Screening Plant Growth-Promoting Bacteria with Antimicrobial Properties for Upland Rice.

This study explores beneficial bacteria isolated from the roots and rhizosphere soil of Khao Rai Leum Pua Phetchabun rice plants. A total of 315 bacterial isolates (KK001 to KK315) were obtained. Plant growth-promoting traits (phosphate solubilization and indole-3-acetic acid (IAA) production), and antimicrobial activity against three rice pathogens (Curvularia lunata NUF001, Bipolaris oryzae 2464, and Xanthomonas oryzae pv. oryzae) were assessed. KK074 was the most prolific in IAA production, generating 362.6 ± 28.0 µg/ml, and KK007 excelled in tricalcium phosphate solubilization, achieving 714.2 ± 12.1 µg/ml. In antimicrobial assays using the dual culture method, KK024 and KK281 exhibited strong inhibitory activity against C. lunata, and KK269 was particularly effective against B. oryzae. In the evaluation of antimicrobial metabolite production, KK281 and KK288 exhibited strong antifungal activities in cell-free supernatants. Given the superior performance of KK281, taxonomically identified as Bacillus sp. KK281, it was investigated further. Lipopeptide extracts from KK281 had significant antimicrobial activity against C. lunata and a minimum inhibitory concentration (MIC) of 3.1 mg/ml against X. oryzae pv. oryzae. LC-ESI-MS/MS analysis revealed the presence of surfactin in the lipopeptide extract. The crude extract was non-cytotoxic to the L-929 cell line at tested concentrations. In conclusion, the in vitro plant growth-promoting and disease-controlling attributes of Bacillus sp. KK281 make it a strong candidate for field evaluation to boost plant growth and manage disease in upland rice.

Actinomycins from Soil-Inhabiting Streptomyces as Sources of Antibacterial Pigments for Silk Dyeing.

Actinobacteria produce a broad spectrum of bioactive substances that are used in the pharmaceutical, agricultural, and biotechnology industries. This study investigates the production of bioactive substances in Streptomyces, isolated from soil under five tropical plants, focusing on their potential as natural antibacterial dyes for silk fabrics. Out of 194 isolates, 44 produced pigments on broken rice as a solid substrate culture. Eight antibacterial pigmented isolates from under Magnolia baillonii (TBRC 15924, TBRC 15927, TBRC 15931), Magnolia rajaniana (TBRC 15925, TBRC 15926, TBRC 15928, TBRC 15930), and Cinnamomum parthenoxylon (TBRC 15929) were studied in more detail. TBRC 15927 was the only isolate where all the crude extracts inhibited the growth of the test organisms, Staphylococcus epidermidis TISTR 518 and S. aureus DMST 4745. The bioactive compounds present in TBRC 15927 were identified through LC-MS/MS analysis as belonging to the actinomycin group, actinomycin D (or X1), X2, and X0ß. Also, the ethyl acetate crude extract exhibited non-toxicity at an IC50 value of 0.029 ± 0.008 µg/mL on the mouse fibroblast L-929 assay. From the 16S rRNA gene sequence analysis, TBRC 15927 had 100% identity with Streptomyces gramineus JR-43T. Raw silk dyed with the positive antimicrobial TBRC 15927 extract (8.35 mg/mL) had significant (>99.99%) antibacterial properties. Streptomyces gramineus TBRC 15927 is the first actinomycin-producing strain reported to grow on broken rice and shows promise for antibacterial silk dyeing.

Bioactivities and genome insights of a thermotolerant antibiotics-producing Streptomyces sp. TM32 reveal its potentials for novel drug discovery.

A way to defeat antimicrobial resistance (AMR) crisis is to supply novel drugs to the pharmaceutical industry. This effort leads to a global call for seeking the beneficial microbes from underexplored habitats. To support this call, we isolated Streptomyces sp. TM32 from the rhizosphere soil of a medicinal plant, turmeric (Curcuma longa L.). TM32 exhibited strong antimicrobial activities against both human and plant pathogens, including an AMR pathogen, Staphylococcus haemolyticus MR-CoNS. Surprisingly, such antimicrobial results of TM32's autoclaved crude extract remained the same. Based on the genome data analysis, TM32 belongs to the same genomic species with Streptomyces sioyaensis DSM 40032T , supported by the relatively high-average nucleotide identity values (ANIb: 96.80% and OrthoANIu: 97.14%) and in silico DNA-DNA relatedness value of 75.40%. Importantly, the gene annotation analyses revealed that TM32's genome contains various genes encoding the biosynthesis of either known or unknown antibiotics and some metabolites involved in plant growth-promoting traits. However, bioactivities and genome data comparison of TM32 and DSM 40032T showed a set of apparent differences, for example, antimicrobial potentials, genome size, number, and occurrence of coding DNA sequences in the chromosomes. These findings suggest that TM32 is a new strain of S. sioyaensis and serves as an emerging source for further discovery of valuable and novel bioactive compounds.

Seed phytochemicals shape the community structures of cultivable actinobacteria-inhabiting plant interiors of Thai pigmented rice.

We examined abundance, bioactivity, and endophytism of cultivable actinobacteria isolated from plant interiors of two Thai pigmented rice cultivars: Hom Nin (HN) rice and Luem Pua (LP) glutinous rice. Both rice cultivars housed the same amount of endophytic actinobacteria (33 isolates each). Microbispora (76%) and Streptomyces (73%) were the predominant endophytic actinobacteria of LP glutinous rice and HN rice, respectively. Sphaerisporangium (9%) was found only in LP glutinous rice. Twelve percent of endophytic actinobacteria was the possibility of discovering novel species from both rice cultivars. Most endophytic actinobacteria exhibited plant growth-promoting potentials, including antimicrobial activity against test bacteria and phytopathogenic fungi, solubilization of phosphate, and production of biostimulants (i.e., ammonia, indole-3-acetic acid, and siderophore) and biocatalysts (i.e., amylase, cellulase, chitinase, lipase, and protease). Our findings revealed that seed phytochemicals of pigmented rice (e.g., anthocyanin, γ-oryzanol, phytate, antioxidants, and content of amylose) were effectors, shaping the community structures and biofunctions of endophytic actinobacteria. We conclude that pigmented rice is yet a challenging source for discovery of bioactive and novel actinobacteria. This study also provides new insights into the plant-endophyte interactions by which seed phytochemicals act as a primary checkpoint in the natural selection for establishing unique plant endophytomes.

The genus Nonomuraea: A review of a rare actinomycete taxon for novel metabolites.

The genus Nonomuraea is a rare actinomycete taxon with a long taxonomic history, while its generic description was recently emended. The genus is less known among the rare actinomycete genera as its taxonomic position was revised several times. It can be found in diverse ecological niches, while most of its member species were isolated from soil samples. However, new trends to discover the genus in other habitats are increasing. Generic abundance of the genus was found to be dependent on geographical changes. Novel sources together with selective and invented isolation techniques might increase a chance to explore the genus and its novel candidates. Interestingly, some of its members have been revealed as a valuable source of novel metabolites for medical and industrial purposes. Broad-range of potent bioactive compounds including antimicrobial, anticancer, and antipsychotic substances, broad-spectrum antibiotics and biocatalysts can be synthesized by the genus. In order to investigate biosynthetic pathways of the bioactive compounds and self-resistant mechanisms to these compounds, the links from genes to metabolites have yet been needed for further discovery and biotechnological development of the genus Nonomuraea.

Nonomuraea monospora sp. nov., an actinomycete isolated from cave soil in Thailand, and emended description of the genus Nonomuraea.

A novel actinomycete, designated strain PT708(T), was isolated from cave soil collected in Pha Tup Cave Forest Park, Nan province, Thailand. It produced compounds with antimicrobial and anticancer activities. Its chemotaxonomic properties were consistent with those of members of the genus Nonomuraea. The major menaquinone was MK-9(H(4)), with minor amounts of MK-9(H(6)), MK-9(H(2)), MK-10(H(2)) and MK-8(H(4)). The polar lipid profile contained phosphatidylmonomethylethanolamine, diphosphatidylglycerol, hydroxy-phosphatidylmonomethylethanolamine, hydroxy-phosphatidylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol mannoside and phosphatidylinositol. The major fatty acids were iso-C(16:0), 10-methyl C(17:0), C(16:0) and C(17:1)ω6c. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain PT708(T) belonged to the genus Nonomuraea and was most closely related to Nonomuraea rhizophila YIM 67092(T) (98.50% sequence similarity) and Nonomuraea rosea GW 12687(T) (98.30%). The genomic DNA G+C content of strain PT708(T) was 73.3 mol%. Unlike the recognized members of the genus Nonomuraea, the novel strain formed single spores at the tips of aerial hyphae. Based on the phenotypic, phylogenetic and genotypic evidence, strain PT708(T) represents a novel species of the genus Nonomuraea, for which the name Nonomuraea monospora sp. nov. is proposed. The type strain is PT708(T) ( = TISTR 1910(T) = JCM 16114(T)).