Effect of lignin and some of its components on the production and activity of cellulase(s) by Trichoderma reesei

Lignin-Enzyme Interactions in the Hydrolysis of Lignocellulosic Biomass

Lignin is central to overcoming recalcitrance in the enzyme hydrolysis of lignocellulose. While the term implies a physical barrier in the cell wall structure, there are also important biochemical components that direct interactions between lignin and the hydrolytic enzymes that attack cellulose in plant cell walls. Progress toward a deeper understanding of the lignin synthesis pathway - and the consistency between a range of observations over the past 40 years in the very extensive literature on cellulose hydrolysis - is resulting in advances in reducing a major impediment to cellulose conversion: the cost of enzymes. This review addresses lignin and its role in the hydrolysis of hardwood and other lignocellulosic residues.

Inhibition and kinetic studies of cellulose- and hemicellulose-degrading enzymes of Ganoderma boninense by naturally occurring phenolic compounds

AIM

Ganoderma sp, the causal pathogen of the basal stem rot (BSR) disease of oil palm, secretes extracellular hydrolytic enzymes. These play an important role in the pathogenesis of BSR by nourishing the pathogen through the digestion of cellulose and hemicellulose of the host tissue. Active suppression of hydrolytic enzymes secreted by Ganoderma boninense by various naturally occurring phenolic compounds and estimation of their efficacy on pathogen suppression is focused in this study.

METHODS AND RESULTS

Ten naturally occurring phenolic compounds were assessed for their inhibitory effect on the hydrolytic enzymes of G. boninense. The enzyme kinetics (V_max and K_m ) and the stability of the hydrolytic enzymes were also characterized. The selected compounds had shown inhibitory effect at various concentrations. Two types of inhibitions namely uncompetitive and noncompetitive were observed in the presence of phenolic compounds. Among all the phenolic compounds tested, benzoic acid was the most effective compound suppressive to the growth and production of hydrolytic enzymes secreted by G. boninense. The phenolic compounds as inhibitory agents can be a better replacement for the metal ions which are known as conventional inhibitors till date. The three hydrolytic enzymes were stable in a wide range of pH and temperature.

CONCLUSION

These findings highlight the efficacy of the applications of phenolic compounds to control Ganoderma.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study has proved a replacement for chemical controls of G. boninense with naturally occurring phenolic compounds.

Fractionation of cellulase and fermentation inhibitors from steam pretreated mixed hardwood

The purpose of liquid hot water and steam pretreatment of wood is to fractionate hemicelluloses, partially solubilize lignin, and enhance enzyme hydrolysis of cellulose. The pretreatment also solubilizes sugar oligomers, lignin-derived phenolic compounds, acetic acid, and furan derivatives that inhibit cellulase enzymes and/or impede fermentation of hydrolysates by yeasts. This work extends knowledge of the relative contribution of identified inhibitors, and the effect of temperature on their release when pretreated materials are washed and filtered with hot water. Dramatic yield improvements occur when polymeric or activated carbon adsorbs and removes inhibitors. By desorbing, recovering, and characterizing adsorbed molecules we found phenolic compounds were strong inhibitors of enzyme hydrolysis and fermentation of concentrated filtrates by Saccharomyces cerevisiae wine yeast NRRL Y-1536 or xylose fermenting yeast 424A (LNH-ST). These data show that separation of inhibitors from pretreatment liquid will be important in achieving maximal enzyme activity and efficient fermentations.

Bioenergy feedstock-specific enrichment of microbial populations during high-solids thermophilic deconstruction

Thermophilic microbial communities that are active in a high-solids environment offer great potential for the discovery of industrially relevant enzymes that efficiently deconstruct bioenergy feedstocks. In this study, finished green waste compost was used as an inoculum source to enrich microbial communities and associated enzymes that hydrolyze cellulose and hemicellulose during thermophilic high-solids fermentation of the bioenergy feedstocks switchgrass and corn stover. Methods involving the disruption of enzyme and plant cell wall polysaccharide interactions were developed to recover xylanase and endoglucanase activity from deconstructed solids. Xylanase and endoglucanase activity increased by more than a factor of 5, upon four successive enrichments on switchgrass. Overall, the changes for switchgrass were more pronounced than for corn stover; solids reduction between the first and second enrichments increased by a factor of four for switchgrass while solids reduction remained relatively constant for corn stover. Amplicon pyrosequencing analysis of small-subunit ribosomal RNA genes recovered from enriched samples indicated rapid changes in the microbial communities between the first and second enrichment with the simplified communities achieved by the third enrichment. The results demonstrate a successful approach for enrichment of unique microbial communities and enzymes active in a thermophilic high-solids environment.

Effect of phenolic monomers on biomass and hydrolytic enzyme activities of an anaerobic fungus isolated from wild nil gai (Baselophus tragocamelus)

AIMS

To test the anaerobic fungus, Piromyces sp. FNG5, for its tolerance to phenolic monomers released in the rumen by degradation of lignocellulosic poor-quality feeds.

METHODS AND RESULTS

Effects of phenolic monomers on biomass and fibrolytic enzyme activities of a pure culture of lignocellulolytic anaerobic fungus (Piromyces sp. FNG5) isolated from faeces of wild nil gai (blue bull, Baselophus tragocamelus) were evaluated. There was a reduction in fungal biomass at 1 mm concentration of catechol with complete inhibition at 10 mm. p-Coumaric acid caused a reduction in biomass at 10 mm and no growth was observed above 20 mm concentration. The fungal isolate could tolerate up to 5 mm of ferulic acid without any reduction in biomass level, and was able to grow to some extent up to the highest level of ferulic acid tested (20 mm). Vanillic acid had no effect on biomass of the fungus even up to 50 mm level. The phenolic monomers varied in their potential to inhibit the secretion of carboxymethyl cellulase, xylanase, beta-glucosidase and acetyl esterase activities with catechol being the most inhibitory and vanillic acid being the least inhibitory. After 14 days of incubation, 38.49-65.14%p-Coumaric acid, 65.22-74.10% ferulic acid and 34.13-66.78% vanillic acid disappeared from the medium under anaerobic conditions.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

It is concluded that the anaerobic fungus Piromyces sp. FNG5 is tolerant to phenolic monomers and has ability to degrade them. Therefore, such anaerobic fungi may play an important role in fibre degradation in the rumen.

Effect of phenolic monomers on the growth and beta-glucosidase activity of Bacteroides ruminicola and on the carboxymethylcellulase, beta-glucosidase, and xylanase activities of Bacteroides succinogenes

trans-p-Coumaric acid inhibited the growth of Bacteroides ruminicola on both cellobiose and glucose, while trans-ferulic acid and vanillin retarded growth. The phenolic monomers varied in their potential to inhibit the Bacteroides succinogenes beta-glucosidase, carboxymethylcellulase, and xylanase, with p-coumaric acid being the most inhibitory. The B. ruminicola beta-glucosidase was inhibited less than 10% by all three compounds.

Influence of Plant Phenolic Acids on Growth and Cellulolytic Activity of Rumen Bacteria

Isolated rumen bacteria were examined for growth and, where appropriate, for their ability to degrade cellulose in the presence of the hydroxycinnamic acids trans-p -coumaric acid and trans -ferulic acid and the hydroxybenzoic acids vanillic acid and 4-hydroxybenzoic acid. Ferulic and p -coumaric acids proved to be the most toxic of the acids examined and suppressed the growth of the cellulolytic strains Ruminococcus albus, Ruminococcus flavefaciens , and Bacteroides succinogenes when included in a simple sugars medium at concentrations of >5 mM. The extent of cellulose digestion by R. flavefaciens and B. succinogenes but not R. albus was also substantially reduced. Examination of rumen fluid from sheep maintained on dried grass containing 0.51% phenolic acids showed the presence of phloretic acid (0.1 mM) and 3-methoxyphloretic acid (trace) produced by hydrogenation of the 2-propenoic side chain of p -coumaric and ferulic acids, respectively. The parent acids were found in trace amounts only, although they represented the major phenolic acids ingested. Phloretic and 3-methoxyphloretic acids proved to be considerably less toxic than their parent acids. All of the cellulolytic strains (and Streptococcus bovis ) showed at least a limited ability to hydrogenate hydroxycinnamic acids, with Ruminococcus spp. proving the most effective. No further modification of hydroxycinnamic acids was produced by the single strains of bacteria examined. However, a considerable shortfall in the recovery of added phenolic acids was noted in media inoculated with rumen fluid. It is suggested that hydrogenation may serve to protect cellulolytic strains from hydroxycinnamic acids.

Effect of dithiocarbamates on cellulase activity in culture filtrates of Trichoderma reesei

Different concentrations of tetramethylthiuram disulfide (TMTD), sodium dimethyldithiocarbamate (NaDDC), and zinc dimethyldithiocarbamate (ZnDDC) affected the amount of cellulase(s) activity in the culture of Trichoderma reesei. After eight days incubation at 28 degrees C the greatest increase in Avicelase, CMCase, and beta-glucosidase over the control were observed at 0.1 ppm (TMTD) and 0.4 ppm (NaDDC and ZnDCC). There was decrease in the growth in the ZnDDC, but beta-glucosidase activity was reduced considerably. Total protein in the culture filtrate increased with the increase in cellulase(s) activity. No change in pH was observed at eight days incubation but pH increased (not exceeding 5.9) at 12 days incubation.