Publications

3780

AbstractCandidatus Magnetoglobus multicellularis is an uncultured magnetotactic multicellular prokaryote composed of 17-40 Gram-negative cells that are capable of synthesizing organelles known as magnetosomes. The magnetosomes of Ca. M. multicellularis are composed of greigite and are organized in chains that are responsible for the microorganism's orientation along magnetic field lines. The characteristics of the microorganism, including its multicellular life cycle, magnetic field orientation, and swimming behavior, and the lack of viability of individual cells detached from the whole assembly, are considered strong evidence for the existence of a unique multicellular life cycle among prokaryotes. It has been proposed that the position of each cell within the aggregate is fundamental for the maintenance of its distinctive morphology and magnetic field orientation. However, the cellular organization of the whole organism has never been studied in detail. Here, we investigated the magnetosome organization within a cell, its distribution within the microorganism, and the intercellular relationships that might be responsible for maintaining the cells in the proper position within the microorganism, which is essential for determining the magnetic properties of Ca. M. multicellularis during its life cycle. The results indicate that cellular interactions are essential for the determination of individual cell shape and the magnetic properties of the organism and are likely directly associated with the morphological changes that occur during the multicellular life cycle of this species.

Yellow leaf disease (YLD) with phytoplasmal aetiology is a serious disease of arecanut palm in India. The present study was undertaken to characterize the 16S rRNA and secA gene sequences of the Indian arecanut YLD phytoplasma for ‘Candidatus Phytoplasma ’ species assignment and 16Sr group/subgroup classification. Phytoplasma 16S rRNA genes were amplified using three sets of semi-nested/nested primers, 1F7/7R3–1F7/7R2, 4Fwd/3Rev–4Fwd/5Rev and P1/P7–R16F2n/R16R2, producing amplicons of 491, 1150 and 1250 bp, respectively, from diseased samples. The amplicons were cloned and sequenced. A blast search showed that the sequences had 99 % similarity with sugar cane white leaf phytoplasma (16SrXI) and Napier grass stunt phytoplasma (16SrXI). Phylogenetic analysis based on the 16S rRNA gene revealed the clustering of YLD phytoplasma with the rice yellow dwarf and Bermuda grass white leaf groups. The YLD phytoplasma F2nR2 sequence shared 97.5 % identity with that of ‘Candidatus Phytoplasma oryzae ’ and 97.8 % identity with that of ‘Candidatus Phytoplasma cynodontis ’. Hence, for finer differentiation, we examined the secA gene-based phylogeny, where the YLD phytoplasma clustered with Napier grass stunt and sugar cane grassy shoot phytoplasmas, both belonging to the rice yellow dwarf group. Hence, we are assigning the Indian arecanut YLD phytoplasma as a ‘Candidatus Phytoplasma oryzae ’-related strain. Virtual RFLP analysis of a 1.2 kb fragment of the 16S rRNA gene (F2nR2 region) identified the Indian arecanut YLD phytoplasma as a member of 16SrXI-B subgroup. We name the phytoplasma Indian yellow leaf disease phytoplasma, to differentiate it from the Hainan YLD phytoplasma, which belongs to group 16SrI.

Cauliflower stunt, caused by a phytoplasma of the group 16SrIII-J, was reported in the beginning of 2012 and has occurred with high incidences of infected plants (up to 90%) in crops located in the state of São Paulo in the southeast region of Brazil (3). Diseased plants exhibit general stunting, malformation of inflorescence, reddening leaves, and vessel necrosis (3). Further investigations with plants displaying identical symptoms collected in Nova Bassano, state of Rio Grande do Sul, Brazilian south region, have revealed the presence of a phytoplasma distinct from 16SrIII-J subgroup. Four symptomatic plus four asymptomatic samples were assayed from a field, and the presence of phytoplasma was evidenced by nested PCR assays performed with primers P1/Tint followed by R16F2n/16R2 in three affected plants, which amplified genomic fragments of 1.2 kb from the 16S rRNA gene. No amplification occurred in non-affected samples. Nested PCR products analyzed by conventional RFLP (2) using the enzymes AluI, RsaI, KpnI, HpaII, MseI, HhaI, MboI, and BstUI pointed to the presence of a phytoplasma belonging to group 16SrXV-A in all three phytoplasma-positive samples. Virtual RFLP analysis based on restriction patterns, derived from in silico digestion with 17 endonucleases (4), confirmed the previous results obtained from those samples by conventional RFLP. The 16S rDNA sequences of this phytoplasma identified in cauliflower (GenBank Accession No. JN818845) shared 99% sequence similarity with the reference phytoplasma for subgroup 16SrXV-A (Hibiscus witches'-broom phytoplasma, AF147708), designated ‘Candidatus Phytoplasma brasiliense.’ Analysis of putative restriction sites showed excellent identity between the phytoplasma studied here and the reference phytoplasma. In addition, the arrangement of branches of a phylogenetic tree constructed with phytoplasmas representing diverse 16Sr groups and subgroups supported that the phytoplasma found in cauliflower is closed related to the representative of the subgroup 16SrXV-A. Association of distinct phytoplasmas with the same kind of disease is not rare and the present pathosystem constitutes a new example. Members of this subgroup have been described almost exclusively in Brazil and previously reported in Sida sp., periwinkle, and hibiscus (1). In some European countries, as well as in the United States and Canada, phytoplasmas belonging to group 16SrI has been associated with this type of disease, which has been reported for various species of the genus Brassica, as published in previous works (3). However, a representative of the group 16SrVI was described in infected plants in Iran (3). Although the 16SrIII-J phytoplasma is currently the most important agent of cauliflower stunt in Brazil, and members of 16SrI are prevalent in other countries, this study revealed that a 16Sr XV-A phytoplasma may be also associated with this important disease of brassicas. Besides, the findings here reported expand the natural host range, including cauliflower as new host for phytoplasmas affiliated with 16SrXV-A. References: (1) B. Eckstein et al. Plant Dis. 95:363, 2009. (2) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (3) M. C. C. Rappussi et al. Eur. J. Plant. Pathol. 133:829, 2012. (4) Wei et al. Int. J. Syst. Evol. Microbiol. 57:1855, 2007.

ABSTRACT Three cohorts of farmed yellowtail kingfish ( Seriola lalandi ) from South Australia were examined for Chlamydia -like organisms associated with epitheliocystis. To characterize the bacteria, 38 gill samples were processed for histopathology, electron microscopy, and 16S rRNA amplification, sequencing, and phylogenetic analysis. Microscopically, the presence of membrane-enclosed cysts was observed within the gill lamellae. Also observed was hyperplasia of the epithelial cells with cytoplasmic vacuolization and fusion of the gill lamellae. Transmission electron microscopy revealed morphological features of the reticulate and intermediate bodies typical of members of the order Chlamydiales . A novel 1,393-bp 16S chlamydial rRNA sequence was amplified from gill DNA extracted from fish in all cohorts over a 3-year period that corresponded to the 16S rRNA sequence amplified directly from laser-dissected cysts. This sequence was only 87% similar to the reported “ Candidatus Piscichlamydia salmonis” (AY462244) from Atlantic salmon and Arctic charr. Phylogenetic analysis of this sequence against 35 Chlamydia and Chlamydia -like bacteria revealed that this novel bacterium belongs to an undescribed family lineage in the order Chlamydiales . Based on these observations, we propose this bacterium of yellowtail kingfish be known as “ Candidatus Parilichlamydia carangidicola” and that the new family be known as “ Candidatus Parilichlamydiaceae.”