Recent advances in industrial fermentation in Japan

Understanding D-xylonic acid accumulation: a cornerstone for better metabolic engineering approaches

The xylose oxidative pathway (XOP) has been engineered in microorganisms for the production of a wide range of industrially relevant compounds. However, the performance of metabolically engineered XOP-utilizing microorganisms is typically hindered by D-xylonic acid accumulation. It acidifies the media and perturbs cell growth due to toxicity, thus curtailing enzymatic activity and target product formation. Fortunately, from the growing portfolio of genetic tools, several strategies that can be adapted for the generation of efficient microbial cell factories have been implemented to address D-xylonic acid accumulation. This review centers its discussion on the causes of D-xylonic acid accumulation and how to address it through different engineering and synthetic biology techniques with emphasis given on bacterial strains. In the first part of this review, the ability of certain microorganisms to produce and tolerate D-xylonic acid is also tackled as an important aspect in developing efficient microbial cell factories. Overall, this review could shed some insights and clarity to those working on XOP in bacteria and its engineering for the development of industrially applicable product-specialist strains. KEY POINTS: D-Xylonic acid accumulation is attributed to the overexpression of xylose dehydrogenase concomitant with basal or inefficient expression of enzymes involved in D-xylonic acid assimilation. Redox imbalance and insufficient cofactors contribute to D-xylonic acid accumulation. Overcoming D-xylonic acid accumulation can increase product formation among engineered strains. Engineering strategies involving enzyme engineering, evolutionary engineering, coutilization of different sugar substrates, and synergy of different pathways could potentially address D-xylonic acid accumulation.

Lactobacillus brevis strains from fermented aloe vera survive gastroduodenal environment and suppress common food borne enteropathogens

Five novel Lactobacillus brevis strains were isolated from naturally fermented Aloe vera leaf flesh. Each strain was identified by Random Amplified Polymorphic DNA (RAPD) analysis and 16S rRNA sequence comparison. These strains were highly tolerant to acid, surviving in pH2.5 for up to 4 hours, and resistant to 5% bile salts at 37°C for 18 hours. Due to its tolerance to acid and bile salts, one strain passed through the gastric barrier and colonised the intestine after oral administration. All five strains inhibited the growth of many harmful enteropathogens without restraining most of normal commensals in the gut and hence named POAL (Probiotics Originating from Aloe Leaf) strains. Additionally, each strain exhibited discriminative resistance to a wide range of antibiotics. The L. brevis POAL strains, moreover, expressed high levels of the glutamate decarboxylase (GAD) gene which produces a beneficial neurotransmitter, γ-aminobutyric acid (GABA). These characteristics in all suggest that the novel L. brevis strains should be considered as potential food additives and resources for pharmaceutical research.

Sugarcane-pressmud as a novel substrate for production of citric acid by solid-state fermentation

Sugarcane-pressmud, a by-product of cane-sugar manufacture, was used as a substrate for production of citric acid by Aspergillus niger CFTRI 30, in a solid-state fermentation system. Of the 170 g of sugar supplied, 131 g were consumed, with a 79% yield of citric acid over 120 h. Potassium ferrocyanide improved the conversion to about 88% and lowered the fermentation time by 24 h. Enrichment with sugar and NH4NO3 was essential to improve productivity. About 174 g citric acid/kg dry sugarcane-pressmud were produced after 120 h in ferrocyanid-treated medium which initially contained 12.5% (w/w) effective sugar and 0.1% (w/w) NH4NO3. About 3% (w/w) of the original sugar present in the sugarcane-pressmud was non-utilizable. This is the first report on the potential of sugarcane-pressmud for citric acid production.

Comparison of pretreatment strategies of sugarcane baggase: experimental design for citric acid production

Solid state fermentation was carried out to compare efficiency of acid, alkaline and urea pretreatment of sugarcane bagasse for production of citric acid using Aspergillus niger ATCC 9142. Plackett-Burman statistical design was used to evaluate significance of variables. Pretreatment of bagasse by urea was known as the most influential treatment to increase citric acid production (137.6g/kg of dry sugarcane bagasse and citric acid yield of 96% based on sugar consumed). Finally, up scaling was achieved to a 20L solid state fermentor in which humidity was constant in gas phase and urea-treated sugarcane bagasse. The produced acid concentration and yield in fermentor was 82.38g/kg of dry substrate and 26.45g/kgday, respectively.

Production of Aspergillus niger pectolytic enzymes by solid state bioprocessing of apple pomace

The aim of this work was to develop a low cost process for apple pomace utilisation. Accordingly this production of pectynolitic enzymes based on solid state bioprocessing of this actual waste, was developed. Production of pectolytic enzymes of Aspergillus niger, pectinesterase and polygalacturonase as well as the activity of pectolytic enzymatic complex by solid state bioprocessing were studied. The results of preliminary substrate optimization, on open trays in laboratory scale experiments, were transferred to 15 1 horizontal solid state stirred tank reactor (HSS STR). In situ sterilization of solid substrate with periodical mixing was used. Secondary raw material, apple pomace the waste from food and agriculture industry combined with soya flour, wheat bran and simple mineral salts was utilised. Various substrate moistures were studied. Process parameters such as inoculation, influence of mixing, aeration, temperature and moisture content on pectolytic enzymes production were studied. Maximal amounts of 15 g kg-1 of solid medium of polygalacturonase, 200 mg kg-1 pectinesterase at activity up to 900 AJDA U ml-1 of enzyme mixture was obtained on average.

The production of organic acids

The production of organic acids covers two aspects: first, the metabolic pathways involved in the biosynthesis, and, second, the industrial process strategy adopted. The review seeks to show the underlying biochemical similarities in the biosynthesis of organic acids and the resulting similarities in the commercial processes. Two groups of acids are defined, those with a "long" biosynthetic path from glucose, involving much of the glycolytic pathway and the tricarboxylic acid cycle, and those acids with a "short pathway", essentially a biotransformation of glucose. The regulation of the pathways and the future developments in metabolic control theory and genetic manipulations relating to them are considered. The organisms used industrially are also limited, Aspergillus sp. and Candida yeasts; again the underlying metabolic similarities lead to similar strategies for all the acids discussed.

Solid state fermentation for cephalosporin production by Streptomyces clavuligerus and Cephalosporium acremonium

Solid state fermentation systems were developed for the production of cephalosporins with Streptomyces clavuligerus and Cephalosporium acremonium. S. clavuligerus NRRL 3585 was grown on moistened barley under optimum solid state fermentation conditions for 7 days; approximately 300 micrograms cephalosporins per g substrate were extracted from the kernels. C. acremonium C-10 produced approximately 950 micrograms cephalosporin C per g substrate after 10 days of solid state fermentation.