Publications (2826)

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First Report on the Transmission of ‘Candidatus Liberibacter americanus’ from Citrus to Nicotiana tabacum cv. Xanthi

Citation
Francischini et al. (2007). Plant Disease 91 (5)
Names
Ca. Liberibacter americanus
Subjects
Agronomy and Crop Science Plant Science
Abstract
Huanglongbing (HLB), also known as greening, is one of the most important diseases of citrus worldwide. The causal agent is a gram-negative bacterium known to inhabit the phloem of infected plants. Three different candidate species infect citrus: ‘Candidatus Liberibacter africanus’ found in the African continent; ‘Ca. L. asiaticus’ found in Asia, Brazil, and the United States; and ‘Ca. L. americanus’ found in Brazil. (1). Tobacco is an easily transformable plant species that can be used as an experimental host system to quickly screen for candidate genes useful to control plant pathogens. However, no evidence exists on the ability of this plant species to sustain populations of ‘Ca. L. americanus’. With the purpose of transmitting ‘Ca. L. americanus’ from citrus to tobacco, fragments of healthy stems of Cuscuta spp. (dodder) were used to connect an HLB-infected sweet orange plant to each of 10 healthy plants of Nicotiana tabacum L. cv. Xanthi and allowed to remain connected for 30, 45, and 50 days. Three different HLB-infected orange plants and 30 tobacco plants were used in three independent experiments. Most HLB-exposed Xanthi plants exhibited chlorotic leaves after 50 days of exposure probably because of the parasitic effect of dodder; however, an average of 6, 1, and 3 Xanthi plants exhibited a unique blotchy mottle symptom after 30, 45, and 50 days of exposure, respectively. Symptomatic and asymptomatic leaves were collected and analyzed by PCR. The results consistently confirmed the presence of ‘Ca. L. americanus’ only in symptomatic leaves. Sequencing of the PCR product and comparison to the NCBI database also confirmed the identity of the pathogen as ‘Ca. L. americanus’. Electron microscopy analysis of four symptomatic leaves indicated the presence of bacterium-like bodies with round to elongated bacilliform shapes and surrounded by two membranes. These bodies resembled those already described in HLB-infected citrus in Brazil (1). The evidence presented above confirms the successful transmission of ‘Ca. L. americanus’ from citrus to Xanthi using the parasitic plant Cuscuta spp. Reference: (1) F. A. O. Tanaka et al. Fitopatol. Bras. 31:99, 2006.

Transmission of ‘Candidatus Phytoplasma aurantifolia’ to Bakraee (Citrus reticulata Hybrid) by Feral Hishimonus phycitis Leafhoppers in Iran

Citation
Salehi et al. (2007). Plant Disease 91 (4)
Names
Ca. Phytoplasma aurantifolia
Subjects
Agronomy and Crop Science Plant Science
Abstract
Witches'-broom disease of lime (WBDL) caused by ‘Candidatus Phytoplasma aurantifolia’ is a devastating disease in the Sultanate of Oman, United Arab Emirates, and southern Iran. The disease primarily affects lime (Citrus aurantifolia), but in Iran, it is also found in bakraee, a natural C. reticulata hybrid. The disease has been experimentally transmitted from lime to several citrus cultivars by grafting and to a number of herbaceous hosts by dodder. However, the natural vector of ‘Ca. P. aurantifolia’ has not been determined. The most common phloem-feeding insect associated with lime trees in the area is the leafhopper Hishimonus phycitis. The WBDL phytoplasma has been detected in the body of this leafhopper by ELISA and PCR (1), but previous attempts to establish its vector status have failed. It was recently reported that the leafhopper can release the phytoplasma into a sugar solution by feeding through a Parafilm membrane (4). Here we report successful transmission of WBDL phytoplasma to bakraee seedlings by H. phycitis. The leafhopper nymphs and adults were collected in a WBDL-infected lime orchard in Minab (Hormozgan Province) in May of 2006. Of more than 100 leafhopper samples tested, at least 70% were positive for the phytoplasma by PCR using P1/P7 primer pair (3). Additional field-collected leafhoppers were caged (five per plant) on bakraee seedlings at the two-leaf stage in pots in the greenhouse in Zarghan (Fars Province). After 8 weeks, the remaining leafhoppers were killed with an insecticide. Six months after inoculation, 3 of 10 inoculated plants showed typical symptoms of WBDL, including bud proliferation, general chlorosis, and stunting. Symptomatic plants were strongly positive in PCR assays using primer pair P1/P7. No amplification was obtained with healthy control lime or nonsymptomatic bakraee seedlings. Amplified P1/P7 primed PCR products (1,800 bp) from experimentally vector-challenged bakraee seedlings, captured H. phycitis, and a naturally infected lime tree from Minab were subjected to restriction fragment length polymorphism (RFLP) analysis using AluI, HhaI, HpaII, RsaI, and TaqI enzymes. RFLP patterns from these sources were identical and similar to those reported earlier (2). These analyses verified the identity of WBDL phytoplasma in experimentally infected bakraee seedlings. To our knowledge, this is the first report of natural transmission of ‘Ca. P. aurantifolia’ by H. phycitis. References: (1) J. M. Bové et al. Proc. Conf. IOCV 12:342. 1993. (2) A. J. Khan et al. Phytopathology 92:1038, 2002. (3) B. Schneider et al. Pages 369–380 in: Molecular and Diagnostic Procedures in Mycoplasmology. Vol. 2. S. Razin and J. G. Tully, eds. Academic Press, New York, 1995. (4) M. Siampour et al. Iran. J. Plant Pathol. 41:139 (Farsi) and 35 (English), 2006.

First Report of a Natural Infection of Opuntia sp. by a ‘Candidatus Phytoplasma asteris’-Related Phytoplasma in China

Citation
Wei et al. (2007). Plant Disease 91 (4)
Names
Ca. Phytoplasma asteris
Subjects
Agronomy and Crop Science Plant Science
Abstract
Cacti (Opuntia spp.) are perennial, evergreen, succulent plants native to arid areas of the Americas. Because of their aesthetic appearance, many cacti have been cultivated and introduced to other parts of the world as ornamentals. Cacti are susceptible to phytoplasma infections and develop witches'-broom (WB) disease. Currently, all reported cactus WB cases are associated with infections by phytoplasmas in the peanut witches'-broom group (16SrII) (1,2,4). During a phytoplasma diversity survey carried out during 2004 in Yunnan, China, we collected 29 malformed and 14 healthy-looking naturally occurring cactus plants from 14 locations representing five geographical regions. Each of the 29 malformed plants exhibited stunted growth and possessed clusters of highly proliferating cladodia, typical symptoms of cactus WB disease. Nested-PCR was carried out on the DNA samples extracted from young cladodia of these plants using phytoplasma-universal 16S rDNA primers P1A/P7A and R16F2n/R16R2 (3). Results revealed that all 29 diseased plants that were examined were infected by phytoplasmas, whereas all 14 healthy-looking plants were negative for phytoplasmas. Subsequent restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 1.25-kb 16S rDNA fragments indicated that 28 diseased plants were infected by a phytoplasma of group 16SrII, whereas one plant (from Suan Village) was infected by a ‘Candidatus Phytoplasma asteris’-related (group 16SrI) phytoplasma designated as strain YN26. Nucleotide sequence analysis of the strain YN26 partial rRNA operon (GenBank Accession No. EF190970), covering a near full-length 16S rRNA gene, a 16S-23S rRNA intergenic spacer, a tRNA-Ile gene, and a partial 23S rRNA gene, suggested that this phytoplasma is most closely related to an ash witches'-broom phytoplasma (GenBank Accession No. AY566302, 99.7% identity) and an epilobium phyllody phytoplasma (GenBank Accession No. AY101386, 99.7% identity), both members of subgroup16SrI-B. This YN26-infected cactus plant was transferred to a greenhouse and maintained for more than 2 years, during which time DNA samples were extracted and tested two additional times. The same 16S rDNA RFLP pattern type was consistently obtained in these tests, confirming that the plant remained infected by the 16SrI phytoplasma. To our knowledge, this is the first report of a natural infection of a cactus species by a group 16SrI phytoplasma. Since this 16SrI-cactus WB phytoplasma was found in the same geographical location where 16SrII-cactus WB phytoplasma was detected both in this and a previous study (1), the findings raised the question whether 16SrI- and 16SrII-cactus WB phytoplasmas have overlapping geo- and bioecological niches. References: (1) H. Cai et al. Plant Pathol. 51:394, 2002. (2) E. Choueiri et al. Plant Dis. 89:1129, 2005. (3) I. M. Lee et al. Int. J. Syst. Evol. Microbiol 54:337, 2004. (4) N. Leyva-Lopez et al. Phytopathology (Abstr.) 89(suppl):S45, 1999.

“ Candidatus Helicobacter heilmannii” from a Cynomolgus Monkey Induces Gastric Mucosa-Associated Lymphoid Tissue Lymphomas in C57BL/6 Mice

Citation
Nakamura et al. (2007). Infection and Immunity 75 (3)
Names
Ca. Helicobacter heilmannii
Subjects
Immunology Infectious Diseases Microbiology Parasitology
Abstract
ABSTRACT Both Helicobacter pylori and “ Candidatus Helicobacter heilmannii” infections are associated with peptic ulcers, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue (MALT) lymphomas. However, good animal models of H. pylori clinical diseases are rare. In this study, we aimed to establish an animal model of “ Candidatus Helicobacter heilmannii” gastric MALT lymphoma. We used a urease-positive gastric mucosal and mucus homogenate from a cynomolgus monkey maintained in C57BL/6 mouse stomachs. The bacterium in the homogenate was identified as “ Candidatus Helicobacter heilmannii” based on a DNA sequence analysis of the 16S rRNA and urease genes. Mucosal and mucus homogenates were used to inoculate C57BL/6 mice, which were then examined for 24 months. We observed a gradual increase in the surface area of protrusive lesions in almost all infected C57BL/6 mouse fundic stomachs 6 months after infection. Light microscopic observations revealed an accumulation of B lymphocytes along with destruction of glandular elements and the presence of lymphoepithelial lesions consistent with low-grade MALT lymphomas. Electron microscopic observation revealed numerous “ Candidatus Helicobacter heilmannii” bacilli in the fundic glandular lumen, the intracellular canaliculi, and the cytoplasm of intact cells, as well as damaged parietal cells. In conclusion, “ Candidatus Helicobacter heilmannii” induced gastric MALT lymphomas in almost 100% of infected C57BL/6 mice after a 6-month period associated with the destruction of parietal cells.

Evolutionary Relationships of “ Candidatus Riesia spp.,” Endosymbiotic Enterobacteriaceae Living within Hematophagous Primate Lice

Citation
Allen et al. (2007). Applied and Environmental Microbiology 73 (5)
Names
Ca. Riesia
Subjects
Applied Microbiology and Biotechnology Biotechnology Ecology Food Science
Abstract
ABSTRACT The primary endosymbiotic bacteria from three species of parasitic primate lice were characterized molecularly. We have confirmed the characterization of the primary endosymbiont (P-endosymbiont) of the human head/body louse Pediculus humanus and provide new characterizations of the P-endosymbionts from Pediculus schaeffi from chimpanzees and Pthirus pubis , the pubic louse of humans. The endosymbionts show an average percent sequence divergence of 11 to 15% from the most closely related known bacterium “ Candidatus Arsenophonus insecticola.” We propose that two additional species be added to the genus “ Candidatus Riesia.” The new species proposed within “ Candidatus Riesia” have sequence divergences of 3.4% and 10 to 12% based on uncorrected pairwise differences. Our Bayesian analysis shows that the branching pattern for the primary endosymbionts was the same as that for their louse hosts, suggesting a long coevolutionary history between primate lice and their primary endosymbionts. We used a calibration of 5.6 million years to date the divergence between endosymbionts from human and chimpanzee lice and estimated an evolutionary rate of nucleotide substitution of 0.67% per million years, which is 15 to 30 times faster than previous estimates calculated for Buchnera , the primary endosymbiont in aphids. Given the evidence for cospeciation with primate lice and the evidence for fast evolutionary rates, this lineage of endosymbiotic bacteria can be evaluated as a fast-evolving marker of both louse and primate evolutionary histories.