Mode of action of Bacillus licheniformis pectin methylesterase on highly methylesterified and acetylated pectins

Effect of microbial biostimulants on the antioxidant profile, antioxidant capacity and activity of enzymes influencing the quality level of raspberries (Rubus idaeus L.)

The influence of four microbial biostimulants containing various strains of Bacillus subtilis and/or Paenibacillus sp. on the quality of raspberries cv. Delniwa, Poemat, and Enrosadira cultivated in two consecutive seasons was investigated. The biostimulants influenced the antioxidant level, antioxidant capacity, phenolic acids and flavonoids profiles, enzymatic activity, and the degree of methylation and acetylation of the pectin in the raspberry fruits. The biostimulants had the greatest effect on the antioxidant content (16% - 20% increase) and capacity in the Delniwa raspberry fruits from the first season. A positive correlation was found between the activity of the β-galactosidase enzyme and ferric reducing power. In the second season, a decrease in the activity of pectin esterase and α-L-arabinofuranosidase and an increase in the degree of methylation of pectin were noted. Our results suggest that the changes in raspberry quality were related to the type of biostimulant applied.

Production, statistical optimization, and functional characterization of alkali stable pectate lyase of Paenibacillus lactis PKC5 for use in juice clarification

Pectate lyase is a hydrolytic enzyme used by diverse industries to clarify food. The enzyme occupies a 25% share of the total enzyme used in food industries, and their demand is increasing gradually. Most of the enzymes in the market belong to the fungal origin and take more time to produce with high viscosity in the fermentation medium, limiting its use. The bacteria belonging to the genus Bacillus have vast potential to produce diverse metabolites of industrial importance. The present experiment aimed to isolate pectate lyase-producing bacteria that can tolerate an alkaline environment at moderate temperatures. Bacillus subtilis PKC2, Bacillus licheniformis PKC4, Paenibacillus lactis PKC5, and Bacillus sonorensis ADCN produced pectate lyase. The Paenibacillus lactis PKC5 gave the highest protein at 48 h of incubation that was partially purified using 80% acetone and ammonium sulphate. Purification with 80% acetone resulted in a good enzyme yield with higher activity. SDS-PAGE revealed the presence of 44 kDa molecular weight of purified enzyme. The purified enzyme exhibits stability at diverse temperature and pH ranges, the maximum at 50 °C and 8.0 pH. The metal ions such as Mg2+, Zn2+, Fe2+, and Co2+ significantly positively affect enzyme activity, while increasing the metal ion concentration to 5 mM showed detrimental effects on the enzyme activity. The organic solvents such as methanol and chloroform at 25% final concentration improved the enzyme activity. On the other hand, detergent showed inhibitory effects at 0.05% and 1% concentration. Pectate lyase from Paenibacillus lactis PKC5 had Km and Vmax values as 8.90 mg/ml and 4.578 μmol/ml/min. The Plackett–Burman and CCD designs were used to identify the significant process parameters, and optimum concentrations were found to be pectin (5 gm%) and ammonium sulphate (0.3 gm%). During incubation with pectate lyase, the clarity percentage of the grape juice, apple juice, and orange juice was 60.37%, 59.36%, and 49.91%, respectively.

Homogalacturonan and xylogalacturonan region specificity of self-cloning vector-expressed pectin methylesterases (AoPME1-3) in Aspergillus oryzae

Aspergillus oryzae is a safe microorganism that is commonly used in food production. We constructed a self-cloning vector capable of high expression in A. oryzae. Using the vector, three putative pectin methylesterase (PME) genes belonging to Carbohydrate Esterase family 8 derived from A. oryzae were expressed, and several characteristics of the gene products were examined. The effects of temperature and pH on the three enzymes (AoPME1, 2, and 3) were similar, with optimal reaction temperatures of 50 - 60 °C and optimal reaction pH range of 5 - 6. The specific activities of AoPME1, 2, and 3 for apple pectin were significantly different (34, 7,601, and 2 U/mg, respectively). When the substrate specificity was examined, AoPME1 showed high activity towards pectin derived from soybean and pea. Although AoPME2 showed little activity towards these pectins, it showed very high activity towards apple- and citrus-derived pectins. AoPME3 showed low specific activity towards all substrates tested. Sugar composition analysis revealed that apple- and citrus-derived pectins were rich in homogalacturonan, while soybean- and pea-derived pectins were rich in xylogalacturonan. When pea pectin was treated with endo-polygalacturonase or endo-xylogalacturonase in the presence of each PME, specific synergistic actions were observed (endo-polygalacturonase with AoPME1 or AoPME2 and endo-xylogalacturonase with AoPME1 or AoPME3). Thus, AoPME1 and AoPME3 hydrolyzed the methoxy group in xylogalacturonan. This is the first report of this activity in microbial enzymes. Our findings on the substrate specificity of PMEs should lead to the determination of the distribution of methoxy groups in pectin and the development of new applications in the field of food manufacturing.

Critical Factors for Optimum Biodegradation of Bast Fiber’s Gums in Bacterial Retting

Bast fiber plants require a post-harvest process to yield useable natural cellulosic fibers, denoted as retting or degumming. It encompasses the degradation of the cell wall’s non-cellulosic gummy substances (NCGs), facilitating fibers separations, setting the fiber’s quality, and determining downstream usages. Due to the inconvenience of traditional retting practices, bacterial inoculum and enzyme applications for retting gained attention. Therefore, concurrent changes of agroclimatic and socioeconomic conditions, the conventional water retting confront multiple difficulties, bast industries become vulnerable, and bacterial agents mediated augmented bio-retting processes trying to adapt to sustainability. However, this process’s success demands a delicate balance among substrates and retting-related biotic and abiotic factors. These critical factors were coupled to degrade bast fibers NCGs in bacterial retting while holistically disregarded in basic research. In this study, a set of factors were defined that critically regulates the process and requires to be comprehended to achieve optimum retting without failure. This review presents the bacterial strain characteristics, enzyme potentials, specific bast plant cell wall’s structure, compositions, solvents, and interactions relating to the maximum NCGs removal. Among plants, associated factors pectin is the primary biding material that determines the process’s dynamics, while its degree of esterification has a proficient effect through bacterial enzymatic degradation. The accomplished bast plant cell wall’s structure, macerating solvents pH, and temperature greatly influence the bacterial retting process. This article also highlights the remediation process of water retting pollution in a biocompatible manner concerning the bast fiber industry’s endurance.

New insights into the specificity and processivity of two novel pectinases from Verticillium dahliae

Pectin, the major non-cellulosic component of primary cell wall can be degraded by polygalacturonases (PGs) and pectin methylesterases (PMEs) during pathogen attack on plants. We characterized two novel enzymes, VdPG2 and VdPME1, from the fungal plant pathogen Verticillium dahliae. VdPME1 was most active on citrus methylesterified pectin (55-70%) at pH 6 and a temperature of 40 °C, while VdPG2 was most active on polygalacturonic acid at pH 5 and a temperature of 50 °C. Using LC-MS/MS oligoprofiling, and various pectins, the mode of action of VdPME1 and VdPG2 were determined. VdPME1 was shown to be processive, in accordance with the electrostatic potential of the enzyme. VdPG2 was identified as endo-PG releasing both methylesterified and non-methylesterified oligogalacturonides (OGs). Additionally, when flax roots were used as substrate, acetylated OGs were detected. The comparisons of OGs released from Verticillium-susceptible and partially resistant flax cultivars identified new possible elicitor of plant defence responses.

Characterization of an acidic pectin methylesterase from Paenibacillus xylanexedens and its application in fruit processing

A pectinase-producing bacterial isolate, identified as Paenibacillus xylanexedens SZ 29, was screened by using the soil dilution plate with citrus pectin and congo red. A pectin methylesterase gene (Pxpme) was cloned and expressed in Escherichia coli. The gene coded for a protein with 334 amino acids and a calculated molecular mass of 36.76 kDa. PxPME showed the highest identity of 32.4% with the characterized carbohydrate esterase family 8 pectin methylesterase from Daucus carota. The recombined PxPME showed a specific activity with 39.38 U/mg against citrus pectin with >65% methylesterification. The optimal pH and temperature for PxPME activity were 5.0 and 45 °C. Its K_m and V_max value were determined to be 1.43 mg/mL and 71.5 μmol/mg·min, respectively. Moreover, PxPME could increase the firmness of pineapple cubes by 114% when combined with CaCl₂. The acidic and mesophilic properties make PxPME a potential candidate for application in the fruit processing.

Large-scale cultivation of the bumblebee gut microbiota reveals an underestimated bacterial species diversity capable of pathogen inhibition

A total of 1940 isolates from gut samples of 60 bumblebees representing Bombus pascuorum, Bombus terrestris, Bombus lucorum and Bombus lapidarius was collected and identified through state-of the-art taxonomic methods. The bacterial species diversity in these Bombus species exceeded that suggested by phylotype analysis through 16S rRNA amplicon sequencing, and revealed that B. pascuorum and B. terrestris had a unique microbiota composition, each. Representatives of most phylotypes reported earlier and detected in the present study were effectively isolated, and included several novel bacterial taxa and species reported for the first time in the bumblebee gut. Isolates were screened in pectin degradation assays and growth inhibition assays against the honeybee pathogens Paenibacillus larvae, Melissococcus plutonius and Ascosphaera apis and the bumblebee parasite Crithidia bombi. While inhibitory activity against each of these pathogens was observed, only one single culture was able to degrade pectin and polygalacturonic acid in vitro. The availability of accurately identified microbial isolates will facilitate future evaluation of the functional potential of the bumblebee gut microbiota.

Reassessment of chitosanase substrate specificities and classification

Chitosanases can be used to produce partially acetylated chitosan oligosaccharides (paCOS) for different applications, provided they are thoroughly characterized. However, recent studies indicate that the established classification system for chitosanases is too simplistic. Here, we apply a highly sensitive method for quantitatively sequencing paCOS to reassess the substrate specificities of the best-characterized class I–III chitosanases. The enzymes’ abilities to cleave bonds at GlcNAc residues positioned at subsite (−1) or (+1), on which the classification system is based, vary especially when the substrates have different fractions of acetylation (F_A). Conflicts with the recent classification are observed at higher F_A, which were not investigated in prior specificity determinations. Initial analyses of pectin-degrading enzymes reveal that classifications of other polysaccharide-degrading enzymes should also be critically reassessed. Based on our results, we tentatively suggest a chitosanase classification system which is based on specificities and preferences of subsites (−2) to (+2).

Chitosanases are classified according to their specificity in cleaving bonds at GlcNAc residues but the current system may be too simplistic. Here, the authors use quantitative mass spectrometry to revisit chitosanase specificity and propose additional determinants for their classification.