Identification and characterization of an Endo-glucanase secreted from cellulolytic Escherichia coli ZH-4

Impact of a random TN5 mutation on endoglucanase secretion in ruminal cellulolytic Escherichia coli

OBJECTIVE

Most protein secretion systems are found in gram-negative bacteria, but the mechanism of endoglucanase (BcsZ) secretion in Escherichia coli (E. coli) remains unclear.

METHODS

In this study, we used JBZ-DH5α (which overexpresses BcsZ on the E. coli DH5α genome) as the initial strain. A mutant library was created by randomly inserting the TN5 transposon into the genome, and mutants with reduced transparent circles were identified on Congo red plates. The insertion sites of transposons in the genome were determined through whole-genome sequencing.

RESULTS

The results revealed that the genes rnc, lon, and suhB, which encode RNC-ribonuclease III (RNC), LON-protease (LON), and SuhB-inositol phosphatase (SuhB), respectively, were disrupted. BcsZ secretion decreased in E. coli DH5α when the lon, rnc, or suhB genes were deleted, but the overexpression of these genes restored their secretion levels.

CONCLUSION

These findings suggest that the lon, rnc, and suhB genes play a role in BcsZ secretion in E. coli, potentially enhancing our knowledge of BcsZ secretion and offering a strategy to increase protein secretion in E. coli as a cell factory.

Thermothelomyces thermophilus exo- and endo-glucanases as tools for pathogenic E. coli biofilm degradation

The escalating prevalence of drug-resistant pathogens not only jeopardizes the effectiveness of existing treatments but also increases the complexity and severity of infectious diseases. Escherichia coli is one the most common pathogens across all healthcare-associated infections. Enzymatic treatment of bacterial biofilms, targeting extracellular polymeric substances (EPS), can be used for EPS degradation and consequent increase in susceptibility of pathogenic bacteria to antibiotics. Here, we characterized three recombinant cellulases from Thermothelomyces thermophilus: a cellobiohydrolase I (TthCel7A), an endoglucanase (TthCel7B), and a cellobiohydrolase II (TthCel6A) as tools for hydrolysis of E. coli and Gluconacetobacter hansenii biofilms. Using a design mixture approach, we optimized the composition of cellulases, enhancing their synergistic activity to degrade the biofilms and significantly reducing the enzymatic dosage. In line with the crystalline and ordered structure of bacterial cellulose, the mixture of exo-glucanases (0.5 TthCel7A:0.5 TthCel6A) is effective in the hydrolysis of G. hansenii biofilm. Meanwhile, a mixture of exo- and endo-glucanases is required for the eradication of E. coli 042 and clinical E. coli biofilms with significantly different proportions of the enzymes (0.56 TthCel7B:0.44 TthCel6A and 0.6 TthCel7A:0.4 TthCel7B, respectively). X-ray diffraction pattern and crystallinity index of E. coli cellulose are comparable to those of carboxymethyl cellulose (CMC) substrate. Our results illustrate the complexity of E. coli biofilms and show that successful hydrolysis is achieved by a specific combination of cellulases, with consistent recurrence of TthCel7B endoglucanase.

Bacterial cellulase production via co-fermentation of paddy straw and Litchi waste and its stability assessment in the presence of ZnMg mixed-phase hydroxide-based nanocomposite derived from Litchi chinensis seeds

Co-fermentation via co-cultured bacterial microorganisms to develop enzymes in solid-state fermentation (SSF) is a promising approach. This strategy is imperative in a series of sustainable and effective approaches due to superior microbial growth and the use of a combination of inexpensive feedstocks for enzyme production wherein mutually participating enzyme-producing microbial communities are employed. Moreover, the addition of nanomaterials to this technique may aid in its prominent advantage of enhancing enzyme production. This strategy may be able to decrease the overall cost of the bioprocessing to produce enzymes by further implementing biogenic, route-derived nanomaterials as catalysts.Therefore, the present study attempts to explore endoglucanase (EG) production using a bacterial coculture system by employing two different bacterial strains, namely, Bacillus subtillius and Seretia marchansea under SSF in the presence of a ZnMg hydroxide-based nanocompositeas a nanocatalyst. The nanocatalyst based on ZnMg hydroxide has been prepared via green synthesis using Litchi waste seed, while SSF for EG production has been conducted using cofermentation of litchi seed (Ls) and paddy straw (Ps) waste. Under an optimized substrate concentration ratio of 5:6 Ps:Ls and in the presence of 2.0 mg of nanocatalyst, the cocultured bacterial system produced 1.6 IU/mL of EG enzyme, which was ~1.33 fold higher as compared to the control. Additionally, the same enzyme showed its stability for 135 min in the presence of 1.0 mg of nanocatalyst at 38 °C. The nanocatalyst has been synthesized using the green method, wherein waste litchi seed is used as a reducing agent, and the nanocatalyst could be employed to improve the production and functional stability of crude enzymes. The findings of the present study may have significant application in lignocellulosic-based biorefinaries and cellulosic waste management.

Identification and characterization of a novel endo-β-1,4-glucanase from a soil metagenomic library

A cosmid clone cZFYN1413 with CMCase activity was identified from a soil metagenomic library. The sequence analysis of a subclone of cZFYN1413 revealed an endo-β-1,4-glucanase gene ZFYN1413 belonging to glycoside hydrolase family 6 and a transmembrane region in the N-terminal of ZFYN1413. Expression of ZFYN1413 in Escherichia coli BL21 (DE3) resulted in ZFYN1413-87, which was a truncated protein cleaved in transmembrane region of ZFYN1413. ZFYN1413-87 was expressed and its enzyme properties were studied. ZFYN1413-87 possessed strong endo-β-1,4-glucanase activity, and 52% of the activity could be retained after the protein was treated in buffer of pH 3.0 for 2 h. The study provided a special example of endo-β-1,4-glucanase in GH6 family.

Systematic Analysis of Escherichia coli Isolates from Sheep and Cattle Suggests Adaption to the Rumen Niche

The commonly used laboratory bacterium Escherichia coli normally does not produce and secrete cellulases due to its complex bilayer membrane structure and poor secretory apparatus. In our previous study, the cellulolytic E. coli strain ZH-4 with extracellular cellulase activity was found in the bovine rumen. In this study, we demonstrate that the secretion of cellulase is a common feature of E. coli isolates from the rumen of animals such as sheep and cattle. Physiological phenotype characterization of these E. coli isolates, together with genome, transcriptome, and comparative genomics analysis, suggests their adaption to the rumen niche. The higher growth rate of the isolated strains under aerobic conditions meets the competitive requirements of the strains in rumen microecosystem, while anaerobic accumulation of reduced H₂ and succinate is hypothesized to be the results of adaptation to the rumen environment. Cellulase secretion increased significantly when the molecular chaperone genes ibpA and ibpB were overexpressed. This was also revealed by the transcriptomic data. A possible mechanism for cellulase secretion by E. coli isolates was proposed based on the transcriptomic data and molecular experiments.IMPORTANCE As an important intestinal microorganism, E. coli is present in the intestinal tract of animals and in many other environments. However, it normally does not produce and secret cellulases due to its complex bilayer membrane structure and poor secretory apparatus. Here, we proved that E. coli is widely present in the rumen of sheep and cattle. Systematic analysis of the isolates indicated that they have adapted to the rumen niche, with phenotypes that include secretion of cellulase and fermentative accumulation of succinate and H₂ The finding that overexpression of small heat shock protein genes ibpA and ibpB could facilitate cellulase BcsZ secretion, which provides a possible insight into the protein secretion mechanism of rumen-colonizing E. coli.

Succession of Gut Microbial Structure in Twin Giant Pandas During the Dietary Change Stage and Its Role in Polysaccharide Metabolism

Adaptation to a bamboo diet is an essential process for giant panda growth, and gut microbes play an important role in the digestion of the polysaccharides in bamboo. The dietary transition in giant panda cubs is particularly complex, but it is an ideal period in which to study the effects of gut microbes on polysaccharide use because their main food changes from milk to bamboo (together with some bamboo shoot and coarse pastry). Here, we used 16S rDNA and internal transcribed spacer 1 (ITS1) DNA sequencing and metagenomic sequencing analysis to investigate the succession of the gut microbial structure in feces sampled from twin giant panda cubs during the completely dietary transition and determine the abundances of polysaccharide-metabolizing genes and their corresponding microbes to better understand the degradation of bamboo polysaccharides. Successive changes in the gut microbial diversity and structure were apparent in the growth of pandas during dietary shift process. Microbial diversity increased after the introduction of supplementary foods and then varied in a complex way for 1.5–2 years as bamboo and complex food components were introduced. They then stabilized after 2 years, when the cubs consumed a specialized bamboo diet. The microbes had more potential to metabolize the cellulose in bamboo than the hemicellulose, providing genes encoding cellulase systems corresponding to glycoside hydrolases (GHs; such as GH1, GH3, GH5, GH8, GH9, GH74, and GH94). The cellulose-metabolizing species (or genes) of gut bacteria was more abundant than that of gut fungi. Although cellulose-metabolizing species did not predominate in the gut bacterial community, microbial interactions allowed the giant pandas to achieve the necessary dietary shift and ultimately adapt to a bamboo diet.