Ecology

Abstract Zebra chip, is a potato disease associated with the bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) and vectored by the potato psyllid, Bactericera cockerelli Šulc. Potato psyllids are native to North America, where four haplotypes have been described. They are able to colonize a wide range of solanaceous species, crops, and weeds. The epidemiology of zebra chip disease is still poorly understood and might involve the different haplotypes of psyllids as well as two haplotypes of Lso. As several perennial weeds have been recognized as potential host for potato psyllids and Lso, a yearly monitoring of several patches of bittersweet nightshade (Solanum dulcamara) and field bindweed (Convolvulus arvensis) located in the potato-growing region of southern Idaho was conducted from 2013 to 2017, to gain insight into psyllid dynamics in non-potato hosts and Lso presence in the fields. Potato psyllids caught on each host were individually tested for Lso, and a subset were haplotyped based on the CO1 gene, along with the haplotyping of Lso in positive samples. On bittersweet nightshade, the Northwestern haplotype was numerically dominant, with around 2.7% of psyllids found to be carrying either Lso haplotype A or B, suggesting a limited role in zebra chip persistence, which has infected Idaho fields at a low occurrence since the 2012 outbreak. Field bindweed was found to be a transient, non-overwintering host for potato psyllid of Northwestern, Western and Central haplotypes late in the season, suggesting minor, if any, role in persistence of Lso and field infestation by potato psyllids.

Here, we demonstrate how microbial storage metabolism can adjust to a wide range of environmental conditions. Such flexibility generates a selective advantage under fluctuating environmental conditions. It can also explain the different observations reported in PAO literature, including the capacity of “ Ca . Accumulibacter phosphatis” to act like glycogen-accumulating organisms (GAOs). These observations stem from slightly different experimental conditions, and controversy arises only when one assumes that metabolism can operate only in a single mode. Furthermore, we also show how the study of metabolic strategies is possible when combining omics data with functional cofactor assays and modeling. Genomic information can only provide the potential of a microorganism. The environmental context and other complementary approaches are still needed to study and predict the functional expression of such metabolic potential.

The recently described superphylum DPANN includes several phyla of uncultivated archaea with small cell sizes, reduced genomes, and limited metabolic capabilities. One of these phyla, “ Ca . Micrarchaeota,” comprises an enigmatic group of archaea found in acid mine drainage environments, the archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) group. Analysis of their reduced genomes revealed the absence of key metabolic pathways consistent with their partner-associated lifestyle, and physical associations of ARMAN cells with their hosts were documented. However, “ Ca . Micrarchaeota” include several lineages besides the ARMAN group found in nonacidic environments, and none of them have been characterized. Here, we report a complete genome of “ Ca . Micrarchaeota” from a non-ARMAN lineage. Analysis of this genome revealed the presence of metabolic capacities lost in ARMAN genomes that could enable a free-living lifestyle. These results expand our understanding of genetic diversity, lifestyle, and evolution of “ Ca . Micrarchaeota.”

Abstract The potato psyllid, Bactericera cockerelli (Šulc), is a major pest of potato (Solanum tuberosum L.; Solanales: Solanaceae) as a vector of ‘Candidatus Liberibacter solanacearum’, the pathogen that causes zebra chip. Management of zebra chip is challenging in part because the noncrop sources of Liberibacter-infected psyllids arriving in potato remain unknown. Adding to this challenge is the occurrence of distinct genetic haplotypes of both potato psyllid and Liberibacter that differ in host range. Longleaf groundcherry (Physalis longifolia Nutt.) has been substantially overlooked in prior research as a potential noncrop source of Liberibacter-infected B. cockerelli colonizing fields of potato. The objective of this study was to assess the suitability of P. longifolia to the three common haplotypes of B. cockerelli (central, western, and northwestern haplotypes), and to two haplotypes of ‘Ca. L. solanacearum’ (Liberibacter A and B haplotypes). Greenhouse bioassays indicated that B. cockerelli of all three haplotypes produced more offspring on P. longifolia than on potato and preferred P. longifolia over potato during settling and egg-laying activities. Greenhouse and field trials showed that P. longifolia was also highly susceptible to Liberibacter. Additionally, we discovered that infected rhizomes survived winter and produced infected plants in late spring that could then be available for psyllid colonization and pathogen acquisition. Results show that P. longifolia is susceptible to both B. cockerelli and ‘Ca. L. solanacearum’ and must be considered as a potentially important source of infective B. cockerelli colonizing potato fields in the western United States.

The psyllids Cacopsylla melanoneura and Cacopsylla picta reproduce on apple (Malus × domestica) and transmit the bacterium ‘Candidatus Phytoplasma mali’, the causative agent of apple proliferation. Adult psyllids were collected by the beating-tray method from lower and upper parts of the apple tree canopy in the morning and in the afternoon. There was a trend of catching more emigrant adults of C.melanoneura in the morning and in the lower part of the canopy. For C.melanoneura remigrants, no differences were observed. The findings regarding the distribution of adults were reflected by the number of nymphs collected by wash-down sampling. The density of C.picta was too low for a statistical analysis. The vector monitoring and how it is commonly performed, is suitable for estimating densities of C.melanoneura. Nevertheless, above a certain temperature threshold, prediction of C.melanoneura density might be skewed. No evidence was found that other relatively abundant psyllid species in the orchard, viz. Baeopelma colorata, Cacopsylla breviantennata, Cacopsylla brunneipennis, Cacopsylla pruni and Trioza urticae, were involved in ‘Candidatus Phytoplasma mali’ transmission. The results of our study contribute to an advanced understanding of insect vector behavior and thus have a practical impact for an improved field monitoring.

The bacterial pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) is transmitted by the tomato potato psyllid (TPP), Bactericera cockerelli, to solanaceous crops. In the present study, the changes in metabolic profiles of insect-susceptible (cv CastleMart) and resistant (RIL LA3952) tomato plants in response to TPP vectoring Lso or not, were examined after 48 h post infestation. Non-volatile and volatile metabolites were identified and quantified using headspace solid-phase microextraction equipped with a gas chromatograph-mass spectrometry (HS-SPME/GC-MS) and ultra-high pressure liquid chromatography coupled to electrospray quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS), respectively. Partial least squares-discriminant analysis (PLS-DA) was used to define the major uncorrelated metabolite components assuming the treatments as the correlated predictors. Metabolic changes in various classes of metabolites, including volatiles, hormones, and phenolics, were observed in resistant and susceptible plants in response to the insects carrying the pathogen or not. The results suggest the involvement of differentially regulated and, in some cases, implicates antagonistic metabolites in plant defensive signaling. Upon validation, the identified metabolites could be used as markers to screen and select breeding lines with enhanced resistance to reduce economic losses due to the TPP-Lso vector-pathogen complex in Solanaceous crops.

AbstractPathogens which need a vector for their transmission can alter the vectors’ behaviour to favour their spread. We used the electrical penetration graph technique to investigate this hypothesis by using the tomato potato psyllid Bactericera cockerelli infected or not with the plant pathogen Candidatus Liberibacter solanacearum (CLso) on African boxthorn and tomato. Probing was not affected by the host type but there was a significant effect on probing due to the infection status of the psyllid. More psyllids carried out probing activities in the sieve elements when infected with CLso, and more probing activities were observed from CLso-infected psyllids by comparison to the non-infected groups. Specifically, significant increases in salivation, phloem ingestion and number of probes, before and after reaching the sieve elements, were noticed in the infected groups. Furthermore, time elapsed to reach the sieve elements was significantly shortened by 2 h in the infected group. Remaining probing activities in xylem tissues were not different between all psyllid groups. The observed changes in feeding behaviour by pathogen-infected psyllids may well ensure further spread of the pathogen as greater salivation has the potential to increase transmission, highlighting at the same time the important role that crop and non-crop hosts play in disease epidemiology.

Extensive search for new endosymbiotic systems in ciliates occasionally reverts us to the endosymbiotic bacteria described in the pre-molecular biology era and, hence, lacking molecular characterization. A pool of these endosymbionts has been referred to as a hidden bacterial biodiversity from the past. Here, we provide a description of one of such endosymbionts, retrieved from the ciliate Paramecium nephridiatum. This curve-shaped endosymbiont (CS), which shared the host cytoplasm with recently described “Candidatus Megaira venefica”, was found in the same host and in the same geographic location as one of the formerly reported endosymbiotic bacteria and demonstrated similar morphology. Based on morphological data obtained with DIC, TEM and AFM and molecular characterization by means of sequencing 16S rRNA gene, we propose a novel genus, “Candidatus Mystax”, with a single species “Ca. Mystax nordicus”. Phylogenetic analysis placed this species in Holosporales, among Holospora-like bacteria. Contrary to all Holospora species and many other Holospora-like bacteria, such as “Candidatus Gortzia”, “Candidatus Paraholospora” or “Candidatus Hafkinia”, “Ca. Mystax nordicus” was never observed inside the host nucleus. “Ca. Mystax nordicus” lacked infectivity and killer effect. The striking peculiarity of this endosymbiont was its ability to form aggregates with the host mitochondria, which distinguishes it from Holospora and Holospora-like bacteria inhabiting paramecia.

Holospora-like bacteria (HLB) are obligate intracellular Alphaproteobacteria, inhabiting nuclei of Paramecium and other ciliates such as “Candidatus Hafkinia” is in Frontonia. The HLB clade is comprised of four genera, Holospora, Preeria, “Candidatus Gortzia”, and “Candidatus Hafkinia”. These bacteria have a peculiar life cycle with two morphological forms and some degree of specificity to the host species and the type of nucleus they inhabit. Here we describe a novel species of HLB—“Candidatus Gortzia yakutica” sp. nov.—a symbiont from the macronucleus of Paramecium putrinum, the first described HLB for this Paramecium species. The new endosymbiont shows morphological similarities with other HLB. The phylogenetic analysis of the SSU rRNA gene places it into the “Candidatus Gortzia” clade.