Search

In Xanthomonas spp., the biosynthesis of the yellow pigment xanthomonadin and fatty acids originates in the type II polyketide synthase (PKS II) and fatty acid synthase (FAS) pathways, respectively. The acyl carrier protein (ACP) is the central component of PKS II and FAS and requires posttranslational phosphopantetheinylation to initiate these pathways. In this study, for the first time, we demonstrate that the posttranslational modification of ACPs in X. campestris pv. campestris is performed by an essential 4′-phosphopantetheinyl transferase (PPTase), XcHetI (encoded by Xc_4132). X. campestris pv. campestris strain XchetI could not be deleted from the X. campestris pv. campestris genome unless another PPTase-encoding gene such as Escherichia coli acpS or Pseudomonas aeruginosa pcpS was present. Compared with wild-type strain X. campestris pv. campestris 8004 and mutant XchetI::PapcpS, strain XchetI::EcacpS failed to generate xanthomonadin pigments and displayed reduced pathogenicity for the host plant, Brassica oleracea. Further experiments showed that the expression of XchetI restored the growth of E. coli acpS mutant HT253 and, when a plasmid bearing XchetI was introduced into P. aeruginosa, pcpS, which encodes the sole PPTase in P. aeruginosa, could be deleted. In in vitro enzymatic assays, XcHetI catalyzed the transformation of 4′-phosphopantetheine from coenzyme A to two X. campestris pv. campestris apo-acyl carrier proteins, XcAcpP and XcAcpC. All of these findings indicate that XcHetI is a surfactin PPTase-like PPTase with a broad substrate preference. Moreover, the HetI-like PPTase is ubiquitously conserved in Xanthomonas spp., making it a potential new drug target for the prevention of plant diseases caused by Xanthomonas.[Graphic: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nanoparticles have drawn significant attention in recent years, owing to their unique electrical, optical, biocidal, and catalytic properties. The present study reports an environment friendly, green approach for silver nanoparticles (AgNPs) synthesis using bacterial yellow color pigment, xanthomonadin (XP) derived from Xanthomonas sp. After exposing the reaction mixture to sunlight, a visible colour shift and spectrophotometric measurement proved that nanosized silver particles (XP-AgNPs) were being synthesized by xanthomonadin. The size of XP–AgNPs was in the range between 30 and 100 nm, with the spherical shaped particles. The XP–AgNPs showed excellent biocidal activity against representative Gram positive and Gram negative organisms i.e. Staphylococcus aureus, B. subtilis and Pseudomonas aeruginosa, Escherichia coli. In addition, using standard assays, the photo-protecting/SPF enhancement of commercial sunscreens and DPPH radical scavenging activity of XP, and XP-AgNPs were evaluated. As a result, adding 4 % w/w xanthomonadin in commercial sunscreens have original SPFs 4 and 10 increases by 271 % and 85.2 %, respectively. XP and XP-AgNPs showed significant antioxidant activities with the IC50 values of 46.21 µg/mL and 21.62 µg/mL, respectively. In conclusion, xanthomonadin mediated silver nanomaterial with photo protecting, antioxidant and biocidal potential has been reported.

A characteristic feature of phytopathogenic Xanthomonas bacteria is the production of yellow membrane-bound pigments called xanthomonadins. Previous studies showed that 3-hydroxybenzoic acid (3-HBA) was a xanthomonadin biosynthetic intermediate and also, that it had a signaling role. The question of whether the structural isomers 4-HBA and 2-HBA (salicylic acid) have any role in xanthomonadin biosynthesis remained unclear. In this study, we have selectively eliminated 3-HBA, 4- HBA, or the production of both by expression of the mhb, pobA, and pchAB gene clusters in the Xanthomonas campestris pv. campestris strain XC1. The resulting strains were different in pigmentation, virulence factor production, and virulence. These results suggest that both 3-HBA and 4-HBA are involved in xanthomonadin biosynthesis. When both 3- HBA and 4-HBA are present, X. campestris pv. campestris prefers 3-HBA for Xanthomonadin-A biosynthesis; the 3-HBA-derived Xanthomonadin- A was predominant over the 4-HBA-derived xanthomonadin in the wildtype strain XC1. If 3-HBA is not present, then 4-HBA is used for biosynthesis of a structurally uncharacterized Xanthomonadin-B. Salicylic acid had no effect on xanthomonadin biosynthesis. Interference with 3-HBA and 4-HBA biosynthesis also affected X. campestris pv. campestris virulence factor production and reduced virulence in cabbage and Chinese radish. These findings add to our understanding of xanthomonadin biosynthetic mechanisms and further help to elucidate the biological roles of xanthomonadins in X. campestris pv. campestris adaptation and virulence in host plants. [ABSTRACT FROM AUTHOR]

Summary: Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot in crucifers, produces a membrane‐bound yellow pigment called xanthomonadin to protect against photobiological and peroxidative damage, and uses a quorum‐sensing mechanism mediated by the diffusible signal factor (DSF) family signals to regulate virulence factors production. The Xcc gene XCC4003, annotated as Xcc fabG3, is located in the pig cluster, which may be responsible for xanthomonadin synthesis. We report that fabG3 expression restored the growth of the Escherichia coli fabG temperature‐sensitive mutant CL104 under non‐permissive conditions. In vitro assays demonstrated that FabG3 catalyses the reduction of 3‐oxoacyl‐acyl carrier protein (ACP) intermediates in fatty acid synthetic reactions, although FabG3 had a lower activity than FabG1. Moreover, the fabG3 deletion did not affect growth or fatty acid composition. These results indicate that Xcc fabG3 encodes a 3‐oxoacyl‐ACP reductase, but is not essential for growth or fatty acid synthesis. However, the Xcc fabG3 knock‐out mutant abolished xanthomonadin production, which could be only restored by wild‐type fabG3, but not by other 3‐oxoacyl‐ACP reductase‐encoding genes, indicating that Xcc FabG3 is specifically involved in xanthomonadin biosynthesis. Additionally, our study also shows that the Xcc fabG3‐disrupted mutant affects Xcc virulence in host plants. [ABSTRACT FROM AUTHOR]

Most of the pathogenic microorganisms that cause serious production and economic losses for the agricultural industry are members of the genus Xanthomonas. The main bacterial pathogen causing walnut black spot is Xanthomonas arboricola pv. juglandis (Xaj). Members of the genus Xanthomonas produce a yellow pigment called xanthomonadin, which is membrane-bound and protects the bacteria against photobiological and peroxidative damage. Here, we report the characterization of a gene named XajfabG3 (a homologous gene of fabG3 in Xanthomonas campestris pv. campestris), demonstrating that it is responsible for xanthomonadin synthesis. Expression of XajfabG3 in Escherichia coli fabG temperature-sensitive mutant CL104 restored the growth of CL104 under nonpermissive temperature, although Xaj FabG3 had a lower activity than Xaj FabG1 or FabG from Escherichia coli. In vitro assays demonstrated that Xaj FabG3 could reduce 3-oxoacyl-acyl carrier proteins (-ACPs) of fatty acid synthesis reactions and showed that although deletion of XajfabG3 did not affect bacterial growth and fatty acid composition, xanthomonadin production was abolished in a XajfabG3 -deficient strain. Xanthomonadin production could be restored only by wild-type fabG3 and not by XajfabG1 , another 3-oxoacyl-ACP reductase-encoding gene in Xaj , indicating that Xaj FabG3 specifically participates in the biosynthesis of xanthomonadin. Moreover, our study showed that the XajfabG3 knockout mutant affected virulence in the host Juglans regia L. Our elucidation of the biological function of the fabG3 gene in Xaj provides a target for the development of prevention and treatment agents for walnut blight. • Importance: The study investigates a 3-oxoacyl-ACP reductase (OAR) homolog (FabG3) in Xanthomonas arboricola pv. juglandis (Xaj). FabG3 participates in the biosynthesis of xanthomonadin specifically, and the deletion of fabG3 attenuated virulence. The research will provide evidence for the pathogenesis of X. arboricola pv. juglandis. It may also provide a new target for the development of prevention and treatment agents for walnut bacterial blight. [ABSTRACT FROM AUTHOR]

Polyscias guilfoylei is a popular ornamental belonging to the Araliaceae family. The present study identified and characterized bacterial strains causing leaf lesions on P . guilfoylei in a nursery in Taiwan. Strains Pgu1 to Pgu5 were isolated from infected leaf tissues and Koch's postulates were fulfilled. Observation of Pgu1 under a transmission electron microscope revealed that its cells were single flagellated and rod shaped. Sequencing of Pgu1 to Pgu5's 16S ribosomal DNA showed that they belong to the genus Xanthomonas . The biochemical and physiological traits of these bacteria were determined, and many of them also resemble those of other xanthomonads. However, the strains were unable to produce yellow pigments typically found in most members of the Xanthomonas genus, even when grown on yeast dextrose calcium carbonate (YDC) agar. Physiological assays and phylogenetic analyses based on multiple loci showed that the isolates were closely associated with members of the species Xanthomonas euvesicatoria and phylogenetically distant from X . hortorum pv. hederae , the currently only known xanthomonad capable of inducing diseases on Polyscias spp. Artificial inoculation into different host plants revealed that a representative strain, Pgu1, is specialized to P. guilfoylei and perhaps other members of the Araliaceae family. Based on the results from the phylogenetic and phenotypic analyses, the present work concludes that these strains belong to a novel pathovar of X . euvesicatoria . The pathovar epithet polysciadis is proposed.

We report an overlooked source of artifacts for clinical specimens, where unexpected and normally negligible contaminants can skew the interpretation of results. During an ongoing study of bone fragments from diabetic osteomyelitis, strong Raman signatures were found, which did not correspond with normal bone mineral or matrix. In a bone biopsy from the calcaneus of a patient affected by diabetic osteomyelitis, Raman microspectroscopic analysis revealed regions with both abnormal mineral and degraded collagen in addition to normal bone. Additional bands indicated a pathological material. Stenotrophomonas maltophilia was identified in the wound culture by independent microbiologic examination. We initially assigned the unusual bands to xanthomonadin, a bacterial pigment from S. maltophilia. However, the same bands were also found more than a year later on a second specimen that had been noticeably contaminated with pathology marking dye. Drop deposition/Raman spectroscopy of commonly used pathology dyes revealed that a blue tissue-marking dye was responsible for the unusual bands in both specimens, even in the first specimen where there was no visible evidence of contamination. [ABSTRACT FROM AUTHOR]

Xanthomonadins are membrane-bound yellow pigments that are typically produced by phytopathogenic bacterial Xanthomonas spp., Xylella fastidiosa , and Pseudoxanthomonas spp. They are also produced by a diversity of environmental bacterial species. Considerable research has revealed that they are a unique group of halogenated, aryl-polyene, water-insoluble pigments. Xanthomonadins have been shown to play important roles in epiphytic survival and host-pathogen interactions in the phytopathogen Xanthomonas campestris pv. campestris , which is the causal agent of black rot in crucifers. Here, we review recent advances in the understanding of xanthomonadin chemical structures, physiological roles, biosynthetic pathways, regulatory mechanisms, and crosstalk with other signaling pathways. The aim of the present review is to provide clues for further in-depth research on xanthomonadins from Xanthomonas and other related bacterial species.