Publications

4369

Summary Cyanobacteria of the genus Synechococcus are major contributors to global primary productivity and are found in a wide range of aquatic ecosystems. This Synechococcus collective (SC) is metabolically diverse, with some lineages thriving in polar and nutrient‐rich locations and others in tropical or riverine waters. Although many studies have discussed the ecology and evolution of the SC, there is a paucity of knowledge on its taxonomic structure. Thus, we present a new taxonomic classification framework for the SC based on recent advances in microbial genomic taxonomy. Phylogenomic analyses of 1085 cyanobacterial genomes demonstrate that organisms classified as Synechococcus are polyphyletic at the order rank. The SC is classified into 15 genera, which are placed into five distinct orders within the phylum Cyanobacteria: (i) Synechococcales ( Cyanobium , Inmanicoccus , Lacustricoccus gen. Nov., Parasynechococcus , Pseudosynechococcus , Regnicoccus , Synechospongium gen. nov., Synechococcus and Vulcanococcus ); (ii) Cyanobacteriales ( Limnothrix ); (iii) Leptococcales ( Brevicoccus and Leptococcus ); (iv) Thermosynechococcales ( Stenotopis and Thermosynechococcus ) and (v) Neosynechococcales ( Neosynechococcus ). The newly proposed classification is consistent with habitat distribution patterns (seawater, freshwater, brackish and thermal environments) and reflects the ecological and evolutionary relationships of the SC.

A novel Gram-stain-negative, non-endospore-forming, motile, and aerobic bacterial strain, M105T, was isolated from coral Porites lutea, and was subjected to a polyphasic taxonomic study. Global alignment based on 16S rRNA gene sequences indicated that M105T shares the highest sequence identity of 94.5 % with Aliikangiella marina GYP-15T. The average nucleotide identity (ANI) and average amino acid identity (AAI) between M105T and A. marina GYP-15T was 69.8 and 71.6 %, respectively. On the basis of the results of phenotypic, chemotaxonomic, phylogenetic, phylogenomic, and comparative genomic analyses, it is concluded that M105T should represent a novel species in the genus Aliikangiella , for which the name Aliikangiella coralliicola sp. nov. is proposed. The type strain is M105T (=MCCC 1K03773T= KCTC 72442T). Furthermore, the family Kangiellaceae was classified into two families on the basis of phylogenetic, phylogenomic, polar lipid profile and motility variations. The novel family Pleioneaceae fam. nov. is proposed to accommodate the genera Aliikangiella and Pleionea .

Abstract The African citrus triozid (ACT) Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) and the Asian citrus psyllid (ACP) Diaphorina citri (Kuwayama) (Hemiptera: Liviidae) are primary vectors of the ‘ Candidatus ’ Liberibacter spp. ACT is associated with ‘ Candidatus Liberibacter africanus’ (CLaf) causal agent of the African citrus greening disease (ACGD), whereas ACP vectors ‘ Candidatus Liberibacter asiaticus’ (CLas) and ‘ Candidatus Liberibacter americanus’ (CLam), the Asian and the American strains, respectively, associated with huanglongbing. A preliminary survey in Kenyan citrus groves after the invasion of ACP had revealed that lime‐green sticky traps (Asacp) were not effective in detecting and monitoring ACT and ACP. Therefore, this study compared eight differently coloured double‐sided sticky traps to evaluate, which colour was most effective for detecting ACT and ACP, particularly at low densities. The traps were coded Red, Blue, Asgreen1, GLMgreen, Asacp, Asyellow, White, and Black. Asyellow and GLMgreen traps captured more ACTs and ACPs than any other trap type. However, since there was no clear difference in the efficiency of Asyellow and GLMgreen in trapping ACP, any of the two trap types would be useful in the presence of both pests. Among the eight traps, Asyellow and GLMgreen traps are potentially promising options for monitoring and detecting the pests in areas where they coexist. Our findings will guide biosecurity agencies in decision‐making and designing ecologically friendly integrated pest management (IPM) strategies for citrus greening vectors in Africa as well as serve as an early warning to safeguard against pests' invasion into unaffected areas.

Rickettsia spp. are the second most common pathogens detected in Ixodes ricinus ticks in Austria after Borrelia burgdorferi sensu lato. Species belonging to the spotted fever group (SFG) are the causative agents for tick-borne rickettsiosis across the world. So far, only four SFG Rickettsia spp. were detected in Austria, namely R. helvetica, R. raoultii, R. monacensis and R. slovaca. Here, we describe the identification of a new SFG Rickettsia species detected in an I. ricinus tick. Sequencing of various rickettsial genes revealed a nucleotide sequence similarity of 99.6%, 98.5%, 97.3% and 98.5% to the gltA, ompA, ompB, and sca4 genes, respectively, of known and validated species. Additionally, sequencing of the htrA gene and 23S-5S intergenic spacer region also only showed 99.6% and 99.2%, respectively, similarity to known species. Therefore, and in accordance with current criteria for Rickettsia species discrimination, we hereby describe a new species of the SFG with putative pathogenic potential. We propose the name “Candidatus Rickettsia thierseensis” based on the village Thiersee in the Austrian province of Tyrol, where the carrying tick was found.

‘Candidatus Liberibacter asiaticus’ (CLas) is the pathogenic bacterium that causes the disease Huanglongbing (HLB) in citrus and some model plants, such as Nicotiana benthamiana. After infection, CLas releases a set of effectors to modulate host responses. One of these critical effectors is Sec-delivered effector 1 (SDE1), which induces chlorosis and cell death in N. benthamiana. In this study, we revealed the DEAD-box RNA helicase (DDX3) interacts with SDE1. Gene silencing study revealed that knockdown of the NbDDX3 gene triggers leaf chlorosis, mimicking the primary symptom of CLas infection in N. benthamiana. The interactions between SDE1 and NbDDX3 were localized in the cell membrane. Overexpression of SDE1 resulted in suppression of NbDDX3 gene expression in N. benthamiana, which suggests a critical role of SDE1 in modulating NbDDX3 expression. Furthermore, we verified the interaction of SDE1 with citrus DDX3 (CsDDX3), and demonstrated that the expression of the CsDDX3 gene was significantly reduced in HLB-affected yellowing and mottled leaves of citrus. Thus, we provide molecular evidence that the downregulation of the host DDX3 gene is a crucial mechanism of leaf chlorosis in HLB-affected plants. The identification of CsDDX3 as a critical target of SDE1 and its association with HLB symptom development indicates that the DDX3 gene is an important target for gene editing, to interrupt the interaction between DDX3 and SDE1, and therefore interfere host susceptibility.