Publications

4505

‘Candidatus Liberibacter solanacearum’ (Lso) is a plant pathogenic bacterium transmitted by psyllids that causes significant agricultural damage. Several Lso haplotypes have been reported. Among them, LsoA and LsoB are transmitted by the potato psyllid Bactericera cockerelli and infect solanaceous crops, and LsoD is transmitted by the carrot psyllid B. trigonica and infects apiaceous crops. Several studies evaluated the transmission of these haplotypes by adult psyllids. However, fewer data are available on the transmission of different Lso haplotypes by psyllid nymphs. In this study, we investigated the transmission of these three haplotypes by psyllid nymphs to expand our basic understanding of Lso transmission. Specifically, the objective was to determine if the haplotypes differed in their transmission rates by nymphs and if LsoA and LsoB accumulated at different rates in the guts of nymphs as it occurs in adults. First, we quantified LsoA and LsoB titers in the guts of third- and fifth-instar potato psyllid nymphs. We found similar LsoA titers in the two nymphal stages, while LsoB titer was lower in the gut of the third-instar nymphs compared to fifth-instar nymphs. Second, we assessed the transmission efficiency of LsoA and LsoB by third-instar nymphs to tomato plants, revealing that LsoA was transmitted earlier and with higher efficiency than LsoB. Finally, we examined the transmission of LsoD by carrot psyllid nymphs to celery plants and demonstrated an age-related difference in the transmission rate. These findings provide valuable insights into the transmission dynamics of different Lso haplotypes by nymphal vectors, shedding light on their epidemiology and interactions with their psyllid vectors.

This study aimed to evaluate the efficacy of biotic inducers for the management of phyllody disease in sesame, as well as in analyzing the defense enzyme activity. The field trial experiments were conducted with the biotic inducers [salicylic acid (SA), methyl jasmonate (MeJA), and beta amino butyric acid (BABA)] in individually (50 ppm, 100 ppm and 150 ppm) and in combination. Concerning biotic inducers, SA 50 / 100 ppm pre-seed treatment and exogenous application at 30th, 45th and 60th DAS resulted in no/less phyllody disease incidence and added significant value by increasing defense enzyme activity (PO, PPO, PAL and SOD).

ABSTRACT We present here a comprehensive phylogenomic analysis of Acetobacteraceae , a vast group of alphaproteobacteria that has been widely studied for their economic importance. Our results indicate that the ancestor of Acetobacteraceae most likely was photosynthetic and evolved via a progressive transition from versatile photoferrotrophy to the incomplete oxidation of organic substrates defining acetous physiology. Vestigial signs of photosynthetic carotenoid metabolism are present in non-photosynthetic acetous taxa that have lost cytochrome oxidase, while their sister taxa retain such traits. The dominant terminal oxidase of acetous bacteria, the bo 3 ubiquinol oxidase, is derived from duplication and diversification of operons present in Acidocella taxa that have lost photosynthesis. We analyzed the bioenergetic traits that can compensate for the electron transfer function of photosynthetic reaction centers or constitute alternative pathways for the oxidoreduction of c -type cytochromes, such as iron oxidation. The latter pathway bypasses the deranged cytochrome bc 1 complex that is characteristically present in acidophilic taxa due to the loss of conserved ligands in both the Rieske iron-sulfur protein and cytochrome b subunit. The deranged or non-functional bc 1 complex may be retained for its structural role in stabilizing Complex I. The combination of our phylogenetic analysis with in-depth functional evaluations indicates that the order Acetobacterales needs to be emended to include three families: Acetobacteraceae sensu stricto , Roseomonadaceae fam. nov., and Acidocellaceae fam. nov. IMPORTANCE Acetobacteraceae are one of the best known and most extensively studied groups of bacteria, which nowadays encompasses a variety of taxa that are very different from the vinegar-producing species defining the family. Our paper presents the most detailed phylogeny of all current taxa classified as Acetobacteraceae , for which we propose a taxonomic revision. Several of such taxa inhabit some of the most extreme environments on the planet, from the deserts of Antarctica to the Sinai desert, as well as acidic niches in volcanic sites like the one we have been studying in Patagonia. Our work documents the progressive variation of the respiratory chain in early branching Acetobacteraceae into the different respiratory chains of acidophilic taxa such as Acidocella and acetous taxa such as Acetobacter . Remarkably, several genomes retain remnants of ancestral photosynthetic traits and functional bc 1 complexes. Thus, we propose that the common ancestor of Acetobacteraceae was photosynthetic.

The bacterial strain WB46 was isolated from the rhizosphere of willow plants (Salix purpurea L.) growing in soil contaminated with petroleum hydrocarbons. The strain was subjected to whole-genome shotgun sequencing using Illumina HiSeq. Its draft genome is 7.15 Mb, with a 69.55% GC content, containing 6387 protein-coding genes and 51 tRNA and 15 rRNA sequences. The quality and reliability of the genome were assessed using CheckM, attaining an estimated genome completeness of 98.75% and an estimated contamination of 1.68%. These results indicate a high-quality genome (>95%) and low contamination (<5%). Many of these genes are responsible for petroleum hydrocarbon degradation, such as alkane 1-monooxygenase (alkB) and naphthalene dioxygenase (ndo). 16S rRNA gene analysis, including in silico DNA–DNA hybridization (DDH) and average nucleotide identity (ANI), showed that strain WB46 belongs to the genus Nocardia, and the most closely related species is Nocardia asteroides. The strain WB46 showed a distance of 63.4% and sequence identity of 88.63%, respectively. These values fall below the threshold levels of 70% and 95%, respectively, suggesting that the strain WB46 is a new species. We propose the name of Nocardia canadensis sp. nov. for this new species. Interestingly, the sequence divergence of the 16S rRNA gene showed that the divergence only occurred in the V2 region. Therefore, the conventional V3–V4, V5–V7, or V8–V9 targeting metabarcoding, among others, would not be able to assess the diversity related to this new species.

The digestive organs of terrestrial isopods harbor bacteria of the recently proposed mollicute family Hepatoplasmataceae. The only complete genome available so far for Hepatoplasmataceae is that of “Candidatus Hepatoplasma crinochetorum”. The scarcity of genome sequences has hampered our understanding of the symbiotic relationship between isopods and mollicutes. Here, we present four complete metagenome-assembled genomes (MAGs) of uncultured Hepatoplasmataceae members identified from shotgun sequencing data of isopods. We propose genomospecies names for three MAGs that show substantial sequence divergence from any previously known Hepoatoplamsataceae members: “Candidatus Tyloplasma littoralis” identified from the semiterrestrial isopod Tylos granuliferus, “Candidatus Hepatoplasma vulgare” identified from the common pill bug Armadillidium vulgare, and “Candidatus Hepatoplasma scaber” identified from the common rough woodlouse Porcellio scaber. Phylogenomic analysis of 155 mollicutes confirmed that Hepatoplasmataceae is a sister clade of Metamycoplasmataceae in the order Mycoplasmoidales. 16S ribosomal RNA gene sequences and phylogenomic analysis showed that “Candidatus Tyloplasma littoralis” and other semiterrestrial isopod-associated mollicutes represent the placeholder genus “g_Bg2” in the r214 release of the Genome Taxonomy Database, warranting their assignment to a novel genus. Our analysis also revealed that that Hepatoplasmataceae lack major metabolic pathways but has a likely intact type IIA CRISPR-Cas9 machinery. Although the localization of the Hepatoplasmatacae members have not been verified microscopically in this study, these genomic characteristics are compatible with the idea that these mollicutes have an ectosymbiotic lifestyle with high nutritional dependence on their host, as has been demonstrated for other members of the family. We could not find evidence that Hepatoplasmataceae encode polysaccharide-degrading enzymes that aid host digestion. If they are to provide nutritional benefits, it may be through extra-copy nucleases, peptidases, and a patatin-like lipase. Exploration of potential host-symbiont interaction-associated genes revealed large, repetitive open reading frames harboring beta-sandwich domains, possibly involved with host cell adhesion. Overall, genomic analyses suggest that isopod-mollicute symbiosis is not characterized by carbohydrate degradation, and we speculate on their potential role as defensive symbionts through spatial competition with pathogens to prevent infection.

Two phloem-limited pathogens, ‘Candidatus Arsenophonus phytopathogenicus’ and ‘Candidatus Phytoplasma solani’, threaten sugar beet production in France, Switzerland, and Germany. Previous studies of these pathogens in Germany had focused on its western and southern regions, leaving a knowledge gap about eastern Germany. Despite their importance, this study is the first to investigate phytoplasmas in sugar beet in Saxony-Anhalt, Germany. A phytoplasma strain related to ‘Ca. P. solani’ is found predominant in Saxony-Anhalt, unlike in France, where ‘Ca. P. solani’ has a minor role compared with ‘Ca. A. phytopathogenicus’. The phytoplasma strain infecting sugar beet in Saxony-Anhalt was classified into a new subgroup designated as 16SrXII-P. The multilocus sequence analysis (MLSA) of nonribosomal genes of the novel phytoplasma strain showed that it is significantly different from the reference and all previously reported ‘Ca. P. solani’ strains including the strain from western Germany. Analyses of sugar beet samples from previous years confirmed the presence of the 16SrXII-P strain in sugar beet as early as 2020 and also in Bavaria in southern Germany. Based on 16S rDNA analysis, ‘Ca. A. phytopathogenicus’ in Saxony-Anhalt is identical to strains in sugar beet in other parts of Germany and France, as well as to a strain in potato from Germany. The presence and prevalence of two phytoplasmas in sugar beet in Germany suggest that more attention should be directed toward understanding phytoplasma infection in sugar beet in this country.

Phosphatidylcholine (PtdCho) is an unusual membrane phospholipid present in some endosymbiotic and intracellular pathogenic prokaryotes. ‘ Candidatus Liberibacter asiaticus’ (CLas) is a phloem-limited, uncultured, fastidious α-Proteobacterium associated with the devastating citrus “greening” disease (huanglongbing). Phylogenetically related but nonpathogenic Liberibacter crescens (Lcr) was used as a culturable surrogate to examine PtdCho biosynthesis in pathogenic CLas. Genes encoding key enzymes for two alternative PtdCho biosynthetic routes are present in the Lcr genome: the one-step cytidine diphosphate (CDP)-choline ( pcs-encoding phosphatidylcholine synthase) and the three-step methyl-transferase pathway ( pmt-encoding phospholipid N-methyltransferase). However, only the CDP-choline pathway genes for incorporating exogenous Cho were identified in the CLas genome. Exogenous Cho enhanced growth and alleviated osmotic stress in wild-type Lcr and in the pmt insertion mutant strains when cultured in a sugar-rich medium. Quantitative RT-PCR analyses confirmed active uptake and condensation of nutritional Cho into PtdCho by CLas in both its plant host and psyllid vector. CLas-infected grapefruit leaves showed transcriptional activation of Cho biosynthesis genes and 2.8-fold higher levels of Cho. In plant cells, the compatible osmolyte glycine-betaine (GlyBet) is also derived from Cho. Expression of GlyBet biosynthesis genes and the GlyBet content were similar in both CLas-infected and healthy leaf tissue. The data presented here suggest that CLas likely exploits the Cho biosynthetic pathway in citrus hosts to expand the nutritional Cho pool. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .