Multiphasic investigations imply transfer of orange-/red-pigmented strains of the bean pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens to a new species as C. aurantiacum sp. nov., elevation of the poinsettia pathogen C. flaccumfaciens pv. poinsettiae to the species level as C. Poinsettiae sp. nov., and synonymy of C. albidum with C. citreum.

Curtobacterium flaccumfaciens (Microbacteriaceae), a plant-pathogenic coryneform species includes five pathovars with valid names and a number of proposed - but unvalidated - new members. In this study, phenotypic features and DNA similarity indexes were investigated among all C. flaccumfaciens members. Results showed that the C. flaccumfaciens pv. poinsettiae strains causing bacterial canker of Euphorbia pulcherrima in the USA as well as the orange-/red-pigmented strains of C. flaccumfaciens pv. flaccumfaciens pathogenic on dry beans in Iran are too distinct from each other and from the type strain of the species to be considered members of C. flaccumfaciens. Hence, the latter two groups were elevated at the species level as C. poinsettiae sp. nov. (ATCC 9682T = CFBP 2403T = ICMP 2566T = LMG 3715T = NCPPB 854T as type strain), and C. aurantiacum sp. nov. (50RT = CFBP 8819T = ICMP 22071T as type strain). Within the emended species C. flaccumfaciens comb. nov., yellow-pigmented strains causing bacterial wilt of dry beans and those causing bacterial canker of Euphorbia pulcherrima in Europe were retained as C. flaccumfaciens pv. flaccumfaciens and C. flaccumfaciens pv. poinsettiae, respectively; while taxonomic position of the sugar beet pathogen C. flaccumfaciens pv. beticola ATCC BAA144PT was confirmed. The newly described onion pathogen C. allii was also reclassified as C. flaccumfaciens pv. allii with the pathotype strain LMG 32517PT. Furthermore, C. flaccumfaciens pv. basellae causing bacterial leaf spot of malabar spinach (Basella rubra) was transferred to C. citreum pv. basellae with ATCC BAA143PT as pathotype.

Identification of the chemical profile and evaluation of the antimicrobial effect of Eryngium billardieri Delar essential oil component against bacterial species of agricultural and food interest.

Studies on the antibacterial activity of the essential oil of E. billardieri are limited. In this study, we identified this herb as a natural complex effective against several bacteria by employing disk diffusion and broth microdilution susceptibility methods. Primary estimation of the antimicrobial effect of this herbal compound by disk diffusion method showed that the oil could inhibit the growth of the tested bacteria by the appearance of haloes between 8.25 and 21.25 mm. In the next step, the oil was found to be active against all 24 tested Gram-negative and Gram-positive bacteria in the broth media, at minimum inhibitory concentrations ranging from 0.67 to 34.17 g L-1. Furthermore, Enterococcus faecalis and Curtobacterium flaccumfaciens pv. flaccumfaciens were the most sensitive food and plant pathogenic bacteria, respectively. Gas chromatography-mass spectrometry analysis was conducted to assign the ingredients present in the oil; 34 different components representing 95.71% of the total oil were identified, with n-hexadecanoic acid being the dominant component, followed by 2-Pentadecanone, 6,10,14-trimethyl, 1H-Indene, 1-ethylideneoctahydro-, and Cinnamyl tiglate. These findings demonstrate, for the first time, a broad spectrum of the antibacterial capacity of E. billardieri. Based on these observations, the oil could be applied as a natural preservative with the potential for designing novel products. Its bioactive agents can also be isolated for further use in the food and agricultural industries.

Clavibacter lycopersici sp. nov.: a peach-colored actinobacterium isolated from symptomless tomato plant.

In 2015, Gram-positive peach-coloured actinobacterial strains were isolated from symptomless tomato phyllosphere in Iran. Biochemical and physiological characteristics, as well as 16S rRNA phylogeny showed that the strains belong to Clavibacter sp., while they were non-pathogenic on the host of isolation, and morphologically distinct from the tomato pathogen C. michiganensis and other plant-associated bacteria. Multilocus sequence analysis of five housekeeping genes showed that the two peach-coloured strains CFBP 8615T (Tom532T) and CFBP 8616 (Tom495) were phylogenetically distinct from all validly described Clavibacter species. Whole genome sequence-based indices, i.e. average nucleotide identity (orthoANI) and digital DNA-DNA hybridization (dDDH), showed that the two peach-colored strains share nearly 100 % orthoANI value with one another, while they differ from all validly described Clavibacter species with the orthoANI/dDDH values <93 % and <50 %, respectively. Thus, based on both phenotypic features and orthoANI/dDDH indices the peach-coloured strains could belong to a new species within Clavibacter. In this study, we provide a formal species description for the peach-coloured tomato-associated Clavibacter strains. Clavibacter lycopersici sp. nov. is proposed for the new species with Tom532T = CFBP 8615T = ICMP 22100T as type strain.