The production of extracellular xylanase, beta-xylosidase and alpha-l-arabinofuranosidase by the mesophilic fungus Penicillium janczewskii under submerged cultivation was investigated with different carbon sources. Optimization steps included studies of carbon source concentration, temperature of cultivation and initial pH of culture medium. The production of these enzymes was increased two times when cultures were supplemented with brewer's spent grain at 2% concentration, pH 6.0 and carried out at 25 degrees C. Under these optimized conditions were obtained xylanase activity of 15.19UmL(-1) and 23.54Umgprot(-1), beta-xylosidase activity of 0.16UmL(-1) and 0.25Umgprot(-1) and alpha-l-arabinofuranosidase activity of 0.67UmL(-1) and 1.04Umgprot(-1). Brewer's spent grain is a promising substrate for P. janczewskii growth and xylanolytic enzyme production, since it is the main by-product from the brewing industry, available in large amounts and at low-cost in many countries.

No abstract

BackgroundSecond-generation ethanol production is a clean bioenergy source with potential to mitigate fossil fuel emissions. The engineering of Saccharomyces cerevisiae for xylose utilization is an essential step towards the production of this biofuel. Though xylose isomerase (XI) is the key enzyme for xylose conversion, almost half of the XI genes are not functional when expressed in S. cerevisiae. To date, protein misfolding is the most plausible hypothesis to explain this phenomenon.ResultsThis study demonstrated that XI from the bacterium Propionibacterium acidipropionici becomes functional in S. cerevisiae when co-expressed with GroEL-GroES chaperonin complex from Escherichia coli. The developed strain BTY34, harboring the chaperonin complex, is able to efficiently convert xylose to ethanol with a yield of 0.44 g ethanol/g xylose. Furthermore, the BTY34 strain presents a xylose consumption rate similar to those observed for strains carrying the widely used XI from the fungus Orpinomyces sp. In addition, the tetrameric XI structure from P. acidipropionici showed an elevated number of hydrophobic amino acid residues on the surface of protein when compared to XI commonly expressed in S. cerevisiae.ConclusionsBased on our results, we elaborate an extensive discussion concerning the uncertainties that surround heterologous expression of xylose isomerases in S. cerevisiae. Probably, a correct folding promoted by GroEL-GroES could solve some issues regarding a limited or absent XI activity in S. cerevisiae. The strains developed in this work have promising industrial characteristics, and the designed strategy could be an interesting approach to overcome the non-functionality of bacterial protein expression in yeasts.Electronic supplementary materialThe online version of this article (10.1186/s12896-017-0389-7) contains supplementary material, which is available to authorized users.

The highest production of α-L-arabinofuranosidase by Penicillium janczewskii in medium with brewer's spent grain and orange waste was observed when cultivation was carried out in pH 5.0 at 25°C, for 8.5 days under shaking. The α-L-arabinofuranosidase present in the crude filtrate was optimally active at 60°C and pH 4.0; it was stable in a wide range of pH, maintaining 90% of the activity from 2.0 to 8.0. The enzyme was very stable at 40°C, maintaining 90% of the activity within 1 h. The estimated half-life at 50°C was 10 min, and at 60 and 70°C, it was 5 min. This enzyme was activated in the presence of Ba 2+ , Ca 2+ , Mn 2+ and NH 4 + while the ions Pb 2+ , Mg 2+ , Hg 2+ , Co 2+ and Cu 2+ , as well as PMSF, DTT, βmercaptoethanol, EDTA and SDS inhibited it.