Carlos F. Mignone

Butanol production from apple pomace

SummaryThe use of apple pomace for butanol production was studied by employing strains ofClostridium acetobutylicum andbutylicum. Yields of butanol between 1.9 and 2.2 % of fresh apple pomace are reported.

Aspergillus kawachii produces an acidic pectin releasing enzyme activity

A pectin-releasing (protopectinase, PPase) activity was found in a culture filtrate of Aspergillus kawachii IFO 4308. PPase activity was highest in the pH range of 2.0-2.5 and it was highly stable at 50 degrees C (85% of residual activity was found after a 10-h incubation in citrate-phosphate buffer, pH 3.0). Among other different enzyme activities, which are usually involved in plant cell-wall degradation, only polygalacturonase activity was detected. This result suggests that the PPase activity could correspond to a particular kind of polygalacturonase. Pectin extraction from lemon peels carried out at 50 degrees C for 2 h (pH 3.5) gave yields of ethanol-precipitated pectin equivalent to 17.4% of the initial total solids contained in the peels. Thus, this enzyme activity would allow carrying out a pectin extraction process at lower reaction pHs and higher temperatures in comparison with similar reports using other PPases. These properties seem to be very interesting from the practical point of view.

Bacillus thuringiensis growth and toxicity : basic and applied considerations

Despite the known importance of the composition of culture media and culture conditions onBacillus thuringiensis growth and toxicity, very few reviews are concerned with this subject. This article reviews some aspects of the microbiology ofBacillus thuringinesis, and how toxicity is affected by the composition of growth media and bioreactor operation.

δ-endotoxin activity and spore production in batch and fed-batch cultures of Bacillus thuringiensis

SummaryThe toxicity and the spore count of batch and fed batch cultures of Bacillus thuringiensis var. israelensis were studied. Spore counts reached in both batch and fed batch cultures were as high as those reported in the literature, but the levels of toxicity found in the latter were about one order of magnitude lower than those attained in batch cultures. Avoiding restricted cultures might be necessary to reach high titres of δ-endotoxin, which are essential if a good product is intended. Furthermore, spore count might not be a good parameter to predict insecticidal activity of Bacillus thuringiensis cultures.

Growth and protopectinase production of Geotrichum klebahnii in batch and continuous cultures with synthetic media

Geotrichum klebahnii ATCC 42397 produces a protopectinase (PPase-SE) with polygalacturonase (PGase) activity. The microorganism was aerobically cultivated in synthetic media. Glucose, fructose and xylose yielded the highest enzyme levels (10–11 PGase units ml−1). Galacturonic acid repressed enzyme production and no growth was obtained with disaccharides and pectin. Specific enzyme activity obtained in an O2-limited culture was similar to that found in nonlimited ones. A growth yield (Yx/s) of 0.49 g of cell dry weight per gram of glucose consumed was obtained in a typical batch bioreactor culture. Enzyme production was growth associated, and no major products other than biomass and CO2 were detected. The volumetric enzyme activity reached a maximum around D=0.3–0.4 h−1 in glucose-limited continuous cultures. However, it varied strongly (together with microorganism morphology) even after retention times ≥8 at any D tested (0.035–0.44 h−1) though the rest of the culture variables remained fairly constant. No correlation between morphology and enzyme activity could be obtained. Enzyme production was poor in urea- and vitamin-limited continuous cultures. In all cases, biomass and CO2 accounted for ≅100% of carbon recovery though Yx/s values were different. Journal of Industrial Microbiology & Biotechnology (2000) 25, 260–265.

Quantification of protopectinase SE, an endopolygalacturonase with pectin-releasing activity from Geotrichum klebahnii

Pectin releasing activity of protopectinase SE (PPase-SE) from Geotrichum klebahnii (= G. penicillatum = Trichosporon penicillatum) ATCC 42397 was determined using different batches of lemon protopectin as substrate. Results obtained showed a high degree of variability depending on the batch of protopectin used. As PPase-SE also shows polygalacturonase (PGase) activity, a method for the assay of this activity was optimised. The best assay conditions were: substrate (polygalacturonic acid) concentration of 2.0 g 1−1, reaction time of 10 min and up to 0.17 PGase units per test tube.

Quantification of pectin-releasing activity of protopectinase-SE from Geotrichum klebahnii

A method for quantification of a pectin releasing enzyme (PPase-SE) from Geotrichum klebahnii (= Geotrichum penicillatum = Trichosporon penicillatum) ATCC 42397 is reported. PPase activity was determined by measuring the amount of soluble pectin released from lemon protopectin. Particle size of the substrate, reaction time and linearity range of the assay, were analysed. The best assay conditions were a reaction time of 30 min, 20 mg substrate (mesh 60) and up to 0.045 units PPase activity per test tube.

Role of PPase-SE in Geotrichum klebahnii, a yeast-like fungus able to solubilize pectin

Protopectinases (PPases) constitute a heterogeneous group of extracellular enzymes able to release soluble pectin from insoluble protopectin in plant tissues. Geotrichum klebahnii (ATCC 42397) produces PPase-SE with endopolygalacturonase activity. PPase-SE has been used for pectin extraction and maceration of plant tissues. Here, the capacity of G. klebahnii to use different pectins as carbon and energy sources (CES) was studied, in addition to PPase-SE capacity to release pectin from lemon peel. The strain was unable to use pectin from different origins as CES. When G. klebahnii was cultivated with mixtures of different amounts of glucose and citrus pectin as CES, the biomass obtained was proportional to the initial concentration of glucose, which was completely consumed. In addition, it produced PPase-SE in a glucose-containing medium. A culture was used for the extraction of pectin from lemon peels. Pectin was enzymatically extracted simultaneously with tissue maceration, yielding 3.7 g of (dry) pectin per 100 g of (wet) lemon peel. Extracted pectin was not metabolized by the strain. It was concluded that G. klebahnii uses PPase-SE to macerate, invade and colonize plant tissues, thus releasing soluble sugars to be used as CES without metabolizing solubilized pectin.

Solvents production from whey supplemented with corn steep and malt sprouts at 30°C and 37°C

SummaryCorn steep and malt-sprouts were used to replace yeast extract in solvents production from whey at 30°C and 37°C employing two clostridia producer strains. The results show different temperature and growth factors dependence in the two strains. Yields of solvents between 0.16 and 0.32 (g/g) were obtained.

Influence of temperature on solvents production from whey

SummaryThe influence of temperature on solvent production from whey was investigated by using strains ofClostridium acetobutylicum andbutylicum. Higher yields of solvents were observed at 37°C or at 30°C depending on the strain used.