-based pre-treatment strategy to convert wheat straw into a fermentable hydrolysate. Aspergillus niger was firstly cultured on wheat straw for production of cellulolytic enzymes and then the wheat straw was hydrolyzed by the enzyme solution into a fermentable hydrolysate. The optimum moisture content and three wheat straw modification methods were explored to improve cellulase production. At a moisture content of 89.5%, 10.2 ± 0.13 U/g cellulase activity was obtained using dilute acid modified wheat straw. The addition of yeast extract (0.5% w/v) and minerals significantly improved the cellulase production, to 24.0 ± 1.76 U/g. The hydrolysis of the fermented wheat straw using the fungal culture filtrate or commercial cellulase Ctec2 was performed, resulting in 4.34 and 3.13 g/L glucose respectively. It indicated that the fungal filtrate harvested from the fungal fermentation of wheat straw contained a more suitable enzyme mixture than the commercial cellulase

Lipid production by yeasts growing on commercial xylose in submerged cultures with process water being partially replaced by olive mill wastewaters

Six yeast strains belonging to Rhodosporidium toruloides, Lipomyces starkeyi, Rhodotorula glutinis and Cryptococcus curvatus were shake-flask cultured on xylose (initial sugar – S0 =70±10 g/L) under nitrogen-limited conditions. C. curvatus ATCC 20509 and L. starkeyi DSM 70296 were further cultured in media where process waters were partially replaced by the phenol-containing olive-mill wastewaters (OMWs). In flasks with S0≈100 g/L and OMWs added yielding to initial phenolic compounds concentration (PCC0) between 0.0 g/L (blank experiment) and 2.0 g/L, C. curvatus presented maximum total dry cell weight - TDCWmax ≈27 g/L, in all cases. The more the PCC0 increased, the fewer lipids were produced. In OMW-enriched media with PCC0≈1.2 g/L, TDCW=20.9 g/L containing ≈40% w/w of lipids was recorded. In L. starkeyi cultures, when PCC0≈2.0 g/L, TDCW≈25 g/L was synthesized, whereas lipids in TDCW =24-28% w/w, similar to the experiments without OMWs, were recorded. Non-negligible dephenolization and species-dependant decolorization of the wastewater occurred. A batch-bioreactor trial by C. curvatus only with xylose (S0≈110 g/L) was performed, and TDCW=35.1 g/L (lipids in TDCW=41.3% w/w) was produced. Yeast total lipids were composed of oleic and palmitic and to lesser extent linoleic and stearic acids. C. curvatus lipids were mainly composed of non-polar fractions (i.e. triacylglycerols)

Resposta de um cultivar de pêssego com caroço aderente à irrigação por défice regulado

Regulated deficit irrigation (RDI) involves inducing water stress during specific fruit growth phases by irrigating at less than full evapotranspiration. The objectives of this research were to study the effects of RDI perfomed at stage II of fruit growth and postharvest, on productivity of clingstone peaches, fruit quality as well as photosynthetic rate and midday leaf water potential. The research was conducted in a commercial clingstone peach (Prunus persica L. Batch cv. A-37) orchard in Greece. Trees were irrigated by means of microsprinklers and their frequency was determined using local meteorological station data and the FAO 56 Pennman-Monteith method. Photosynthetic rate was measured by a portable infrared gas analyzer. Midday leaf water potential was measured by the pressure chamber technique. During the years 2005 and 2006, the treatment RDII with irrigation applied at growth stage II of the peach tree did not affect productivity, fresh and dry mass of fruits. RDII reduced preharvest fruit drop in comparison to the control. RDII as well as the combined treatment RDII plus RDIP with irrigation applied at postharvest, at both years reduced shoot length of the vigorous shoots inside the canopy. RDII in comparison to the control increased the soluble solids content of the fruits and the ratio soluble solids/acidity. However it did not affect fruit acidity and fruit firmness. RDII as well as RDII plus RDIP in 2006 increased 'double' fruits and fruits with open cavity in comparison to the control and RDIP. Water savings were considerable and associated with the climatic conditions of each year.A irrigação por défice regulado (RDI) envolve a indução de défice de água durante fases específicas do crescimento das frutas, irrigando a taxas menores que a evapotranspiração. Os objetivos desse estudo foram verificar os efeitos da RDI no estágio II do crescimento das frutas e no periodo pós-colheita, avaliando a produtividade de pêssegos, a qualidade dos frutos, bem como a taxa fotossintética e o potencial da água na folha. A pesquisa foi desenvolvida em um pomar comercial de pêssegos com caroço aderente (Prunus persica L. Batch cv. A-37) da Grécia. As árvores foram irrigadas por meio de microaspersores e sua frequência foi determinada por meio de dados meteorológicos obtidos em estação automática e o método FAO 56 Pennman-Monteith para determinação de evepotranspiração. A taxa de fotossíntese foi medida por analisador de gás na faixa do infravermelho. O potencial da água na folha foi medido ao meio-dia usando a técnica da câmara de pressão. Durante 2005 e 2006 o tratamento RDII com irrigação aplicada no estágio II não apresentou efeito sobre a produção, pesos seco e fresco dos frutos. RDII reduziu a queda de frutos antes da colheita, em relação ao controle. RDII, como também o tratamento combinado de RDII mais RDIP com irrigação aplicada em pós-colheita, reduziu o comprimento de ramos vigorosos dentro do dossel nos dois anos de estudo. Em comparação com o controle, RDII aumentou o conteúdo de sólidos solúveis dos frutos e a relação sólidos solúveis/acidez, mas não afetou a acidez dos frutos e a firmeza da polpa. Em 2006 RDII e RDII mais RDIP aumentaram os `frutos dobrados' e frutos com cavidade aberta, em comparação com o controle. A economia de água foi considerável e associada às condições climáticas de cada ano