TL;DR: The higher frequency of C. flaccumfaciens in asymptomatic plants suggests a role for this organism in the resistance of plants to CVC, and DGGE profiles can be used to detect some endophytic bacteria of citrus plants.
Abstract: Citrus variegated chlorosis (CVC) is caused by Xylella fastidiosa, a phytopathogenic bacterium that can infect all Citrus sinensis cultivars. The endophytic bacterial communities of healthy, resistant, and CVC-affected citrus plants were studied by using cultivation as well as cultivation-independent techniques. The endophytic communities were assessed in surface-disinfected citrus branches by plating and denaturing gradient gel electrophoresis (DGGE). Dominant isolates were characterized by fatty-acid methyl ester analysis as Bacillus pumilus, Curtobacterium flaccumfaciens, Enterobacter cloacae, Methylobacterium spp. (including Methylobacterium extorquens, M. fujisawaense, M. mesophilicum, M. radiotolerans, and M. zatmanii), Nocardia sp., Pantoea agglomerans, and Xanthomonas campestris. We observed a relationship between CVC symptoms and the frequency of isolation of species of Methylobacterium, the genus that we most frequently isolated from symptomatic plants. In contrast, we isolated C. flaccumfaciens significantly more frequently from asymptomatic plants than from those with symptoms of CVC while P. agglomerans was frequently isolated from tangerine (Citrus reticulata) and sweet-orange (C. sinensis) plants, irrespective of whether the plants were symptomatic or asymptomatic or showed symptoms of CVC. DGGE analysis of 16S rRNA gene fragments amplified from total plant DNA resulted in several bands that matched those from the bacterial isolates, indicating that DGGE profiles can be used to detect some endophytic bacteria of citrus plants. However, some bands had no match with any isolate, suggesting the occurrence of other, nonculturable or as yet uncultured, endophytic bacteria. A specific band with a high G+C ratio was observed only in asymptomatic plants. The higher frequency of C. flaccumfaciens in asymptomatic plants suggests a role for this organism in the resistance of plants to CVC.
TL;DR: A study of the diversity of endophytic bacteria present in seeds of a deepwater rice variety revealed the presence of seven types of BOX-PCR fingerprints and one strain was identified as Pantoea agglomerans, genetically tagged with the reporter gene, gusA, which colonized the root surface, root hairs, root cap, points of lateral root emergence, root cortex and the stelar region.
TL;DR: The abundance and composition of Verticillium antagonists was plant species dependent, while antagonists belonging to the Enterobacteriaceae (Serratia spp., Pantoea agglomerans) were mainly isolated from the rhizosphere of oilseed rape.
Abstract: To study the effect of plant species on the abundance and diversity of bacterial antagonists, the abundance, the phenotypic diversity, and the genotypic diversity of rhizobacteria isolated from potato, oilseed rape, and strawberry and from bulk soil which showed antagonistic activity towards the soilborne pathogen Verticillium dahliae Kleb. were analyzed. Rhizosphere and soil samples were taken five times over two growing seasons in 1998 and 1999 from a randomized field trial. Bacterial isolates were obtained after plating on R2A (Difco, Detroit, Mich.) or enrichment in microtiter plates containing high-molecular-weight substrates followed by plating on R2A. A total of 5,854 bacteria isolated from the rhizosphere of strawberry, potato, or oilseed rape or bulk soil from fallow were screened by dual testing for in vitro antagonism towards Verticillium. The proportion of isolates with antagonistic activity was highest for strawberry rhizosphere (9.5%), followed by oilseed rape (6.3%), potato (3.7%), and soil (3.3%). The 331 Verticillium antagonists were identified by their fatty acid methyl ester profiles. They were characterized by testing their in vitro antagonism against other pathogenic fungi; their glucanolytic, chitinolytic, and proteolytic activities; and their BOX-PCR fingerprints. The abundance and composition of Verticillium antagonists was plant species dependent. A rather high proportion of antagonists from the strawberry rhizosphere was identified as Pseudomonas putida B (69%), while antagonists belonging to the Enterobacteriaceae (Serratia spp., Pantoea agglomerans) were mainly isolated from the rhizosphere of oilseed rape. For P. putida A and B plant-specific genotypes were observed, suggesting that these bacteria were specifically enriched in each rhizosphere.
TL;DR: DNA hybridization group 14589 constitutes a discrete species within the family Enterobacteriaceae and is proposed to unite DNA hybridization groups 14589 and 27155 in a single genus, Pantoea gen. nov.
Abstract: Deoxyribonucleic acid (DNA)-DNA hybridization was performed with 10 strains belonging to the “Erwinia herbicola-Enterobacter agglomerans complex” by using the competition method on nitrocellulose filters. These strains exhibited more than 75% DNA binding to Erwinia herbicola ATCC 14589T (T = type strain) and constitute DNA hybridization group 14589 (including strains ATCC 14589T and CDC 1429-71 from DNA hybridization group III [D. J. Brenner, G. R. Fanning, J. K. Leete Knutson, A. G. Steigerwalt, and M. J. Krichevsky, Int. J. Syst. Bacteriol. 34:45-55, 1984]). The high level of genomic relatedness of these strains was confirmed by the similarities observed in their electrophoretic protein patterns. On the basis of our data, DNA hybridization group 14589 constitutes a discrete species within the family Enterobacteriaceae. Its closest relative is DNA hybridization group 27155 (41 to 53% DNA relatedness), which was previously defined and includes the type strains, among others, of Enterobacter agglomerans, Erwinia herbicola, and Erwinia milletiae (A. Beji, J. Mergaert, F. Gavini, D. Izard. K. Kersters, H. Leclerc, and J. De Ley, Int. J. Syst. Bacteriol. 38:77-88, 1988). We propose to unite DNA hybridization groups 14589 and 27155 in a single genus, Pantoea gen. nov. Pantoea agglomerans (Beijerinck 1888) comb. nov. is proposed to contain most strains of DNA hybridization group 27155 (including DNA hybridization group XIII of Brenner et al.), and its type strain is strain ATCC 27155 (= NCTC 9381 = LMG 1286). Pantoea dispersa sp. nov. is proposed to contain DNA hybridization group 14589, and its type strain is strain ATCC 14589 (= LMG 2603). Descriptions of the genus and its two species are given.
TL;DR: New types of antimicrobial compounds were identified in the culture filtrate of Lactobacillus plantarum VTT E‐78076 and the identification was confirmed using pure commercial reference compounds in identical chromatographs and in antimicrobial tests.
Abstract: M.-L. NIKU-PAAVOLA, A. LAITILA, T. MATTILA-SANDHOLM AND A. HAIKARA. 1999.New types of antimicrobial compounds were identified in the culture filtrate of Lactobacillus plantarum VTT E-78076. Activity was detected in the low molecular mass fraction separated by gel chromatography. This fraction totally inhibited the growth of the Gram-negative test organism, Pantoea agglomerans (Enterobacter agglomerans) VTT E-90396. Characteristic compounds from this fraction were identified by GC/MS-analysis and the identification was confirmed using pure commercial reference compounds in identical chromatographs and in antimicrobial tests. The active fraction included benzoic acid (CAS 65‐85‐0), 5methyl-2,4-imidazolidinedione (CAS 616‐03‐5, methylhydantoin), tetrahydro-4hydroxy-4-methyl-2H-pyran-2-one (CAS 674‐26‐0, mevalonolactone) and 3-(2methylpropyl)-2,5-piperazinedione (CAS 5845‐67‐0, cyclo(glycyl-L-leucyl)). These compounds in concentrations of 10 ppm inhibited growth of the test organism by 10‐15% when acting separately, but 100% when all were applied together with 1% lactic acid. The inhibition was 40% by 1% lactic acid alone. The compounds were also active against Fusarium avenaceum (Gibberella avenacea) VTT D-80147. The inhibition was 10‐15% by separate compounds in concentrations of 10 ppm and maximally 20% in combinations. Fungal growth was not inhibited by lactic acid. Inhibition by unfractionated Lact. plantarum culture filtrate was 37% and by the low molecular mass fraction, 27%.