Maria Cândida Reginato Facciotti

Applications of image analysis in the characterization of Streptomyces olindensis in submerged culture

The morphology of Streptomyces olindensis (producer of retamycin, an antitumor antibiotic) grown in submerged culture was assessed by image analysis. The morphology was differentiated into four classes: pellets, clumps (or entangled filaments), branched and unbranched free filaments. Four morphological parameters were initially considered (area, convex area, perimeter, and convex perimeter) but only two parameters (perimeter and convex perimeter) were chosen to automatically classify the cells into the four morphological classes, using histogram analysis. Each morphological class was evaluated during growth carried out in liquid media in fermenter or shaker. It was found that pellets and clumps dominated in early growth stages in fermenter (due to the inoculum coming from a shaker cultivation) and that during cultivation, the breakage of pellets and clumps caused an increase in the percentage of free filaments. The criteria of morphological classification by image analysis proposed were useful to quantify the percentage of each morphological class during fermentations and may help to establish correlations between antibiotic production and microorganism morphology.

A rapid and sensitive method for the screening of DNA intercalating antibiotics

An improved, rapid and inexpensive gel mobility shift assay was developed for the screening of anthracycline antibiotics. The assay based on the intercalation activity of these molecules into dsDNA was used to assess the activity of partially purified antibiotics. Detection limits were of 0.1 ng ml−1 with an average run time of 2 h. The assay is potentially useful for high throughput screening in bioprospecting, for monitoring fermentation production phases and downstream purification process.

Influence of carbon and nitrogen sources on glucoamylase production byAspergillus in batch process

SummaryGlucoamylase production kinetics was greatly affected by medium composition. While maltose and cassava flour induced glucoamylase synthesis, fructose clearly repressed it, reaching a maximum enzyne activity value (Am) of only 6% of those obtained with the former carbon sources. Among the nitrogen sources the best result was obtained with urea, reaching Am values of about 40% higher than those obtained with ammonium sulphate.

Effect of pH on the production of the antitumor antibiotic retamycin by Streptomyces olindensis

The effect of pH on cell growth and retamycin production in batch bioreactor cultures of Streptomyces olindensis ICB20 was investigated. In fermentations pH‐controlled over the range 6.0–8.0, the highest retamycin production was achieved at pH 7.0, and the maximum concentration of retamycin, about 1.36 A (absorbance) units, was about 43, 58 and 232% higher than the values obtained at pH 7.5, 6.0 and 8.0 respectively.

Effect of yeast extract on glucoamylase synthesis byAspergillusawamori NRRL 3112

SummaryGlucoamylase synthesis is strongly affected by yeast extract concentration (CE). An eight fold increase in CE caused a two fold increase in the maximum glucoamylase activity value (Am) for the cultivations conducted with an initial glucose concentration (GO) of about 20 g/l, and a four fold increase in Am in the runs with a Go value of about 40 g/l. Five mathematical correlations are presented, showing a very good adjustment to the experimental results.

RELATIONSHIP BETWEEN MORPHOLOGY, RHEOLOGY AND GLUCOAMYLASE PRODUCTION BY Aspergillus awamori IN SUBMERGED CULTURES

The influence of inoculum preparation on Aspergillus awamori morphology, broth rheology and glucoamylase synthesis in submerged cultures was investigated. A series of runs were performed in fermenters, using initial total reducing sugar concentrations of 20 g/L and 80 g/L. The inocula were prepared in a rotary shaker, at 35oC and 200 rev/min, using a spore concentration of 9.2 x 105 spores/mL and varying both cultivation time and medium pH during the spore germination step. Three types of inocula were used: inoculum cultivated for 24 hours at an initial pH of 5.0, and inocula cultivated for 7 hours at both a pH of 2.5 and a pH of 5.5. Regarding glucoamylase production, the inoculum which provided the best results was shaker cultivated for 7 hours at a pH of 2.5. This inoculum produced glucoamylase of about 1,221 U/L in the fermenter, which was between 20% and 30% higher than those obtained using other inocula.

Carbon catabolite repression of retamycin production by Streptomyces olindensis ICB20

Retamycin is an anthracyclinic antitumoral complex produced by Streptomyces olindensis ICB20. In this work the influence of different glucose concentrations in the feed medium on the production of retamycin was studied. Chemostat cultures employing glucose concentration varying between 10 g/L and 25 g/L showed that use of high glucose concentration resulted in catabolite repression of the biosynthesis of the antitumoral. The highest specific retamycin production rate, qRTM = 7.8 mg/g.h, was obtained when glucose concentration was 10 g/L. The lowest value of qRTM, 2.5 mg/g.h, was observed when glucose concentration was 20 and 25 g/L. The residual glucose concentration varied from 0 to 13 g/L, as the glucose concentration in the feed was increased from 10 to 25 g/L.