Publications

4466

CLas inhibits callose deposition in the sieve pores and the accumulation of reactive oxygen species to favor its cell-to-cell movement.

Citrus Huanglongbing (HLB) is the most devastating citrus disease in the world. Candidatus Liberibacter asiaticus (Las) is the prevalent HLB pathogen, which is yet to be cultivated. A recent study demonstrates that Las does not contain pathogenicity factors that are directly responsible for HLB symptoms. Instead, Las triggers systemic and chronic immune responses, representing a pathogen-triggered immune disease. Importantly, overproduction of reactive oxygen species (ROS) causes systemic cell death of phloem tissues, thus causing HLB symptoms. Because Las resides in the phloem tissues, it is expected that phloem cell might recognize outer membrane proteins, outer membrane vesicle (OMV) proteins and extracellular proteins of Las to contribute to the immune responses. Because Las has not been cultivated, we used Liberibacter crescens (Lcr) as a surrogate to identify proteins in the OM fraction, OMV proteins and extracellular proteins by liquid chromatography with tandem mass spectrometry (LC–MS/MS). We observed OMVs of Lcr under scanning electron microscope, representing the first experimental evidence that Liberibacter can deliver proteins to the extracellular compartment. In addition, we also further analyzed LC–MS/MS data using bioinformatic tools. Our study provides valuable information regarding the biology of Ca. Liberibacter species and identifies many putative proteins that may interact with host proteins in the phloem tissues.

Background: Alfalfa, Medicago sativa L. is the most important and widely grown leguminous fodder crop in temperate and tropical regions of the world. The production of alfalfa crop is limited by several biotic stresses, among which witches’ broom disease (AWB) was reported to cause significant economic losses. Methods: The phytoplasma infected alfalfa plants were collected from a central research farm, ICAR-IGFRI, Jhansi, U.P. Qualitative parameters such as crude protein content, acid detergent fibre and neutral detergent fibre were estimated in diseased and healthy plants. Phytoplasma universal primer (P1/P7) and nested primer (R16mF2/R16mR1) were used for the molecular characterization of AWB infected plants and phytoplasma infected, Parthenium hysterophorus. Result: The incidence of AWB disease ranged from 8-10%. The quantitative analysis of disease plants showed reduced plant height (-35%), fresh weight (-46.89%) and dry weight (-50.08%) compared to healthy plants. The diseased plant recorded low crude protein content (-21.38%) and higher dry matter content (+0.68%), acid detergent fibre (+33.72%) and neutral detergent fibre (+13.06%). The association of phytoplasma in diseased alfalfa and parthenium samples was confirmed by using P1/P7 and R16mF2/R16mR1 primer pair and Blastn analysis shared 99.6-100% similarity with ‘Candidatus Phytoplasma australasia’ belongs to the 16Sr group II-D.

AbstractSymbiotic microbes from the genus ‘CandidatusMegaira’ (Rickettsiales) are known to be common associates of algae and ciliates. However genomic resources for these bacteria are scarce, limiting our understanding of their diversity and biology. We therefore utilized SRA and metagenomic assemblies to explore the diversity of this genus. We successfully extracted four draft ‘Ca. Megaira’ genomes including one complete scaffold for a ‘Ca. Megaira’ and identified an additional 14 draft genomes from uncategorised environmental Metagenome-Assembled Genomes. We use this information to resolve the phylogeny for the hyper-diverse ‘Ca. Megaira’, with hosts broadly spanning ciliates, micro- and macro-algae, and find that the current single genus designation ‘Ca. Megaira’ significantly underestimates their diversity. We also evaluate the metabolic potential and diversity of ‘Ca. Megaira’ from this new genomic data and find no clear evidence of nutritional symbiosis. In contrast, we hypothesize a potential for defensive symbiosis in ‘Ca. Megaira’. Intriguingly, one symbiont genome revealed a proliferation of ORFs with ankyrin, tetratricopeptide and Leucine rich repeats like those observed in the genusWolbachiawhere they are considered important for host-symbiont protein-protein interactions. Onward research should investigate the phenotypic interactions between ‘Ca. Megaira’ and their various potential hosts, including the economically importantNemacystus decipiens, and target acquisition of genomic information to reflect the diversity of this massively variable group.Data SummaryGenomes assembled in this project have been deposited in bioproject PRJNA867165Impact statementBacteria that live inside larger organisms commonly form symbiotic relationships that impact the host’s biology in fundamental ways, such as improving defences against natural enemies or altering host reproduction. Certain groups like ciliates and algae are known to host symbiotic bacteria commonly, but our knowledge of their symbiont’s evolution and function is limited. One such bacteria is ‘CandidatusMegaira’, a Rickettsiales that was first identified in ciliates, then later in algae. To improve the available data for this common but understudied group, we searched the genomes of potential hosts on online databases for Rickettsiales and assembled their genomes. We found 4 ‘Ca. Megaira’ this way and then used these to find a further 14 genomes in environmental metagenomic data. Overall, we increased the number of known ‘Ca. Megaira’ draft genomes from 2 to 20. These new genomes show us that ‘Ca. Megaira’ is far more diverse than previously thought and that it is potentially involved in defensive symbioses. In addition, one genome shows striking resemblance to well characterized symbiont,Wolbachia, in encoding many proteins predicted to interact directly with host proteins. The genomes we have identified and examined here provide baseline resources for future work investigating the real-world interactions between the hyper diverse ‘Ca. Megaira’ and its various potential hosts, like the economically importantNemacystus decipiens.

AbstractMost prokaryotes are not available as pure cultures and therefore ineligible for naming under the rules and recommendations of the International Code of Nomenclature of Prokaryotes (ICNP). Here we summarize the development of the SeqCode, a code of nomenclature under which genome sequences serve as nomenclatural types. This code enables valid publication of names of prokaryotes based upon isolate genome, metagenome-assembled genome or single-amplified genome sequences. Otherwise, it is similar to the ICNP with regard to the formation of names and rules of priority. It operates through the SeqCode Registry (https://seqco.de/), a registration portal through which names and nomenclatural types are registered, validated and linked to metadata. We describe the two paths currently available within SeqCode to register and validate names, includingCandidatusnames, and provide examples for both. Recommendations on minimal standards for DNA sequences are provided. Thus, the SeqCode provides a reproducible and objective framework for the nomenclature of all prokaryotes regardless of cultivability and facilitates communication across microbiological disciplines.

AbstractPseudaminic and legionaminic acids are a subgroup of nonulosonic acids (NulOs) unique to bacterial species. There is a lack of advances in the study of these NulOs due to their complex synthesis and production. Recently, it was seen that “Candidatus Accumulibacter” can produce Pse or Leg analogues as part of its extracellular polymeric substances (EPS). In order to employ a “Ca. Accumulibacter” enrichment as production platform for bacterial sialic acids, it is necessary to determine which fractions of the EPS of “Ca. Accumulibacter” contain NulOs and how to enrich and/or isolate them. We extracted the EPS from granules enriched with “Ca. Accumulibcater” and used size-exclusion chromatography to separate them into different molecular weight fractions. This separation resulted in two high molecular weight (> 5,500 kDa) fractions dominated by polysaccharides, with a NulO content up to 4 times higher than the extracted EPS. This suggests that NulOs in “Ca. Accumulibacter” are likely located in high molecular weight polysaccharides. Additionally, it was seen that the extracted EPS and the NulO-rich fractions can bind and neutralize histones. This suggest that they can serve as source for sepsis treatment drugs, although further purification needs to be evaluated.Graphical abstractHighlightsNulOs in “Ca. Accumulibacter” are likely located in high molecular weight polysaccharides.Size exclusion chromatography allows to obtain high molecular weight polysaccharide-rich fractions enriched with NulOs.EPS and the NulOs-rich fractions can serve as source for sepsis treatment drugs.

Las variedades de papa (Solanum tuberosum L.) producidas en México son susceptibles a Candidatus Liberibacter solanacearum (CaLso), causante de la enfermedad conocida como ‘manchado interno de la pulpa’, por lo que se requiere conocer la respuesta de genotipos experimentales a la bacteria. El presente estudio tuvo como objetivo evaluar el efecto de la infección de los haplotipos LsoA + LsoB de CaLso en el follaje, la biomasa seca y la calidad de tubérculo de papa, variedad Fianna, una colecta de Solanum demissum y los clones experimentales T90-1-63 y T05-13-21 de Solanum spp. El manchado interno de la pulpa del tubérculo se determinó mediante análisis de imágenes de tubérculos. Las plantas de Fianna mostraron la mayor severidad de daño foliar; en cambio, los clones experimentales presentaron 17 % menos daño foliar que Fianna y 8 % más daño foliar que S. demissum. Este último fue el genotipo con la mayor biomasa seca de hoja y produjo tubérculos de un tamaño pequeño; las plantas infectadas de S. demissum presentaron mayor número de tubérculos y mayor rendimiento de tubérculo fresco que las plantas sin inoculación, aunque tuvieron la menor proporción de superficie sana del tubérculo. El clon T90-1-63 presentó los porcentajes más altos de superficie sana de tubérculo (> 79 %) y las menores intensidades del manchado interno de la pulpa del tubérculo.

Thousands of new bacterial and archaeal species and higher-level taxa are discovered each year through the analysis of genomes and metagenomes. The Genome Taxonomy Database (GTDB) provides hierarchical sequence-based descriptions and classifications for new and as-yet-unnamed taxa. However, bacterial nomenclature, as currently configured, cannot keep up with the need for new well-formed names. Instead, microbiologists have been forced to use hard-to-remember alphanumeric placeholder labels. Here, we exploit an approach to the generation of well-formed arbitrary Latinate names at a scale sufficient to name tens of thousands of unnamed taxa within GTDB. These newly created names represent an important resource for the microbiology community, facilitating communication between bioinformaticians, microbiologists and taxonomists, while populating the emerging landscape of microbial taxonomic and functional discovery with accessible and memorable linguistic labels.