Publications

3826

A disease that severely affects processing potatoes (Solanum tuberosum L.), termed zebra chip (ZC), has been identified in several locations in the United States (Texas, Nebraska, Colorado, Kansas, New Mexico, Arizona, and Nevada), Mexico, and Central America (4). The disease name comes from the rapid oxidative darkening of freshly cut tubers and the dark stripes and blotches that occur in chips processed from infected tubers. Recently, the disorder has been associated with a new ‘Candidatus Liberibacter’ species in New Zealand (3). Also, a bacterium designated ‘Candidatus Liberibacter psyllaurous’ has been identified recently in potato plants with “psyllid yellows” symptoms that resemble foliar symptoms of ZC (2). In the fall of 2008, 10 tubers were received at the Prosser laboratory from a commercial potato grower and five had symptoms characteristic of ZC. The tubers, cv. Dakota Pearl, were grown near Lancaster in southern California. The tubers showed rapid oxidation upon slicing and the sunken stolon attachment characteristic of ZC (4). Nucleic acid was extracted from symptomatic tubers (1) and tested by PCR for ‘Ca. Liberibacter’ species with primer pairs OA2/OI2c (5′-GCGCTTATTTTTAATAGGAGCGGCA-3′ and 5′-GCCTCGCGACTTCGCAACCCAT-3′) and CL514F/R (5′-CTCTAAGATTTCGGTTGGTT-3′ and 5′-TATATCTATCGTTGCACCAG-3′), which amplify from the 16S rDNA and rplJ and rplL ribosomal protein genes, respectively (3). Four of the five tubers with distinct ZC symptoms yielded the expected amplicons with both primer pairs. Two tubers with mild internal discoloration yielded correctly sized amplicons but in lesser amounts than from the severely affected tubers. Nucleic acid from healthy potato tubers yielded no product with these primers. One clone of the 1,168-bp OA2/OI2c amplicon and two clones of the 669-bp CL514F/R amplicon from a strongly positive sample were sequenced in both directions (ACGT, Inc., Wheeling, IL). BLAST alignments of the consensus sequences of the OA2/OI2c and CL514F/R amplicons (GenBank Accessions Nos. FJ498802 and FJ498803, respectively) revealed 100% identity with analogous ‘Ca. Liberibacter’ sequences reported from ZC-symptomatic potatoes in New Zealand (GenBank Accession Nos. EU849020 and EU919514). The OA2/OI2c amplicon was also identical to a sequence of ‘Ca. Liberibacter psyllaurous’ (GenBank Accession No. EU812559) from psyllid yellows-affected potatoes in the United States (2) and also showed a 99% identity with sequences from a ‘Ca. Liberibacter’ species reported in ZC tubers from Kansas (GenBank Accession No. EU921626). Potato crops with symptoms of ZC have been observed previously in California (4), but this is the first identification of ‘Ca. Liberibacter psyllaurous’ from diseased potatoes grown in California. Since ZC was first reported in the mid- to late-1990s, information from potato growers and processors suggests that ZC is becoming more important. The disease has caused millions of dollars in losses, particularly in south Texas (4). The identification of ‘Ca. Liberibacter psyllaurous’ in California provides additional evidence that the disease is increasing in importance in other potato-growing regions. References: (1) J. M. Crosslin et al. Plant Dis. 90:663, 2006. (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. Subtrop. Plant Sci. 59:30, 2007.

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.

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.

In São Paulo State, Brazil, ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ are associated with huanglongbing (HLB). Affected municipalities occur mainly in the central and southern regions, where the annual number of hours above 30°C is two to five times lower than that in the extreme northern and western regions. The influence of temperature on sweet orange trees infected with ‘Ca. L. asiaticus’ or ‘Ca. L. americanus’ was studied in temperature-controlled growth chambers. Symptom progression on new shoots of naturally infected and experimentally graft-inoculated symptomatic sweet orange trees was assessed. Mottled leaves developed on all infected trees at 22 to 24°C, but not on any ‘Ca. L. americanus’–infected trees at 27 to 32°C. Quantitative, real time-PCR was used to determine the liberibacter titers in the trees. After 90 days, ‘Ca. L. asiaticus’–infected trees had high titers at 32 and 35°C, but not at 38°C, while ‘Ca. L. americanus’–infected trees had high titers at 24°C, but at 32°C the titers were very low or the liberibacters could not be detected. Thus, the multiplication of ‘Ca. L. asiaticus’ is not yet affected at 35°C, while a temperature of 32°C is detrimental to ‘Ca. L. americanus’. Thus, ‘Ca. L. americanus’ is less heat tolerant than ‘Ca. L. asiaticus’. The uneven distribution of these two liberibacters in São Paulo State might be in relation with these results.