Evaluation of endoglucanase and xylanase production by Aspergillus tamarii cultivated in agro-industrial lignocellulosic biomasses.

To better understand the production of enzymes of industrial interest from microorganisms with biotechnological potential using lignocellulosic biomass, we evaluated the production of endoglucanase and xylanase from Aspergillus tamarii. CAZymes domains were evaluated in the genome, and a screening of the enzymatic potential of A. tamarii in various agricultural biomasses was done. The enzymatic profile could be associated with the biomass complexity, with increased biomass recalcitrance yielding higher activity. A time-course profile defined 48 h of cultivation as the best period for cultivating A. tamarii in sugarcane bagasse reached 12.05 IU/mg for endoglucanase and 74.86 IU/mg for xylanase. Using 0.1% (w/v) tryptone as the only nitrogen source and 12 µmol/L CuSO4 addition had an overall positive effect on the enzymatic activity and protein production. A 22 factorial central composite design was used then to investigate the simultaneous influence of tryptone and CuSO4 on enzyme activity. Tryptone strongly affected enzymatic activity, decreasing endoglucanase activity but increasing xylanase activity. CuSO4 supplementation was advantageous for endoglucanases, increasing their activity, and it had a negative effect on xylanases. But overall, the experimental design increased the enzymatic activity of all biomasses used. For the clean cotton residue, the experimental design was able to reach the highest enzyme activity for endoglucanase and xylanase, with 1.195 IU/mL and 6.353 IU/mL, respectively. More experimental studies are required to investigate how the biomass induction effect impacts enzyme production.

Xylanase from Aspergillus tamarii shows different kinetic parameters and substrate specificity in the presence of ferulic acid.

A 22 kDa xylanase (AtXyl1) from Aspergillus tamarii was purified by two chromatographic steps and presented preference for oat spelt (OSX), birchwood (BrX) and beechwood (BeX) xylans respectively, as substrates. AtXyl1 displays the highest activity at pH 5.5 and 55 °C and showed tolerance over a range of different phenolic compounds. The activity of AtXyl1 was not inhibited when the enzyme was incubated with ferulic acid (FA) using OSX or BrX as substrate. On the other hand, the incubation of AtXyl1 with BeX and FA resulted in an increase in enzyme activity. The molecular docking of a GH11 xylanase from Aspergillus niger with FA showed the preference for binding within the catalytic site. The position of FA was based on the presence or absence of a complexed substrate. When the enzyme from A. niger was docked in the absence of xylan in its crystal structure, FA interacted with Tyr164 and a water molecule. For the enzyme socked with xylo-oligosaccharides, FA interacted with Ser94, Tyr89 and the xylo-oligosaccharide present in the catalytic site. Thermodynamic parameters from the reaction of AtXyl1 with different xylans and FA indicate that FA can cause a conformational change in the enzyme, and this can influence the substrate fitting and makes the enzyme tolerant or active toward the substrate. Our findings suggest that enzyme activation or tolerance to phenolic compounds can be correlated to subtle changes in enzyme conformation due to the presence of the phenolic compound.