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Author: search.filters.author.Kittiwongwattana, ChokchaiSubject: search.filters.subject.Pyricularia oryzae

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    Biocontrol Potential, Genome and Nonribosomal Peptide Synthetase Gene Expression of Bacillus velezensis 2211
    (2023-01-01)
    Niemhom, Nantawan
    ;
    Kittiwongwattana, Chokchai
    Members of the genus Bacillus produced a diverse group of antimicrobial compounds. Here, we presented the antifungal activity and genome sequence analysis of Bacillus sp. 2211, a potential plant-growth-promoting bacterium. Bacterial supernatants from strain 2211 cultures in nutrient broth (NB) and potato dextrose broth (PDB) suppressed the mycelial growth of Pyricularia oryzae, Colletotrichum aenigma, Colletotrichum fructicola and Fusarium oxysporum. The supernatants were also able to suppress spore germination of these fungi, except for F. oxysporum. However, the supernatant from PDB displayed a significantly higher inhibition activity than NB. Additionally, the supernatant from PDB significantly reduced the disease severity caused by P. oryzae on rice seedlings. The genome of strain 2211 was sequenced. The highest digital DNA-DNA hybridization (80.1%) and average nucleotide identity (97.57%) levels indicated that strain 2211 was a member of the species Bacillus velezensis. The phylogenomic analysis showed that it clustered with B. velezensis NRRL B-41580<sup>T</sup>, B. velezensis KACC 13105 and B. velezensis subsp. plantarum FZB42<sup>T</sup>. The gene expression analysis showed the up-regulation of nonribosomal peptide synthetase (NRPS) genes bmyA, fenB and dhbE in PDB, compared to NB. This work demonstrated that the culture media affected the antagonistic activity of strain 2211 possibly through the modification of NRPS biosynthesis genes.
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    Correlation of Antifungal Activities and Nonribosomal Peptide Synthetase Gene Expression of Bacillus siamensis 1021
    (2022-03-01)
    Nuwong, Warinya
    ;
    Kittiwongwattana, Chokchai
    Members of the genus Bacillus were biocontrol agents against various phytopathogenic fungi. Several factors affected the regulation and production of nonribosomal peptides (NRPs) in Bacillus species. The aim of this study was to examine how culture media influenced the antagonistic activities and gene expression of Bacillus siamensis 1021. The bacterial supernatant from potato dextrose broth (PDB) exhibited higher inhibitory effects against mycelia of Pyricularia oryzae and Colletotrichum fructicola, when compared with those from nutrient broth (NB) and minimal salt medium (MSM). However, the biocontrol activities of these supernatants were not significantly different when they were tested against P. oryzae and C. fructicola conidia. Additionally, the bacterial supernatant from PDB significantly reduced the disease severity caused by P. oryzae in rice seedlings when compared with the water-treated control group. The genome of strain 1021 was sequenced, and biosynthetic gene clusters of nonribosomal peptides surfactin, fengycin and bacillibactin were identified. Effects of PDB, NB and MSM media on expression levels of core biosynthetic genes of surfactin (srfAA), fengycin (fenC) and bacillibactin (dhbE) gene clusters were determined by reverse-transcription quantitative PCR. fenC expression was significantly increased in PDB and corresponded with the antagonistic activities against fungal mycelia. Conversely, expression of the regulatory genes comA and codY in PDB were highly reduced in PDB, indicating their negative relation with fenC expression. This expression analysis indirectly suggested that fengycin was potentially the bioactive compound of B. siamensis 1021 against P. oryzae and C. fructicola.
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    Medium Effect on Antagonistic Activity and Detection of Nonribosomal Peptide Synthetase Genes in Epiphytic Bacillus Strains
    (2021-01-01)
    Apimeteethamrong, Suchitra
    ;
    Kittiwongwattana, Chokchai
    The biosynthesis of non-ribosomal peptides (NRPs) in biocontrol bacteria was one of the major antagonistic mechanisms for their application in agriculture. Bacillus spp. 1021, 2211 and 3210 were previously shown to inhibit mycelial growth of the leaf blast fungus Pyricularia oryzae. Here, we aimed to further study the antagonistic mechanism in those three strains. Cell-free supernatants obtained from bacteria grown in potato dextrose broth (PDB) exhibited a higher degree of inhibition against P. oryzae when compared to those obtained from nutrient broth (NB). This indicated the effect of culture media in the production of extracellular antibiotic compounds by these strains. Phylogenetic analysis of their partial 16S rRNA gene sequences indicated a close relationship between the three strains and Bacillus siamensis KCTC13613<sup>T</sup>, Bacillus amyloliquefaciens DSM7<sup>T</sup> and Bacillus velezensis CR-502<sup>T</sup>. Complete genome sequences of these Bacillus species were analyzed on the antiSMASH server to identify the presence of NRP biosynthesis gene clusters. Non-degenerate primers were designed for the detection of the core biosynthesis genes for surfactin (srfAA), fengycin (fenC) and bacillibactin (dhbF). All three genes were amplified in strains 1021 and 2211, while only srfAA and dhbF were detected in strain 3210. Phylogenetic analysis of the deduced amino acid sequences indicated that the sequences of strain 1021 were distinct from those of strains 2211 and 3210. This result indirectly suggests the possibility of NRP production as the antagonistic mechanism of these three strains.
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    Diversity and plant growth promoting activities of rice epiphytic bacteria
    (2019-01-01)
    Aphimeteetamrong, Suchitra
    ;
    Kittiwongwattana, Chokchai
    Plant-associated bacteria have been known for their direct and indirect abilities to promote plant growth. Because of their benefits on plants, they are generally recognized as plant growth promoting bacteria (PGPB). In the present study, epiphytic bacteria were isolated from surfaces of roots, stems and leaves of rice plants that were grown in organic farms. Of 113 bacterial isolates, 68 and 45 isolates were stained Gram-positive and Gram-negative, respectively. Based on their cell shapes, 106 isolates were bacilli while seven isolates were cocci. The use of the 16S rRNA gene sequence analysis indicated that they were members of phyla Fimicutes (54.87%), Proteobacteria (38.05%) and Bacteroidetes ( 7. 08% ). All isolates were assessed for their abilities in nitrogen fixation, phosphate solubilization, siderophore production, auxin production and 1-aminocyclopropane-1-caboxylic acid (ACC) deaminase activity. The result showed that 91 isolates were tested positives for at least one activity. The antagonistic activity against the pathogenic fungus Pyricularia oryzae was also tested. Twenty-three isolates inhibited the growth of the fungal mycelia. The percentage of growth inhibition of these isolates against P. oryzae ranged from 73.10+3.24% to 100.00+0.00%. The protease and chitinase activities were found in 19 and 2 isolates, respectively. However, crude preparation of bioactive compounds from bacterial cultures yielded negative results. Based on the results obtained in this study, the surfaces of rice plants were colonized by various bacteria with potentials in plant growth promotion.