A Comparative Study of Micromechanical Analysis Models for Determining the Effective Properties of Out-of-Autoclave Carbon Fiber-Epoxy Composites.

This study aims to critically assess different micromechanical analysis models applied to carbon-fiber-reinforced plastic (CFRP) composites, employing micromechanics-based homogenization to accurately predict their effective properties. The paper begins with the simplest Voigt and Reuss models and progresses to more sophisticated micromechanics-based models, including the Mori-Tanaka and Method of Cells (MOC) models. It provides a critical review of the areas in which these micromechanics-based models are effective and analyses of their limitations. The numerical analysis results were confirmed through finite element simulations of the periodic representative volume element (RVE). Furthermore, the effective properties predicted by these micromechanics-based models were validated via experiments conducted on IM7/5320-1 composite material with a fiber volume fraction of 0.62.

First report in South Korea of a bacterial leaf blight of oats caused by Pseudomonas salomonii.

In March 2020, approximately 20% of leaves in a commercial oat field growing Avena sativa (cv. Samhan) in Jeongeup, Korea (35.3859°, 126.5607°), displayed leaf blight in the seedling stage of development. The lesions observed in 2020 were of a yellow discoloration that spread from the leaf tip downward with minimal brown delineation (Fig. S1A). These symptoms differed from the haloes delineated at the edges by extensive brown necrosis caused by Pseudomonas coronofaciens (Kim 2020a; Fig. S1C). To isolate the causal agent, 3-cm-long pieces of symptomatic leaves from ten different oat plants were disinfected by submersion in 70% ethanol for 5 min followed by immersion in 1% sodium hypochlorite for 5 min and rinsing extensively with sterile distilled water. The air-dried segments were transferred intact to nutrient agar, and only one colony type (yellow-colored, wet, with a shiny convex surface) was observed. After single colony isolation, three isolates from different 2020 field-grown diseased leaves, termed 2007, 2009, and 2011, were selected at random. The isolates produced fluorescent siderophores on King's medium B and triggered a hypersensitive response (HR) when infiltrated into tobacco (cv. Xanthi) leaves (Fig. S1D). Multilocus sequence typing analysis with four housekeeping genes was used for taxonomic identification of these isolates (Maiden et al. 1998). The 16S rRNA sequences were amplified with the 27F/1492R universal primers (Weisburg et al. 1991). The primers for three housekeeping genes were designed using genome sequence of P. coronaficiens X-1 causing halo blight disease in Korea (NZ_CP050260.1, Kim, 2020b). The products obtained had sizes of 640 bp for gltA (using primers F: 5'-CCT GGT AGC CAA GAT GCC GAC-3'; R: 5'-CAA AGA TCA CGG TGA ACA TGC TGG-3'), 710 bp for gyrB (with primers F: 5'-TCG GCA GCC GAG GTC ATC ATG AC-3'; R: 5'-TTG TCT TTG GTC TGC GAG CTG AA-3'), and 870 bp for rpoD ( with primers F: 5'-GTG AAG GCG AAA TCG AAA TCG-3'; R: 5'-CCG ATG TTG CCT TCC TGG ATC AG-3'). The concatenated sequences (2,353 bp/2,376 bp) had 99% identity with the gene sequences from P. salomonii type strain (AY091528.1, NZ_FNOX01000003, LC486864.1, LC486849.1), but lesser identity (90%) with P. coronafaciens (Fig. S2). Pathogenicity of the Korean isolates was confirmed by fulfilling Koch's postulates using leaves of 2 week-old greenhouse-grown 'Samhan' seedlings. Plants (n=50) were sprayed with 108 cfu/ml bacterial suspensions in water or with sterile water as controls. The plants were incubated for a week at 23 °C in 100% relative humidity under a 10 h light/14 h dark photoperiod. Five days after bacterial inoculation, yellow discoloration appeared at the leaf tips which progressed downward with time (Fig. S1B). Three bacterial isolates extracted from yellowed, inoculated leaves had 16S rRNA gene sequences identical to that of P. salomonii Korean isolates, 2007, 2009 and 2011, and they caused the anticipated symptoms when inoculated into oat leaves. These findings indicate that P. salomonii should be added to the potential pathogens of oats grown in Korea. Understanding whether spring weather conditions (warmth and humidity) boost this oat disease will help devise disease alert systems for farmers (Anderson 2004; Chakraborty 2005).

Root-Associated Bacteria Are Biocontrol Agents for Multiple Plant Pests.

Biological control is an important process for sustainable plant production, and this trait is found in many plant-associated microbes. This study reviews microbes that could be formulated into pesticides active against various microbial plant pathogens as well as damaging insects or nematodes. The focus is on the beneficial microbes that colonize the rhizosphere where, through various mechanisms, they promote healthy plant growth. Although these microbes have adapted to cohabit root tissues without causing disease, they are pathogenic to plant pathogens, including microbes, insects, and nematodes. The cocktail of metabolites released from the beneficial strains inhibits the growth of certain bacterial and fungal plant pathogens and participates in insect and nematode toxicity. There is a reinforcement of plant health through the systemic induction of defenses against pathogen attack and abiotic stress in the plant; metabolites in the beneficial microbial cocktail function in triggering the plant defenses. The review discusses a wide range of metabolites involved in plant protection through biocontrol in the rhizosphere. The focus is on the beneficial firmicutes and pseudomonads, because of the extensive studies with these isolates. The review evaluates how culture conditions can be optimized to provide formulations containing the preformed active metabolites for rapid control, with or without viable microbial cells as plant inocula, to boost plant productivity in field situations.

Lorlatinib Therapy for Rapid and Dramatic Control of Brain and Spinal Leptomeningeal Metastases From ALK-Positive Lung Adenocarcinoma.

We report a patient with severe neurological deterioration due to leptomeningeal metastases involving brain and spinal cord from anaplastic lymphoma kinase (ALK)-positive lung adenocarcinoma, managed rapidly and successfully with lorlatinib therapy. A 48-year-old male patient presented with acute mental deterioration, severe headache, and weakness of both legs. The patient's previous medical history included cerebral metastases from ALK-positive lung adenocarcinoma, which had been successfully managed via whole brain radiation therapy and gamma knife radiosurgery one year and three months before, respectively. Physical examination revealed neck stiffness and paraparesis with motor grade I. Gadolinium-enhanced brain MRI showed newly developed leptomeningeal enhancement along cerebellar folia, and whole spine MRI revealed similar leptomeningeal metastasis along the whole spinal axis. Lorlatinib was started orally with a dose of 100 mg/day. The patient showed rapid clinical improvement after one week. The patient was alert and the headache disappeared, while the paraparesis improved to normal ambulatory status. Two months of lorlatinib treatment resulted in almost complete disappearance of previous leptomeningeal enhancement of brain and spinal cord, and absence of newly developed metastatic lesions in the central nervous system, based on MRI results. The patient had been regularly followed with ongoing lorlatinib therapy for 5 months without any systemic complications or neurological abnormality. Conclusively, lorlatinib could be a rapid and effective treatment for patients with central nervous system leptomeningeal metastases arising from ALK-positive lung cancer.

The Plant-Stress Metabolites, Hexanoic Aacid and Melatonin, Are Potential "Vaccines" for Plant Health Promotion.

A plethora of compounds stimulate protective mechanisms in plants against microbial pathogens and abiotic stresses. Some defense activators are synthetic compounds and trigger responses only in certain protective pathways, such as activation of defenses under regulation by the plant regulator, salicylic acid (SA). This review discusses the potential of naturally occurring plant metabolites as primers for defense responses in the plant. The production of the metabolites, hexanoic acid and melatonin, in plants means they are consumed when plants are eaten as foods. Both metabolites prime stronger and more rapid activation of plant defense upon subsequent stress. Because these metabolites trigger protective measures in the plant they can be considered as "vaccines" to promote plant vigor. Hexanoic acid and melatonin instigate systemic changes in plant metabolism associated with both of the major defense pathways, those regulated by SA- and jasmonic acid (JA). These two pathways are well studied because of their induction by different microbial triggers: necrosis-causing microbial pathogens induce the SA pathway whereas colonization by beneficial microbes stimulates the JA pathway. The plant's responses to the two metabolites, however, are not identical with a major difference being a characterized growth response with melatonin but not hexanoic acid. As primers for plant defense, hexanoic acid and melatonin have the potential to be successfully integrated into vaccination-like strategies to protect plants against diseases and abiotic stresses that do not involve man-made chemicals.

Crash Analysis of Aluminum/CFRP Hybrid Adhesive Joint Parts Using Adhesive Modeling Technique Based on the Fracture Mechanics.

This study describes the numerical simulation results of aluminum/carbon-fiber-reinforced plastic (CFRP) hybrid joint parts using the explicit finite-element solver LS-DYNA, with a focus on capturing the failure behavior of composite laminates as well as the adhesive capacity of the aluminum-composite interface. In this study, two types of adhesive modeling techniques were investigated: a tiebreak contact condition and a cohesive zone model. Adhesive modeling techniques have been adopted as a widely commercialized model of structural adhesives to simulate adhesive failure based on fracture mechanics. CFRP was studied with numerical simulations utilizing LS-DYNA MAT54 to analyze the crash capability of aluminum/CFRP. To evaluate the simulation model, the results were compared with the force-displacement curve from numerical analysis and experimental results. A parametric study was conducted to evaluate the effect of different fracture toughness values used by designers to predict crash capability and adhesive failure of aluminum/CFRP parts.

In Vitro and In Vivo Antibacterial Activity of Serratamid, a Novel Peptide-Polyketide Antibiotic Isolated from Serratia plymuthica C1, against Phytopathogenic Bacteria.

A new hybrid non-ribosomal peptide-polyketide antibiotic (serratamid) for phytoprotection was isolated from the ethyl acetate layer of tryptic soy agar culture of the soil bacterium Serratia plymuthica C1 through bioassay-guided fractionation. Its chemical structure was elucidated using instrumental analyses, such as mass and nuclear magnetic resonance spectrometry. Serratamid showed antibacterial activity against 15 phytopathogenic bacteria, with minimum inhibitory concentration (MIC) values ranging from 0.244 to 31.25 µg/mL. In vitro, it displayed strong antibacterial activity against Ralstonia solanacearum and four Xanthomonas spp., with MIC values (0.244-0.488 µg/mL) superior to those of streptomycin sulfate, oxolinic acid, and oxytetracycline. Further, serratamid and the ethyl acetate layer of S. plymuthica C1 effectively reduced bacterial wilt caused by R. solanacearum on tomato seedlings and fire blight caused by Erwinia on apple fruits in a dose-dependent manner. These results suggest that serratamid is a promising candidate as a potent bactericide for controlling bacterial diseases.

Complete Genome Resource of Serratia plymuthica C-1 that Causes Root Rot Disease in Korean Ginseng.

Serratia plymuthica C-1, a biocontrol agent, was isolated from soil collected from a mountain forest in Korea. Previous studies have shown that certain strains of S. plymuthica cause root rot disease in ginseng. To the best of our knowledge, this is the first report of the sequence of the circular chromosome of S. plymuthica C-1, which plays a dual role by causing root rot in ginseng and exhibiting biocontrol activity. The findings of this study will assist in analyzing the genes associated with the pathogenicity and biocontrol properties of S. plymuthica.

Recent Progress in Birdcage RF Coil Technology for MRI System.

The radio frequency (RF) coil is one of the key components of the magnetic resonance imaging (MRI) system. It has a significant impact on the performance of the nuclear magnetic resonance (NMR) detection. Among numerous practical designs of RF coils for NMR imaging, the birdcage RF coil is the most popular choice from low field to ultra-high field MRI systems. In the transmission mode, it can establish a strong and homogeneous transverse magnetic field B1 for any element at its Larmor frequency. Similarly, in the reception mode, it exhibits extremely high sensitivity for the detection of even faint NMR signals from the volume of interest. Despite the sophisticated 3D structure of the birdcage coil, the developments in the design, analysis, and implementation technologies during the past decade have rendered the development of the birdcage coils quite reasonable. This article provides a detailed review of the recent progress in the birdcage RF coil technology for the MRI system.

First Report of Leaf Spots on Oat Caused by Alternaria alternata in South Korea.

Oat, a gluten-free source of vitamins, minerals, fiber, and antioxidants required for human health (Rasane et al., 2015), is increasingly being cultivated in South Korea (Ju et al. 2011). In May 2020, ~30 % Avena sativa (cv. Samhan) leaves of a commercial oat field in Jeongeup, Korea (35.3859°N, 126.5607°E), displayed a leaf spot disease at the tillering growth stage. Small, brown spots appeared initially on the lower leaves, but progressed to dark-brown oval or irregular, necrotic spots with a light-yellowish border. To isolate the pathogen, tissue excised from growing edges of about 50 lesions was surface sterilized (immersion in 70 % ethanol then 1 % sodium hypochlorite), rinsed and transferred to potato dextrose agar. Five isolates were purified using the single-spore culture method on water agar plates (Choi et al. 1999). Conidia from the PDA cultures (n = 50) were elongated, ellipsoidal, and obclavate, with one to five septa (primarily transverse), 18 to 35 µm × 7 to 12 µm. The morphological characteristics of the fungus from each culture were consistent with those observed for Alternaria alternata (Chen et al. 2020; Simmons 2007). To confirm the identity of the fungal pathogen, the internal transcribed spacer (ITS) region was amplified with universal primers ITS1/ITS4 and sequenced (White et al. 1990). BLAST analysis of the resulting nucleotide sequence of one representative isolate, Oaa-2 (GenBank MT786424), showed 100 % identity with A. alternata-type strains, such as CBS916.96. Further, nine nuclear protein-coding genes from the Oaa-2 isolate were amplified using previously described primers (Lawrence et al. 2013; Wouderengerg et al. 2015). These sequences were deposited under the following GenBank accession numbers: MT795660 (rpb2), MT795656 (His), MT795657 (CML), MT795658 (ACT), MT787343 (CHSD), MT795655 (GAPDH), MT795661 (endoPG), and MT795662 (TEF1). The nine sequences of the Oaa-2 isolate showed 99%-100 % identity to those of A. alternata-type strain CBS916.96 in NCBI. Fig. S2 shows the phylogenetic trees for the ITS and GAPDH sequences indicating high homology. Pathogenicity of this isolate was confirmed by spraying leaves of surface-sterilized, glasshouse-grown, "Samhan" oats with suspensions (5 × 106 spores/ml) of Oaa-2 conidia. Experimental seedlings were grown for 2 weeks in a chamber at 20 ± 3 °C in 60 % relative humidity with a 10-h light/14-h dark cycle (200 µmol/m2/s). Conidial suspensions were prepared for inoculation by flooding with sterile water, followed by filtering the suspension through three layers of sterile cheesecloth to remove debris. Three pots each containing twenty oat seedlings were sprayed with the Oaa-2 isolate conidial suspension (5 × 106 conidia/ml) and incubated for 10 days at 20 ± 3 °C in 100 % humidity with a 10-h photoperiod. Three healthy seedlings were sprayed with sterile water as a control. After 10 days, dark brown spots developed in the inoculated plants; however, no spots were observed in the controls. Fungi with the same conidial characteristics as Oaa-2 were isolated from the infected plants, and the ITS sequence and the nine nuclear protein-encoding genes of these plant isolates was identical to those of Oaa-2. Pathogenicity tests also were conducted with isolate Oaa-2 with two oat cultivars, Sunyang and Joyang, with the same result. To our knowledge, A. alternata has not been previously reported to cause disease on oats in South Korea, although it does cause economic losses in China (Chen et al. 2020).

Complete Genome Resource of Pseudomonas coronafaciens X-1 Causing Halo Blight Disease in Oats.

Pseudomonas coronafaciens X-1 was isolated from halo blight lesions on oat leaves in Korea. Currently, no genome resource on the oat halo blight pathogen is available. Here, the complete genome sequence of this strain, containing a circular chromosome and one circular megaplasmid is reported. This is the first genome sequence of the oat halo blight pathogen and will contribute to our understanding of the pathogenicity and ecological aspects of the halo blight pathogen and the interactions between P. coronafaciens and oats.

Dexamethasone delivery for hearing preservation in animal cochlear implant model: continuity, long-term release, and fast release rate.

Background: Clinically, steroids have been used for hearing preservation both topically and systemically during cochlear implantation.Objective: This study compared steroid efficacy for hearing preservation among different types of delivery modes using an animal experiment.Materials and methods: For 76 guinea pigs, topical and systemic delivery methods, four pump types with different infusion rates, delivery durations, and total steroid amounts were used. Threshold changes of 8, 16, and 32 kHz after dummy electrode insertion were evaluated at 1 and 4 weeks and compared among delivery method and pump types. Inflammatory response in the cochlea was histologically compared.Results: For topical delivery groups, long-term release showed advantages in preserving hearing. Systemic delivery groups showed smaller threshold shifts than control group in all frequencies (p > .05). In short-term low dose application, compared to topical delivery, systemic delivery showed advantage in hearing preservation at both time point. However, others fail to show significant difference between two methods. Histologically, inflammatory response in the scala tympani at the basal turn was less in systemic delivery, especially in high dose and long-term.Conclusion and significance: The difference of hearing preservation was not obvious between two delivery methods. Higher dose and longer duration might have advantages in hearing preservation.

Insights into plant-beneficial traits of probiotic Pseudomonas chlororaphis isolates.

Pseudomonas chlororaphis isolates have been studied intensively for their beneficial traits. P. chlororaphis species function as probiotics in plants and fish, offering plants protection against microbes, nematodes and insects. In this review, we discuss the classification of P. chlororaphis isolates within four subspecies; the shared traits include the production of coloured antimicrobial phenazines, high sequence identity between housekeeping genes and similar cellular fatty acid composition. The direct antimicrobial, insecticidal and nematocidal effects of P. chlororaphis isolates are correlated with known metabolites. Other metabolites prime the plants for stress tolerance and participate in microbial cell signalling events and biofilm formation among other things. Formulations of P. chlororaphis isolates and their metabolites are currently being commercialized for agricultural use.

Tobacco Growth Promotion by the Entomopathogenic Fungus, Isaria javanica pf185.

Isaria javanica pf185 is an important entomopathogenic fungus with potential for use as an agricultural biocontrol agent. However, the effect of I. javanica pf185 on plant growth is unknown. Enhanced tobacco growth was observed when tobacco roots were exposed to spores, cultures, and fungal cell-free culture supernatants of this fungus. Tobacco seedlings were also exposed to the volatiles of I. javanica pf185 in vitro using I-plates in which the plant and fungus were growing in separate compartments connected only by air space. The length and weight of seedlings, content of leaf chlorophyll, and number of root branches were significantly increased by the fungal volatiles. Heptane, 3-hexanone, 2,4-dimethylhexane, and 2-nonanone were detected, by solid-phase micro-extraction and gas chromatography-mass spectrophotometry, as the key volatile compounds produced by I. javanica pf185. These findings illustrate that I. javanica pf185 can be used to promote plant growth, and also as a biocontrol agent of insect and plant diseases. Further studies are necessary to elucidate the mechanisms by which I. javanica pf185 promotes plant growth.

Dibutyl succinate, produced by an insect-pathogenic fungus, Isaria javanica pf185, is a metabolite that controls of aphids and a fungal disease, anthracnose.

BACKGROUND: An entomopathogenic fungus, Isaria javanica pf185, causes mortality in nymphs of the green peach aphid and inhibits the growth of fungal plant pathogens. However, the metabolites of pf185 involved in these antifungal and aphicidal activities are unknown. This study was performed to identify the metabolites with these activities. RESULTS: An antifungal metabolite was purified by repetitive column chromatography and preparative high-performance liquid chromatography. Based on data from mass spectrometry and nuclear magnetic resonance, the active metabolite was identified as dibutyl succinate. The minimum concentration of dibutyl succinate to inhibit germination of conidia of the cause of anthracnose, Colletotrichum acutatum, was 4 mg mL-1 . Dibutyl succinate at 2 µg mL-1 inhibited mycelial growth. It also had strong aphicidal activity against the nymphs of the green peach aphid, Myzus persicae, median lethal concentration (LC50) of 306 mg L-1 at 24 h exposure, and median lethal time (LT50) of 14.5 h at 388 mg L-1 exposure. CONCLUSION: This is the first report indicating that a single metabolite, dibutyl succinate, from the beneficial fungus I. javanica, has potential for use in integrated pest management to inhibit both insect and fungal plant pathogens. © 2018 Society of Chemical Industry.

Hydrogen cyanide produced by Pseudomonas chlororaphis O6 is a key aphicidal metabolite.

A biocontrol bacterium, Pseudomonas chlororaphis O6 promotes plant health through multifaceted mechanisms. In this study, we used P. chlororaphis O6 mutants to examine metabolites with aphicidal activity. Direct application of intact P. chlororaphis cells to the surface of second-instar nymphs of the green peach aphid resulted in no mortality. However, nymphs died when exposed only to the volatiles produced by the P. chlororaphis O6 wild-type strain grown on rich media. Mutants lacking the production of two antibiotics, phenazine and pyrrolnitrin, or the insect toxin FitD retained the aphicidal potential of the wild-type strain. However, the volatiles produced by mutants deficient in the production of hydrogen cyanide (HCN) or defective in the synthesis of the global regulator GacS, which regulates HCN synthesis, showed no aphicidal activity. Direct application of potassium cyanide caused mortality of green peach aphid nymphs. These results indicate that HCN production by a plant probiotic is involved in preventing insect growth.

Biocontrol Efficacy of Formulated Pseudomonas chlororaphis O6 against Plant Diseases and Root-Knot Nematodes.

Commercial biocontrol of microbial plant diseases and plant pests, such as nematodes, requires field-effective formulations. The isolate Pseudomonas chlororaphis O6 is a Gram-negative bacterium that controls microbial plant pathogens both directly and indirectly. This bacterium also has nematocidal activity. In this study, we report on the efficacy of a wettable powder-type formulation of P. chlororaphis O6. Culturable bacteria in the formulated product were retained at above 1 × 108 colony forming units/g after storage of the powder at 25 °C for six months. Foliar application of the diluted formulated product controlled leaf blight and gray mold in tomato. The product also displayed preventative and curative controls for root-knot nematode (Meloidogyne spp.) in tomato. Under laboratory conditions and for commercially grown melon, the control was at levels comparable to that of a standard commercial chemical nematicide. The results indicated that the wettable powder formulation product of P. chlororaphis O6 can be used for control of plant microbial pathogens and root-knot nematodes.

Rhizosphere pseudomonads as probiotics improving plant health.

Many root-colonizing microbes are multifaceted in traits that improve plant health. Although isolates designated as biological control agents directly reduce pathogen growth, many exert additional beneficial features that parallel changes induced in animal and other hosts by health-promoting microbes termed probiotics. Both animal and plant probiotics cause direct antagonism of pathogens and induce systemic immunity in the host to pathogens and other stresses. They also alter host development and improve host nutrition. The probiotic root-colonizing pseudomonads are generalists in terms of plant hosts, soil habitats and the array of stress responses that are ameliorated in the plant. This article illustrates how the probiotic pseudomonads, nurtured by the carbon (C) and nitrogen (N) sources released by the plant in root exudates, form protective biofilms on the root surface and produce the metabolites or enzymes to boost plant health. The findings reveal the multifunctional nature of many of the microbial metabolites in the plant-probiotic interplay. The beneficial effects of probiotics on plant function can contribute to sustainable yield and quality in agricultural production.

Hydrogen Cyanide Produced by Pseudomonas chlororaphis O6 Exhibits Nematicidal Activity against Meloidogyne hapla.

Root-knot nematodes (Meloidogyne spp.) are parasites that attack many field crops and orchard trees, and affect both the quantity and quality of the products. A root-colonizing bacterium, Pseudomonas chlororaphis O6, possesses beneficial traits including strong nematicidal activity. To determine the molecular mechanisms involved in the nematicidal activity of P. chlororaphis O6, we constructed two mutants; one lacking hydrogen cyanide production, and a second lacking an insecticidal toxin, FitD. Root drenching with wild-type P. chlororaphis O6 cells caused juvenile mortality in vitro and in planta. Efficacy was not altered in the fitD mutant compared to the wild-type but was reduced in both bioassays for the mutant lacking hydrogen cyanide production. The reduced number of galls on tomato plants caused by the wild-type strain was comparable to that of a standard chemical nematicide. These findings suggest that hydrogen cyanide-producing root colonizers, such as P. chlororaphis O6, could be formulated as "green" nematicides that are compatible with many crops and offer agricultural sustainability.

Polyamine is a critical determinant of Pseudomonas chlororaphis O6 for GacS-dependent bacterial cell growth and biocontrol capacity.

The Gac/Rsm network regulates, at the transcriptional level, many beneficial traits in biocontrol-active pseudomonads. In this study, we used Phenotype MicroArrays, followed by specific growth studies and mutational analysis, to understand how catabolism is regulated by this sensor kinase system in the biocontrol isolate Pseudomonas chlororaphis O6. The growth of a gacS mutant was decreased significantly relative to that of the wild-type on ornithine and arginine, and on the precursor of these amino acids, N-acetyl-l-glutamic acid. The gacS mutant also showed reduced production of polyamines. Expression of the genes encoding arginine decarboxylase (speA) and ornithine decarboxylases (speC) was controlled at the transcriptional level by the GacS sensor of P. chlororaphis O6. Polyamine production was reduced in the speC mutant, and was eliminated in the speAspeC mutant. The addition of exogenous polyamines to the speAspeC mutant restored the in vitro growth inhibition of two fungal pathogens, as well as the secretion of three biological control-related factors: pyrrolnitrin, protease and siderophore. These results extend our knowledge of the regulation by the Gac/Rsm network in a biocontrol pseudomonad to include polyamine synthesis. Collectively, our studies demonstrate that bacterial polyamines act as important regulators of bacterial cell growth and biocontrol potential.