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Cellular behaviors and a xylanolytic-cellulolytic enzyme system of Tepidimicrobium xylanilyticum BT14 towards xylan-rich plant biomass degradation were characterized. During the exponential growth phase, the bacterial cells were bound tightly to the growth substrate where the degradation zones appeared mostly around the cells, indicating that the xylanolytic-cellulolytic enzyme system was linked to the cell surfaces. Interestingly, several cells appeared to secrete extracellular matrix to connect to their neighbors, and the matrix disappeared when cells passed to the stationary growth phase. Cationized-ferritin staining resulted in a dense assembly of bulbs, protuberance-like structures on the growing bacterial cell surfaces. The cell-associated proteins derived by sonication contained predominated xylanase with relatively low carboxymethyl-cellulase (CMCase) activities, suggesting that the xylanolytic-cellulolytic enzyme system occurred as a cell-associated enzyme. By means of gel-filtration chromatography, a high molecular mass protein with the estimated size of 2000 kDa was retrieved from the cell-associated enzymes, and it appeared as a single protein band on non-denaturing gel. However, more bands were obtained after the protein was boiled with sodium dodecyl sulfate and β-mercaptoethanol - which contained 4 xylanases and one CMCase - suggesting that these proteins were organized as a multienzyme complex (MEC) in natural form. Additionally, the predominated xylanolytic MEC preferred binding to cellulose rather than xylan. [ABSTRACT FROM AUTHOR]

The effect of biomass loading from 50 to 200 g/L on enzymatic hydrolysis was studied using switchgrass samples pretreated by dilute acid and hypochlorite-alkaline methods. It was confirmed that an increase of initial loading of the pretreated biomass leads to a decrease of enzymatic digestibility, probably due to difficulty of mass transfer of cellulolytic enzymes in the high-viscous substrate slurry and also because of an inhibiting effect of the formed sugars. An additional sharp problem connected with enzymatic hydrolysis at the high-solids loading is absorption and retention of liquid hydrolysate by residual non-hydrolyzed biomass that causes diminution of the available volume (Va) of the sugar solution and decreases productivity of the saccharification process. To optimize the high-solids enzymatic hydrolysis, the maximal amount of the formed sugars was determined Am = Cm x Va,m , where Cm is maximal concentration of the sugar solution and Va,m is maximal available volume. Such an approach makes it possible to find the optimal conditions for the hydrolysis: optimal biomass loading and hydrolysis time. After enzymatic hydrolysis at these optimal conditions, the low-lignified biomass pretreated by hypochlorite-alkaline method displayed much more available volume of sugar solution and higher digestibility characteristics than the cellolignin obtained by acidic pretreatment of the initial biomass sample. [ABSTRACT FROM AUTHOR]

The effect of mild acidic and alkaline pretreatments of various plant biomasses on their enzymatic hydrolysis has been studied. The yield of reducing sugars and utilization rate of the biomass were used as reliable characteristics of enzymatic digestibility of the biomasses. The experiments showed that alkaline pretreatment was more efficient than acidic pretreatment. As a result of alkaline pretreatment, a more efficient delignification of the biomasses and considerable improvement of the digestibility parameters were observed. It was found that residual lignin content in the biomass after alkaline pretreatment was related to initial lignin content in untreated biomass. Moreover, residual lignin showed an evident negative effect on enzymatic hydrolysis of pretreated biomass samples, and its removal contributed to higher enzymatic digestibility. It is more preferred to select a mild alkaline pretreatment for biomass that has low content of initial lignin. Such treatment yielded highly delignified biomass with increased percentage of cellulose fraction, which enhanced digestibility at low enzyme loading with a relatively short hydrolysis time. [ABSTRACT FROM AUTHOR]

Enzymatic hydrolysis of non-dried and dried cellulose samples having various particles size, degree of polymerization, porosity, crystalline polymorph, and content of non-crystalline domains has been studied. Regression analysis was carried out to determine contribution of various structural features of cellulose samples to their hydrolysability. It was found that particle size, degree of polymerization, and crystalline polymorph had a negligible influence on the conversion degree of cellulose into glucose under the effect of the cellulolytic enzyme. Such characteristics as the pores volume had a fair impact on the conversion degree of cellulose. Drying of the wet samples caused decreasing of the hydrolysability of cellulose due to irreversible collapse of the pores volume. The content of non-crystalline domains (Ax) in cellulose had the highest effect on the rate of enzymatic hydrolysis and average conversion degree (aa) of cellulose into glucose. A linear dependence aa = f(Ax) was established both for dried and non-dried cellulose samples. [ABSTRACT FROM AUTHOR]