Publications

4479

Huanglongbing (HLB), caused by “Candidatus liberibacter asiaticus” (CaLas), is one of the most devastating diseases in citrus but its pathogenesis remains poorly understood. Here, we reported the role of the CaLasSDE115 (CLIBASIA_05115) effector, encoded by CaLas, during pathogen-host interactions. Bioinformatics analyses showed that CaLasSDE115 was 100% conserved in all reported CaLas strains but had sequence differences compared with orthologs from other “Candidatus liberibacter.” Prediction of protein structures suggested that the crystal structure of CaLasSDE115 was very close to that of the invasion-related protein B (IalB), a virulence factor from Bartonella henselae. Alkaline phosphatase (PhoA) assay in E. coli further confirmed that CaLasSDE115 was a Sec-dependent secretory protein while subcellular localization analyses in tobacco showed that the mature protein of SDE115 (mSDE115), without its putative Sec-dependent signal peptide, was distributed in the cytoplasm and the nucleus. Expression levels of CaLasSDE115 in CaLas-infected Asian citrus psyllid (ACP) were much higher (∼45-fold) than those in CaLas-infected Wanjincheng oranges, with the expression in symptomatic leaves being significantly higher than that in asymptomatic ones. Additionally, the overexpression of mSDE115 favored CaLas proliferation during the early stages (2 months) of infection while promoting the development of symptoms. Hormone content and gene expression analysis of transgenic plants also suggested that overexpressing mSDE115 modulated the transcriptional regulation of genes involved in systemic acquired resistance (SAR) response. Overall, our data indicated that CaLasSDE115 effector contributed to the early colonization of citrus by the pathogen and worsened the occurrence of Huanglongbing symptoms, thereby providing a theoretical basis for further exploring the pathogenic mechanisms of Huanglongbing disease in citrus.

A novel micro-organism designated AS10Twas isolated from dry salt collected from Aveiro saltern in the north of Portugal. Cells were Gram-stain-positive, non-motile, non-endospore-forming, rod-shaped and aerobic. Strain AS10Twas characterized by long filaments of rod-shaped cells, presenting also coccoid cellular forms at the end of the filaments, unveiling some pleomorphism. Rod-shaped cells varied from 0.3 to 0.6 µm wide and from 0.6 to 2 µm long. Growth of AS10Toccurred at 15–40 °C (optimum, 20–30 °C), 0–10% (w/v) NaCl (optimum, 2%) and pH 4.5–11.0 (optimum, pH 8.0–11.0). The peptidoglycan type was A1ϒ-type with 3-hydroxy-diaminopimelic acid. The major fatty acids were C16:0, iso-C14:0, C17:0and C14:0. The major respiratory quinone was MK-9(H4). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain AS10Twas similar to actinobacterial members of the classNitriliruptoria, withNitriliruptor alkaliphilusANL-iso2Tbeing the closest relative the species with a sequence pairwise similarity of 91.21%. Average nucleotide identity, average amino acid identity andin silicoDNA–DNA hybridization values between strain AS10TandN. alkaliphilusANL-iso2Twere 71.34, 53.57 and 18.90%, respectively. The genome DNA G+C content of AS10Twas 71.8 mol%. Based on genomic, phylogenetic, phenotypic and chemotaxonomic studies, we describe a new species of a novel genus represented by strain AS10T(=LMG 31937T=CECT 30148T) for which we propose the nameSalsipaludibacter albusgen. nov., sp. nov. We also propose that this organism represents a new family namedSalsipaludibacteraceaefam. nov. of a novel order namedSalsipaludibacteralesord. nov.

Little is known about the bacterial phylum “ Candidatus Dependentiae,” because only three isolates have been reported. Here, I report the isolation and genome sequencing of a new member of this phylum, strain Noda2021. This is the fourth strain isolated from the phylum “ Candidatus Dependentiae.”

“Cand. Nanosynbacter sp. HMT352” strain KC1 is an ectoparasitic saccharibacterium/TM7 that was co-isolated from a human saliva sample with its obligate bacterial host, Schaalia odontolytica . The genome of strain KC1 enables studies of the mechanisms and evolution of interspecies interactions and, for oral species, studies of their potential roles in health and disease.

The bacterium “ Candidatus Hydrogenosomobacter endosymbioticus” is an intracellular symbiont of anaerobic scuticociliate GW7, which is associated with hydrogenosome together with methanogenic archaea. Here, we report a complete genome sequence of the symbiont consisting of 827 kbp. Knowing this sequence would contribute to the understanding of the metabolic interactions and evolution of the tripartite symbiosis.

Abstract This study explored the microbial population dynamics of Accumulibacter (Acc) at low temperature and metabolic shift to limiting polyphosphate (Poly-P) in enhanced biological phosphorus removal (EBPR) system. The Accumulibacter-enriched EBPR systems, fed with acetate (HAc) and propionate (HPr) at 10 ± 1 °C respectively, were operated for 60 days in two identical SBR reactors (SBR-1 and SBR-2). The phosphorus removal performance in two systems was stable at 10 ± 1 °C, while the microbial community structure changed. Compared with the population structure in seed sludge, Accumulibacter clades reduced in the HAc system, while Acc I increased significantly in the HPr system. Low temperature was beneficial to the formation of granular sludge in the EBPR system, and the sludge granulation in the HAc system was more homogeneous than that in the HPr system. Accumulibacter in the HPr system can get ATP through glycogen accumulating metabolism (GAM) under limiting Poly-P condition at 10 ± 1 °C, while that in the HAc system cannot. This work suggests that poly-P levels can affect the metabolic pathway of Accumulibacter in EBPR systems under low temperature.

The goal of the present work was to determine the diversity of prokaryotes involved in anaerobic oil degradation in oil fields. The composition of the anaerobic oil-degrading methanogenic enrichment obtained from an oil reservoir was determined by 16S rRNA-based survey, and the facultatively anaerobic chemoorganotrophic bacterial strain HO-Ch2T was isolated and studied using polyphasic taxonomy approach and genome sequencing. The strain HO-Ch2T grew optimally at 28 °C, pH 8.0, and 1–2% (w/v) NaCl. The 16S rRNA gene sequence of the strain HO-Ch2T had 98.8% similarity with the sequence of Actinotalea ferrariae CF5-4T. The genomic DNA G + C content of strain HO-Ch2T was 73.4%. The average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between the genome of strain HO-Ch2T and Actinotalea genomes were 79.8–82.0% and 20.5–22.2%, respectively, i.e., below the thresholds for species delineation. Based on the phylogenomic, phenotypic, and chemotaxonomic characterization, we propose strain HO-Ch2T (= VKM Ac-2850T = KCTC 49656T) as the type strain of a new species within the genus Actinotalea, with the name Actinotalea subterranea sp. nov. Based on the phylogenomic analysis of 187 genomes of Actinobacteria we propose the taxonomic revision of the genera Actinotalea and Pseudactinotalea and of the family Actinotaleaceae. We also propose the reclassification of Cellulomonas carbonis as Actinotalea carbonis comb. nov., Cellulomonas bogoriensis as Actinotalea bogoriensis comb. nov., Actinotalea caeni as Pseudactinotalea caeni comb. nov., and the transfer of the genus Pseudactinotalea to the family Ruaniaceae of the order Ruaniales.

AbstractIntracellular pathogens are challenged with limited space and resources while replicating in a single host cell. Mechanisms for direct invasion of neighboring host cells have been discovered in cell culture, but we lack an understanding of how bacteria directly spread between host cells in vivo. Here, we describe the discovery of intracellular bacteria that use filamentation for spreading between the intestinal epithelial cells of a natural host, the rhabditid nematode Oscheius tipulae. The bacteria, which belong to the new species Bordetella atropi, can infect the nematodes following a fecal-oral route, and reduce host life span and fecundity. Filamentation requires UDP-glucose biosynthesis and sensing, a highly conserved pathway that is used by other bacteria to detect rich conditions and inhibit cell division. Our results indicate that B. atropi uses a pathway that normally regulates bacterial cell size to trigger filamentation inside host cells, thus facilitating cell-to-cell dissemination.

Summary Holosporales are an alphaproteobacterial lineage encompassing bacteria obligatorily associated with multiple diverse eukaryotes. For most representatives, little is known on the interactions with their hosts. In this study, we characterized a novel Holosporales symbiont of the ciliate Paramecium polycaryum . This bacterium inhabits the host cytoplasm, frequently forming quite large aggregates. Possibly due to such aggregates, host cells sometimes displayed lethal division defects. The symbiont was also able to experimentally stably infect another Paramecium polycaryum strain. The bacterium is phylogenetically related with symbionts of other ciliates and diplonemids, forming a putatively fast‐evolving clade within the family Holosporaceae . Similarly to many close relatives, it presents a very small genome (<600 kbp), and, accordingly, a limited predicted metabolism, implying a heavy dependence on Paramecium , thanks also to some specialized membrane transporters. Characterized features, including the presence of specific secretion systems, are overall suggestive of a mild parasitic effect on the host. From an evolutionary perspective, a potential ancestral trend towards pronounced genome reduction and possibly linked to parasitism could be inferred, at least among fast‐evolving Holosporaceae , with some lineage‐specific traits. Interestingly, similar convergent features could be observed in other host‐associated lineages, in particular Rickettsiales among Alphaproteobacteria .

Abstract The symbiont “Candidatus Aquarickettsia rohweri” infects a diversity of aquatic hosts. In the threatened Caribbean coral, Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality of coral. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting threatened corals, Ac. cervicornis, and Ac. palmata and their hybrid (“Ac. prolifera”). Aquarickettsia was found in all acroporids, with coral host and geographic location impacting the infection magnitude. Phylogenomic and genome-wide single-nucleotide variant analysis of Aquarickettsia found phylogenetic clustering by geographic region, not by coral taxon. Analysis of Aquarickettsia fixation indices suggests multiple sequential infections of the same coral colony are unlikely. Furthermore, relative to other Rickettsiales species, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to other Caribbean locations. This may be due in part to Aquarickettsia proliferating in response to greater nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia was not found to significantly codiversify with either the coral animal or the coral’s algal symbiont (Symbiodinium “fitti”). Quantitative PCR analysis showed that gametes, larvae, recruits, and juveniles from susceptible, captive-reared coral genets were not infected with Aquarickettsia. Thus, horizontal transmission of Aquarickettsia via coral mucocytes or an unidentified host is more likely. The prevalence of Aquarickettsia in Ac. cervicornis and its high abundance in the Florida coral population suggests that coral disease mitigation efforts focus on preventing early infection via horizontal transmission.