Chryseobacterium tagetis sp. nov., a plant growth promoting bacterium with an antimicrobial activity isolated from the roots of medicinal plant (Tagetes patula)

Diversity and functional features of the root-associated bacteriome are dependent on grapevine susceptibility to Plasmopara viticola

BACKGROUND

Plant health depends on beneficial interactions between the roots and their microbiomes. Despite recent progress on the role of the grapevine microbiome, the taxonomic identity and functional traits of microbial taxa specific to healthy or Plasmopara viticola-diseased plants, as well as to the susceptible or resistant cultivar are unknown. Using metabarcoding and shotgun metagenomics sequencing, we investigated the effect of downy mildew on the root-associated microbiome (rhizospheric soil, rhizoplane and endosphere) of 41B-grafted susceptible cultivar (Chardonnay) and resistant interspecific hybrid (Voltis) at flowering and veraison stages. The impact of conventional treatment on the rhizomicrobiome assembly of Chardonnay was also evaluated.

RESULTS

Analyses revealed a core bacteriome shared between both susceptible and resistant cultivars. This also highlighted common functional traits between the rhizosphere and rhizoplane bacteriomes in both cultivars. A dysbiosis state was also evidenced by a loss of beneficial communities in the rhizosphere of the P. viticola-infected cultivar. Microbial genome assemblies showed functional differences between healthy and diseased plants, with a loss of Pseudomonas and Phyllobacterium taxa at veraison. This state was mainly characterized by a loss of genes involved in polyamine transport and metabolism in the susceptible cultivar. It was also marked by an increase in population evenness and total bacterial diversity, and the presence of pathogenic species in susceptible plants.

CONCLUSIONS

This study reveals distinct and overlapping bacterial communities and functional genes in the rhizospheric soil, rhizoplane and root endosphere of both susceptible and resistant grapevine cultivars to downy mildew. Microbial diversity and abundant taxa of grapevine roots are influenced by downy mildew and cultivar susceptibility. Common bacterial functions are shared among rhizocompartments of susceptible and resistant cultivars, revealing a dysbiosis state and functional signatures related to plant immunity, especially in the infected-susceptible plants.

Shift patterns of internal bacterial communities across five life stages of laboratory-maintained Eremobelba eharai (Acari: Oribatida: Eremobelbidae)

Microbial communities play a crucial role in the physiological characteristics, adaptability, and reproductive success of arthropods. However, the patterns and functions of microbial variation across different life stages of mites remain poorly understood. In this study, we used high throughput Illumina sequencing of the 16S rRNA gene to investigate the composition and functional potential of bacterial communities in five life stages (larva, protonymph, deutonymph, tritonymph, and adult) of the oribatid mite Eremobelba eharai. We found significant differences in bacterial diversity and community structure across the different life stages despite being fed the same diet. The bacterial diversity was highest at the protonymph stage and lowest at the tritonymph stage. Beta diversity analysis indicated distinct bacterial community compositions among the different life stages. Bacteroidota, Proteobacteria, and Firmicutes dominated the bacterial communities throughout the host's life cycle. Key bacterial genera, such as Bacillus, Streptomyces, Achromobacter, and Tsukamurella, showed significant differences in abundance across the different life stages. Predicted functional profiles revealed substantial changes in metabolic pathways, which may reflect changes in the nutritional needs of E. eharai during its developmental process. PICRUSt prediction results also showed that in most KEGG pathways, the larval and adult stages consistently maintain similar relative abundances of bacteria. Different stages such as the deutonymph and adult stages show consistent differences in the "biosynthesis of other secondary metabolites" and "glycan biosynthesis and metabolism" pathways. This study provides new insights into the dynamic changes of bacterial communities within oribatid mites and lays a foundation for further research on the interactions between oribatid mites and microorganisms.

Assessing Normandy Soil Microbial Diversity for Antibacterial Activities Using Traditional Culture and iChip Methods

Uncultured microorganisms represent a promising and untapped source of antibacterial compounds, crucial in the fight against the significant threat of antimicrobial resistance (AMR). In this study, both traditional and isolation chip (iChip) cultivation techniques were employed to enhance the recovery of known and unknown microorganisms from soils located in Normandy, France. The isolates obtained were identified using 16S rDNA or ITS regions analysis and MALDI-TOF mass spectrometry and were screened for antibacterial activity. A total of 386 isolates, belonging to 6 microbial phyla and distributed across 65 genera, were recovered using both methods. In total, 11 isolates are potentially new bacterial species, and 34 were associated with 22 species described recently. The iChip method yielded a higher diversity of microorganisms (47 genera) than the traditional method (38 genera) and was particularly effective in enriching Actinomycetota. Antibacterial screening against target bacteria showed that 85 isolates (22%) exhibited antibacterial activity. The Streptomyces, Pseudomonas, and Bacillaceae taxa accounted for most antibacterial-producing bacteria with some presenting promising undescribed characteristics. Other active isolates were affiliated with less-known antibacterial producers such as Arthrobacter, Chryseobacterium, Delftia, Ensifer, Flavobacterium, Rahnella, and Stenotrophomonas, among others. These results highlight the potential of our microbial collection as a source of new antibacterial natural products.

Isolation of Massilia species capable of degrading Poly(3-hydroxybutyrate) isolated from eggplant (Solanum melongena L.) field

Poly(3-hydroxybutyrate) (PHB) is crucial for replacing petroleum-based plastics, an essential step towards fostering a bio-based economy. This shift is urgently needed to safeguard human health and preserve natural ecosystems. PHB is one of the most extremely commercialized bio-plastics. Although. significant progress has been made in identifying bacteria that produce PHB, fewer bacteria capable of degrading it have been discovered. Four newly isolated Massilia strains capable of degrading PHB were discovered in eggplant (Solanum melongena L.) field soil. Their PHB-degrading abilities were investigated under different temperatures and media using emulsified solid-media based cultures. The strains belong to the genus Massilia, were evaluated for their effectiveness. Among them, Massilia sp. JJY02, was selected for its exceptional PHB degradation. PHB degradation was confirmed by monitoring changes in the physical and chemical properties of PHB films using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). After 20 days of cultivation with PHB film, Massilia sp. JJY02 achieved approximately 90% PHB degradation at 28 °C. All the novel strains were capable of producing carotenoid-type pigments and indole-acetic acid (IAA). Among them, Massilia sp. JJY03 and JJY04 showed phosphate solubilization activity. This study demonstrated that soil bacteria from eggplant have both PHB-degrading and plant growth promoting capabilities, marking the first instance of showing that species of Massilia can degrade PHB.

Rapid Loss of Nutritional Symbionts in an Endemic Hawaiian Herbivore Radiation Is Associated with Plant Galling Habit

Insect herbivores frequently cospeciate with symbionts that enable them to survive on nutritionally unbalanced diets. While ancient symbiont gain and loss events have been pivotal for insect diversification and feeding niche specialization, evidence of recent events is scarce. We examine the recent loss of nutritional symbionts (in as little as 1 MY) in sap-feeding Pariaconus, an endemic Hawaiian insect genus that has undergone adaptive radiation, evolving various galling and free-living ecologies on a single host-plant species, Metrosideros polymorpha within the last ∼5 MY. Using 16S rRNA sequencing, we investigated the bacterial microbiomes of 19 Pariaconus species and identified distinct symbiont profiles associated with specific host-plant ecologies. Phylogenetic analyses and metagenomic reconstructions revealed significant differences in microbial diversity and functions among psyllids with different host-plant ecologies. Within a few millions of years, Pariaconus species convergently evolved the closed-gall habit twice. This shift to enclosed galls coincided with the loss of the Morganella-like symbiont that provides the essential amino acid arginine to free-living and open-gall sister species. After the Pariaconus lineage left Kauai and colonized younger islands, both open- and closed-gall species lost the Dickeya-like symbiont. This symbiont is crucial for synthesizing essential amino acids (phenylalanine, tyrosine, and lysine) as well as B vitamins in free-living species. The recurrent loss of these symbionts in galling species reinforces evidence that galls are nutrient sinks and, combined with the rapidity of the evolutionary timeline, highlights the dynamic role of insect-symbiont relationships during the diversification of feeding ecologies. We propose new Candidatus names for the novel Morganella-like and Dickeya-like symbionts.

Streptomyces tagetis sp. nov., a chromomycin producing bacteria isolated from the roots of Tagetes patula

A novel halotolerant actinobacterium, designated as RG38T, capable of producing black extracellular melanin pigment on SP2 agar, was isolated from the roots of Tagetes patula. Comparative analysis of the 16S rRNA gene sequence revealed the highest similarity to Streptomyces collinus NBRC 12759T (99.3%). Phylogenetic analysis showed that strain RG38T clustered within the genus Streptomyces forming a monophyletic cluster with its close relatives. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and amino-acid identity (AAI) values between strain RG38T and related species within the genus Streptomyces were below the standard threshold for prokaryotic species delineation. The DNA G + C content of the strain RG38T was determined to be 73.3%. The genome size measured 7,150,598 bp comprising 17 contigs and encompassed 6,053 protein coding genes. AntiSMASH analysis of the whole genome revealed 35 putative biosynthetic gene clusters (BGCs) responsible for various secondary metabolites. Among these clusters, two gene clusters exhibited 100% similarity to the chromomycin A3, albaflavenone, and anthracimycin, respectively. These compounds were reported to possess significant anticancer and antibacterial activities. LC-MS-based analysis, coupled with further isolation studies, confirmed the production of chromomycins A2 (1), A3 (2), and their derivatives, along with their antibiotic activities. These findings underscore the potential of this novel strain as a novel resource for the discovery of diverse antimicrobial compounds. This study is the first to report an antimicrobial compound producing Streptomyces species isolated from medicinal plant T. patula. Based on a polyphasic study, the strain RG38T isolated from an unexplored habitat with a high potential for new natural products represents a novel species within the genus Streptomyces. Accordingly, we propose the name Streptomyces tagetis sp. nov. for this novel species, with the type strain is RG38T (=KCTC 49624T = TBRC 15113T).

Isolation, identification, and biological characterization of bacterial endophytes isolated from Gunnera perpensa L

In the present study, eleven endophytic bacterial strains, Herbaspirillum sp. (GP-SGM1, GP-SGM2, GP-SGM3, and GP-SGM11), Pseudomonas sp. (GP-SGM4, GP-SGM5), Novosphingobium sp. GP-SGM6, Chryseobacterium sp. GP-SGM7, Labedella sp. GP-SGM8, Brevibacterium sp. GP-SGM9, and Pseudomonas sp. GP-SGM10, were isolated from the rhizomes of Gunnera perpensa L. The growth kinetics, assessed through maximum growth rates (μmax) and optical density (OD) values, revealed that GP-SGM7 exhibited highest μmax values of 0.33 ± 0.01 hours (h)-1 with an OD of 4.20 ± 0.04. In contrast, GP-SGM11 exhibited the lowest μmax of 0.12 ± 0.05 h-1 and the smallest OD of 1.50 ± 0.00. In addition, the endophyte crude extracts were tested for antibacterial activity against five pathogenic strains using the disk diffusion method, with GP-SGM7 crude extracts exhibiting promising antibacterial activity against Klebsiella pneumoniae and Staphylococcus aureus. Antioxidant activity was determined by DPPH (2, 2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays. The crude extracts of GP-SGM1, GP-SGM7, GP-SGM9, and GP-SGM10 were the most effective at scavenging DPPH radicals, with GP-SGM7 also exhibiting a high FRAP value of 0.54 ± 0.01. These findings emphasize the therapeutic potential of endophytic bacteria from G. perpensa L. in addressing skin-related issues, including bacterial infections and free radicals.

GC-MS profiling of Pistachio vera L., and effect of antioxidant and antimicrobial compounds of it's essential oil compared to chemical counterparts

All elements of the pistachio tree are considered raw pistachio by-products. The soft hull makes up the majority of these by-products. It contains proteins, fats, minerals, vitamins, phenolics contents (TPC), and antioxidants. Early smiling pistachios are one of the most important sources of pistachio contamination with aflatoxin in the garden and processing stages. The present study aimed to evaluate pistachio hull essential oil (EO) composition, and antioxidant and antimicrobial properties under in vitro conditions. TPC, antioxidant, and antimicrobial activity were measured using the Folin-Ciocalteu reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging method, and serial dilution titration method, respectively. A gas chromatography system with a mass spectrometer (GC-MS) was utilized to determine the chemical components of the EO. The findings revealed that the quantity of TPC and anti-radical activity in IC50 were 245.43 mg gallic acid/mL and 206.32 µL/L, respectively. The free radical absorption activity of DPPH (%) increased with EO content. The inhibitory activity of EO on Staphylococcus aureus and Bacillus subtilis was much lower than that of streptomycin and penicillin. Aspergillus flavus was effectively inhibited by pistachio hull EO, comparable to fluconazole. The results obtained from GC-MS showed that the major compounds in pistachio hull essential oil include α-pinene (47.36%), terpinolene (10.57%), limonene (9.13%), and L-bornyl acetate (8.57%). The findings indicated that pistachio hull EO has potent antibacterial and antioxidant components and can be employed as a natural antimicrobial and antioxidant in food systems.

Comparative genomic analysis of Chryseobacterium species: deep insights into plant-growth-promoting and halotolerant capacities

Members of the genus Chryseobacterium have attracted great interest as beneficial bacteria that can promote plant growth and biocontrol. Given the recent risks of climate change, it is important to develop tolerance strategies for efficient applications of plant-beneficial bacteria in saline environments. However, the genetic determinants of plant-growth-promoting and halotolerance effects in Chryseobacterium have not yet been investigated at the genomic level. Here, a comparative genomic analysis was conducted with seven Chryseobacterium species. Phylogenetic and phylogenomic analyses revealed niche-specific evolutionary distances between soil and freshwater Chryseobacterium species, consistent with differences in genomic statistics, indicating that the freshwater bacteria have smaller genome sizes and fewer genes than the soil bacteria. Phosphorus- and zinc-cycling genes (required for nutrient acquisition in plants) were universally present in all species, whereas nitrification and sulphite reduction genes (required for nitrogen- and sulphur-cycling, respectively) were distributed only in soil bacteria. A pan-genome containing 6842 gene clusters was constructed, which reflected the general features of the core, accessory and unique genomes. Halotolerant species with an accessory genome shared a Kdp potassium transporter and biosynthetic pathways for branched-chain amino acids and the carotenoid lycopene, which are associated with countermeasures against salt stress. Protein-protein interaction network analysis was used to define the genetic determinants of Chryseobacterium salivictor NBC122 that reduce salt damage in bacteria and plants. Sixteen hub genes comprised the aromatic compound degradation and Por secretion systems, which are required to cope with complex stresses associated with saline environments. Horizontal gene transfer and CRISPR-Cas analyses indicated that C. salivictor NBC122 underwent more evolutionary events when interacting with different environments. These findings provide deep insights into genomic adaptation to dynamic interactions between plant-growth-promoting Chryseobacterium and salt stress.

Drought stress-mediated differences in phyllosphere microbiome and associated pathogen resistance between male and female poplars

Phyllosphere-associated microbes play a crucial role in plant-pathogen interactions while their composition and diversity are strongly influenced by drought stress. As dioecious plant species exhibited secondary dimorphism between the two sexes in response to drought stress, whether such difference will lead to sex-specific differences in phyllosphere microbiome and associated pathogen resistance between male and female conspecifics is still unknown. In this study, we subjected female and male full siblings of a dioecious poplar species to a short period of drought treatment followed by artificial infection of a leaf pathogenic fungus. Our results showed that male plants grew better than females with or without drought stress. Female control plants had more leaf lesion area than males after pathogen infection, whereas drought stress reversed such a difference. Further correlation and in vitro toxicity tests suggested that drought-mediated sexual differences in pathogen resistance between the two plant sexes could be attributed to the shifts in structure and function of phyllosphere-associated microbiome rather than the amount of leaf main defensive chemicals contained in plant leaves. Supportively, the microbiome analysis through high-throughput sequencing indicated that female phyllosphere enriched a higher abundance of ecologically beneficial microbes that serve as biological plant protectants, while males harbored abundant phytopathogens under drought-stressed conditions. The results could provide potential implications for the selection of suitable poplar sex to plants in drought or semi-drought habitats.

Chryseobacterium edaphi sp. nov. and Chryseobacterium gilvum sp. nov., isolated from soil

Two Gram-stain-negative, aerobic, yellow and rod-shaped bacteria, designated as strains PBS4-4^T and GMJ5^T, were isolated from soil samples collected in Goyang-si and Paju-si, Gyeonggi-do, Republic of Korea. Strains PBS4-4^T and GMJ5^T were both positive for catalase and oxidase. Strain PBS4-4^T grew at 15-37 °C and pH 5.0-12.0. Strain GMJ5^T grew at 15-37 °C and pH 5.0-11.0. Neither strain required NaCl for growth. 16S rRNA sequence analysis revealed that strains PBS4-4^T and GMJ5^T form a closely related cluster with the genus Chryseobacterium. The average nucleotide identity and digital DNA-DNA hybridization values between strain PBS4-4^T and its closely related strains were 79.4-84.5% and 23.2-28.7 %, respectively. For GMJ5^T, the values were 78.3-79.3% and 22.0-22.6 %, respectively. The major fatty acids shared by both novel strains were iso-C_15 : 0 and summed feature 3 (C_16 : 1 ω7c/C_16 : 1 ω6c). Strain GMJ5^T had one other major fatty acid: iso-C_17 : 0 3OH. Based on phenotypic, genomic and phylogenetic results, strains PBS4-4^T and GMJ5^T represent novel species within the genus Chryseobacterium, and the names Chryseobacterium edaphi sp. nov. and Chryseobacterium gilvum sp. nov. are proposed, respectively. The type strain of C. edaphi is PBS4-4^T (=KACC 22882^T=TBRC 17052^T) and the type strain of C. gilvum is GMJ5^T (=KACC 22883^T=TBRC 17053^T).

Disclosing the native blueberry rhizosphere community in Portugal-an integrated metagenomic and isolation approach

Backgorund

The production of red fruits, such as blueberry, has been threatened by several stressors from severe periods of drought, nutrient scarcity, phytopathogens, and costs with fertilization programs with adverse consequences. Thus, there is an urgent need to increase this crop's resilience whilst promoting sustainable agriculture. Plant growth-promoting microorganisms (PGPMs) constitute not only a solution to tackle water and nutrient deficits in soils, but also as a control against phytopathogens and as green compounds for agricultural practices.

Methods

In this study, a metagenomic approach of the local fungal and bacterial community of the rhizosphere of Vaccinium corymbosum plants was performed. At the same time, both epiphytic and endophytic microorganisms were isolated in order to disclose putative beneficial native organisms.

Results

Results showed a high relative abundance of Archaeorhizomyces and Serendipita genera in the ITS sequencing, and Bradyrhizobium genus in the 16S sequencing. Diversity analysis disclosed that the fungal community presented a higher inter-sample variability than the bacterial community, and beta-diversity analysis further corroborated this result. Trichoderma spp., Bacillus spp., and Mucor moelleri were isolated from the V. corymbosum plants.

Discussion

This work revealed a native microbial community capable of establishing mycorrhizal relationships, and with beneficial physiological traits for blueberry production. It was also possible to isolate several naturally-occurring microorganisms that are known to have plant growth-promoting activity and confer tolerance to hydric stress, a serious climate change threat. Future studies should be performed with these isolates to disclose their efficiency in conferring the needed resilience for this and several crops.

Enhanced biodegradation of thiamethoxam with a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar immobilized Chryseobacterium sp H5

Long-term and extensive usage of thiamethoxam, the second-generation neonicotinoid insecticide, has caused a serious threat to non-target organisms and ecological security. Efficient immobilized microorganism techniques are a sustainable solution for bioremediation of thiamethoxam contamination. A Gram-negative aerobic bacterium Chryseobacterium sp H5 with high thiamethoxam-degrading efficiencies was isolated from activated sludge. Then we developed a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar bead with this functional microbe immobilization to enhance the biodegradation and removal of thiamethoxam. Results indicated that the total removal and biodegradation rate of thiamethoxam with PVA/SA/biochar (0.7 %) beads with Chryseobacterium sp H5 immobilization at 30 °C and pH of 7.0 within 7 d reached about 90.47 % and 68.03 %, respectively, much higher than that using PVA/SA immobilized microbes (75.06 %, 56.05 %) and free microbes (61.72 %). Moreover, the PVA/SA/biochar (0.7 %) immobilized microbes showed increased tolerance to extreme conditions. Biodegradation metabolites of thiamethoxam were identified and two intermediates were first reported. Based on the identified biodegradation intermediates, cleavage of C-N between the 2-chlorothiazole ring and oxadiazine, dichlorination, nitrate reduction and condensation reaction would be the major biodegradation routes of thiamethoxam. Results of this work suggested the novel PVA/SA/biochar beads with Chryseobacterium sp H5 immobilization would be helpful for the effective bioremediation of thiamethoxam contamination.

Paraburkholderia tagetis sp. nov., a novel species isolated from roots of Tagetes patula enhances the growth and yield of Solanum lycopersicum L. (tomato)

A multifunctional, Gram-stain-negative, aerobic, motile by flagella, short-rod shaped bacteria, designated strain RG36^T was isolated from roots of marigold plant (Tagetes patula) sampled at Dongguk University, Republic of Korea. A 16S rRNA sequences indicated that the closest phylogenetic neighbors were Paraburkholderia acidiphila 7Q-K02^T (99.0%) and Paraburkholderia sacchari IPT101^T (98.9%) of the family Burkholderiaceae. The draft genome size was 8.52 Mb (63.7% GC). The genome contained 7,381 coding sequences. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of strain RG36^T with its most closely related species were only 83.1-88.7 and 27.6-36.7%, respectively. Strain RG36^T contained Q-8 as the major respiratory quinone and its main fatty acids (>10%) were C_16:0, C_17:0 cyclo, C_19:0 cyclo ω8c, and summed feature 8 (comprising C_18:1 ω7c and/or C_18:1 ω6c). Strain RG36^T accumulates polyhydroxybutyrates (PHB) and exhibits multiple plant growth-promoting properties including production of indole-3-acetic acid (IAA), siderophores, protease, phosphate solubilization, and harboring gene clusters for its multifunctional properties. A pot experiment was conducted to evaluate the effect of PGPR on the growth of Solanum lycopersicum L. (Tomato). Result also confirmed the ability of strain RG36^T to promote tomato plant growth, especially it increases the yield of tomatoes. Structural assessment of the bioplastic by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and GC-MS spectroscopy, which confirmed the structure of the polymer as PHB. Our study revealed the potential of strain RG36^T to promote the growth of tomato plant and fruit yield by stimulating the various phytohormones, which could be use as bio-fertilizers to reduce the use of chemical fertilizers and promotes sustainable agricultural production. The phenotypic, chemotaxonomic and phylogenetic data, and genome analysis showed that strain RG36^T represents a novel species of the genus Paraburkholderia, for which the name Paraburkholderia tagetis sp. nov. is proposed. The type strain is RG36^T (=KACC 22685^T = TBRC 15696^T).

Toxicity test of flavonoid compounds from the leaves of Dendrophthoe pentandra (L.) Miq. using in vitro culture cell models

Background and Aim

The flavonoids from mistletoe are thought to have antimicrobial action. This encouraging finding supports the benefits of medicinal plants as a substitute for synthetic antimicrobials, thus promoting healthy lifestyles. In contrast, it is known that the use of topical drug formulations made from flavonoids of mistletoe (Dendrophthoe pentandra (L.) Miq. Loranthaceae) with Indonesian name, Benalu duku (BD) is required in skin cell irritation. This study aimed to assess the toxic effects of the flavonoid substances of BD, as an initial screening.

Materials and Methods

A myeloma cell line was cultured in Roswell Park Memorial Institute medium, and the Baby Hamster Kidney clone 12 (BHK₂₁) cell line was cultured in Dulbecco's Modified Eagle's Medium from stock (±9 × 10⁷ cells/mL), and 1.2 mL of culture were distributed into each well of a microtiter plate. Subsequently, 0.2 mL of serially diluted flavonoid compounds (0.5-3 μg/mL) were added to 12 wells for each concentration, as trial groups (including control groups), followed by a 2-day incubation. Observations were performed based on the cytopathic effect (CPE) using an inverted microscope at a magnification of 100×.

Results

Cytopathic effect was detected on the microtiter plate wells for the groups of myeloma and BHK₂₁ cells at a flavonoid concentration of 0.5 μg/mL-3 μg/mL.

Conclusion

Flavonoid compounds from BD were safely used for topical treatment of cancer cells at a concentration <2.491 μg/mL, whereas for non-cancerous cells, a concentration <2.582 μg/mL was sufficient (p < 0.05).

An Isolated Arthrobacter sp. Enhances Rice (Oryza sativa L.) Plant Growth

Rice is a symbol of life and a representation of prosperity in South Korea. However, studies on the diversity of the bacterial communities in the rhizosphere of rice plants are limited. In this study, four bundles of root samples were collected from the same rice field located in Goyang, South Korea. These were systematically analyzed to discover the diversity of culturable bacterial communities through culture-dependent methods. A total of 504 culturable bacteria were isolated and evaluated for their plant growth-promoting abilities in vitro. Among them, Arthrobacter sp. GN70 was selected for inoculation into the rice plants under laboratory and greenhouse conditions. The results showed a significantly positive effect on shoot length, root length, fresh plant weight, and dry plant weight. Moreover, scanning electron microscopic (SEM) images demonstrated the accumulation of bacterial biofilm networks at the junction of the primary roots, confirming the root-colonizing ability of the bacterium. The strain also exhibited a broad spectrum of in vitro antimicrobial activities against bacteria and fungi. Here, we first report the rice plant growth-promoting ability of the Arthrobacter species with the biofilm-producing and antimicrobial activities against plant and human pathogens. Genome analyses revealed features attributable to enhance rice plant growth, including the genes involved in the synthesis of plant hormones, biofilm production, and secondary metabolites. This study revealed that the rhizobacteria isolated from the roots of rice plants have dual potential to be utilized as a plant growth promoter and antimicrobial agent.