Guilhermina Marques

Enzymatic saccharification of biologically pre-treated wheat straw with white-rot fungi

Wheat straw was submitted to a pre-treatment by the basidiomycetous fungi Euc-1 and Irpex lacteus, aiming to improve the accessibility of cellulose towards enzymatic hydrolysis via previous selective bio-delignification. This allowed the increase of substrate saccharification nearly four and three times while applying the basidiomycetes Euc-1 and I. lacteus, respectively. The cellulose/lignin ratio increased from 2.7 in the untreated wheat straw to 5.9 and 4.6 after the bio-treatment by the basidiomycetes Euc-1 and I. lacteus, respectively, thus evidencing the highly selective lignin biodegradation. The enzymatic profile of both fungi upon bio-treatment of wheat straw have been assessed including laccase, manganese-dependent peroxidase, lignin peroxidase, carboxymethylcellulase, xylanase, avicelase and feruloyl esterase activities. The difference in efficiency and selectivity of delignification within the two fungi treatments was interpreted in terms of specific lignolytic enzyme profiles and moderate xylanase and cellulolytic activities.

Influence of ligninolytic enzymes on straw saccharification during fungal pretreatment.

Solid state and submerged fermentations in the presence of white-rot basidiomycetes (Bjerkandera adusta, Fomes fomentarius, Ganoderma resinaceum, Irpex lacteus, Phanerochaete chrysosporium, Trametes versicolor and basidiomycete Euc-1) and the litter-decomposing basidiomycete Lepista nuda were evaluated as a pretreatment to increase enzymatic saccharification of wheat straw. Enzymatic hydrolysis of holocellulose after solid state pretreatment showed a significant (P<0.05) increase of saccharification process for T. versicolor, Euc-1, G. resinaceum and I. lacteus, being T. versicolor (strain Tv2) the best one with a sugar yield increase of 91% compared with untreated straw. In submerged medium the pretreatment with I. lacteus, Euc-1 and P. chrysosporium enhanced saccharification but at a lesser extent. Covariance analysis was used to evaluate the relationships between ligninolytic enzymes (lignin peroxidase, manganese-dependent peroxidase and laccase) and saccharification increase. Results showed that only the presence of lignin peroxidase during pretreatment can lead to a significant (P<0.05) increase in the saccharification yield.

The potential of white‐rot fungi to degrade phorbol esters of Jatropha curcas L. seed cake

The potential of solid‐state cultivation, with three white‐rot fungi (Bjerkandera adusta, Ganoderma resinaceum and Phlebia rufa), to decrease phorbol esters concentration of Jatropha curcas L. was evaluated in this study. Incubation was conducted in 250 mL Erlenmeyer flasks without agitation at 28°C for 30 days. Phorbol esters were analyzed by reverse‐phase HPLC after an extraction procedure using dichloromethane. All fungi studied were able to decrease the concentration of phorbol esters, mainly B. adusta and P. rufa which significantly reduced (p<0.05) phorbol esters contents to non‐toxic levels. These results suggest that white‐rot fungi could be potentially used as a possible approach for the biological treatment of the oilseed cake.

Influence of culture medium growth variables on Ganoderma lucidum exopolysaccharides structural features

In this work the effect of carbon and nitrogen levels and initial pH of the wheat extract culture medium of submerged culture of Ganoderma lucidum on the amount, purity and structural features of exopolysaccharides (EPS) were studied. A low peptone level (1.65 g L(-1)) favored mycelium biomass, EPS purity, but a higher supply of peptone (4.80 g L(-1)) is needed for maximum EPS production. The carbohydrate composition of the EPS and structural features also changed significantly according to the different growing conditions, being observed significant differences in the (1 → 3)/(1 → 4)-Glcp ratio and also on the branching degree of EPS. As the biological activities of EPS are highly dependent on the polysaccharide structural features, this variability can have implications on the EPS biological activities, but can also be used advantageously to produce tailor made polysaccharides with specific applications.

Increased protein content of chickpea (Cicer arietinum L.) inoculated with arbuscular mycorrhizal fungi and nitrogen-fixing bacteria under water deficit conditions

BACKGROUND Chickpea (Cicer arietinum L.) is a widely cropped pulse and an important source of proteins for humans. In Mediterranean regions it is predicted that drought will reduce soil moisture and become a major issue in agricultural practice. Nitrogen (N)-fixing bacteria and arbuscular mycorrhizal (AM) fungi have the potential to improve plant growth and drought tolerance. The aim of the study was to assess the effects of N-fixing bacteria and AM fungi on the growth, grain yield and protein content of chickpea under water deficit. RESULTS Plants inoculated with Mesorhizobium mediterraneum or Rhizophagus irregularis without water deficit and inoculated with M. mediterraneum under moderate water deficit had significant increases in biomass. Inoculation with microbial symbionts brought no benefits to chickpea under severe water deficit. However, under moderate water deficit grain crude protein was increased by 13%, 17% and 22% in plants inoculated with M. mediterraneum, R. irregularis and M. mediterraneum + R. irregularis, respectively. CONCLUSION Inoculation with N-fixing bacteria and AM fungi has the potential to benefit agricultural production of chickpea under water deficit conditions and to contribute to increased grain protein content.

Insect-associated fungi from naturally mycosed vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae)

ABSTRACT Vine mealybug, Planococcus ficus, is a major pest of grapevine, which is present in at least 39 countries. According to American Vineyard Foundation, P. ficus is in the top ranks among major insect-pests of grapevine. It is the ‘top priority concerns’ by grape growers and a ‘threat to the sustainability of wine industry’ demanding a ‘high priority research’. In Douro vineyards, it is considered as an occasional insect-pest; however, its importance is increasing in some localities. The present study investigates the occurrences of P. ficus-associated fungi. Vine mealybugs were observed in two of the four surveyed farms. Out of the 183 collected mealybugs, 58 were dead of which 25 had symptoms of mycosis and 13 were parasitised. Subculturing cadavers and subsequent pathogenicity test yielded 22 entomopathogenic fungi (EPF) including yeasts. The yeast Meyerozyma (=Pichia) guilliermondii, and the EPF Sarocladium kiliense and Purpureocillium lilacinum were the most abundant, i.e. representing 18.18% (N = 4), 13.64% (N = 3) and 13.64% (N = 3) of the isolates, respectively. Considering biological affinities, fungal families Nectriaceae and Microascaceae had the most similar count-data profiles. To our knowledge, this work reports the first isolations of EPF from vine mealybug worldwide; and Pseudocosmospora rogersonii in Europe and as EPF worldwide. The mortality rate originated by mycoses on P. ficus was significantly higher than by its parasitoids, suggesting that fungi as P. ficus biocontrol agents are relatively more important than considered before. Overall, this report provides new insights into the development of mycoinsecticides and conservation biocontrol strategies for P. ficus pest management.

Potential use of cowpea (Vigna unguiculata (L.) Walp.) stover treated with white-rot fungi as rabbit feed

BACKGROUND Lignin inhibitory effects within the cell wall structure constitute a serious drawback in maximizing the utilization of fibrous feedstuffs in animal feeding. Therefore treatments that promote efficient delignification of these materials must be applied. This study evaluated the potential of white-rot fungi to upgrade the nutritive value of cowpea stover for rabbit feeding. RESULTS There was an increase in the crude protein content of all substrates as a result of fungi treatments, reaching a net gain of 13% for Pleurotus citrinopileatus incubation. Overall, net losses of dry and organic matter occurred during fungi treatments. Although the fiber content remained identical, higher consumption of cell wall contents was measured for P. citrinopileatus incubation (between 40 and 45%). The incubation period did not influence lignin degradation for any of the fungi treatments. Differences within the fungal degradation mechanisms indicate that P. citrinopileatus treatment was most effective, enhancing in vitro organic matter digestibility by around 30% compared with the control. CONCLUSION Treatment of cowpea stover with P. citrinopileatus led to an efficient delignification process which resulted in higher in vitro organic matter digestibility, showing its potential in the nutritional valorization of this feedstuff.

Improved grain yield of cowpea (Vigna unguiculata) under water deficit after inoculation with Bradyrhizobium elkanii and Rhizophagus irregularis

Abstract. Cowpea (Vigna unguiculata (L.) Walp.), a plant broadly cultivated for human consumption and animal feed, is among the most nutritious grain legumes. Most of the areas where cowpea is grown are drought-prone, and there is a need to address this issue, with water scarcity becoming a major concern in agriculture. Cowpea is known to form mutualistic associations with nitrogen-fixing (NF) bacteria and arbuscular mycorrhizal (AM) fungi. These beneficial soil microorganisms have the capacity to benefit plants by reducing the effects of environmental stresses, including drought. Our aim was to study the effect of inoculation with Bradyrhizobium elkanii and Rhizophagus irregularis on the growth and grain yield of cowpea under water-deficit conditions. Under moderate water deficit, grain yield was increased by 63%, 55% and 84% in plants inoculated with B. elkanii, R. irregularis and B. elkanii + R. irregularis, respectively. Under severe water deficit, inoculation with B. elkanii and B. elkanii + R. irregularis resulted in grain-yield enhancement of 45% and 42%, respectively. The use of cowpea inoculated with NF bacteria and AM fungi has great potential for sustainable agricultural production under drought conditions.

Neuroprotective properties of Cantharellus cibarius polysaccharide fractions in different in vitro models of neurodegeneration

The percentage of people suffering from neurodegenerative diseases is constantly increasing, because of that searching for substances able to prevent or inhibit neuronal death sseems to be reasonable. Because of the high popularity the search of new neuroprotective agents we started from Cantharellus cibarius. Neuroprotective properties of C. cibarius polysaccharides fractions was investigated in different models of neurodegeneration including trophic stress, excitotoxicity and andoxidative stress. Fractions influence on neurons viability was examined using Neurite Outgrowth Staining, MTT and LDH tests, while antioxidant capacity was determined by commercial antioxidant assays. Performed studies revealed beneficial effect of C. cibarius fractions (CC2a, CC3) on neurons viability and neurite outgrowth in normal and different stress conditions. Both tested fractions have shown antioxidant capacity and effectively neutralize the negative changes induced by glutamatergic system activators. Discovered neuroprotective properties of investigated compounds suggested the their use for developing effective and safety therapeutic strategy for neurodegenerative diseases.