Generation of recombinant viruses directly from clinical specimens of COVID-19 patients.

Rapid characterization of the causative agent(s) during a disease outbreak can aid in the implementation of effective control measures. However, isolation of the agent(s) from crude clinical samples can be challenging and time-consuming, hindering the establishment of countermeasures. In the present study, we used saliva specimens collected for the diagnosis of SARS-CoV-2-a good example of a practical target-and attempted to characterize the virus within the specimens without virus isolation. Thirty-four saliva samples from coronavirus disease 2019 patients were used to extract RNA and synthesize DNA amplicons by PCR. New primer sets were designed to generate DNA amplicons of the full-length spike (S) gene for subsequent use in a circular polymerase extension reaction (CPER), a simple method for deriving recombinant viral genomes. According to the S sequence, four clinical specimens were classified as BA. 1, BA.2, BA.5, and XBB.1 and were used for the de novo generation of recombinant viruses carrying the entire S gene. Additionally, chimeric viruses carrying the gene encoding GFP were generated to evaluate viral propagation using a plate reader. We successfully used the RNA purified directly from clinical saliva samples to generate chimeric viruses carrying the entire S gene by our updated CPER method. The chimeric viruses exhibited robust replication in cell cultures with similar properties. Using the recombinant GFP viruses, we also successfully characterized the efficacy of the licensed antiviral AZD7442. Our proof-of-concept demonstrates the novel utility of CPER to allow rapid characterization of viruses from clinical specimens. IMPORTANCE: Characterization of the causative agent(s) for infectious diseases helps in implementing effective control measurements, especially in outbreaks. However, the isolation of the agent(s) from clinical specimens is often challenging and time-consuming. In this study, saliva samples from coronavirus disease 2019 patients were directly subjected to purifying viral RNA, synthesizing DNA amplicons for sequencing, and generating recombinant viruses. Utilizing an updated circular polymerase extension reaction method, we successfully generated chimeric SARS-CoV-2 viruses with sufficient in vitro replication capacity and antigenicity. Thus, the recombinant viruses generated in this study were applicable for evaluating the antivirals. Collectively, our developed method facilitates rapid characterization of specimens circulating in hosts, aiding in the establishment of control measurements. Additionally, this approach offers an advanced strategy for controlling other (re-)emerging viral infectious diseases.

Involvement of SARS-CoV-2 accessory proteins in immunopathogenesis.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the largest single-stranded RNA virus known to date. Its genome contains multiple accessory protein genes that act against host immune responses but are not required for progeny virus production. The functions of the accessory proteins in the viral life cycle have been examined, but their involvement in viral pathogenicity remains unclear. Here, we investigated the roles of the accessory proteins in viral immunopathogenicity. To this end, recombinant SARS-CoV-2 possessing nonsense mutations in the seven accessory protein open reading frames (ORFs) (ORF3a, ORF3b, ORF6, ORF7a, ORF8, ORF9b, and ORF10) was de novo generated using an early pandemic SARS-CoV-2 strain as a backbone. We confirmed that the resultant virus (termed ORF3-10 KO) did not express accessory proteins in infected cells and retained the desired mutations in the viral genome. In cell culture, the ORF3-10 KO virus exhibited similar virus growth kinetics as the parental virus. In hamsters, ORF3-10 KO virus infection resulted in mild weight loss and reduced viral replication in the oral cavity and lung tissue. ORF3-10 KO virus infection led to mild inflammation, indicating that an inability to evade innate immune sensing because of a lack of accessory proteins impairs virus growth in vivo and results in quick elimination from the body. Overall, we showed that SARS-CoV-2 accessory proteins are involved in immunopathogenicity.

Association Between Aortic Stiffness and Exercise Tolerance in Patients at the Risk Stage of Heart Failure.

BACKGROUND: The number of patients with heart failure (HF) has increased, and it is crucial to prevent the development of HF in patients at risk of HF. The present study aimed to risk stratify patients in Stage A and B HF based on associations between exercise-induced changes in aortic stiffness and exercise tolerance.Methods and Results: Patients in Stage A and B HF who performed a cardiopulmonary exercise test were enrolled in the study (n=106; median age 65.0 years [interquartile range 52.8-73.0 years]). Exercise tolerance was examined by the percentage of predicted peak oxygen consumption (%V̇O2peak). The ascending aortic pressure waveform was estimated non-invasively. Aortic stiffness was assessed using the augmentation index (AIx) and reflection magnitude (RM). Multivariable regression analysis showed that AIx measured both before and after exercise was significantly associated with %V̇O2peak (ß=-0.221 [P=0.049] and ß=-0.342 [P=0.003], respectively). When participants were divided into %V̇O2peak subgroups using a cut-off value of 60%, RM decreased immediately after exercise and remained lower 5 min after exercise in the group with preserved exercise tolerance, but recovered to baseline levels 5 min after exercise in the group with reduced exercise tolerance. CONCLUSIONS: Exercise-induced increases in aortic stiffness were associated with exercise tolerance in patients at risk of HF, suggesting that exercise-induced changes in aortic stiffness may be useful to stratify high-risk patients.

Correction: Mori et al. Involvement of DPY19L3 in Myogenic Differentiation of C2C12 Myoblasts. Molecules 2021, 26, 5685.

In the original article [...].

Involvement of LH3 and GLT25D1 for glucosyl-galactosyl-hydroxylation on non-collagen-like domain of FGL1.

Glucosyl-galactosyl-hydroxylation (GGH) is one type of post-translational modification, which is mainly observed in collagen-like domain-containing proteins. Using LC-MS/MS analysis, we found a GGH-like modification at Lys65 of fibrinogen-like protein 1 (FGL1), although it does not contain a collagen-like domain. To identify the glycosyltransferases responsible for this modification, we established LH3/GLT25D1-knockout FGL1-overexpressing HT1080 cell lines. The result showed that knockout of LH3 or GLT25D1 significantly inhibited the glycosylation. Furthermore, deficiency of GGH by point mutation of the FGL1 protein or knockout of the GGH-related glycosyltransferase reduced FGL1 protein levels. Taken together, these data indicate that Lys65 of FGL1 is glucosyl-galactosyl-hydroxylated by LH3 and GLT25D1. Our results provide novel insights to regulate various FGL1 functions.

Involvement of DPY19L3 in Myogenic Differentiation of C2C12 Myoblasts.

DPY19L3 has been identified as a C-mannosyltransferase for thrombospondin type-1 repeat domain-containing proteins. In this study, we focused on the role of DPY19L3 in the myogenic differentiation of C2C12 mouse myoblast cells. We carried out DPY19L3 gene depletion using the CRISPR/Cas9 system. The result showed that these DPY19L3-knockout cells could not be induced for differentiation. Moreover, the phosphorylation levels of MEK/ERK and p70S6K were suppressed in the DPY19L3-knockout cells compared with that of parent cells, suggesting that the protein(s) that is(are) DPY19L3-mediated C-mannosylated and regulate(s) MEK/ERK or p70S6K signaling is(are) required for the differentiation.

Development of the ReaxFF Methodology for Electrolyte-Water Systems.

A new ReaxFF reactive force field has been developed for water-electrolyte systems including cations Li+, Na+, K+, and Cs+ and anions F-, Cl-, and I-. The reactive force field parameters have been trained against quantum mechanical (QM) calculations related to water binding energies, hydration energies and energies of proton transfer. The new force field has been validated by applying it to molecular dynamics (MD) simulations of the ionization of different electrolytes in water and comparison of the results with experimental observations and thermodynamics. Radial distribution functions (RDF) determined for most of the atom pairs (cation or anion with oxygen and hydrogen of water) show a good agreement with the RDF values obtained from DFT calculations. On the basis of the applied force field, the ReaxFF simulations have described the diffusion constants for water and electrolyte ions in alkali metal hydroxide and chloride salt solutions as a function of composition and electrolyte concentration. The obtained results open opportunities to advance ReaxFF methodology to a wide range of applications involving electrolyte ions and solutions.

Total Synthesis of Clavilactones.

Clavilactones A, B, and D are epidermal growth factor receptor tyrosine kinase inhibitors that were isolated from cultures of the fungus Clitocybe clavipes. Here, we report full details of the total synthesis of these clavilactones. A key feature of our synthetic approach is a ring-opening/ring-closing metathesis strategy that allows the concise transformation of a cyclobutenecarboxylate into a γ-butenolide. Coupled with enantioselective Ti/BINOL-catalyzed alkynylation of a multisubstituted benzaldehyde and ring-closing metathesis of a diene-bearing silylene acetal to construct the 10-membered carbocycle, this strategy enabled the total synthesis of the natural enantiomers (+)-clavilactone A and (-)-clavilactone B. In addition, the correct structure of clavilactone D was determined by the synthesis of two newly proposed structures. This research resulted in the asymmetric synthesis of the revised (+)-clavilactone D.

Compensatory Increase in Heart Rate Is Responsible for Exercise Tolerance among Male Patients with Permanent Atrial Fibrillation.

Atrial fibrillation (AF) is an exacerbating factor for exercise tolerance due to the loss of atrial kick. However, many patients with permanent AF, which lasts for at least a year without interruption, and preserved left ventricular ejection fraction (LVEF ≥ 50%) are asymptomatic and have good exercise tolerance. In such cases, the possible mechanism that compensates for the decrease in cardiac output accompanying the loss of atrial kick is a sufficient increase in heart rate (HR) during exercise. We investigated the relationship between exercise tolerance and peak HR during exercise using cardiopulmonary exercise testing in 242 male patients with preserved LVEF, 214 with sinus rhythm (SR) and 28 with permanent AF. Peak HR was significantly higher in the AF group than the SR group (148.9 ± 41.9 vs. 132.0 ± 22.0 beats/min, p = 0.001). However, oxygen uptake at peak exercise did not differ between the AF and SR groups (19.4 ± 5.7 vs. 21.6 ± 6.0 mL/kg/min, p = 0.17). In multiple regression analysis, peak HR (ß, 0.091; p < 0.001) and the interaction term constructed by peak HR and presence of permanent AF (ß, 0.05; p = 0.04) were selected as determinants for peak VO2; however, presence of permanent AF was not selected (ß, -0.38; p = 0.31). Therefore, the impact of peak HR on exercise tolerance differed between the AF and SR groups, suggesting that a sufficient increase in HR during exercise is an important factor to preserve exercise tolerance among patients with AF.

Total Synthesis and Structural Revision of Clavilactone†D.

A structural revision of clavilactone D, a potent inhibitor of protein tyrosine kinases, was achieved by total syntheses of two newly proposed structures. The syntheses relied on ring-opening/ring-closing metathesis, which transformed a cyclobutenecarboxylate into a γ-butenolide. The syntheses confirmed that the correct structure of clavilactone D has an amino group at C-3 instead of a hydroxy group at C-2 in the originally proposed structure.

Vascular Physiology according to Clinical Scenario in Patients with Acute Heart Failure: Evaluation using the Cardio-Ankle Vascular Index.

Increased aortic stiffness may be an important cause of acute heart failure (AHF). Clinical scenario (CS), which classifies the pathophysiology of AHF based on the initial systolic blood pressure (sBP), was proposed to provide the most appropriate therapy for AHF patients. In CS, elevated aortic stiffness, vascular failure, has been considered as a feature of patients categorized as CS1 (sBP > 140 mmHg at initial presentation). However, whether elevated aortic stiffness, vascular failure, is present in such patients has not been fully elucidated. Therefore, we assessed aortic stiffness in AHF patients using the cardio-ankle vascular index (CAVI), which is considered to be independent of instantaneous blood pressure. Sixty-four consecutive AHF patients (mean age, 70.6 ± 12.8 years; 39 men) were classified with CS, based on their initial sBP: CS1: sBP > 140 mmHg (n = 29); CS2: sBP 100-140 mmHg (n = 22); and CS3: sBP < 100 mmHg (n = 13). There were significant group differences in CAVI (CS1 vs. CS2 vs. CS3: 9.7 ± 1.4 vs. 8.4 ± 1.7 vs. 8.3 ± 1.7, p = 0.006, analysis of variance). CAVI was significantly higher in CS1 than in CS2 (p = 0.02) and CS3 (p = 0.04). CAVI did not significantly correlate with sBP at the time of measurement of CAVI (r = 0.24 and p = 0.06). Aortic stiffness assessed using blood pressure-independent methodology apparently increased in CS1 AHF patients. We conclude that vascular failure is a feature of CS1 AHF initiation.

Induction of necrosis symptoms by potato virus X in AGO2-silenced tomato plants associates with reduced transcript accumulation of copper chaperon for superoxide dismutase gene.

RNA silencing is a prominent antiviral defense mechanism in plants. When infected with a virus, RNA silencing-deficient plants tend to show exacerbated symptoms along with increased virus accumulation. However, how symptoms are exacerbated is little understood. Here, we investigated the role of the copper chaperon for superoxide dismutase (CCS) 1, in systemic necrosis observed in Argonaute (AGO)2-silenced tomato plants infected with potato virus X (PVX). While infection with the UK3 strain of PVX induced mosaic symptoms in tomato plants, systemic necrosis occurred when AGO2 was silenced. The CCS1 mRNA level was reduced and micro RNA398 (miR398), which potentially target CCS1, was increased in AGO2-knockdown tomato plants infected with PVX-UK3. Ectopic expression of CCS1 using recombinant PVX attenuated necrosis, suggesting that CCS1 alleviates systemic necrosis by activating superoxide dismutases to scavenge reactive oxygen species. Previous reports have indicated a decrease in the levels of CCS1 and superoxide dismutases along with an increased level of miR398 in plants infected with other viruses and viroids, and thus might represent shared regulatory mechanisms that exacerbate symptoms in these plants.

Clinical characteristics and short-term outcomes in patients with cardiogenic shock undergoing mechanical circulatory support escalation from intra-aortic balloon pump to impella: From the J-PVAD registry.

BACKGROUND: An escalation strategy from intra-aortic balloon pump (IABP) to Impella (AbioMed, Danvers, MA, USA) is proposed in patients with cardiogenic shock (CS) refractory to IABP therapy, but its clinical data are lacking. This study aimed to elucidate the clinical characteristics and short-term outcomes in patients undergoing IABP-Impella escalation. METHODS AND RESULTS: From the Japanese nationwide registry of Impella (J-PVAD), a total of 2578 patients with CS receiving Impella support were classified into the IABP-Impella group (n = 189) or the Primary Impella group (n = 2389). We applied 1:3 propensity score (PS) matching, selecting 185 patients and 555 patients, respectively. Before matching, the IABP-Impella group presented longer shock-to-Impella time, worse laboratory data, and more frequent inotropes and pulmonary artery catheter use than the Primary Impella group. After matching, the baseline characteristics were well-balanced. Regarding the 30-day clinical outcomes in the PS-matched cohort, there were no significant differences in the rates of mortality and major complications (a composite of bleeding, hemolysis, infection, stroke, myocardial infarction, limb ischemia, and vascular injury) between the groups. However, The IABP-Impella group showed a significantly higher rate of infection (10.3 % vs. 5.6 %, p = 0.042) and additional mechanical circulatory support use (34.1 % vs. 23.8 %, p = 0.008) than the Primary Impella group. CONCLUSIONS: Compared to patients with primary Impella support, those undergoing IABP-Impella escalation showed similar 30-day mortality and major complications despite poorer clinical conditions before Impella support and a more complicated clinical course after Impella insertion.

Mutations in nuclear pore complex promote osmotolerance in Arabidopsis by suppressing the nuclear translocation of ACQOS and its osmotically induced immunity.

We have previously reported a wide variation in salt tolerance among Arabidopsis thaliana accessions and identified ACQOS, encoding a nucleotide-binding leucine-rich repeat (NLR) protein, as the causal gene responsible for the disturbance of acquired osmotolerance induced after mild salt stress. ACQOS is conserved among Arabidopsis osmosensitive accessions, including Col-0. In response to osmotic stress, it induces detrimental autoimmunity, resulting in suppression of osmotolerance, but how ACQOS triggers autoimmunity remains unclear. Here, we screened acquired osmotolerance (aot) mutants from EMS-mutagenized Col-0 seeds and isolated the aot19 mutant. In comparison with the wild type (WT), this mutant had acquired osmotolerance and decreased expression levels of pathogenesis-related genes. It had a mutation in a splicing acceptor site in NUCLEOPORIN 85 (NUP85), which encodes a component of the nuclear pore complex. A mutant with a T-DNA insertion in NUP85 acquired osmotolerance similar to aot19. The WT gene complemented the osmotolerant phenotype of aot19. We evaluated the acquired osmotolerance of five nup mutants of outer-ring NUPs and found that nup96, nup107, and aot19/nup85, but not nup43 or nup133, showed acquired osmotolerance. We examined the subcellular localization of the GFP-ACQOS protein and found that its nuclear translocation in response to osmotic stress was suppressed in aot19. We suggest that NUP85 is essential for the nuclear translocation of ACQOS, and the loss-of-function mutation of NUP85 results in acquired osmotolerance by suppressing ACQOS-induced autoimmunity in response to osmotic stress.

Malondialdehyde-Modified Low-Density Lipoprotein as a Predictor of Major Adverse Limb Events after Endovascular Therapy in Patients with Lower Extremity Arterial Disease.

AIM: Adverse limb events after endovascular therapy (EVT) are a major concern. This study aimed to investigate the relationship between serum malondialdehyde-modified low-density lipoprotein (MDA-LDL) level, a potentially potent indicator of atherosclerosis, and clinical outcomes after EVT in patients with lower extremity arterial disease (LEAD). METHODS: A total of 208 LEAD patients who underwent EVT and MDA-LDL measurements were retrospectively analyzed. Those with chronic limb-threatening ischemia (CLTI) were included in the CLTI subgroup (n=106). Patients were further categorized into the High or Low MDA-LDL groups according to the cut-off value calculated by receiver operating characteristic analysis. Major adverse limb events (MALE), a composite of cardiovascular death, limb-related death, major amputation, and target-limb revascularization, were evaluated. RESULTS: MALE occurred in 73 (35%) patients. The median follow-up interval was 17.4 months. The MDA-LDL cut-off values were 100.5 U/L (area under the curve [AUC] 0.651) in the overall population and 98.0 U/L (AUC 0.724) in the CLTI subgroup. Overall, the High MDA-LDL group showed significantly higher total cholesterol (189.7±37.5 mg/dL vs. 159.3±32.0 mg/dL, p＜0.01), low-density lipoprotein cholesterol (114.3±29.7 mg/dL vs. 87.3±25.3 mg/dL, p＜0.01), and triglyceride (166.9±91.1 mg/dL vs. 115.8±52.3 mg/dL, p＜0.01) than the Low MDA-LDL group. Multivariate Cox regression analyses revealed that MDA-LDL and C-reactive protein were independent predictors of MALE. In the CLTI subgroup, MDA-LDL was an independent predictor of MALE. The High MDA-LDL group showed worse MALE-free survival rates than the Low MDA-LDL group in overall (p＜0.01) and in the CLTI subgroup (p=0.01). CONCLUSIONS: Serum MDA-LDL level was associated with MALE after EVT.

Intraprocedural Thrombotic Events during Percutaneous Coronary Intervention Due to Acquired Antithrombin Deficiency-related Heparin Resistance Successfully Treated with Antithrombin Gamma Supplementation.

A 75-year-old man receiving treatment for necrotizing pancreatitis developed septic disseminated intravascular coagulation and acute coronary syndrome (ACS). During percutaneous coronary intervention (PCI), a large amount of fresh thrombi appeared after balloon dilatation for the ACS-culprit lesion. Given the low plasma antithrombin (AT) activity and poorly prolonged activated clotting time (ACT), we suspected that acquired AT deficiency-related heparin resistance (HR) was responsible for the thrombus formation. Administration of AT gamma markedly improved ACT, and we successfully completed PCI. We suggest that AT gamma be considered a treatment option for AT deficiency-related HR and subsequent intraprocedural thrombotic events.

Reclassification of Heart Failure with Preserved Ejection Fraction Following Cardiac Sympathetic Nervous System Activation: A New Cutoff Value of 58.

Heart failure (HF) with preserved left ventricular ejection fraction (LVEF) is a heterogeneous syndrome. An LVEF of 50% is widely used to categorize patients with HF; however, this is controversial. Previously, we have reported that patients with an LVEF of ≥ 58% have good prognoses. Further, cardiac sympathetic nervous system (SNS) activation is a feature of HF. In this retrospective, observational study, the cardiac SNS activity of HF patients (n = 63, age: 78.4 ± 9.6 years; male 49.2%) with LVEF ≥ 58% (n = 15) and LVEF < 58% (n = 48) were compared using 123I-metaiodobenzylguanidine scintigraphy. During the follow-up period (median, 3.0 years), 18 all-cause deaths occurred. The delayed heart/mediastinum (H/M) ratio was significantly higher in the LVEF ≥ 58% group than in the LVEF < 58% group (2.1 ± 0.3 vs. 1.7 ± 0.4, p = 0.004), and all-cause mortality was significantly lower in patients in the former than those in the latter group (log-rank, p = 0.04). However, when these patients were divided into LVEF ≥ 50% (n = 22) and LVEF < 50% (n = 41) groups, no significant differences were found in the delayed H/M ratio, and the all-cause mortality did not differ between the groups (log-rank, p = 0.09). In conclusion, an LVEF of 58% is suitable for reclassifying patients with HF according to cardiac SNS activity.

A case of an elderly female who developed subacute pleuropericarditis following BNT162b2 mRNA COVID-19 vaccination.

Despite the established safety of BNT162b2 coronavirus disease 2019 (COVID-19) vaccine, some rare but serious complications have been previously reported. Here, we report a rare case of an elderly female who developed subacute pleuropericarditis after the vaccination. An 88-year-old female experienced weight gain and dyspnea three days after the second dose of BNT162b2 vaccination, and one month later, presented to our hospital due to the exacerbation of the symptoms. Computed tomography showed remarkable pericardial and bilateral pleural effusions, and transthoracic echocardiogram visualized collapse signs of right and left atrium which indicates pre-tamponade. Percutaneous drainages of pericardial and pleural effusions stabilized her vital condition and revealed that all of them were exudative, indicating the presence of pleuropericarditis. Finally, we diagnosed this case as COVID-19 vaccine-associated pleuropericarditis because there were no signs of bacterial/viral infection or any other relevant causes except for the vaccination. When the pericardial and pleural effusions are concurrently found after COVID-19 vaccination, vaccine-associated pleuropericarditis should be considered as a differential diagnosis. The aggressive drainage of pericardial and pleural effusions could be helpful not only for diagnosis but also for treatment in the clinical management of COVID-19 vaccine-associated pleuropericarditis. Learning objective: Although the safety and efficacy of BNT162b2 have been widely accepted, it is clinically important to know the potential risk of side effects. When the pericardial and pleural effusions are concurrently found after the vaccination, coronavirus disease 2019 vaccine-associated pleuropericarditis should be considered as a differential diagnosis.

Multimorbidity, polypharmacy, and mortality in older patients with pacemakers.

BACKGROUND: The prevalence of multimorbidity and polypharmacy and its association with all-cause mortality in older patients with pacemakers are largely unknown. We aimed to clarify the prevalence of multimorbidity and polypharmacy, and its association with all-cause mortality in patients ≥75 years of age with pacemakers. METHODS: We retrospectively investigated 256 patients aged ≥75 years (mean age 84.0 ± 5.3 years; 45.7% male) with newly implanted pacemakers. The study endpoint was all-cause mortality ("with events"). Multimorbidity was defined as a Charlson Comorbidity Index ≥3. Polypharmacy was defined as the use of ≥5 medications. RESULTS: During the follow-up period (median, 3.1 years), 60 all-cause deaths were reported. The Charlson Comorbidity Index (2.9 ± 1.9 vs. 1.7 ± 1.7, p < .001) and prevalence of multimorbidity (56.7% vs. 26.0%, p < .001) were significantly higher in deceased patients than in survivors. The number of drugs (6.9 ± 3.0 vs. 5.9 ± 3.3, p = .03) and the prevalence of polypharmacy (78.3% vs. 63.8%, p = .04) were significantly higher in patients with events than in those without events. The event-free survival rate was significantly higher among patients without multimorbidity than in those with multimorbidity (log-rank, p < .001), and was also significantly higher among patients without polypharmacy than in those with polypharmacy (log-rank, p < .001). Multimorbidity (hazard ratio [HR]: 3.21; 95% confidence interval [CI]: 1.85-5.58; p < .001) and polypharmacy (HR: 1.97; 95% CI: 1.03-3.77; p = .04) were independent predictors of all-cause mortality. CONCLUSIONS: Multimorbidity and its associated polypharmacy, which are common in the older population, are prevalent in patients with pacemakers and are independent predictors of poor prognosis.

Induction of spontaneous phenotype conversion in Ralstonia solanacearum by addition of iron compounds in liquid medium.

Ralstonia solanacearum is a soil-borne pathogen that causes bacterial wilt in plants. The wild-type strain of R. solanacearum undergoes spontaneous phenotype conversion (PC), from a fluidal to non-fluidal colony morphology. PC mutants are non-pathogenic due to reduced virulence factors, and can control wilt diseases as biological control agents. The induction factors of PC in R. solanacearum are currently unclear. Here, we investigated the effect of iron treatment on bacterial growth of wild-type strain and PC mutant, and PC of the wild-type strain in liquid medium. Interestingly, PC was frequently induced in the single cultured wild-type strain by iron treatment; however, PC was not induced in the co-culture. In a co-culture of both strains, the PC mutant showed increased growth compared to the wild-type strain by iron treatment. Furthermore, we investigated the effects of iron treatment on the bacterial growth and PC of the wild-type strain under different culture conditions of medium type (MM broth, BG broth, and water medium), iron compounds, and pH. In BG broth, PC occurred frequently regardless of iron treatment. In MM broth, the optimal conditions for high frequency induction of PC by iron treatments were treatment of iron (III) EDTA, and under pH 7-8. Conversely, PC was not induced by iron treatment in water medium and in MM broth under pH 5 conditions. Common to the culture conditions wherein PC was not induced by iron treatment, the bacterial density of the wild-type strain was as low as 106 CFU mL-1 or less. Finally, we investigated the effects on bacterial growth and PC of the wild-type strain by the iron treatment and addition of culture filtrate after cultivation of the wild-type strain at high concentration. In medium containing only the culture filtrate, PC did not occur. However, in medium containing the culture filtrate and iron, PC occurred frequently. Our results thus suggest that high-density growth of the wild-type strain as well as the presence of iron are involved in inducing PC in R. solanacearum.