Induction of xylanase and β-xylosidase in Cellulomonas flavigena growing on different carbon sources

Divergent microbial communities in groundwater and overlying soils exhibit functional redundancy for plant-polysaccharide degradation

Light driven primary production by plants is the main source of biomass in terrestrial ecosystems. But also in subsurface habitats like aquifers, life is fueled largely by this plant-derived biomass. Here, we investigate the degradation of plant-derived polysaccharides in a groundwater microbiome to identify the microbial key players involved, and compare them to those from soil of the groundwater recharge area. We quantified the activities of enzymes degrading the abundant plant polymers starch, cellulose and hemicellulose in oligotrophic groundwater samples, despite the low cell numbers present. Normalized to 16S rRNA gene copy numbers, these activities were only one order of magnitude lower than in soil. Stimulation of the groundwater microbiome with either starch or cellulose and hemicellulose led to changes of the enzymatic activity ratios, indicating autochthonous production of enzymes in response to the plant polymers. Furthermore, DNA stable isotope probing with 13C labelled plant polymers allowed us to identify microbes involved in the degradation of these compounds. In (hemi)cellulose microcosms, Bacteroidia and Candidatus Parcubacteria were active, while the active community in starch microcosms mostly comprised Candidatus Saccharibacteria, Cytophagia, and Actinobacteria. Not a single one of the active OTUs was also found to be labelled in soil microcosms. This indicates that the degradation of plant-derived polysaccharides in groundwater is driven by organisms completely distinct from those active in soil. The involvement of members of the candidate phyla Cand. Parcubacteria and Cand. Saccharibacteria, organisms known to be abundant in groundwater, in plant-derived organic matter degradation might strongly impact subsurface carbon cycling.

Lactic Acid Fermentation of Arabinoxylan From Nejayote by Streptococcus infantarius ssp. infantarius 25124 Isolated From Pozol

Streptococcus infantarius ssp. infantarius 25124 (Sii-25124) is a lactic acid bacterium (LAB) isolated from pozol, a refreshing beverage prepared by suspending fermented nixtamal (a thermal and alkali-treated maize dough) in water. Although Lactobacillus are the predominant strains in fermented doughs, such as sourdoughs, and non-nixtamalized fermented maize foods, the pozol microbiota is markedly different. This may be the result of the nixtamalization process, which could act as a selective force of some strains. Sii-25124 has been reported as the main amylolytic LAB in pozol; starch is the primary carbon source on nixtamal since monosaccharides and disaccharides are lost during nixtamalization; however, non-amylolytic LAB counts are higher than amylolytic LAB in pozol after 24-h fermentation suggesting that another carbon source is being used by the former bacteria. Hemicellulose (arabinoxylan in maize) becomes available via nixtamalization and is subsequently metabolized by LAB. The aim of this work was to determine whether this bacterium is able to use arabinoxylan as the only carbon source in a defined medium containing arabinoxylan extracted from either nejayote (wash water produced during nixtamal preparation), or beechwood xylan. Xylanase activity in the presence of nejayote arabinoxylan (135.8 ± 48.7 IU/mg protein) was higher than that of beechwood (62.5 ± 19.8 IU/mg protein). Other enzymatic activities, such as arabinofuranosidase and acetyl esterase, were also detected, suggesting the adaptation of the bacterium studied to nixtamal dough. It was concluded that Streptococcus infantarius 25124 isolated from pozol was able to use arabinoxylans, which are present in nixtamal dough, so fermentation does not depend exclusively on free sugars and starch.

Use of organic waste for the production of added-value holocellulases with Cellulomonas flavigena PR-22 and Trichoderma reesei MCG 80

We evaluated the production of holocellulases from the cellulolytic microorganisms Cellulomonas flavigena PR-22 and Trichoderma reesei MCG 80 using as substrates the organic fraction of municipal solid waste (OFMSW) and digestates from a hydrogenogenic-methanogenic bioenergy production process. The first set of experiments (E1) used the mutant actinobacteria C. flavigena PR-22 whereas another set (E2) used the mutant filamentous fungi T. reesei MCG 80. In E1 with OFMSW as substrate, xylanolytic activities ranged from 1800 to 3900 international units g(holocellulose)(-1) (IU g(hol)(-1)), whereas the cellulolytic activities ranged from 220 to 420 IU g(hol)(-1). The variation of agitation speed did not have a significant effect on enzyme activity, whereas the increase of substrate concentration had a significant negative effect on both xylanolytic and cellulolytic activities on a holocellulose feed basis. Regarding E2, the OFMSW was evaluated at 1, 2 and 3 % volatile solids (VS). At 2 % VS the best filter paper activities were 1200 filter paper units (FPU) l(-1); however, in a holocellulase basis the best result was 67 FPU g(hol)(-1), corresponding to 1 % VS. Next, OFMSW was compared with OFMSW supplemented with lactose, digested solids from hydrogenogenic fermentation (D1) and digested solids from a two-stage process (D2). Against expectations, no positive effect was found in OFMSW due to lactose. The best enzymatic titres were in the order D1 > OFMSW ≈ OFMSW + lactose > D2. The use of digestates from hydrogenogenic fermentation for enzyme production holds promise for waste management. It promotes energy and added-value bioproduct generation-a green alternative to common practice of management and disposal of organic wastes.

Cellulases of mesophilic microorganisms: cellulosome and noncellulosome producers

The cellulolytic activity of mesophilic bacteria and fungi is described, with special emphasis on the large extracellular enzyme complex called the cellulosome. The cellulosome is composed of a scaffolding protein, which is attached to various cellulolytic and hemicellulolytic enzymes, and this complex allows the organisms to degrade plant cell walls very efficently. The enzymes include a variety of cellulases, hemicellulases, and pectinases that work synergistically to degrade complex cell-wall molecules.

Differential expression of cellulases and xylanases by Cellulomonas flavigena grown on different carbon sources

The diversity of cellulases and xylanases secreted by Cellulomonas flavigena cultured on sugar cane bagasse, Solka-floc, xylan, or glucose was explored by two-dimensional gel electrophoresis. C. flavigena produced the largest variety of cellulases and xylanases on sugar cane bagasse. Multiple extracellular proteins were expressed with these growth substrates, and a limited set of them coincided in all substrates. Thirteen proteins with carboxymethyl cellulase or xylanase activity were liquid chromatography/mass spectrometry sequenced. Proteins SP4 and SP18 were identified as products of celA and celB genes, respectively, while SP20 and SP33 were isoforms of the bifunctional cellulase/xylanase Cxo recently sequenced and characterized in C. flavigena. The rest of the detected proteins were unknown enzymes with either carboxymethyl cellulase or xylanase activities. All proteins aligned with glycosyl hydrolases listed in National Center for Biotechnology Information database, mainly with cellulase and xylanase enzymes. One of these unknown enzymes, protein SP6, was cross-induced by sugar cane bagasse, Solka-floc, and xylan. The differences in the expression maps of the presently induced cultures revealed that C. flavigena produces and secretes multiple enzymes to use a wide range of lignocellulosic substrates as carbon sources. The expression of these proteins depends on the nature of the cellulosic substrate.

Purification and characterization of two sugarcane bagasse-absorbable thermophilic xylanases from the mesophilic Cellulomonas flavigena

We report the purification and characterization of two thermophilic xylanases from the mesophilic bacteria Cellulomonas flavigena grown on sugarcane bagasse (SCB) as the only carbon source. Extracellular xylanase activity produced by C. flavigena was found both free in the culture supernatant and associated with residual SCB. To identify some of the molecules responsible for the xylanase activity in the substrate-bound fraction, residual SCB was treated with 3 M guanidine hydrochloride and then with 6 M urea. Further analysis of the eluted material led to the identification of two xylanases Xyl36 (36 kDa) and Xyl53 (53 kDa). The pI for Xyl36 was 5.0, while the pI for Xyl53 was 4.5. Xyl36 had a Km value of 1.95 mg/ml, while Xyl53 had a Km value of 0.78 mg/ml. In addition to SCB, Xyl36 and Xyl53 were also able to bind to insoluble oat spelt xylan and Avicel, as shown by substrate-binding assays. Xyl36 and Xyl53 showed optimal activity at pH 6.5, and at optimal temperature 65 and 55 degrees C, respectively. Xyl36 and Xyl53 retained 24 and 35%, respectively, of their original activity after 8 h of incubation at their optimal temperature. As far as we know, this is the first study on the thermostability properties of purified xylanases from microorganisms belonging to the genus Cellulomonas.

Induction of xylanases by sugar cane bagasse at different cell densities of Cellulomonas flavigena

The effect of cell density on xylanolytic activity and productivity of Cellulomonas flavigena was evaluated under two different culturing conditions: fed-batch culture with discontinuous feed of sugar cane bagasse (SCB; condition 1) and glycerol fed-batch culture followed by addition of SBC as xylanases inducer (condition 2). The enzymatic profile of xylanases was similar in both systems, regardless of the initial cell density at time of induction. However, the xylanolytic activity changed with initial cell density at the time of induction (condition 2). The maximum volumetric xylanase activity increased with increased initial cell density from 4 to 34 g l(-1) but decreased above this value. The largest total volumetric xylanase productivity under condition 2 (1.3 IU ml(-1) h(-1)) was significantly greater compared to condition 1 (maximum 0.6 IU ml(-1) h(-1)). Consequently, induction of xylanase activity by SCB after growing of C. flavigena on glycerol at intermediate cell density can be a feasible alternative to improve activity and productivity of xylanolytic enzymes.

Use of xylan-rich cost effective agro-residues in the production of xylanase by Streptomyces cyaneus SN32

AIM

The present study aimed at optimization of cultural and nutritional parameters for enhanced production of xylanase from Streptomyces cyaneus SN32.

METHODS AND RESULTS

The xylanase production by S. cyaneus SN32 on most of the agro-residues tested in this study was more, as compared with the xylanase yield in the medium supplemented with commercial xylan. The presence of wheat bran as carbon source in the medium induced the highest production of xylanase followed by corn cob. Utilization of maize stalk, gram husk and black gram husk for microbial xylanase production has been reported first time in the present study. Among all the organic and inorganic sources of nitrogen tested in the study, peptone was found to be the best in stimulating xylanase production by S. cyaneus SN32.

CONCLUSION

The production of xylanase from this thermoalkalophilic actinomycete has been enhanced 1.44-fold. To the best of our knowledge, the magnitude of enzyme yield i.e. 720 IU ml(-1) by S. cyaneus SN32 has not been reported for any other actinomycete so far.

SIGNIFICANCE AND IMPACT OF STUDY

Present studies revealed that thermoalkalophilic S. cyaneus SN32, because of its simple nutritional requirements and its ability to exhibit considerably good enzyme yield, is a potent xylanase producer for its economical application in various industries.

β-Methyl-xyloside: positive effect on xylanase induction in Cellulomonas flavigena

Synthesis of extracellular xylanase in Cellulomonas flavigena is induced in the presence of xylan and sugarcane bagasse as substrates. The essential factors for efficient production of xylanase are the appropriate medium composition and an inducing substrate. The increase in xylanase production levels in C. flavigena were tested with a number of carbon sources and different culture conditions. Xylose, arabinose, glycerol and glucose did not induce xylanase production in this microorganism. beta-Methyl-xyloside (beta-mx), a structural analog of xylobiose, also did not induce xylanase when used as the sole carbon source, but when xylan or sugar cane bagasse was supplemented with beta-mx, extracellular xylanase production increased by 25 or 46%, respectively. The response of C. flavigena to xylan plus beta-mx was accompanied by a significant accumulation of reducing sugar, an effect not observed with the combination sugarcane bagasse plus beta-mx as substrate. To our knowledge, this is the first report on the effect of beta-mx on the induction of xylanase in C. flavigena.

Regulation of cellulases and xylanases from a derepressed mutant of Cellulomonas flavigena growing on sugar-cane bagasse in continuous culture

When the wild type Cellulomonas flavigena was grown on glycerol, xylose or cellobiose, it produced basal levels of carboxymethyl-cellulase (CMCase), filter-paperase (FPase) and xylanase activities. By comparison, a catabolic derepressed mutant strain of the same organism produced markedly higher levels of these enzymes when grown on the same carbon sources. Sugar-cane bagasse induced both the wild type and the mutant strain to produce three- to eight-time higher levels of FPase and xylanase than was observed with xylose or cellobiose. Continuous culture was used to determine the minimal cellobiose or glucose concentrations that repress the enzyme synthesis in both strains. 2.5 g l(-1) glucose repressed FPase and xylanases from wild type, while 1.6 times more glucose was needed to repress the same activities in the PN-120 strain. In the same way, twofold more cellobiose was needed to reduce by 75% the CMCase and xylanase activities in the mutant compared to the wild type. The FPase in the presence of 4 g l(-1) cellobiose did not change in the same strain. Therefore, its derepressed and feedback resistant characters of PN-120 mutant are evident. On the other hand, isoelectrofocused crude extracts of mutant and wild strains induced by sugar-cane bagasse, did not show differences in protein patterns, however, the Schiffs staining was more intense in the PN-120 than in the wild strain. These results point out that the mutational treatment did not apparently change the extracellular proteins from mutant PN-120 and this could affect their regulation sites, since derepressed and feed-back resistant enzymes may be produced.

Molecular and biotechnological aspects of xylanases

Hemicellulolytic microorganisms play a significant role in nature by recycling hemicellulose, one of the main components of plant polysaccharides. Xylanases (EC 3.2.1.8) catalyze the hydrolysis of xylan, the major constituent of hemicellulose. The use of these enzymes could greatly improve the overall economics of processing lignocellulosic materials for the generation of liquid fuels and chemicals. Recently cellulase-free xylanases have received great attention in the development of environmentally friendly technologies in the paper and pulp industry. In microorganisms that produce xylanases low molecular mass fragments of xylan and their positional isomers play a key role in regulating its biosynthesis. Xylanase and cellulase production appear to be regulated separately, although the pleiotropy of mutations, which causes the elimination of both genes, suggests some linkage in the synthesis of the two enzymes. Xylanases are found in a cornucopia of organisms and the genes encoding them have been cloned in homologous and heterologous hosts with the objectives of overproducing the enzyme and altering its properties to suit commercial applications. Sequence analyses of xylanases have revealed distinct catalytic and cellulose binding domains, with a separate non-catalytic domain that has been reported to confer enhanced thermostability in some xylanases. Analyses of three-dimensional structures and the properties of mutants have revealed the involvement of specific tyrosine and tryptophan residues in the substrate binding site and of glutamate and aspartate residues in the catalytic mechanism. Many lines of evidence suggest that xylanases operate via a double displacement mechanism in which the anomeric configuration is retained, although some of the enzymes catalyze single displacement reactions with inversion of configuration. Based on a dendrogram obtained from amino acid sequence similarities the evolutionary relationship between xylanases is assessed. In addition the properties of xylanases from extremophilic organisms have been evaluated in terms of biotechnological applications.