Overexpression and activities of 1-Cys peroxiredoxin from Pseudomonas fluorescens GcM5-1A carried by pine wood nematode

A thermostable xylanase hydrolyzes several polysaccharides from Bacillus altitudinis JYY-02 showing promise for industrial applications

Polysaccharides have attracted immense attention as the largest source of bioactive compounds. Its bioavailability and bioactivity can be improved by utilizing degradation enzymes to reduce their molecular weight and viscosity. In this study, a 654 bp gene encoding xylanase was screened from the genome of Bacillus altitudinis JYY-02 and overexpressed in Escherichia coli Rosetta (DE3). The recombinant xylanase with a molecular weight of 27.98 kDa was purified (11.7-fold) using Ni-NTA affinity chromatography, with a 43.6% final yield. Through molecular docking, Glu, Arg, Tyr, and Trp were found to be the main amino acids involved in the interaction between xylanase and xylobiose. The effects of pH, temperature, metal ions, and substrates on xylanase activity were determined, and the results showed that the highest catalytic activity was displayed at pH 6.5, 50 °C temperature, with Cu2+ as an activator and xylan as the substrate. The Km (substrate concentration that yields a half-maximal velocity) and Vmax (maximum velocity) of recombinant xylanase were 6.876 mg/mL and 10984.183 μmol/mg∙pr/min, respectively. The recombinant xylanase was thermostable, with 85% and 39% of the enzymatic activity retained after 1 h at 60 °C and 1 h at 90 °C, respectively. The recombinant xylanase demonstrated a significant clarifying effect on fruit juices.

Production of selenium nanoparticles occurs through an interconnected pathway of sulphur metabolism and oxidative stress response in Pseudomonas putida KT2440

The soil bacterium Pseudomonas putida KT2440 has been shown to produce selenium nanoparticles aerobically from selenite; however, the molecular actors involved in this process are unknown. Here, through a combination of genetic and analytical techniques, we report the first insights into selenite metabolism in this bacterium. Our results suggest that the reduction of selenite occurs through an interconnected metabolic network involving central metabolic reactions, sulphur metabolism, and the response to oxidative stress. Genes such as sucA, D2HGDH and PP_3148 revealed that the 2-ketoglutarate and glutamate metabolism is important to convert selenite into selenium. On the other hand, mutations affecting the activity of the sulphite reductase decreased the bacteria's ability to transform selenite. Other genes related to sulphur metabolism (ssuEF, sfnCE, sqrR, sqr and pdo2) and stress response (gqr, lsfA, ahpCF and sadI) were also identified as involved in selenite transformation. Interestingly, suppression of genes sqrR, sqr and pdo2 resulted in the production of selenium nanoparticles at a higher rate than the wild-type strain, which is of biotechnological interest. The data provided in this study brings us closer to understanding the metabolism of selenium in bacteria and offers new targets for the development of biotechnological tools for the production of selenium nanoparticles.

Acaricidal Activity and Field Efficacy Analysis of the Potential Biocontrol Agent Bacillus vallismortis NBIF-001 against Spider Mites

In recent years, spider mites have caused considerable economic losses to global agriculture. However, currently available management strategies are limited because of the rapid development of resistance. In this study, Bacillus vallismortis NBIF-001 was isolated and evaluated for its acaricidal activity. NBIF-001 exhibited a significant lethal effect on spider mites within 48 h. The median lethal concentration (LC₅₀) of the culture powders (3.2 × 10¹⁰ CFU/g) was 50.2 µg/mL for Tetranychus urticae (red form), 18.0 µg/mL for T. urticae (green form), and 15.7 µg/mL for Panonychus citri (McGregor). Cultivation optimisation experiments showed that when the number of spores increased, fermentation toxicity also increased. Moreover, field experiments demonstrated that NBIF-001 performed well in the biocontrol of P. citri, which showed a similar corrected field efficacy with the chemical control (67.1 ± 7.9% and 71.1 ± 6.4% after 14 days). Genomics analysis showed that NBIF-001 contains 231 factors and seven gene clusters of metabolites that may be involved in its acaricidal activity. Further bioassays of the fermentation supernatants showed that 50× dilution treatments killed 72.5 ± 5.4% of the mites in 48 h, which was similar with those of the broth. Bioassays of the supernatant proteins confirmed that various proteins exhibited acaricidal activity. Five candidate proteins were expressed and purified successfully. The bioassays showed that the small protein BVP8 exhibited significant acaricidal activity with an LC₅₀ of 12.4 μg/mL (T. urticae). Overall, these findings suggest that B. vallismortis NBIF-001 is a potential biocontrol agent for spider mite management.

UGT440A1 Is Associated With Motility, Reproduction, and Pathogenicity of the Plant-Parasitic Nematode Bursaphelenchus xylophilus

Pine wilt disease (PWD) caused by Bursaphelenchus xylophilus is considered a major threat to pine forests worldwide. Uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyze the conjugation of small lipophilic compounds with sugars and play crucial roles in the detoxification and homeostatic processes in all living organisms. We investigated the molecular characteristics and biological functions of the gene UGT440A1 that encodes UGTs in B. xylophilus. The in situ hybridization results indicated that UGT440A1 is expressed in all developmental stages of B. xylophilus, particularly in the head, intestine, and hypodermis of the second-stage of juveniles (J2), third-stage of juveniles (J3) and fourth-stage of juveniles (J4) females and in almost the whole body of J4 males and adults. Recombinant UGT440A1 was observed mainly in the inclusion bodies, and the enzyme activity assay revealed that UGT440A1 could catalyze the glycosylation reaction of two types of flavonols (kaempferol and quercetin). RNA interference (RNAi) of UGT440A1 suppressed motility, feeding, and reproduction of B. xylophilus. Furthermore, UGT440A1 knockdown caused a delay in the development of PWD symptoms in the pine seedlings inoculated with the nematodes. These results suggest that UGT440A1 is involved in the pathogenic process of B. xylophilus and the information may facilitate a better understanding of the molecular mechanism of PWD.

Genome analysis of Pseudomonas chlororaphis subsp. aurantiaca mutant strains with increased production of phenazines

Genomes of three strains-phenazine producers-Pseudomonas chlororaphis subsp. aurantiaca (B-162 (wild type), mutant strain B-162/255, and its derivative B-162/17) were sequenced and compared. Comparison of a wild-type strain and B-162/255 mutant genomes revealed 32 mutations. 19 new mutations were detected in the genome of B-162/17. Further bioinformatics analysis allowed us to predict mutant protein functions and secondary structures of five gene products, mutations which might potentially influence phenazine synthesis and secretion in Pseudomonas bacteria. These genes encode phenylalanine hydroxylase transcriptional activator PhhR, type I secretion system permease/ATPase, transcriptional regulator MvaT, GacA response regulator, and histidine kinase. Amino acid substitutions were found in domains of studied proteins. One deletion in an intergenic region could affect a potential transcription factor binding site that participates in the regulation of gene that encodes ABC transporter.

Multi-copy alpha-amylase genes are crucial for Ditylenchus destructor to parasitize the plant host

Ditylenchus destructor is a migratory plant-parasitic nematode that causes huge damage to global root and tuber production annually. The main plant hosts of D. destructor contain plenty of starch, which makes the parasitic environment of D. destructor to be different from those of most other plant-parasitic nematodes. It is speculated that D. destructor may harbor some unique pathogenesis-related genes to parasitize the starch-rich hosts. Herein, we focused on the multi-copy alpha-amylase genes in D. destructor, which encode a key starch-catalyzing enzyme. Our previously published D. destructor genome showed that it has three alpha-amylase encoding genes, Dd_02440, Dd_11154, and Dd_13225. Comparative analysis of alpha-amylases from different species demonstrated that the other plant-parasitic nematodes, even Ditylenchus dipsaci in the same genus, harbor only one or no alpha-amylase gene, and the three genes from D. destructor were closely clustered in the phylogenetic tree, indicating that there was a unique expansion of the alpha-amylase gene in D. destructor. The enzymatic activity of the three alpha-amylase proteins was verified by an enzyme assay. Quantitative real-time PCR assay showed that the expression of the three alpha-amylase genes in the post-hatching stage of D. destructor was found to be significantly higher than that in eggs. In the in situ hybridization assay, the expression of the genes was localized to the intestine, implying the association of these genes with nematode digestion. An infection assay in sweet potato demonstrated that RNA interference of any one alpha-amylase gene had no influence on the infectivity of D. destructor. Using the multi-target dsRNA cocktail method, it was found that silencing of two of the three genes inhibited nematode infection, and the infectivity of worms treated with three dsRNA simultaneously changed the most, which decreased by 76.6%. Thus, the multi-copy alpha-amylase genes in D. destructor are compensatory and crucial for nematodes to parasitize the plant host.

The alcohol dehydrogenase with a broad range of substrate specificity regulates vitality and reproduction of the plant-parasitic nematode Bursaphelenchus xylophilus

Pine wilt disease, which is caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, has caused huge damage to pine forests around the world. In this study, we analysed the PWN transcriptome to investigate the expression of genes related to the associated bacterial species Pseudomonas fluorescens and found that the gene adh-1 encoding alcohol dehydrogenase (ADH) was upregulated. The open reading frame of adh-1, which encoded a protein of 352 amino acid residues, was cloned from B. xylophilus. Recombinant ADH with a relative molecular weight of 39 kDa, was present mainly in inclusion bodies and was overexpressed in Escherichia coli BL21 (DE3) and purified after refolding. The biochemical assay revealed that recombinant ADH could catalyse the dehydrogen reaction of eight tested alcohols including ethanol in the presence of NAD+. Quantitative real-time RT-PCR analysis indicated that ethanol upregulated adh-1 expression in PWN. Results of RNA interference and inhibition of ADH treatment indicated that downregulating expression of adh-1 or inhibition of ADH could reduce ethanol tolerance and the vitality and reproduction ability of B. xylophilus, suggesting that adh-1 is involved in pathogenicity of PWN.