Screening of winery and olive mill wastes for lignocellulolytic enzyme production from Aspergillus species by solid-state fermentation

Wastes from olive oil and wine industries (as exhausted grape marc, vineshoot trimmings, two-phase olive mill waste, vinasses, and olive mill wastewater) were evaluated for lignocellulolytic enzyme production (as endocellulases, endoxylanases, and feruloyl esterases) by solid-state fermentation (SSF) with Aspergillus niger, Aspergillus ibericus, and Aspergillus uvarum. To study the effect of different solid medium composition and time in enzyme production, a PlackettBurman experimental design was used. Variables that had a higher positive effect in lignocellulolytic enzyme production were urea, time, and exhausted grape marc. The maximum values of enzymatic activity per unit of substrate dry mass were found with A. niger for feruloyl esterase. Enzymatic extracts from SSF with A. niger achieved maximum feruloyl esterase activity (89.53 U/g) and endoxylanase activity (3.06 U/g) and with A. uvarum for endocellulase activity (6.77 U/g). The enzyme cocktails obtained in the SSF extracts may have applications in biorefinery industries.Jose Manuel Salgado is grateful for the postdoctoral fellowship (EX-2010-0402) of the Education Ministry of Spanish Government. Luis Abrunhosa was supported by the grant SFRH/BPD/43922/2008 from Fundacao para a Ciencia e Tecnologia-FCT, Portugal

Production and partial characterization of pectinases from forage palm by Aspergillus niger URM4645

The activity of endo-polygalacturonase (endo-PG), exo-polygalacturonase (exo-PG), pectin lyase (PL) and pectinesterase (PE) produced by Aspergillus niger URM4645 was studied in solid-state fermentation (SSF) using forage palm as the substrate. The effect of variable substrate amount, inoculum concentration and temperature on the pectinase production was studied using a full factorial design (2³). The maximum activity obtained was 66.19 U/g for endo-PG, 3.590 U/g for exo-PG and 40,615.62 U/g for PL at 96, 24 and 72 h of fermentation, respectively. PE showed no activity. The production of endo-PG and exo-PG was significantly influenced by varying substrate amount, inoculum concentration and temperature, but these variables had no influence on PL production. The best conditions for production of the three enzymes at the same time were obtained with 10.0 g of substrate, 107 spores/g at 28°C. Endo-PG and PL presented optimum activity at pH 5.0 and exo-PG at pH 7.0. The maximal activity of endo-PG and PL was determined at 50°C and exo-PG at 40°C. Endo-PG and exo-PG were stable at a pH range of 3.5 - 11.0 and at 50 and 80°C, respectively. PL showed stability only at pH 5.0 and at 50°C.Key words: Aspergillus niger, pectinolytic activities, forage palm, solid-state fermentation

Pectinolytic complex production by Aspergillus niger URM 4645 using yellow passion fruit peels in solid state fermentation

The activities of endo-polygalacturonase (endo-PG), exo-polygalacturonase (exo-PG), pectin lyase (PL), and pectin methylesterase (PE), produced by Aspergillus niger URM 4645, were studied in solid state fermentation (SSF) using yellow passion fruit peels as substrate. The effect of substrate amount, initial moisture content, and temperature on pectinase production was studied using a full factorial design (2³). Maximum endo-PG, exo-PG, PL, and PE activities were 31.35, 7.98, 551,299.39, and 447.93 U g−1 dry substrate, respectively. Optimum activities of the four enzymes were obtained with 5.0 g of the substrate and an initial moisture content of 30% at 34°C with 96 h of fermentation. Optimum endo-PG activity was found at pH 7.5 at an optimum temperature of 40°C; exo-PG and PL at pH 7.0 at an optimum temperature of 80°C; and PE at pH 3.5 at an optimum temperature of 30°C. Endo-PG was stable at pH 7.0 to 8.0 at 40°C, and exo-PG and PL at pH 6.0 to 8.0 and 6.0 to 7.5, respectively at 60 to 70°C. PE was stable at pH 3.5 to 5.0 at 30 to 60°C. The enzyme production optimization clearly demonstrated the impact of process parameters on the yield of pectinolytic enzymes. Keywords: Aspergillus niger, residue, pectinolytic activities, solid state fermentation, characterization.African Journal of Biotechnology, Vol 13(31) 3313-332

Modulation of synchrony without changes in firing rates

It was often reported and suggested that the synchronization of spikes can occur without changes in the firing rate. However, few theoretical studies have tested its mechanistic validity. In the present study, we investigate whether changes in synaptic weights can induce an independent modulation of synchrony while the firing rate remains constant. We study this question at the level of both single neurons and neuronal populations using network simulations of conductance based integrate-and-fire neurons. The network consists of a single layer that includes local excitatory and inhibitory recurrent connections, as well as long-range excitatory projections targeting both classes of neurons. Each neuron in the network receives external input consisting of uncorrelated Poisson spike trains. We find that increasing this external input leads to a linear increase of activity in the network, as well as an increase in the peak frequency of oscillation. In contrast, balanced changes of the synaptic weight of excitatory long-range projections for both classes of postsynaptic neurons modulate the degree of synchronization without altering the firing rate. These results demonstrate that, in a simple network, synchronization and firing rate can be modulated independently, and thus, may be used as independent coding dimensions