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A neutral serine protease (designated Aozl) was purified to homogeneity from a strain of Arthrobotrys oligospora, obtained from soil in Yunnan Province. The purified protein showed a molecular mass of approximately 38 000 Dalton, pI 4.9 and displayed optimal activity at 45 C and pH 6--8. The protein could hydrolyze gelatin, casein and the chromogenic substrate azocoll, and it could immobilize nematodes in vitro (Panagrellus redivivus L. [Goodey]). The level of activity in culture medium was found to increase with increasing gelatin concentration. Scanning electron micrographs demonstrated dramatic structural changes in nematode cuticle treated with the purified protease. A partial peptide sequence obtained by N-terminal sequence analysis was used to design degenerate primers for the isolation of a cDNA gene encoding the mature protease. Analysis of the cDNA and corresponding genomic sequence revealed 97% identity with PII, a gene previously described from A. oligospora, and we conclude that this gene is likely a PII ortholog. [ABSTRACT FROM AUTHOR]

The rhizosphere bacterium ZKB-2 showed strong nematostatic activity against Meloidogyne incognita. Our study aimed to identify the nematostatic metabolites and evaluate the biocontrol efficiency in pot experiments. As the bacterial culture filtrate showed 100% nematostatic activity against M. incognita juveniles in 12 hr, we isolated and identified six compounds following activity guiding. 3-methoxycyclobutane-1, 2-dione showed 58.9% and 72.2% nematostatic activities against juveniles of M. incognita in 12 and 48 hr, with strong LC50 value at 447 μg mL−1. In pot experiments, treatments with the bacterial culture filtrate of strain ZKB-2 showed significant efficacy, especially at doses of 150 mL/pot, which were close to that of avermectin (positive control) at 0.01 g kg−1 soil. The most effective treatment inhibited 85.1% population of juveniles of M. incognita in the roots and 76.9% in the rhizosphere soil after 30 days. Furthermore, the promoting tomato growth also significantly increased in a dose-dependent manner. Our results revealed the potential of strain ZKB-2 to act as a biocontrol agent in the integrated management of root-knot nematodes on tomatoes. [ABSTRACT FROM AUTHOR]

Introduction: Trichoderma species establish symbiotic relationships with plants through both parasitic and mutualistic mechanisms. While some Trichoderma species act as plant pathogenic fungi, others utilize various strategies to protect and enhance plant growth., Methods: Phylogenetic positions of new species of Trichoderma were determined through multi-gene analysis relying on the internal transcribed spacer (ITS) regions of the ribosomal DNA, the translation elongation factor 1-α ( tef1- α) gene, and the RNA polymerase II ( rpb2 ) gene. Additionally, pathogenicity experiments were conducted, and the aggressiveness of each isolate was evaluated based on the area of the cross-section of the infected site., Results: In this study, 13 Trichoderma species, including 9 known species and 4 new species, namely, T. delicatum, T. robustum, T. perfasciculatum , and T. subulatum were isolated from the diseased tubers of Gastrodia elata in Yunnan, China. Among the known species, T. hamatum had the highest frequency. T. delicatum belonged to the Koningii clade. T. robustum and T. perfasciculatum were assigned to the Virens clade. T. subulatum emerged as a new member of the Spirale clade. Pathogenicity experiments were conducted on the new species T. robustum, T. delicatum , and T. perfasciculatum , as well as the known species T. hamatum, T. atroviride , and T. harzianum . The infective abilities of different Trichoderma species on G. elata varied, indicating that Trichoderma was a pathogenic fungus causing black rot disease in G. elata ., Discussion: This study provided the morphological characteristics of new species and discussed the morphological differences with phylogenetically proximate species, laying the foundation for research aimed at preventing and managing diseases that affect G. elata ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Ye, You, Li, Jing, Mo, Qiao and Yu.)

Introduction: Tobacco root-knot nematode (RKN) is a highly destructive soil-borne disease worldwide. However, there is a lack of research on the relationship between RKN and tobacco root microbial community composition under large-scale geographical conditions in China., Methods: In this study, we collected 65 samples from 28 main tobacco-growing areas across 10 provinces in China and conducted 16S rDNA sequencing to investigate the dynamic microbial changes in tobacco soil infected by RKN compared to healthy tobacco soil. Based on the analysis of rhizosphere soil bacterial communities, changes after RKN infection, and soil environmental factors., Results: We found the 28 tobacco-growing areas could be divided into two distinct groups with different microbial compositions and varying responses to RKN infection. In group1 of the provinces of Anhui, Henan, Shanxi, and Heilongjiang, Vicinamibacteria dominated the bacterial community, while Acidobacteriae was present in low abundance. In contrast, group2 of the other six provinces (Yunnan, Guizhou, Chongqing, Guangxi, Hubei, and Shandong) exhibited an opposite pattern. After infected by RKN, the genera Chitinophaga increased significant in group 1, while the genera Rhodococcus in group 2 exhibited a substantial increase. Alpha-diversity analysis revealed that RKN-infected tobacco exhibited a richer and more diverse rhizosphere soil bacterial community compared to healthy tobacco in most growing areas. A total of 12 kinds of soil environmental factors were measured in healthy and RKN-infected tobacco soil, and based on the co-occurrence and correlation analysis between environmental factors and microbial species, the pH level, calcium (Ca), magnesium (Mg), phosphorus (P), iron (Fe), and sodium (Na) were identified as key environmental factors influencing the population composition of rhizosphere microorganisms during RKN infection. We observed that RKN infection further increased the pH in weakly alkaline group 1 soil, while weakly acidic group 2 soil experienced a further decrease in pH. Furthermore, we identified three genera as potential biocontrol or plant growth-promoting bacteria for tobacco., Discussion: These findings provide valuable reference data for managing RKN disease in different tobacco-growing areas and contribute to the exploration of new and effective biological control methods., Competing Interests: CL was employed by Bijie Tobacco Company of Guizhou Province. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Cao, Lu, Yang, Mo, Zhang, Li and Shang.)

Objective: This study characterized the phylogenetic diversity of soil bacteria producing nematode-attracting volatiles and their nematode-attracting compounds. Results would enhance our understanding on the interaction between nematodes and soil microorganisms and potentially enhance the biocontrol efficiency when combined the attractants with nemacides., Methods: Bacteria producing volatiles with functions of nematode-attracting activities were isolated from 187 agricultural soil samples collected in 26 provinces of China with the method of double-Petri dishes. The phylogenetic diversity of these bacteria was characterized by RFLP-16S rRNA gene sequence analysis. The nematode-attracting volatiles of bacteria were detected using the SPME-GC/MS, and volatile compounds with attractive activity were determined by confirming with individual commercial compounds., Results: Among the 3800 bacteria isolated from the 187 soil samples, 196 isolates(5.16% of the total) showed attractive activity (AN)more than 30% to Panagrellus redivivus. Of the 196 isolates, 66 (1.74%) showed AN > or = 70%, 62 isolates (1.63%) showed AN between 50% and 70%, and 68 isolates (1.79%) showed AN less than 50%. Phylogenetic analysis revealed that the 196 bacteria were clustered into 5 groups: Bacilli, Gammaproteobacteria, Alphaproteobacteria, Sphingobacteria and Actinobacteria. But, Bacillus were the dominant, which covered 13 species. And 11 volatiles with nematode-attracting activity were determined, including benzaldehyde, 2-heptanone, benzyl benzoate, ethyl palmitate, (+)-longifolene, benzyl alcohol, p-anisaldehyde, vanatone, ethyl butyrate, isovanilin and d-alaninol., Conclusion: Some species of bacteria in agriculture soil can produce volatiles to attract nematodes.

Four series (S, M, R, and W) of Alternaria longipes isolates were obtained based on consecutive induction with Dimethachlon (Dim) and ultraviolet irradiation. These isolates were then characterized according to their tolerance to Dim, sensitivity to osmotic stress, and phenotypic properties. All the induced Dim-resistant isolates showed a higher osmosensitivity than the parental strains, and the last generation was more resistant than the first generation in the M, R, and W series. In addition, the changes in the Dim resistance and osmotic sensitivity were not found to be directly correlated, and no distinct morphologic characteristics were found among the resistant and sensitive isolates, with the exception of the resistant isolate K-11. Thus, to investigate the molecular basis of the fungicide resistance, a group III two-component histidine kinase (HK) gene, AlHK1, was cloned from nineteen A. longipes isolates. AlHK1p was found to be comprised of a six 92- amino-acid repeat domain (AARD), HK domain, and response regulator domain, similar to the Os-1p from Neurospora crassa. A comparison of the nucleotide sequences of the AlHK1 gene from the Dim-sensitive and -resistant isolates revealed that all the resistant isolates contained a single-point mutation in the AARD of AlHK1p, with the exception of isolate K-11, where the AlHK1p contained a deletion of 107 amino acids. Moreover, the AlHK1p mutations in the isolates of each respective series involved the same amino acid substitution at the same site, although the resistance levels differed significantly in each series. Therefore, these findings suggested that a mutation in the AARD of AlHK1p was not the sole factor responsible for A. longipes resistance to dicarboximide fungicides.

The objective of this study was to analyze the phylogenetic composition of bacterial community in the soil of an earth-cave (Niu Cave) using a culture-independent molecular approach. 16S rRNA genes were amplified directly from soil DNA with universally conserved and Bacteria-specific rRNA gene primers and cloned. The clone library was screened by restriction fragment length polymorphism (RFLP), and representative rRNA gene sequences were determined. A total of 115 bacterial sequence types were found in 190 analyzed clones. Phylogenetic sequence analyses revealed novel 16S rRNA gene sequence types and a high diversity of putative bacterial community. Members of these bacteria included Proteobacteria (42.6%), Acidobacteria (18.6%), Planctomycetes (9.0%), Chloroflexi (Green nonsulfur bacteria, 7.5%), Bacteroidetes (2.1%), Gemmatimonadetes (2.7%), Nitrospirae (8.0%), Actinobacteria (High G+C Gram-positive bacteria, 6.4%) and candidate divisions (including the OP3, GN08, and SBR1093, 3.2%). Thirty-five clones were affiliated with bacteria that were related to nitrogen, sulfur, iron or manganese cycles. The comparison of the present data with the data obtained previously from caves based on 16S rRNA gene analysis revealed similarities in the bacterial community components, especially in the high abundance of Proteobacteria and Acidobacteria. Furthermore, this study provided the novel evidence for presence of Gemmatimonadetes, Nitrosomonadales, Oceanospirillales, and Rubrobacterales in a karstic hypogean environment.