J. Carlos Roseiro

The effects of the oxygen transfer coefficient and substrate concentration on the xylose fermentation by Debaryomyces hansenii

Relevant production of xylitol by Debaryomyces hansenii requires semiaerobic conditions since in aerobic conditions the accumulated reduced adenine dinucleotide coenzyme is fully reoxidized leading to the conversion of xylitol into xylulose. For oxygen transfer coefficient values from 0.24 to 1.88 min-1, in shake flasks experiments, biomass formation increased proportionally to the aeration rate as shown in the oxygen transfer coefficient and xylose concentration isoresponse contours. The metabolic products under study, xylitol and ethanol were mainly growth associated. However, for oxygen transfer coefficient above 0.5 min-1 higher initial xylose concentration stimulated the rate of production of xylitol. This fact was less evident for ethanol production. The direct relationship between increased biomass and products formation rate, indicated that the experimental domain in respect to the aeration rate was below the threshold level before the decreasing in metabolic production rates reported in literature for xylose-fermenting yeasts. The fact that ethanol was produced, albeit in low levels, throughout the experimental design indicated that the semiaerobic conditions were always attained. Debaryomyces hansenii showed to be an important xylitol producer exhibiting a xylitol/ethanol ratio above four and a carbon conversion of 54% for xylitol.

Antimicrobial activity of resin acid derivatives

The wide potential of resin acids as bioactive agents gave rise to a growing effort in the search for new applications of the natural forms and their derivatives. In some of these compounds, the antimicrobial activity is associated to the presence in the molecules of functional groups such as the hydroxyl, aldehyde, and ketone or to their cis or trans configurations. The resin acid family covers a spectrum of antimicrobial activities against several microorganisms, from bacteria to fungi, in which the mode of action was studied by electron microscopy. The morphological alterations are consistent with an unspecific mode of action causing inhibition of the fungal growth or damaging the fungal cells in parallel with a mechanism of resistance based on the retention of the compound by the lipid accumulation. The sterol composition of phytopathogenic fungi Botrytis cinerea and Lophodermium seditiosum treated with methyl cis-7-oxo-deisopropyldehydroabietate revealed the presence of ergosterol (M+ 396) and dihydroergosterol (M+ 398) in both cultures showing that this compound did not interfere with the ergosterol metabolic pathway of both fungi.

Effect of oxygen transfer rate on levels of key enzymes of xylose metabolism in Debaryomyces hansenii

Abstract The titers of key enzymes of xylose metabolism were measured and correlated with the kinetics of xylitol production by Debaryomyces hansenii under different oxygen transfer rates (OTR) in a batch reactor. An OTR change from 2.72 to 4.22 mmol O2 l−1 min−1 resulted in a decrease in NADPH-dependent xylose reductase (XR) and NAD ± -dependent xylitol dehydrogenase (XDH) activities. For higher values of OTR (12.93 mmol O2 l−1 min−1, the XDH titer increased twofold whereas the XR titer did not show a significant change. At the lowest OTR (2.72 mmol O2 l−1 min−1), xylitol (and ethanol) production rates showed the highest values. However, xylitol specific productivity was twice as high as ethanol specific productivity. The titer of the NADPH-forming enzyme, glucose-6-phosphate dehydrogenase (GPDH), increased from 333 to 412 mU mg−1 when the OTR was increased. However, 6-phosphogluconate dehydrogenase (PGDH) activity remained unchanged and at a lower level, which indicates that this enzyme is responsible for the carbon flux control of the oxidative branch of the pentose phosphate pathway. The activity of the alcohol-forming enzyme was repressed at the higher amount of oxygen, decreasing its activity more than 50%. The changes in ADH suggested that two different metabolic regions under oxygen-limited conditions can be hypothesized for xylose metabolism by D. hansenii. For low OTR values (up to 4.22 mmol O2 l−1 min−1), a fermentative-type activity is displayed. At higher OTR values (above 4.22 mmol O2 l−1 min−1), no significant fermentative activity is reported.

Antimicrobial activity of diterpene resin acid derivatives

C-13 deisopropylated and/or C-7 oxidized resin acid derivatives were tested against various microorganisms to determine structural features responsible for biological activity and to determine the influence of the C-13 isopropyl group on antimicrobial activity. Test results show that methyl cis and trans 7-oxo-13-deisopropyldehydroabietate and a mixture of both isomers exhibited activity against fungi and bacteria.

Diversity of microfungi in the phylloplane of plants growing in a Mediterranean ecosystem

Mediterranean ecosystems have not been investigated as natural habitats for microorganisms in general, and microfungi in particular. Plants harvested in “Serra da Arrábida” (38°27′ N, 9°02′ W), a Mediterranean ecosystem in Portugal, were analyzed for the filamentous microfungi inhabiting their surface. Two field locations with distinct climatic characteristics were studied: ‘Fonte do Veado’ (38°28′50″ N, 9°0′17″ W; 300 m elevation) located on the northern slope, and ‘Mata do Solitário’ (38°27′55″ N, 8°59′35″ W; 50 m elevation), on the southern slope. From Veado zone, leaf samples yielded a total of 3049 isolates, ranging from 317 to 1328/sample (mean = 762). The number of species/sample ranged from 12 to 24. From Solitario zone, leaf samples yielded a total of 1337 isolates, ranging from 189 to 528/sample (mean = 334). The number of species/sample, in this case, ranged from 10 to 17. Veado zone showed a wider range of species. The fungal species more frequently isolated from both zones (Aureobasidium pullulans (De Bary) Arnaud, Cladosporium cladosporioides (Fresen.) De Vries, C. sphaerospermum Penzig and Alternaria alternata (Fr.) Keissler) were found in all plant samples and represents 80% (Veado) and 85% (Solitario) of the total isolates.

Interactive Effects of pH and Temperature on Cell Growth and Polymer Production by Xanthomonas campestris

Abstract An experimental statistical design was used to determine pH and temperature optima for growth and polymer production by Xanthomonas campestris . A pH between 6·0-7·5 and a temperature between 25–27°C were optimal for growth. While for xanthan production and broth consistency index, the pH and temperature optimal ranges were between 7·0-8·0 and 25–30°C, respectively. At these optimal ranges a cell concentration of 3·2 g litre −1 , polysaccharide concentration of 17·7 g litre −1 and a consistency index of 100 mPa s 11 was obtained.

Method on multiwell plates for the evaluation of the antimicrobial activity of resin acid derivatives

A method performed in solid medium on multiwell plates was adapted in order to assess the antimicrobial activity of methyl cis-7-oxo-deisopropyldehydroabietate (MCOD) and methyl trans-7-oxo-deisopropyldehydroabietate (MTOD), resin acid derivatives obtained from pine rosin. (MCOD) and (MTOD) completely or partially inhibited spore germination of filamentous fungi Mucor racemosus, Syncephalastrum racemosum, Rhizopus stolonifer and R. arrhizus and growth of bacteria Staphylococcus aureus and Enterococcus faecalis. The combination of both compounds inhibited growth of Escherichia coli and Klebsiella pneumoniae. The stereoconfiguration of the molecule seems to play a role in the antibacterial activity of these compounds and a possible synergistic effect seems to increase their antibiotic activity. The technique described in the present work showed to be reproducible and sensitive in the evaluation of antimicrobial activity towards fungi and bacteria.

Biological conversion of tomato pomace by pure and mixed fungal cultures

Abstract The hydrolysis of tomato pomace by Trichoderma reesei and Sporotrichum sp. pure solid state cultures resulted in 36% and 67% cellulose conversion and 73% and 41·5% hemicellulose degradation, respectively. In consortium these microorganisms revealed 56·5% cellulose and 36·2% hemicellulose conversion yields. The Trichoderma reesei culture displayed a four-fold specific enzyme activity as compared to the Sporotrichum sp. and the mixed culture. The final products obtained from the different microbial treatments contained enhanced quantities of lignin, indicating a considerable loss of solid material and protein.

Yield improvements in carob sugar extraction

Abstract Two multistage methods of sugar extraction from carob pods were compared with a single stage extraction/pressing process. A multistep extraction/pressing process produced a yield improvement of 6·6%. A second process based on the recycling of press liquor through a multistage series of vessels was not only considerably simpler and more economical in use of labour but also showed a further improvement of 1·4% to give a final sugar yield of 60%. A comparison of the calculated diffusion coefficients showed that the enhanced yield in the recycle flow process resulted from a decrease of a diffusion limitation observed in static operation. A diffusion coefficient of 9·9 × 10 3 m 2 /h was obtained at the highest yield.

Ethanol-induced dimorphism and lipid composition changes in Mucor fragilis CCMI 142.

Aims: To study the effect of ethanol on morphology, lipid production and fatty acid profile of Mucor fragilis CCMI 142 cultures.