A simple and efficient diffusion technique for assay of endo β-1,4-xylanase activity

Valorization of lignocellulosic wastes for sustainable xylanase production from locally isolated Bacillus subtilis exploited for xylooligosaccharides' production with potential antimicrobial activity

The worldwide availability of lignocellulosic wastes represents a serious environmental challenge with potential opportunities. Xylanases are crucial in lignocellulosic bio-hydrolysis, but the low enzyme productivity and stability are still challenges. In the current study, Bacillus subtilis (coded ARSE2) revealed potent xylanase activity among other local isolates. The enzyme production optimization revealed that maximum enzyme production (490.58 U/mL) was achieved with 1% xylan, 1.4% peptone, and 5% NaCl at 30 °C and pH 9. Furthermore, several lignocellulosic wastes were exploited for sustainable xylanase production, where sugarcane bagasse (16%) under solid-state fermentation and woody sawdust (2%) under submerged fermentation supported the maximum enzyme titer of about 472.03 and 485.7 U/mL, respectively. The partially purified enzyme revealed two protein bands at 42 and 30 kDa. The partially purified enzyme revealed remarkable enzyme activity and stability at 50-60 °C and pH 8-9. The enzyme also revealed significant stability toward tween-80, urea, DTT, and EDTA with Vmax and Km values of 1481.5 U/mL and 0.187 mM, respectively. Additionally, the purified xylanase was applied for xylooligosaccharides production, which revealed significant antimicrobial activity toward Staphylococcus aureus with lower activity against Escherichia coli. Hence, the locally isolated Bacillus subtilis ARSE2 could fulfill the xylanase production requirements in terms of economic production at a high titer with promising enzyme characteristics. Additionally, the resultant xylooligosaccharides revealed a promising antimicrobial potential, which paves the way for other medical applications.

Production of Thermo-Alkali-Stable Xylanase from Bacillus licheniformis Isolated from Natural Hot Water Geyser

Context:

Xylanase constitutes 20% of world enzyme market. Significantly, they are used in poultry feed, paper pulp, bakery, and textile industries. In view of the increasing demand of the enzyme, it is vital to develop indigenous strains and scalable technologies for the production of industrial enzymes.

Aims:

The objective of the present paper was to isolate a high-yielding strain of thermo-alkali-stable xylanase-producing bacteria for potential application in paper and pulp and biofuel industry.

Methods:

Sampling for prospecting of suitable organism was carried out from the places with dead and decaying lignocellulosic waste, and then Congo red screening was employed for the primary isolation of xylanase producers.

Results:

We report the isolation of 18 different strains of xylanase producer bacteria from natural hot water geyser of Sohna, Haryana, India. Subsequently, two of these isolates were chosen for further studies based on xylanase yield and desirable properties such as thermostability and alkali stability of xylanase produced.

Conclusion:

Isolate B2 was later identified as Bacillus licheniformis, whereas isolate Y3 was identified as Brevibacillus borstelensis. This strain when cultured at 35°C for 72 h showed xylanase production at 128 U/ml. The molecular weight of xylanase was determined to be 25 kDa. The production was scaled up in a 5-L stirred-tank bioreactor which led to high xylanase concentration of 380 U/ml in the first 48 h of culture.

Optimization of xylanase from Pseudomonas mohnii isolated from Simlipal Biosphere Reserve, Odisha, using response surface methodology

Background

Xylanase has long been recognized as a widely used industrially important enzyme. There are some bacterial species already reported to produce xylanase which have potent xylanolytic activity towards the use of this enzyme in the production of bioethanol from lignocellulosic biomass. In this view, an efficient xylanolytic bacterial strain was isolated and screened from the soil sample of Simlipal Biosphere Reserve. Enzymatic assay for the xylanase activity was evidenced from the most potent bacterial strain, and the culture condition was optimized for obtaining the maximum enzyme activity. The most potent xylanolytic strain was also identified using biochemical and molecular methods.

Results

Nineteen xylanolytic bacteria (SXB1-SXB19) were isolated from Simlipal forest soil samples following dilution plate technique using corn cob xylan-enriched nutrient agar medium and screened for their xylanase-producing ability. Among these isolates, SXB19 showed maximum xylanolytic potential with a halozone size of 2.5 cm as evident in the formation of prominent yellow patches surrounding its growth in xylan-enriched nutrient agar plate. In unoptimized condition, SXB19 showed the highest enzymatic activity of 22.5 IU/ml among the 19 bacterial strains. In order to optimize the culture conditions for maximizing the xylanase production, Box-Behnken design of response surface methodology (RSM) was used. Four variables such as incubation time, pH, substrate (corn cob xylan) concentration, and temperature were considered for the RSM optimization study. From the results, it is evident that in an optimized condition of incubation time 36 h, pH 6.0, xylan concentration 0.5%, and temperature 42.5 °C, the enzyme activity reached a maximum of 152 IU/ml with nearly 6.75 times increase from the unoptimised condition. Besides, xylanase production from SXB19 was considerable in the presence of xylan followed by starch, nitrogen source such as urea followed by yeast extract, and mineral ion sources such as KCl followed by MgSO₄ and ZnSO₄. From different biochemical tests, 16S rRNA gene sequencing, and phylogenetic analysis, the bacterial strain SXB19 was identified as Pseudomonas mohnii.

Conclusion

The isolation of Pseudomonas mohnii, a potent xylanolytic bacterium from Simlipal, is a new report which opens up an opportunity for industrial production of xylanase for bioethanol production and other applications.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-020-00099-7.

Mangrove soil as a source for novel xylanase and amylase as determined by cultivation-dependent and cultivation-independent methods

Xylanase and α-amylase enzymes participate in the degradation of organic matter, acting in hemicellulose and starch mineralization, respectively, and are in high demand for industrial use. Mangroves represent a promising source for bioprospecting enzymes due to their unique characteristics, such as fluctuations in oxic/anoxic conditions and salinity. In this context, the present work aimed to bioprospect xylanases from mangrove soil using cultivation-dependent and cultivation-independent methods. Through screening from a metagenomic library, three potentially xylanolytic clones were obtained and sequenced, and reads were assembled into contigs and annotated. The contig MgrBr135 was affiliated with the Planctomycetaceae family and was one of 30 ORFs selected for subcloning that demonstrated only amylase activity. Through the cultivation method, 38 bacterial isolates with xylanolytic activity were isolated. Isolate 11 showed an enzymatic index of 10.9 using the plate assay method. Isolate 39 achieved an enzyme activity of 0.43 U/mL using the colorimetric method with 3,5-dinitrosalicylic acid. Isolate 39 produced xylanase on culture medium with salinity ranging from 1.25 to 5%. Partial 16S rRNA gene sequencing identified isolates in the Bacillus and Paenibacillus genera. The results of this study highlight the importance of mangroves as an enzyme source and show that bacterial groups can be used for starch and hemicellulose degradation.

Optimization of fermentation media and growth conditions for microbial xylanase production

Efficiency of cellulase-free xylanases is one of the determining factors in paper and pulp industries. Use of microbes which can produce cellulase-free xylanases may help to overcome the current challenges in kraft pulp processing. Isolation and screening of microorganisms from local samples offers a possibility for obtaining the potential microbes for this purpose. This research was therefore aimed to collect, screen, characterize and identify potential cellulase-free xylanase producers. A total of 313 microbial isolates were collected while using selective media (EBAM and XAM) to determine the xylanolytic potential of microbes. Qualitative and quantitative analyses were performed and finally 11 bacterial and 6 fungal strains were selected for characterization and identification. The potential isolates were identified as Bacillus pumilus (388.82 U/mg), Bacillus safensis (385.26 U/mg), Aspergillus flavus (493.33 U/mg) and Aspergillus niger (419.33 U/mg). Optimization of the microbial strains while using agro-industrial waste is suggested.