Publications

4857

The prokaryotic generic names Bogoriella Groth et al. 1997 and Stella Vasilyeva 1985 are illegitimate because they are later homonyms of the genus names Bogoriella Zahlbr. 1928 (Ascomycota) and Stella Massee 1889 (Basidiomycota) (Principle 2 and Rule 51b(4) of the International Code of Nomenclature of Prokaryotes). We therefore propose the replacement names Allobogoriella gen. nov., Allobogoriella caseilytica comb. nov., Allobogoriellaceae fam. nov., Allobogoriellales ord. nov., Allostella gen. nov., Allostella humosa comb. nov. and Allostellaceae fam. nov. as replacement names for the illegitimate prokaryotic names Bogoriella, Bogoriella caseilytica, Bogoriellaceae, Bogoriellales, Stella, Stella humosa, Stella vacuolata and Stellaceae, respectively.

Abstract Numerous cyanobacterial strains previously identified as Scytonema hyalinum were determined to be phylogenetically distant from the type species of Scytonema, S. hofmannii . Morphological and molecular evidence suggests this distinct clade necessitates placement in a new genus, and we have described Kalymmatonema gen. nov. herein. Kalymmatonema has been demonstrated to exhibit five ribosomal operons, all of which differed in both sequence and secondary structure of conserved helical domains in the 16S–23S internal transcribed spacer rRNA region. Four of these operon copies were highly similar in 16S and 23S rRNA gene sequences, whereas the divergent fifth copy is thought to represent a whole‐operon horizontal gene transfer event. Through in‐depth analysis, we were able to recognize seven species new to science, the type species K. desertorum sp. nov., K. arcangelii comb. nov., K. chimaera sp. nov., K. ethiopiense sp. nov., K. gypsitolerans sp. nov., K. mateoae sp. nov., and K. oahuense sp. nov. We also created the new combination, K. hyalinum comb. nov., in order to include the original Scytonema hyalinum in this new genus based upon the common morphological feature of a mucilaginous apical cap on the trichomes. Kalymmatonema displays a complex evolution of its ribosomal operons, with evidence not only of horizontal gene transfer but also of internal rearrangements and mobile genetic elements that have transposed the tRNA‐containing region of the ITS rRNA region among the four similar operons. Additional investigation of the evolutionary history of this interesting genus will likely lead to a better understanding of the processes shaping ribosomal evolution in cyanobacteria.

‘Candidatus Liberibacter asiaticus’ (CLas), the agent associated with the Huanglongbing citrus disease, is commonly detected using quantitative PCR (qPCR) with hydrolysis probes. Internal standards are typically included in the qPCR assays to reduce the risk of false negatives caused by inhibitors. When the internal standard is detected but CLas is not, it is generally assumed that the pathogen is absent from the tested sample. However, our study shows that trace amounts of CLas may go undetected if the internal standard is either overly abundant or too dissimilar to CLas. To overcome these limitations, we developed a synthetic internal standard (IS) that uses the same primer as the CLas target sequence, along with three to four downstream nucleotides, but with a unique internal sequence derived from smooth hammerhead shark (Sphyrna zygaena; IS-SHK). This sequence matches the guanine-cytosine content and melting temperature of the CLas target and was specifically selected to minimize potential interference from other nucleic acid materials in citrus samples. To minimize competition between the IS-SHK standard and the CLas target, an average of only 21 molecules of IS-SHK standard is added to each qPCR reaction. Therefore, when IS-SHK standard is detected at expected levels and CLas is not, the absence of CLas is confirmed rather than inhibition of the detection. Conversely, the absence of both IS-SHK standard and CLas suggests the presence of a qPCR inhibitor, warranting retesting of the sample.

Abstract Citrus greening disease, caused by ‘Candidatus Liberibacter asiaticus’, severely impacts citrus production worldwide. The development of sustainable control strategies for this disease is restricted by the unavailability of the bacterium in pure culture. Herein, the metabolic profile of the waxworm larvae, Galleria mellonella, was compared to that of Diaphorina citri, the vector of ‘Ca. L. asiaticus’. Our findings showed that G. mellonella larvae possess the nutritional needs to host ‘Ca. L. asiaticus’, supporting its short-term persistence, and responds to infection with a visible immune reaction by producing melanin upon bacterial invasion. The inoculated larvae exhibit detectable bacterial titers for up to four days when inoculated with infected citrus phloem sap or D. citri haemolymph, after which bacterial titers decline, and infected larvae show reduced survival compared to mock-treated and ‘Ca. L. asiaticus’-free controls. Metabolic profiling of G. mellonella, D. citri, and honeybees (Apis mellifera) reveals distinct chemical compositions in their haemolymph. G. mellonella contains higher levels of amino acids, organic acids, nucleotides, and sugar-nucleotides, providing essential nutrients for ‘Ca. L. asiaticus’, while D. citri is enriched in monosaccharides and sugar-alcohols. Citric acid was detected exclusively in the haemolymph of G. mellonella. These findings suggest G. mellonella as a convenient model that can transiently host ‘Ca. L. asiaticus’ for short-term use, which would facilitate high-throughput screening of antimicrobial compounds against ‘Ca. L. asiaticus’, as well as exploring host-pathogen interactions. This model could accelerate the development of effective treatments against citrus greening and inform broader strategies for managing vector-borne plant diseases.

Phytoplasmas (‘Candidatus Phytoplasma’) are intracellular pleomorphic plant pathogens belonging to the class Mollicutes. They colonize both plant hosts and insect vectors in their life cycle. Apple proliferation (AP) is one of the most important phytoplasmoses present in Europe, causing significant economic losses in apple production. The causal agent, ‘Ca. P. mali’, was identified in apple and Cacopsylla picta samples using both real-time PCR and nested PCR based on the amplification of 16S rDNA. The objective of this study was to gain deeper insights into the epidemiology of apple proliferation in Croatia. Variability of genetic markers other than 16S rRNA was used for characterization of strains. Four molecular markers differing in level of conservation, aceF, pnp, imp, and secY, were selected in line with previously typed fruit tree phytoplasmas. New genotypes were discerned for each genetic marker, and 20 different sequence types were revealed in the Croatian strains of ‘Ca. P. mali’. On the basis of this comprehensive analysis, the founder sequence type ST1 (A13–P10–S12–I21) can be proposed. This is the first extensive research and multigene typing performed on Croatian ‘Ca. P. mali’ strains. Obtained results reveal considerable genetic diversity of epidemiological relevance limited to only two locations in north-western Croatia. Additionally, novel primers were constructed to amplify fragments larger than the entire coding region for all four genes in order to further expand the phytoplasma multi-locus sequence typing scheme.