Characters of homogentisate oxygenase gene mutation and high clonality of the natural pigment-producing Vibrio cholerae strains

<p>Abstract</p> <p>Background</p> <p>Some microorganisms can produce pigments such as melanin, which has been associated with virulence in the host and with a survival advantage in the environment. In <it>Vibrio cholerae</it>, studies have shown that pigment-producing mutants are more virulent than the parental strain in terms of increased UV resistance, production of major virulence factors, and colonization. To date, almost all of the pigmented <it>V. cholerae </it>strains investigated have been induced by chemicals, culture stress, or transposon mutagenesis. However, during our cholera surveillance, some nontoxigenic serogroup O139 strains and one toxigenic O1 strain, which can produce pigment steadily under the commonly used experimental growth conditions, were obtained in different years and from different areas. The genes VC1344 to VC1347, which correspond to the El Tor strain N16961 genome and which comprise an operon in the tyrosine catabolic pathway, have been confirmed to be associated with a pigmented phenotype. In the present study, we investigated the mechanism of pigment production in these strains.</p> <p>Results</p> <p>Sequencing of the VC1344, VC1345, VC1346, and VC1347 genes in these pigmented strains suggested that a deletion mutation in the homogentisate oxygenase gene (VC1345) may be associated with the pigmented phenotype, and gene complementation confirmed the role of this gene in pigment production. An identical 15-bp deletion was found in the VC1345 gene of all six O139 pigment-producing strains examined, and a 10-bp deletion was found in the VC1345 gene of the O1 strain. Strict sequence conservation in the VC1344 gene but higher variance in the other three genes of this operon were observed, indicating the different stress response functions of these genes in environmental adaption and selection. On the basis of pulsed-field gel electrophoresis typing, the pigment-producing O139 strains showed high clonality, even though they were isolated in different years and from different regions. Additionally all these O139 strains belong to the rb4 ribotype, which contains the O139 strains isolated from diarrheal patients, although these strains are cholera toxin negative.</p> <p>Conclusion</p> <p>Dysfunction of homogentisate oxygenase (VC1345) causes homogentisate accumulation and pigment formation in naturally pigmented strains of <it>V. cholerae</it>. The high clonality of these strains may correlate to an environmental survival advantage in the <it>V. cholerae </it>community due to their pigment production, and may imply a potential protective function of melanin in environmental survival of such strains.</p

Areca palm velarivirus 1 infection caused disassembly of chloroplast and reduction of photosynthesis in areca palm

The expansion of betel palm cultivation is driven by rising demand for betel nut, yet this growth is accompanied by challenges such as decreased agricultural biodiversity and the spread of infectious pathogens. Among these, Yellow Leaf Disease (YLD) emerges as a prominent threat to betel palm plantation. Areca Palm Velarivirus 1 (APV1) has been identified as a primary causative agent of YLD, precipitating leaf yellowing, stunted growth, and diminished yield. However, the precise mechanisms underlying APV1-induced damage remain elusive. Our study elucidates that APV1 infiltrates chloroplasts, instigating severe damage and consequential reductions in chlorophyll a/b and carotene levels, alongside notable declines in photosynthetic efficiency. Moreover, APV1 infection exerts broad regulatory effects on gene expression, particularly suppressing key genes implicated in chloroplast function and photosynthesis. These disruptions correlate with growth retardation, yield diminishment, and compromised nut quality. Intriguingly, the paradoxical destruction of the host's photosynthetic machinery by APV1 prompts inquiry into its evolutionary rationale, given the virus's dependence on host resources for replication and proliferation. Our findings reveal that APV1-induced leaf yellowing acts as a beacon for transmission vectors, hinting at a nuanced “host-pathogen-vector co-evolutionary” dynamic

A novel pathogenic species of genus Stenotrophomonas: Stenotrophomonas pigmentata sp. nov

IntroductionStenotrophomonas is a prominent genus owing to its dual nature. Species of this genus have many applications in industry and agriculture as plant growth-promoting rhizobacteria and microbial biological control agents, whereas species such as Stenotrophomonas maltophilia are considered one of the leading gram-negative multi-drug-resistant bacterial pathogens because of their high contribution to the increase in crude mortality and significant clinical challenge. Pathogenic Stenotrophomonas species and most clinical isolates belong to the Stenotrophomonas maltophilia complex (SMc). However, a strain highly homologous to S. terrae was isolated from a patient with pulmonary tuberculosis (TB), which aroused our interest, as S. terrae belongs to a relatively distant clade from SMc and there have been no human association reports.MethodsThe pathogenicity, immunological and biochemical characteristics of 610A2T were systematically evaluated.Results610A2T is a new species of genus Stenotrophomonas, which is named as Stenotrophomonas pigmentata sp. nov. for its obvious brown water-soluble pigment. 610A2T is pathogenic and caused significant weight loss, pulmonary congestion, and blood transmission in mice because it has multiple virulence factors, haemolysis, and strong biofilm formation abilities. In addition, the cytokine response induced by this strain was similar to that observed in patients with TB, and the strain was resistant to half of the anti-TB drugs.ConclusionsThe pathogenicity of 610A2T may not be weaker than that of S. maltophilia. Its isolation extended the opportunistic pathogenic species to all 3 major clades of the genus Stenotrophomonas, indicating that the clinical importance of species of Stenotrophomonas other than S. maltophilia and potential risks to biological safety associated with the use of Stenotrophomonas require more attention

Bacterial strains, their susceptibilities to VFJΦ and primers used in this study.

a<p>ND, no Kan^r colonies detected.</p

Growth curves of <i>E. coli</i> strain DH5α and three types of <i>V. cholerae</i> strains before and after infection by the VFJ phage.

<p>Growth curves of <i>E. coli</i> strain DH5α and three types of <i>V. cholerae</i> strains before and after infection by the VFJ phage.</p

Circular diagram of the VFJ genome and predicted ORFs (A).

<p><b>The non-identical region is marked with a grey box.</b> Sequence alignment of the <i>attP</i> regions of VFJΦ and fs2 Φ (accession no. NC_001956) and schematic representation of adjacent areas (B). Electron microscopy image of VFJΦ precipitated from the ICDC-4470 culture supernatant (C).</p

Proteins involved in difference of sorbitol fermentation rates of the toxigenic and nontoxigenic <it>Vibrio cholerae </it>El Tor strains revealed by comparative proteome analysis

Abstract Background The nontoxigenic V. cholerae El Tor strains ferment sorbitol faster than the toxigenic strains, hence fast-fermenting and slow-fermenting strains are defined by sorbitol fermentation test. This test has been used for more than 40 years in cholera surveillance and strain analysis in China. Understanding of the mechanisms of sorbitol metabolism of the toxigenic and nontoxigenic strains may help to explore the genome and metabolism divergence in these strains. Here we used comparative proteomic analysis to find the proteins which may be involved in such metabolic difference. Results We found the production of formate and lactic acid in the sorbitol fermentation medium of the nontoxigenic strain was earlier than of the toxigenic strain. We compared the protein expression profiles of the toxigenic strain N16961 and nontoxigenic strain JS32 cultured in sorbitol fermentation medium, by using fructose fermentation medium as the control. Seventy-three differential protein spots were found and further identified by MALDI-MS. The difference of product of fructose-specific IIA/FPR component gene and mannitol-1-P dehydrogenase, may be involved in the difference of sorbitol transportation and dehydrogenation in the sorbitol fast- and slow-fermenting strains. The difference of the relative transcription levels of pyruvate formate-lyase to pyruvate dehydrogenase between the toxigenic and nontoxigenic strains may be also responsible for the time and ability difference of formate production between these strains. Conclusion Multiple factors involved in different metabolism steps may affect the sorbitol fermentation in the toxigenic and nontoxigenic strains of V. cholerae El Tor.</p

Transmission of areca palm velarivirus 1 (APV1) by Pseudococcus cryptus

Abstract Betel palm is one of the most economically important crops in Southeast Asia. The occurrence and expansion of yellow leaf disease (YLD) have significantly impacted betel palm plantations. Our previous research demonstrated that areca palm velarivirus 1 (APV1) was associated with YLD and transmitted by Ferrisia virgata (striped mealybug), causing YLD in betel palms. This finding provides strong etiological evidence of the role played by APV1 in YLD. Controlling YLD is a pressing issue with significant challenges. One viable approach is to prevent the virus from spreading by disrupting the transmission vectors. Therefore, it is imperative to identify potential vectors of APV1. In this study, we detected APV1 in the stylet, foregut, midgut, and hindgut of Pseudococcus cryptus (cryptic mealybug) using immunocapture RT-PCR and in situ immunofluorescence localization. P. cryptus transmitted APV1 in a non-circulative, semi-persistent manner. The retention time of APV1 in P. cryptus was notably longer than that in F. virgata. Additionally, field investigations revealed that three other insects infesting betel palms also carried APV1. In summary, APV1 may also be transmitted by other mealybug species, and the lower specificity of transmission vectors makes it challenging to control the spread of this devastating disease. This work provides timely knowledge for the prevention and management of YLD