Publications

4787

Summary Multicellular magnetotactic prokaryotes (MMPs) represent highly organized, spherical and motile aggregates of 10–40 bacterial cells containing magnetosomes. Although consisting of different cells, each with its own magnetosomes and flagellation, MMPs orient themselves within a magnetic field and exhibit magnetotaxis. So far, MMPs have only been found in several North and South American coastal lagoons and salt marshes. In the present study, a novel type of MMP was discovered in coastal tidal sand flats of the North Sea. High‐resolution scanning electron microscopy revealed the presence of bullet‐shaped magnetosomes which were aligned in several parallel chains. Within each aggregate, the magnetosome chains of individual cells were oriented in the same direction. Energy dispersive X‐ray (EDX) analysis showed that the magnetosomes are composed of iron sulfide. This particular morphology and arrangement of magnetosomes has previously not been reported for other MMPs. 16S rRNA gene sequence analysis revealed a single phylotype which represented a novel phylogenetic lineage with ≥ 4% sequence divergence to all previously described MMP sequences and was related to the dissimilatory sulfate‐reducing Desulfosarcina variabilis within the family Desulfobacteraceae of the subphylum Deltaproteobacteria . Fluorescence in situ hybridization with a specific oligonucleotide probe revealed that all MMPs in the tidal flat sediments studied belonged to the novel phylotype. Within each MMP, all bacterial cells showed a hybridization signal, indicating that the aggregates are composed of cells of the same phylotype. Genes for dissimilatory sulfite reductase ( dsr AB) and dissimilatory adenosine‐5′‐phosphate reductase ( apr A) could be detected in purified MMP samples, suggesting that MMPs are capable of sulfate reduction. Chemotaxis assays with 41 different test compounds yielded strong responses towards acetate and propionate, whereas other organic acids, alcohols, sugars, sugar alcohols or sulfide did not elicit any response. By means of its coordinated magnetotaxis and chemotaxis, the novel type of MMP is well adapted to the steep chemical gradients which are characteristic for intertidal marine sediments.

In North America, elm yellows, aster yellows (AY), and X-disease phytoplasmas have been detected in American grapevines (1), and recently, Bois noir was detected in Canadian vineyards from British Columbia (BC) and Ontario (ON) (2). Typical symptoms of grapevine yellows (GY) include leaf rolling and chlorosis, uneven or total lack of lignification of canes, flower abortion or berry withering, and stunting. In 2006 and 2007, independent surveys were conducted by the Canadian Food Inspection Agency (CFIA) and Agriculture and Agri-Food Canada (AAFC) to detect phytoplasmas in Canadian vineyards containing different cultivars in BC, ON, Québec (QC), Nova Scotia, New Brunswick, and Prince Edward Island. The CFIA collected and tested 651 fresh leaf samples from recently imported grapevines and older grapevines in the same or neighboring blocks displaying symptoms typical of those associated with disease caused by phytoplasmas. Many vineyards were surveyed only once. AAFC collected and tested 3,485 samples from symptomatic and asymptomatic grapevines from established vineyards in ON, BC, and QC. The same vineyards were sampled in ON and BC both years; QC vineyards were only sampled in 2007. AAFC-collected leaf samples were freeze dried and stored at –20°C before processing. CFIA samples were tested by a modified real-time PCR assay and TaqMan probe targeting the 16S ribosomal RNA gene that detects a wide range of known phytoplasmas (2). Positive samples were confirmed by conventional PCR using the phytoplasma-specific primers P1/P7 (3) and the resulting ~1,800-bp fragment was cloned and sequenced as previously described (2). DNA extracted by AAFC was amplified by nested PCR technology with universal phytoplasma specific primer pairs P1/P6 and R16R2/R16F2 (3) and the resulting 1,200-bp fragment was cloned and sequenced. Two plants, one located in ON in 2006 and the other in BC in 2007, were found to be infected with an AY-like phytoplasma by the CFIA. The phytoplasmas detected in both infected plants had a 99.9% nt sequence identity with AY phytoplasma sequences from GenBank (Accession Nos. AF222063 and AY665676, respectively), with the BC isolate also showing 100% identity to a strain of AY, ash witches'-broom phytoplasma (GenBank Accession No. AY566302). AAFC detected phytoplasma DNA in both years in a total of 17 symptomatic plants and 21 asymptomatic plants from different vine varieties in ON, BC, and QC. Positive samples were found to have a 99.0% nt sequence identity to AY subgroup 16SrI-A (GenBank Accession No. AY180956). Sequences were exchanged for confirmation of phytoplasma identity and were deposited in Genbank under Accession Nos. FJ659844 and FJ824597. Phytoplasma strains were identified for all plants in which phytoplasmas were detected. Results show that AY is present in vineyards in the provinces of ON, BC, and QC. To our knowledge, this is the first report of AY being detected in grapevines in Canada. References: (1) E. Boudon-Padieu. Bull. O I V, 79:299, 2003. (2) M. Rott et al. Plant Dis. 91:1682, 2007. (3) E. Tanne et al. Phytopathology 91:741, 2001.

A new disease of potatoes, tentatively named zebra chip (ZC) because of the intermittent dark and light symptom pattern in affected tubers which is enhanced by frying, was first found in Mexico in 1994 and in the southwestern United States in 2000. The disease can cause severe economic losses in all market classes of potatoes. The cause of ZC has been elusive, and only recently has been associated with ‘Candidatus Liberibacter’ sp. Field samples of potato plants were collected from several locations in the United States, Mexico, and Guatemala to determine transmission to potato and tomato by grafting of ZC-infected scions and psyllid feeding. The disease was successfully transmitted, through up to three generations, by sequential top- and side-grafting ZC-infection scions to several potato cultivars and to tomato. The disease was also successfully transmitted to potato and tomato plants in greenhouse experiments by potato psyllids collected from potato plants naturally affected with ZC. Transmission electron microscopic observation of ZC-affected tissues revealed the presence of bacteria-like organisms (BLOs) in the phloem of potato and tomato plants inoculated by grafting and psyllid feeding. The BLOs were morphologically similar in appearance to BLOs associated with other plant diseases. Polymerase chain reaction (PCR) amplified 16S rDNA sequences from samples representing different geographic areas, including the United States, Mexico, and Guatemala, were almost identical to the 16S rDNA of ‘Ca. L. solanacearum’ previously reported from solanaceous plants in New Zealand and the United States. Two subclades were identified that differed in two single base-pair substitutions. New specific primers along with an innovative rapid PCR were developed. This test allows the detection of the bacteria in less than 90 min. These data confirm the association of ‘Ca. L. solanacearum’ with potatoes affected by ZC in the United States, Mexico, and Guatemala.

ABSTRACT Insect intestinal tracts harbor several novel, deep-rooting clades of as-yet-uncultivated bacteria whose biology is typically completely unknown. Here, we report the isolation of the first representative of the termite group 1 (TG1) phylum from sterile-filtered gut homogenates of a humivorous scarab beetle larva. Strain Pei191 T is a mesophilic, obligately anaerobic ultramicrobacterium with a gram-negative cell envelope. Cells are typically rod shaped, but cultures are pleomorphic in all growth phases (0.3 to 2.5 μm long and 0.17 to 0.3 μm wide). The isolate grows heterotrophically on sugars and ferments d -galactose, d -glucose, d -fructose, d -glucosamine, and N -acetyl- d -glucosamine to acetate, ethanol, hydrogen, and alanine as major products but only if amino acids are present in the medium. PCR-based screening and comparative 16S rRNA gene sequence analysis revealed that strain Pei191 T belongs to the “intestinal cluster,” a lineage of hitherto uncultivated bacteria present in arthropod and mammalian gut systems. It is only distantly related to the previously described so-called “endomicrobia” lineage, which comprises mainly uncultivated endosymbionts of termite gut flagellates. We propose the name “ Elusimicrobium minutum ” gen. nov., sp. nov. (type strain, Pei191 T = ATCC BAA-1559 T = JCM 14958 T ) for the first isolate of this deep-branching lineage and the name “ Elusimicrobia ” phyl. nov. for the former TG1 phylum.

Biosulfidogenesis (the generation of hydrogen sulfide by microorganisms) in acidic liquors was investigated using two metabolically-distinct bacteria. One was a novel acidophilic sulfate-reducing bacterium (isolate CL4) that grew at pH 3.0 and above using glycerol as electron donor, and the other was the type strain of Acidithiobacillus ferrooxidans which was grown at pH 2.5 using hydrogen (derived from dissolution of metallic iron) as electron donor and elemental sulfur as electron acceptor. Both bacteria were grown in pH-controlled bioreactors. Isolate CL4 mediated the selective precipitation of zinc in situ, while the At. ferrooxidans bioreactor operated as an off-line system, generating hydrogen sulfide that precipitated copper in a separate reaction vessel. The potential of using acidophilic sulfidogens for the selective recovery of metals from acidic waste streams is discussed.

Bamboos are ecologically and economically valuable plants. Young shoots of almost all species are edible, either raw or cooked, and are major components of Asian cuisine while culms are used for furniture or handicrafts as well as fuel wood. Symptoms indicative of phytoplasma disease were observed on Sasa fortunei (van Houtte) Fiori during a survey in Yangling, Shaanxi Province, China during 2007. Symptoms included internode shortening, a mosaic pattern on leaves of diminished size, stunted growth, and death of entire plants. Total nucleic acids were extracted from leaf veins of 10 diseased plants and 6 symptomless plants with a modified cetyltrimethylammoniumbromide (CTAB) method (1). Phytoplasma infection of plants was demonstrated by a nested PCR assay employing primer pair R16mF2/R16mR1 followed by R16F2n/R16R2 (2), which generated a 16S rDNA product of approximately 1.2 kb from all symptomatic plants only. Restriction fragment length polymorphism analysis by digestion of nested PCR products with restriction enzymes AluI and MseI indicated that S. fortunei plants contained group 16SrI (aster yellows), subgroup B phytoplasmas. Sequencing and phylogenetic analysis of phytoplasma 16S rDNA from S. fortunei (GenBank Accession No. FJ501958) revealed this strain to be very similar (99.7 and 99.6%, respectively) to phytoplasmas previously associated with Henon bamboo (Phyllostachys nigra) witches'-broom (GenBank Accession No. AB242433) (4) and sasa (S. borealis) witches'-broom (GenBank Accession No. AB293421) in Korea but less so (98.6%) to bamboo (Phyllostachys spp.) witches'-broom (GenBank Accession No. AY635145) disease in China (3). To our knowledge, this is the first report of a ‘Ca. Phytoplasma asteris’-related strain infecting S. fortunei in China. References: (1) E. Angelini et al. Vitis 40:79, 2001. (2) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) C. Hong et al. Plant Prot. 31:39, 2005. (4) H. Jung et al. J. Gen. Plant Pathol. 72:261, 2006.

Zebra Chip (ZC), an emerging disease of potato (Solanum tuberosum L.) first documented in potato fields around Saltillo in México in 1994, has been identified in the southwestern United States, México, and Central America and is causing losses of millions of dollars to the potato industry (4). Recently, this damaging potato disease was also documented in New Zealand (3). This disease is characterized by a striped pattern of necrosis in tubers produced on infected plants, and fried chips processed from these infected tubers are commercially unacceptable (4). Recent studies conducted in the United States and New Zealand have associated ZC with a new species of ‘Candidatus Liberibacter’ vectored by the potato psyllid, Bactericera cockerelli Sulc (1,3,4). A bacterium designated ‘Candidatus Liberibacter psyllaurous’ has recently been identified in potato plants with “psyllid yellows” symptoms that resemble those of ZC (2). To investigate whether liberibacter is associated with ZC in México, 11 potato (cv. Atlantic) tuber samples exhibiting strong ZC symptoms and six asymptomatic tubers were collected from a ZC-affected commercial potato field near Saltillo City, Coahuila, México in September 2008 and tested for this bacterium by PCR. Total DNA was extracted from symptomatic and asymptomatic tubers with cetyltrimethylammoniumbromide (CTAB) buffer (4). DNA samples were tested by PCR using primer pair OA2/OI2c (5′-GCGCTTATTTTTAATAGGAGCGGCA-3′ and 5′-GCCTCGCGACTTCGCAACCCAT-3′, respectively) specific for 16S rDNA and primer pair CL514F/R (5′-CTCTAAGATTTCGGTTGGTT-3′ and 5′-TATATCTATCGTTGCACCAG-3′, respectively) designed from ribosomal protein genes (3). Seven of eleven (63.7%) ZC-symptomatic tubers and one of six (16.7%) asymptomatic potatoes yielded the expected 1,168-bp 16S rDNA and 669-bp CL514F/R amplicons, indicating the presence of liberibacter. Amplicons generated from symptomatic tubers were cloned into pCR2.1-Topo plasmid vectors (Invitrogen, Carlsbad, CA) and one clone of each amplicon was sequenced in both directions (ACGT, Inc., Wheeling, IL). BLAST analysis of the ZC OA2/OI2c sequence (GenBank Accession No. FJ498806) showed 100% identity to liberibacter 16S rDNA sequences amplified from potato psyllids from Dalhart, TX and potato tubers from Garden City, KS (GenBank Accession Nos. EU921627 and EU921626, respectively). The ZC CL514F/R sequence (GenBank Accession No. FJ498807) was 98% identical to analogous rplJ and rplL liberibacter ribosomal protein gene sequences amplified from several solanaceous plants in New Zealand (GenBank Accession Nos. EU834131 and EU935005). The OA2/OI2c sequence was also identical to the 16S rDNA sequence (Genbank Accession No. EU812559) of ‘Ca. Liberibacter psyllaurous’ (2). To our knowledge, this is the first report of ‘Ca. Liberibacter psyllaurous’ associated with ZC-affected potatoes in México. References: (1) J. A. Abad et al. Plant Dis. 93:108, 2009. (2) A. K. Hansen et al. Appl. Environ. Microbiol. 74:5862, 2008. (3) L. W. Liefting et al. Plant Dis. 92:1474, 2008. (4) J. E. Munyaneza et al. J. Econ. Entomol. 100:656, 2007.