Gil-Jae Joo

Growth promotion of red pepper plug seedlings and the production of gibberellins by Bacillus cereus, Bacillus macroides and Bacillus pumilus.

The growth of red pepper plug seedlings was promoted by Bacillus cereus MJ-1, B. macroides CJ-29, and B. pumilus CJ-69 isolated from the rhizosphere. Gibberellins (GAs), a well-known plant growth-promoting hormone, were detected in the culture broth of their rhizobacteria. Among the GAs, the contents of GA1, GA3, GA4, and GA7, physiologically active GAs, were comparatively higher than those of others, suggesting that the growth promoting effect was originated from the GAs. This is the first report on the production of GA5, GA8, GA34, GA44, and GA53 by bacteria.

Production of an anti-fungal substance for biological control of Phytophthora capsici causing phytophthora blight in red-peppers by Streptomyces halstedii

The culture broth of Streptomyces halstedii AJ-7 suppressed the growth of Phytophthora capsici, which causes phytophthora blight in red-peppers, with less than 1% survival of the pathogen after 12 h of treatment. The low molecular fraction (⩽ 10 kDa) of the culture broth retained anti-fungal activity against P. capsici after being held at 100 °C for 6 h.

Gibberellin-producing Promicromonospora sp. SE188 improves Solanum lycopersicum plant growth and influences endogenous plant hormones

Plant growth-promoting rhizobacteria (PGPR) producing gibberellins (GAs) can be beneficial to plant growth and development. In the present study, we isolated and screened a new strain of Promicromonospora sp., SE188, isolated from soil. Promicromonospora sp. SE188 secreted GAs into its growth medium and exhibited phosphate solubilization potential. The PGPR produced physiologically active (GA1 and GA4) and inactive (GA9, GA12, GA19, GA20, GA24, GA34, and GA53) GAs in various quantities detected by GC/MS-SIM. Solanum lycopersicum (tomato) plants inoculated with Promicromonospora sp. SE188 showed a significantly higher shoot length and biomass as compared to controls where PGPR-free nutrient broth (NB) and distilled water (DW) were applied to plants. The presence of Promicromonospora sp. SE188 significantly up-regulated the non C-13 hydroxylation GA biosynthesis pathway (GA12→GA24→GA9→GA4→ GA34) in the tomato plants as compared to the NB and DW control plants. Abscisic acid, a plant stress hormone, was significantly down-regulated in the presence of Promicromonospora sp. SE188. Contrarily, salicylic acid was significantly higher in the tomato plant after Promicromonospora sp. SE188 inoculation as compared to the controls. Promicromonospora sp. SE188 showed promising stimulation of tomato plant growth. From the results it appears that Promicromonospora sp. SE188 has potential as a bio-fertilizer and should be more broadly tested in field trials for higher crop production in eco-friendly farming systems.

Burkholderia sp. KCTC 11096BP as a newly isolated gibberellin producing bacterium

We isolated 864 bacteria from 553 soil samples and bioassayed them on cucumber and crown daisy for plant growth promotion. A new bacterial strain, Burkholderia sp. KCTC 11096BP gave maximum growth promotion and was selected for further investigations. The culture filtrate of this bacterium was thus analyzed for the presence of gibberellins and we found physiologically active gibberellins were found (GA1, 0.23 ng/100 ml; GA3, 5.11 ng/100 ml and GA4, 2.65 ng/100 ml) along with physiologically inactive GA9, GA12, GA15, GA20, and GA24. The bacterial isolate also solubilised tricalcium phosphate and lowered the pH of the medium during the process. The isolate was identified as a new strain of Burkholderia through phylogenetic analysis of 16S rDNA sequence. Gibberellin production capacity of genus Burkholderia is reported for the first time in current study.

Effects of Green Tea Catechin on Polymorphonuclear Leukocyte 5′-Lipoxygenase Activity, Leukotriene B4 Synthesis, and Renal Damage in Diabetic Rats

The purpose of this study was to investigate the effects of green tea catechin on polymorphonuclear leukocyte 5′-lipoxygenase activity, leukotriene B4 synthesis, and renal damage in diabetic rats. Male Sprague-Dawley rats weighing 100 ± 10 g were randomly assigned to 1 normal group and 3 diabetic groups given a catechin-free diet (DM-0C group), 0.25% catechin diet (DM-0.25C group), or 0.5% catechin diet (DM-0.5C group), respectively. 5′-Lipoxygenase activity in the polymorphonuclear leukocytes significantly increased by 54% in the DM-0C group compared to the normal group, while the level in the DM-0.5C group remained the same as in the normal group. The leukotriene B4 content in the polymorphonuclear leukocytes increased 55% in the DM-0C group compared to the normal group, whereas the DM-0.25C and DM-0.5C groups exhibited the same level as the normal group. The superoxide radical content in the kidney microsomes increased 116% in the DM-0C group when compared to the normal group, yet decreased 29% in the DM-0.25C group and 50% in the DM-0.5C group compared to DM-0C group. The lipofuscin content was 197 and 136% higher in the DM-0C and DM-025C groups, respectively, than in the normal group, whereas the DM-0.5C group exhibited the same content as in the normal group. The carbonyl value increased 118% in the DM-0C group compared to the normal group, and the DM-0.25C and DM-0.5C groups were not significantly different from the DM-0C group. Accordingly, these results indicate that dietary catechin inhibited the generation of superoxide radicals, oxidized protein, and lipid peroxide in the kidney of streptozotocin-induced diabetic rats. Furthermore, green tea catechin supplementation in diabetic rats also appeared to inhibit the production of leukotriene B4 based on regulating the activity of 5′-lipoxygenase, thereby potentially reducing renal oxidative damage and inflammatory reactions.

Enterococcus faecium LKE12 Cell-Free Extract Accelerates Host Plant Growth via Gibberellin and Indole-3-Acetic Acid Secretion.

The use of microbial extracts containing plant hormones is a promising technique to improve crop growth. Little is known about the effect of bacterial cell-free extracts on plant growth promotion. This study, based on phytohormonal analyses, aimed at exploring the potential mechanisms by which Enterococcus faecium LKE12 enhances plant growth in oriental melon. A bacterial strain, LKE12, was isolated from soil, and further identified as E. faecium by 16S rDNA sequencing and phylogenetic analysis. The plant growth-promoting ability of an LKE12 bacterial culture was tested in a gibberellin (GA)-deficient rice dwarf mutant (waito-C) and a normal GA biosynthesis rice cultivar (Hwayongbyeo). E. faecium LKE12 significantly improved the length and biomass of rice shoots in both normal and dwarf cultivars through the secretion of an array of gibberellins (GA1, GA3, GA7, GA8, GA9, GA12, GA19, GA20, GA24, and GA53), as well as indole-3-acetic acid (IAA). To the best of our knowledge, this is the first study indicating that E. faecium can produce GAs. Increases in shoot and root lengths, plant fresh weight, and chlorophyll content promoted by E. faecium LKE12 and its cell-free extract inoculated in oriental melon plants revealed a favorable interaction of E. faecium LKE12 with plants. Higher plant growth rates and nutrient contents of magnesium, calcium, sodium, iron, manganese, silicon, zinc, and nitrogen were found in cell-free extract-treated plants than in control plants. The results of the current study suggest that E. faecium LKE12 promotes plant growth by producing GAs and IAA; interestingly, the exogenous application of its cell-free culture extract can be a potential strategy to accelerate plant growth.

Isolation and characterization of a novel silicate-solubilizing bacterial strain Burkholderia eburnea CS4-2 that promotes growth of japonica rice (Oryza sativa L. cv. Dongjin)

ABSTRACT The current study aimed to isolate and identify japonica rice (Oryza sativa L. cv. Dongjin) root-associated rhizobacteria and to investigate their ability to solubilize silicate, produce indole acetic acid (IAA), promote plant growth, and encourage silicon (Si) uptake and deposit in plants. A single bacterial isolate was selected on the basis of its silica-solubilizing ability and IAA production. The 16S rRNA gene sequence of the isolate identified it as Burkholderia eburnea CS4-2. Burkholderia eburnea CS4-2 produced high amounts of IAA at pH 8. When combined with silica fertilization, soil inoculation with CS4-2 promoted all growth attributes over those of the water-treated (control) and insoluble silica-fertilized plants. Microscopic observations also demonstrated a significant difference in the Si deposits on the leaf epidermis of rice plants under different treatments, indicating that more Si was deposited in plants fertilized with both B. eburnea CS4-2 and insoluble silica than in either insoluble silica-fertilized or water-treated plants. Inductively coupled plasma spectrometry analysis confirmed the same trend of Si concentration in whole-plant biomass of the rice that received the same treatments, respectively. Therefore, we conclude that B. eburnea CS4-2 has the ability to produce IAA under high-pH conditions, solubilize silicate, and promote plant growth. Graphical Abstract