Cadmium biosorption and mechanism investigation using two cadmium-tolerant microorganisms isolated from rhizosphere soil of rice.

Microbial remediation of cadmium-contaminated soil offers advantages like environmental friendliness, cost-effectiveness, and simple operation. However, the efficacy of this remediation process relies on obtaining dominant strains and a comprehensive understanding of their Cd adsorption mechanisms. This study identified two Cd-resistant bacteria, Burkholderia sp. 1-22 and Bacillus sp. 6-6, with significant growth-promoting effects from rice rhizosphere soil. The strains showed remarkable Cd resistance up to ∼200 mg/L and alleviated Cd toxicity by regulating pH and facilitating bacterial adsorption of Cd. FTIR analysis showed crucial surface functional groups, like carboxyl and amino groups, on bacteria played significant roles in Cd adsorption. The strains could induce CdCO3 formation via a microbially induced calcium precipitation (MICP) mechanism, confirmed by SEM-EDS, X-ray analysis, and elemental mapping. Pot experiments showed these strains significantly increased organic matter and enzyme activity (e.g., urease, sucrase, peroxidase) in the rhizosphere soil versus the control group. These changes are crucial for restricting Cd mobility. Furthermore, strains 6-6 and 1-22 significantly enhance plant root detoxification of Cd, alleviating toxicity. Notably, increased pH likely plays a vital role in enhancing Cd precipitation and adsorption by strains, converting free Cd into non-bioavailable forms.

Structural and enzymatic characterization of a novel metallo-serine keratinase KerJY-23.

KerJY-23 was a novel keratinase from feather-degrading Ectobacillus sp. JY-23, but its enzymatic characterization and structure are still unclear. In this study, the KerJY-23 was obtained by heterologous expression in Escherichia coli BL21(DE3), and enzymatic properties indicated that KerJY-23 was optimal at 60 °C and pH 9.0 and could be promoted by divalent metal ions or reducing agents. Furthermore, KerJY-23 had a broad substrate specificity towards casein, soluble keratin, and expanded feather powder, but its in vitro degradation against chicken feathers required an additional reducing agent. Homology modeling indicated that KerJY-23 contained a highly conserved zinc-binding HELTH motif and a His-Asp-Ser catalytic triad that belonged to the typical characteristics of M4-family metallo-keratinase and serine-keratinase, respectively. Molecular docking revealed that KerJY-23 achieved a reinforced binding on feather keratin via abundant hydrogen bonding interactions. This work not only deepened understanding of the novel and interesting metallo-serine keratinase KerJY-23, but also provided a theoretical basis for realizing the efficient use of waste feather keratin.

Characterization and Antioxidant Activity of the Polysaccharide Hydrolysate from Lactobacillus plantarum LPC-1 and Their Effect on Spinach (Spinach oleracea L.) Growth.

This study presents a comparison between two hydrolysis systems (MnO2/H2O2 and ascorbic acid (VC)/H2O2) for the depolymerization of exopolysaccharide (EPS) from Lactobacillus plantarum LPC-1. Response surface methodology (RSM) was used to optimize these two degradation systems, resulting in two H2O2-free degradation products, MEPS (MnO2/H2O2-treated EPS) and VEPS (VC/H2O2-treated EPS), where H2O2 residues in the final products and their antioxidant activity were considered vital points. The relationship between the structural variations of two degraded polysaccharides and their antioxidant activity was characterized. Physicochemical tests showed that H2O2 had a notable impact on determining the total and reducing sugars in the polysaccharides, and both degradation systems efficiently eliminated this effect. After optimization, the average molecular weight of EPS was reduced from 265.75 kDa to 135.41 kDa (MEPS) and 113.11 kDa (VEPS), improving its antioxidant properties. Characterization results showed that the two hydrolysis products had similar major functional groups and monosaccharide composition as EPS. The crystal structure, main chain length, and branched chain number were crucial factors affecting the biological activity of polysaccharides. In pot testing, two degraded polysaccharides improved spinach quality more than EPS due to their lower molecular weights, suggesting the advantages of low-molecular-weight polysaccharides. In summary, these two degradation techniques offer valuable insights for further expanding the utilization of microbial resources.

Effective biodegradation on chicken feather by the recombinant KerJY-23 Bacillus subtilis WB600: A synergistic process coupled by disulfide reductase and keratinase.

Keratin wastes are abundantly available but rich in hard-degrading fibrous proteins, and the keratinase-producing microorganisms have gained significant attention due to their biodegradation ability against keratinous materials. In order to improve the degradation efficiency of feather keratins, the keratinase gene (kerJY-23) from our previously isolated feather-degrading Ectobacillus sp. JY-23 was overexpressed in Bacillus subtilis WB600 strain. The recombinant KerJY-23 strain degraded chicken feathers rapidly within 48 h, during which the activities of disulfide reductase and keratinase KerJY-23 were sharply increased, and the free amino acids especially the essential phenylalanine and tyrosine were significantly accumulated in feather hydrolysate. The results of structural characterizations including scanning electron microscopy, Fourier transform infrared spectrum, X-ray diffraction, and X-ray photoelectron spectroscopy, demonstrated that the feather microstructure together with the polypeptide bonds and SS bonds in feather keratins were attacked and destroyed by the recombinant KerJY-23 strain. Therefore, the recombinant KerJY-23 strain contributed to feather degradation through the synergistic action of the secreted disulfide reductase to break the SS bonds and keratinase (KerJY-23) to hydrolyze the polypeptide bonds in keratins. This study offers a new insight into the underlying mechanism of keratin degradation, and provides a potential recombinant strain for the valorization of keratin wastes.

Preparation of polysaccharide-conjugated selenium nanoparticles from spent mushroom substrates and their growth-promoting effect on rice seedlings.

Selenium nanoparticles (SeNPs) have gained significant attention in the agricultural field due to their favorable bioavailability and low toxicity, making them a highly researched subject. In this study, crude polysaccharides from spent mushroom substrate of Agrocybe aegerita (AaPs) were extracted for preparing the polysaccharide­selenium-nanoparticles (AaPs-SeNPs) by ascorbic acid reduction method. The structure of AaPs-SeNPs was analyzed and their growth-promoting effects on rice seedlings were studied by adopting different application methods. The results revealed that AaPs-SeNPs exhibited improved free radical scavenging ability, with a lower half-maximal inhibitory concentrations compared to AaPs. Rice seedlings treated with AaPs-SeNPs showed significant enhancements in growth characteristics when compared to AaPs treatment, and foliar application exhibited a better growth-promoting effect compared to root application. Moreover, the growth performance and antioxidant enzyme activities of rice seedlings were enhanced by the addition of AaPs-SeNPs, and the absorption efficiency of essential nutrients such as N/P/K and Fe/Zn/Mn was also improved at appropriate concentrations, which could be one of the key factors contributing to the improved growth performance of plants. This study provides new aspects for the utilization of SMS, and also offers new insights from the perspective of nutrient absorption on how polysaccharide-conjugated selenium nanoparticles enhance crop growth.

Isolation of a novel feather-degrading Ectobacillus sp. JY-23 strain and characterization of a new keratinase in the M4 metalloprotease family.

Microbial keratinases have prominent potential in biotransformation of recalcitrant keratin substrates to value-added products which has made keratinases a research focus in the past decades. In this study, an efficient feather-degrading bacterium was isolated and identified as a novel species in Ectobacillus genus and designated as Ectobacillus sp. JY-23. The degradation characteristics analysis revealed that Ectobacillus sp. JY-23 could utilize chicken feathers (0.4% w/v) as the sole nutrient source and degraded 92.95% of feathers in 72 h. A significant increase in sulfite and free sulfydryl group content detected in the feather hydrolysate (culture supernatant) indicated efficient reduction of disulfide bonds, which inferred that the degradation mechanism of isolated strain was a synergetic action of sulfitolysis and proteolysis. Moreover, abundant amino acids were also detected, among which proline and glycine were the predominant free amino acids. Then, the keratinase of Ectobacillus sp. JY-23 was mined and Y1_15990 was identified as the keratinase encoding gene of Ectobacillus sp. JY-23 and designated as kerJY-23. Escherichia coli strain overexpressing kerJY-23 degraded chicken feathers in 48 h. Finally, bioinformatics prediction of KerJY-23 demonstrated that it belonged to the M4 metalloprotease family, which was a third keratinase member in this family. KerJY-23 showed low sequence identity to the other two keratinase members, indicating the novelty of KerJY-23. Overall, this study presents a novel feather-degrading bacterium and a new keratinase in the M4 metalloprotease family with remarkable potential in feather keratin valorization.

A marine lipopeptides-producing Bacillus amyloliquefaciens HY2-1 with a broad-spectrum antifungal and antibacterial activity and its fermentation kinetics study.

The antagonistic Bacillus amyloliquefaciens HY2-1 was a marine microbiology that was isolated previously from the seabed silt of Beibu Gulf in China by dual culture with Penicillium digitatum. As a continuous study, the present work focused on evaluating the antimicrobial activity, identifying the produced active components, and revealing the fermentation characteristics of B. amyloliquefaciens HY2-1, respectively. It was found that B. amyloliquefaciens HY2-1 exhibited a broad-spectrum antimicrobial activity against the tested seven phytopathogenic fungi and five pathogenic bacteria by producing Bacillus lipopeptides such as fengycin A (C14 to C19 homologues) and surfactin (C14 and C15 homologues). Morphological observation of P. digitatum under light microscope, scanning electron microscopy, transmission electron microscopy, and fluorescence microscope inferred that B. amyloliquefaciens exerted the antagonistic activity by damaging the fungal cell membrane, thus inhibiting the mycelium growth and sporification of phytopathogenic fungi. As a marine microbiology, our results showed that B. amyloliquefaciens could survive and metabolize even at the culture condition with 110 g/L of NaCl concentration, and the produced antimicrobial compounds exhibited excellent thermostability and acid-alkali tolerance. The dynamic models were further constructed to theoretically analyze the fermentation process of B. amyloliquefaciens HY2-1, suggesting that the synthesis of antimicrobial compounds was coupled with both cell growth and cell biomass. In conclusion, the marine lipopeptides-producing B. amyloliquefaciens HY2-1 showed a promising prospect to be explored as a biocontrol agent for plant disease control of crops and postharvest preservation of fruits and vegetables, especially due to its outstanding stress resistance and the broad-spectrum and effective antagonist on various phytopathogenic fungi.

Overexpression of chaperones GroEL/ES from Escherichia coli enhances indigo biotransformation production of cytochrome P450 BM3 mutant.

The self-sufficient cytochrome P450 BM3 mutant (A74G/F87V/D168H/L188Q) can serve as a biocatalyst for whole-cell catalysis process of indigo. Nevertheless, the bioconversion yield of indigo is generally low under normal cultivation conditions (37 °C, 250 rpm). In this study, a recombinant E. coli BL21(DE3) strain was constructed to co-express the P450 BM3 mutant gene and GroEL/ES genes to investigate whether GroEL/ES can promote the indigo bioconversion yield in E. coli. The results revealed that the GroEL/ES system could significantly increase the indigo bioconversion yield, and the indigo bioconversion yield of the strain co-expressing P450 BM3 mutant and GroEL/ES was about 21-fold that of the strain only expressing the P450 BM3 mutant. In addition, the P450 BM3 enzyme content and in vitro indigo bioconversion yield were determined to explore the underlying mechanism for the improvement of indigo bioconversion yield. The results revealed that GroEL/ES did not increase indigo bioconversion yield by increasing the content of P450 BM3 enzyme and its enzymatic transformation efficiency. Moreover, GroEL/ES could improve the intracellular nicotinamide adenine dinucleotide phosphate (NADPH)/NADP+ ratio. Given that NADPH is an important coenzyme in the catalytic process of indigo, the underlying mechanism for the improvement of indigo bioconversion yield is probably related to an increase in the intracellular NADPH/NADP+ ratio.

Root cell wall remodeling: A way for exopolysaccharides to mitigate cadmium toxicity in rice seedling.

Exopolysaccharides (EPS) are macromolecules with environment beneficial properties. Currently, numerous studies focus on the absorption of heavy metals by EPS, but less attention has been paid to the effects of EPS on the plants. This study explored the effects of EPS from Lactobacillus plantarum LPC-1 on the structure and function of cell walls in rice seedling roots under cadmium (Cd) stress. The results showed that EPS could regulate the remodeling process of the cell walls of rice roots. EPS affects the synthesis efficiency and the content of the substances that made up the cell wall, and thus plays an essential role in limiting the uptake and transport of Cd in rice root. Furthermore, EPS could induce plant resistance to heavy metals by regulating the lignin biosynthesis pathway in rice roots. Finally, the cell wall remodeling induced by EPS likely contributes to plant stress responses by activating the reactive oxygen species (ROS) signaling.

Exopolysaccharides from Lactobacillus plantarum reduces cadmium uptake and mitigates cadmium toxicity in rice seedlings.

Exopolysaccharides (EPSs) can be used as effective exogenous substances to alleviate the toxic effect of cadmium (Cd) on rice and other crops, thus improving plant growth characteristics under stress conditions, and reducing the accumulation of Cd in grains, but the underlying mechanism is still unclear. In the present work, the effects of EPSs from Lactobacillus plantarum on the efficiency of Cd absorption and distribution in rice seedlings under Cd stress were investigated. The results revealed that growth of rice seedlings was severely inhibited by exposure to Cd, resulting in the decrease of plant height, leaf length and biomass. This inhibition phenomenon was alleviated by the addition of EPSs from L. plantarum LPC-1. The underlying mechanism might be that EPSs could facilitate the accumulation efficiency of Cd in rice roots and reduce the transportation rate of Cd from root to leaves, therefore decreasing the Cd content in leaves. Further research showed that Cd contents in the cell wall fraction of the rice seedling root were increased by the addition of EPSs, while the proportions of Cd in the cell organelle and cell soluble component were reduced. Application of EPSs promotes the proportion of pectate- and protein- integrated Cd in rice roots. While the content of water-soluble Cd, which is more toxic to plants, decreased continuously both in roots and leaves. Our study clearly confirmed the positive effects of EPSs on alleviating Cd toxicity and decreasing Cd translocation in rice above-ground parts. Furthermore, the subcellular distribution and chemical forms of Cd in different rice seedlings parts were also affected by the addition of EPSs, which might be an important potential mechanism for EPSs in respect of alleviating Cd toxicity for rice. These findings provided a foundation for the application of exogenous substances on improving the growth performance of crops under heavy metal stress.

Acetone, butanol, and ethanol production from puerariae slag hydrolysate through ultrasound-assisted dilute acid by Clostridium beijerinckii YBS3.

In this study, puerariae slag (PS) was evaluated as a renewable raw material for acetone-butanol-ethanol (ABE) fermentation. To accelerate the hydrolysis of PS, the method of ultrasound-assisted dilute acid hydrolysis (UAAH) was used. With this effort, 0.69 g reducing sugar was obtained from 1 g raw material under the optimal pretreatment condition. Subsequently, the butanol and total solvent production of 8.79 ± 0.16 g/L and 12.32 ± 0.26 g/L were obtained from the non-detoxified diluted hydrolysate, and the yield and productivity of butanol were 0.19 g/g and 0.12 g/L/h, respectively. Additionally, the changes in the structure of PS after different pretreatment methods were observed using SEM and FT-IR. UAAH resulted in more severe and distinct damage to the dense structure of PS. This study suggests that the UAAH is an attainable but effective pretreatment method, thereby is a promising technique for lignocellulose hydrolysis and improve butanol production.

Co-expression of chaperones from P. furiosus enhanced the soluble expression of the recombinant hyperthermophilic α-amylase in E. coli.

The extracellular α-amylase from the hyperthermophilic archaeum Pyrococcus furiosus (PFA) is extremely thermostable and of an industrial importance and interest. PFA aggregates and accumulates as insoluble inclusion bodies when expressed as a heterologous protein at a high level in Escherichia coli. In the present study, we investigated the roles of chaperones from P. furiosus in the soluble expression of recombinant PFA in E. coli. The results indicate that co-expression of PFA with the molecular chaperone prefoldin alone significantly increased the soluble expression of PFA. Although, co-expression of other main chaperone components from P. furiosus, such as the small heat shock protein (sHSP) or chaperonin (HSP60), was also able to improve the soluble expression of PFA to a certain extent. Co-expression of chaperonin or sHSP in addition to prefoldin did not further increase the soluble expression of PFA. This finding emphasizes the biotechnological potentials of the molecular chaperone prefoldin from P. furiosus, which may facilitate the production of recombinant PFA.