Purification and characterization of a 1,3-β-d-glucanase from Streptomyces torulosus PCPOK-0324

Streptomyces Strains and Their Metabolites for Biocontrol of Phytopathogens in Agriculture

Sustainable agriculture is increasingly linked to biological pesticides as alternatives to agro-chemicals. Streptomyces species suppress plant diseases through their unique traits and numerous metabolites. Although many Streptomyces strains have been developed into commercial products, their roles in the biocontrol of phytopathogens and mechanisms of functional metabolite synthesis remain poorly understood. In this review, biocontrol of plant diseases by Streptomyces is summarized on the basis of classification of fungal and bacterial diseases and secondary metabolites produced by Streptomyces that act on phytopathogenic microorganisms are discussed. The associated non-ribosomal peptide synthetases and polyketide synthetases responsible for biosynthesis of these secondary metabolites are also investigated, and advances in fermentation of Streptomyces are described. Finally, the need to develop precise and effective biocontrol methods for plant diseases is highlighted.

Biocontrol activity of Bacillus halotolerans strain Pl7 against Botryosphaeria dothidea causing apple postharvest decay and potential mechanisms

Apple ring rot, one of the most common apple postharvest diseases during storage, is caused by Botryosphaeria dothidea. Fungicide application is the most widely used method to control this disease, but the increasing environmental and food safety concerns greatly limit their use. The present study aimed to examine the biocontrol activity and underlying action mechanism of Bacillus halotolerans strain Pl7 against B. dothidea. The results revealed that B. halotolerans strain Pl7 exhibited strong inhibitory activity against B. dothidea by 69% in vitro. The culture filtrate of strain Pl7 possessed cellulase, β-1, 3-glucanase, protease activity and mediated the antifungal activity against B. dothidea. Further analysis demonstrated that culture filtrate of strain Pl7 could cause cell membrane permeabilization of B. dothidea. Apple fruit suffering from ring rot induced by a carbendazim (CBZ)-sensitive or -resistant B. dothidea isolate was much suppressed after being treated with strain Pl7, maintaining postharvest quality. The ability of strain Pl7 to swiftly colonize and thrive in apple fruit wounds was demonstrated by a re-isolation assay. Additional transcriptome studies of untreated and treated apple fruit with strain Pl7 revealed that strain Pl7 mostly changed the expression of genes functioning in plant secondary metabolite biosynthesis and plant-pathogen interaction. In light of these outcomes, the underlying antagonistic mechanism was investigated, and B. halotolerans strain Pl7 was identified as a promsing microbial biocontrol agent against apple postharvest decay.

Biocontrol activity and action mechanism of Paenibacillus polymyxa strain Nl4 against pear Valsa canker caused by Valsa pyri

Pear Valsa canker caused by Valsa pyri is among the most destructive diseases of pear, which causes significant economic loss. The present study was developed to explore the biocontrol efficiency and underlying antagonistic mechanism of Paenibacillus polymyxa strain Nl4 against V. pyri. P. polymyxa strain Nl4, one of the 120 different endophytic bacterial strains from pear branches, exhibited strong inhibitory effects against the mycelial growth of V. pyri and caused hyphal malformation. Culture filtrate derived from strain Nl4 was able to effectively suppress mycelial growth of V. pyri, and was found to exhibit strong protease, cellulase and β-1, 3-glucanase activity. Through re-isolation assay, strain Nl4 was confirmed to be capable of colonizing and surviving in pear branch. Treatment with strain NI4 effectively protected against pear Valsa canker symptoms on detached pear twigs inoculated with V. pyri. Moreover, strain Nl4 promoted enhanced plant growth probably through the solubilization of phosphorus. Comparative transcriptomic analyses revealed that strain NI4 was able to suppress V. pyri growth in large part through the regulation of the expression of membrane- and energy metabolism-related genes in this pathogen. Further transcriptomic analyses of pear trees indicated that strain NI4 inoculation was associated with changes in the expression of genes associated with secondary metabolite biosynthesis, signal transduction, and cutin, suberine, and wax biosynthesis. Together, these data highlighted P. polymyxa strain Nl4 as a promising biocontrol agent against pear Valsa canker and investigated the possible mechanisms of strain Nl4 on control of this devastating disease.

Isolation and characterization of antagonistic Paenibacillus polymyxa HX-140 and its biocontrol potential against Fusarium wilt of cucumber seedlings

Objective

The aim of this study is to evaluate the efficacy of the strain Paenibacillus polymyxa HX-140, isolated from the rhizosphere soil of rape, to control Fusarium wilt of cucumber seedlings caused by Fusarium oxysporum f. sp. cucumerinum.

Results

Strain HX-140 was able to produce protease, cellulase, β-1,3-glucanase and antifungal volatile organic compounds. An in vitro dual culture test showed that strain HX-140 exhibited broad spectrum antifungal activity against soil-borne plant pathogenic fungi. Strain HX-140 also reduced the infection of Fusarium wilt of cucumber seedlings by 55.6% in a greenhouse pot experiment. A field plot experiment confirmed the biocontrol effects and further revealed that antifungal activity was positively correlated with inoculum size by the root-irrigation method. Here, inoculums at 10⁶ 10⁷ and 10⁸ cfu/mL of HX-140 bacterial suspension reduced the incidence of Fusarium wilt of cucumber seedling by 19.5, 41.1, and 50.9%, respectively.

Conclusions

Taken together, our results suggest that P. polymyxa HX-140 has significant potential in the control of Fusarium wilt and possibly other fungal diseases of cucumber.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02131-3.

Antagonistic action of Streptomyces pratensis S10 on Fusarium graminearum and its complete genome sequence

Wheat scab, mainly caused by Fusarium graminearum, can decrease wheat yield and grain quality. Chemical pesticides are currently the main control method but have an inevitable negative consequence on the environment and in food safety. This research studies a promising substitute, Streptomyces pratensis S10, which was isolated from tomato leaf mould and shows a significant inhibition effect on F. graminearum based on antagonism assays. The biocontrol mechanism is studied by enhanced green fluorescent protein labelling, quantitative real-time PCR, the Doskochilova 8 solvents system test and complete genome sequencing. Strain S10 can colonize in the wheat root, control wheat scab and decrease deoxynivalenol (DON) content. The control effects in vitro, planta and the plot experiments were 92.86%, 68.67% and 40.87% to 86.62%, respectively. S10 decreased DON content by inhibiting the mycelium growth and DON synthesis gene expression. The active substances of the S10 secondary metabolites had a high-temperature resistance and 29 putative biosynthetic gene clusters in its genome. The S10 control mechanism is multivariate, which shows potential in controlling wheat scab.

Isolation of β-1,3-Glucanase-Producing Microorganisms from Poria cocos Cultivation Soil via Molecular Biology

β-1,3-Glucanase is considered as a useful enzymatic tool for β-1,3-glucan degradation to produce (1→3)-linked β-glucan oligosaccharides with pharmacological activity properties. To validly isolate β-1,3-glucanase-producing microorganisms, the soil of Wolfiporia extensa, considered an environment rich in β-1,3-glucan-degrading microorganisms, was subjected to high throughput sequencing. The results demonstrated that the genera Streptomyces (1.90%) and Arthrobacter (0.78%) belonging to the order Actinomycetales (8.64%) in the phylum Actinobacteria (18.64%) were observed in soil for P. cocos cultivation (FTL₁). Actinomycetes were considered as the candidates for isolation of glucan-degrading microorganisms. Out of 58 isolates, only 11 exhibited β-1,3-glucan-degrading activity. The isolate SYBCQL belonging to the genus Kitasatospora with β-1,3-glucan-degrading activity was found and reported for the first time and the isolate SYBC17 displayed the highest yield (1.02 U/mg) among the isolates. To check the β-1,3-glucanase contribution to β-1,3-glucan-degrading activity, two genes, 17-W and 17-Q, encoding β-1,3-glucanase in SYBC17 and one gene QLK1 in SYBCQL were cloned and expressed for verification at the molecular level. Our findings collectively showed that the isolates able to secrete β-1,3-glucanase could be obtained with the assistance of high-throughput sequencing and genes expression analysis. These methods provided technical support for isolating β-1,3-glucanase-producing microorganisms.

Production and partial characterization of β-1,3-glucanase obtained from Rhodotorula oryzicola

The current study aims to assess the kinetics of population growth of Rhodotorula oryzicola and the production of β-1,3-glucanase (EC 3.2.1.39) enzyme by this yeast. It also aims to obtain the optimum conditions of β-1,3-glucanase enzymatic activity by varying the pH as well as to study the enzyme thermostability. R. oryzicola population doubled within 12 hr. During this period, 9.26 generations were obtained, with 1 hr and 29 min of interval from one generation to the other, with specific growth rate (µ) of 0.15 (hr^-1). The entire microorganism growth process was monitored during β-1,3-glucanases production, and the maximum value was obtained in the stationary phase in the 48-hr fermentation period. pH and temperature optimum values were 4.7 and 96°C, respectively. The enzyme maintained 88% of its activity when submitted to the temperature of 90°C for an incubation period of 1 hr. The results show that the enzyme can be used in industrial processes that require high temperatures and acidic pH.

Heterologous coexpression of Vitreoscilla hemoglobin and Bacillus megaterium glucanase in Streptomyces lydicus A02 enhanced its production of antifungal metabolites

Streptomyces lydicus A02 is a novel producer of commercially important polyene macrocyclic antibiotic natamycin and a potential biocontrol agent to several plant fungal diseases, including wilt caused by Fusarium oxysporum f. spp. To improve the natamycin production and the antifungal activity of S. lydicus A02, we coexpressed gene vgb encoding Vitreoscilla hemoglobin (VHb) and bglC encoding Bacillus megaterium L103 glucanase, both under the control of the strong constitutive ermE* promoter, in S. lydicus A02. Our results showed that coexpressing VHb and glucanase improved cell growth, and the engineered strain produced 26.90% more biomass than the wild-type strain after 72h fermentation in YSG medium. In addition, coexpressing genes encoding VHb and glucanase led to increased natamycin production, higher endogenous chitinase activity and exogenous glucanase activity, as well as enhanced antifungal activity in the engineered S. lydicus AVG02 and AGV02, regardless of the position of the two genes on the plasmids. Compared with model strains, few reports have successfully coexpressed VHb and other foreign proteins in industrial strains. Our results illustrated an effective approach for improving antifungal activity in an industrial strain by the rational engineering of combined favorable factors.

Mycolytic enzymes produced by Streptomyces violaceusniger and their role in antagonism towards wood-rotting fungi

Extracellular mycolytic enzymes produced under submerged fermentation by the fungal antagonist Streptomyces violaceusniger MTCC 3959 were characterized. This streptomycete produced higher amounts of extracellular chitinase and protease during late exponential phase, whereas β-1,3-glucanase production was at peak in mid-stationary phase. Cell-free culture filtrate (CCF) exhibited a broad range of antifungal activity against both white rot and brown rot fungi. The inhibitory activity was completely lost after treatment with proteinase K and heat, indicating that extracellular antifungal metabolites are heat labile and proteinaceous in nature. Optimum pH and temperature for enzyme activity were: 9.0 and 60 °C for chitinase; 6.0 and 60 °C for β-1,3-glucanase; and 9.0 and 70 °C for protease. Mycolytic enzymes were moderately thermostable, and had a wide pH stability range extending from pH 5.0 to 10.0. The zymogram analysis of CCF revealed five chitinase isoenzymes with an apparent molecular weight of 20.8, 33.3, 45.6, 67.4, and 114.8 kDa, one β-1,3-glucanase appeared as a single band of ∼131.8 kDa and four protease isoenzymes with approximate molecular weights of 22.8, 62.52, 74.64, and 120.5 kDa. S. violaceusniger MTCC 3959 produced mycolytic enzymes that can be effectively used for suppression of phytopathogenic basidiomycetes. It has the potential to be an effective biofungicide.