Publications

4474

The present study investigated the phylogenetic affiliation and physiological characteristics of bacteria responsible for anaerobic ammonium oxidization (anammox); these bacteria were enriched in an anammox reactor with a nitrogen removal rate of 26.0 kg N m−3day−1. The anammox bacteria were identified as representing ‘CandidatusBrocadia sinica’ on the basis of phylogenetic analysis of rRNA operon sequences. Physiological characteristics examined were growth rate, kinetics of ammonium oxidation and nitrite reduction, temperature, pH and inhibition of anammox. The maximum specific growth rate (μmax) was 0.0041 h−1, corresponding to a doubling time of 7 days. The half-saturation constants (Ks) for ammonium and nitrite of ‘Ca.B. sinica’ were 28±4 and 86±4 µM, respectively, higher than those of ‘CandidatusBrocadia anammoxidans’ and ‘CandidatusKuenenia stuttgartiensis’. The temperature and pH ranges of anammox activity were 25–45 °C and pH 6.5–8.8, respectively. Anammox activity was inhibited in the presence of nitrite (50 % inhibition at 16 mM), ethanol (91 % at 1 mM) and methanol (86 % at 1 mM). Anammox activities were 80 and 70 % of baseline in the presence of 20 mM phosphorus and 3 % salinity, respectively. The yield of biomass and dissolved organic carbon production in the culture supernatant were 0.062 and 0.005 mol C (molNH4+)−1, respectively. This study compared physiological differences between three anammox bacterial enrichment cultures to provide a better understanding of anammox niche specificity in natural and man-made ecosystems.

The taxonomic status of the families Actinosynnemataceae and Pseudonocardiaceae was assessed based on 16S rRNA gene sequence data available for the 151 taxa with validly published names, as well as chemotaxonomic and morphological properties available from the literature. 16S rRNA gene sequences for the type strains of all taxa within the suborder Pseudonocardineae were subjected to phylogenetic analyses using different algorithms in arb and phylip. The description of many new genera and species within the suborder Pseudonocardineae since the family Actinosynnemataceae was proposed in 2000 has resulted in a markedly different distribution of chemotaxonomic markers within the suborder from that observed at that time. For instance, it is noted that species of the genera Actinokineospora and Allokutzneria contain arabinose in whole-cell hydrolysates, which is not observed in the other genera within the Actinosynnemataceae, and that there are many genera within the family Pseudonocardiaceae as currently described that do not contain arabinose. Phylogenetic analyses of 16S rRNA gene sequences for all taxa within the suborder do not provide any statistical support for the family Actinosynnemataceae, nor are signature nucleotides found that support its continued differentiation from the family Pseudonocardiaceae. The description of the family Pseudonocardiaceae is therefore emended to include the genera previously classified within the family Actinosynnemataceae and the description of the suborder Pseudonocardineae is also emended to reflect this reclassification.

Potatoes (Solanum tuberosum) are one of the most important crops in China following rice, wheat, and corn. Aster yellows phytoplasma appeared to be widespread in China; it was found to cause diseases on alfalfa, oranges, peaches, periwinkles, bamboo (1), and cactus (4). However, scant information of this pathogen on potatoes is available except for a few short reports published during the 1950s. During the potato disease surveys conducted from 2005 to 2010 in Yunnan and Inner Mongolia, 10 to 35% of potato plants exhibited symptoms of yellowing or purpling of apical leaves, with the top leaves rolling inward and aerial tubers formation. Total DNA was extracted from midveins of leaves and roots of 125 diseased and asymptomatic plants with a DNeasy Plant Mini Kit (Qiagen, Valencia, CA) according to the manufacturer's instructions. A nested PCR was carried out with the first round primer pair P1/P7 followed by the second round primer pair R16F2n/R16R2 (2,3). A PCR product of approximately 1.2 kb was amplified from diseased plants but not from asymptomatic plants. Restriction fragment length polymorphism (RFLP) patterns were analyzed by digesting a 1.2-kb product using restriction enzymes AluI, BfaI, BstUI, HhaI, HpaI, KpnI, MseI, and RsaI. Comparing the RFLP patterns with previously published phytoplasma strains (2), aster yellows phytoplasma found on potato plants in Yunnan and Inner Mongolia belong to group I, subgroup B (16SrI-B). The PCR product from P1/P7, diluted 1:30, was amplified by using primer pair P1A/P7A (3) and P1A/16S-SR (3). The nested-PCR products from P1A/P7A and P1A/16S-SR were cloned into pCR8/GW/TOPO vector (Invitrogen, Carlsbad, CA) and sequenced by the Core Lab of the University of Alaska–Fairbanks and GENEWIZ (South Plainfield, NJ). The nucleotide sequence (GenBank Accession No. HQ599228) was analyzed by iPhyClassifier software and had 99.53% sequence identity to the reference strain (GenBank Accession No. M30790) for ‘Candidatus Phytoplasma asteris’. The RFLP similarity is identical (coefficient 1.00) to the reference pattern of 16Sr group I, subgroup B (GenBank Accession No. NC_005303). To our knowledge, this is the first report revealing the molecular characteristics of a phytoplasma associated with aster yellows-diseased potatoes in China. References: (1) H. Cai et al. Plant Prot. 31:38, 2005. (2) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (3) I.-M. Lee et al. Int. J. Syst. Evol. Microbiol. 54:337, 2004. (4) W. Wei et al. Plant Dis. 91:461, 2007.