Spiroplasmas from coleopterous insects: New ecological dimensions

Effects of feeding on different parts of Ailanthus altissima on the intestinal microbiota of Eucryptorrhynchus scrobiculatus and Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

Eucryptorrhynchus brandti and Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae) are two monophagous weevil pests that feed on Ailanthus altissima (Mill.) Swingle but differ in their diet niche. In the field, adults of E. brandti prefer to feed on the trunk of A. altissima, whereas adults of E. scrobiculatus prefer to feed on the tender parts. We conducted Illumina sequencing of 16S rRNA to examine changes in bacterial diversity in the adults of these two weevil species after they fed on different parts of A. altissima (trunk, 2–3-year-old branches, annual branches, and petioles). Proteobacteria, Tenericutes, and Firmicutes were the dominant phyla in E. brandti (relative abundance was 50.64, 41.56, and 5.63%, respectively) and E. scrobiculatus (relative abundance was 78.63, 11.91, and 7.41%, respectively). At the genus level, Spiroplasma, endosymbionts2, Unclassified Enterobacteriaceae, and Lactococcus were dominant in E. brandti, and Unclassified Enterobacteriaceae, Wolbachia and Spiroplasma, and endosymbionts2 were dominant in E. scrobiculatus. Linear discriminant analysis effect size analysis revealed microbial biomarkers in the different treatment group of adults of both weevil species. Adults of E. brandti may require the trunk, and adults of E. scrobiculatus may require the petioles and annual branches to maintain the high diversity of their gut microbes. The results of this study indicate that feeding on different parts of A. altissima affects the composition and function of the microbes of E. brandti and the microbial composition of E. scrobiculatus. Variation in the abundance of Wolbachia and Spiroplasma in E. brandti and E. scrobiculatus is associated with dietary niche changes, and this might explain the evolution of reproductive isolation between these two sibling weevil species.

Gut Microbiota-Related Evidence Provides New Insights Into the Association Between Activating Transcription Factor 4 and Development of Salt-Induced Hypertension in Mice

Activating transcription factor 4 (ATF4), which regulates genes associated with endoplasmic reticulum stress, apoptosis, autophagy, the gut microbiome, and metabolism, has been implicated in many diseases. However, its mechanistic role in hypertension remains unclear. In the present study, we investigated its role in salt-sensitive hypertensive mice. Wild-type (WT) C57BL/6J mice were used to establish Atf4 knockout (KO) and overexpression mice using CRISPR-Cas9 and lentiviral overexpression vectors. Then, fecal microbiota transplantation (FMT) from Atf4 ^± mice and vitamin K₂ (VK2) supplementation were separately carried out in high-salt-diet (8% NaCl)-induced mice for 4 weeks. We found that Atf4 KO inhibited and Atf4 overexpression enhanced the increase in blood pressure and endothelial dysfunction induced by high salt intake in mice, while regulating the gut microbiota composition and VK2 expression. It was further verified that ATF4 is involved in the regulation of salt-sensitive hypertension and vascular endothelial function, which is achieved through association with gut microbiota and may be related to VK2 and different bacteria such as Dubosiella. In addition, we found that VK2 supplementation prevents the development of salt-sensitive hypertension and maintains vascular endothelial function; moreover, VK2 supplementation increases the abundance of intestinal Dubosiella and downregulates the relative expression of Atf4 in the thoracic aorta of mice. We conclude that ATF4 plays an important role in regulating gut microbiota and VK2 production, providing new insights into the association between ATF4 and development of salt-induced hypertension in mice, meanwhile contributing to the development for a new preventive strategy of hypertension.

Nitrogen Fertilizer Amendment Alter the Bacterial Community Structure in the Rhizosphere of Rice (Oryza sativa L.) and Improve Crop Yield

Availability of nitrogen (N) in soil changes the composition and activities of microbial community, which is critical for the processing of soil organic matter and health of crop plants. Inappropriate application of N fertilizer can alter the rhizosphere microbial community and disturb the soil N homeostasis. The goal of this study was to assess the effect of different ratio of N fertilizer at various early to late growth stages of rice, while keeping the total N supply constant on rice growth performance, microbial community structure, and soil protein expression in rice rhizosphere. Two different N regimes were applied, i.e., traditional N application (NT) consists of three sessions including 60, 30 and 10% at pre-transplanting, tillering and panicle initiation stages, respectively, while efficient N application (NF) comprises of four sessions, i.e., 30, 30, 30, and 10%), where the fourth session was extended to anthesis stage. Soil metaproteomics combined with Terminal Restriction Fragment Length Polymorphism (T-RFLP) were used to determine the rhizosphere biological process. Under NF application, soil enzymes, nitrogen utilization efficiency and rice yield were significantly higher compared to NT application. T-RFLP and qPCR analysis revealed differences in rice rhizosphere bacterial diversity and structure. NF significantly decreased the specific microbes related to denitrification, but opposite result was observed for bacteria associated with nitrification. Furthermore, soil metaproteomics analysis showed that 88.28% of the soil proteins were derived from microbes, 5.74% from plants, and 6.25% from fauna. Specifically, most of the identified microbial proteins were involved in carbohydrate, amino acid and protein metabolisms. Our experiments revealed that NF positively regulates the functioning of the rhizosphere ecosystem and further enabled us to put new insight into microbial communities and soil protein expression in rice rhizosphere.

Honey bee colonies act as reservoirs for two Spiroplasma facultative symbionts and incur complex, multiyear infection dynamics

Two species of Spiroplasma (Mollicutes) bacteria were isolated from and described as pathogens of the European honey bee, Apis mellifera, ~30 years ago but recent information on them is lacking despite global concern to understand bee population declines. Here we provide a comprehensive survey for the prevalence of these two Spiroplasma species in current populations of honey bees using improved molecular diagnostic techniques to assay multiyear colony samples from North America (U.S.A.) and South America (Brazil). Significant annual and seasonal fluctuations of Spiroplasma apis and Spiroplasma melliferum prevalence in colonies from the U.S.A. (n = 616) and Brazil (n = 139) occurred during surveys from 2011 through 2013. Overall, 33% of U.S.A. colonies and 54% of Brazil colonies were infected by Spiroplasma spp., where S. melliferum predominated over S. apis in both countries (25% vs. 14% and 44% vs. 38% frequency, respectively). Colonies were co-infected by both species more frequently than expected in both countries and at a much higher rate in Brazil (52%) compared to the U.S.A. (16.5%). U.S.A. samples showed that both species were prevalent not only during spring, as expected from prior research, but also during other seasons. These findings demonstrate that the model of honey bee spiroplasmas as springtime-restricted pathogens needs to be broadened and their role as occasional pathogens considered in current contexts.

Army ants harbor a host-specific clade of Entomoplasmatales bacteria

In this article, we describe the distributions of Entomoplasmatales bacteria across the ants, identifying a novel lineage of gut bacteria that is unique to the army ants. While our findings indicate that the Entomoplasmatales are not essential for growth or development, molecular analyses suggest that this relationship is host specific and potentially ancient. The documented trends add to a growing body of literature that hints at a diversity of undiscovered associations between ants and bacterial symbionts.

Cell-Assisted Growth of a Fastidious Spiroplasma

The Colorado potato beetle spiroplasma, which is not cultivable in conventional cell-free media, grew in tissue culture media in the presence of several coleopteran and lepidopteran insect cell lines. The cultured organisms attained titers of 1.2 x 10(9) spiroplasmas per milliliter of culture at the 100th passage and retained infectivity and a high capacity for translational motility at the 15th passage. Cell culture systems may facilitate the isolation of other presently uncultivable microorganisms and may be useful in the study of the role of microbial physiology and behavior in pathogenicity.

Studies on the pathogenicity of spiroplasmas for Drosophila pseudoobscura

Representatives of several currently available spiroplasma serovars were used in feeding and injection experiments involving Drosophila pseudoobscura adult flies in order to evaluate the host-range of the spiroplasmas and to determine their pathogenicity for flies. Many of the isolates injected into flies either do not survive or grow poorly, and have no negative effects on longevity or fecundity. Two spiroplasma strains, honey-bee (serovar I-2) and cornstunt (serovar I-3), can grow to high titres in injected flies but are not pathogenic. In addition to the special pathology of male lethality caused by the sex-ratio organisms (spiroplasmas) which occur naturally in several neotropical species of Drosophila, two spiroplasma serovars resulted in the death of injected flies. Spiroplasmas isolated from syrphid flies (serovar VIII) and from Cotinus beetles (serovar IX) induced the appearance of symptoms of pathology that eventually culminated in death. All such flies which were examined for the presence of spiroplasmas in their haemolymph showed them to be present in very high concentrations. The numbers of progeny which these flies produced were greatly reduced, but did consist of equal numbers of flies of both sexes. Spiroplasmas from their infected female parents were not vertically (transovarially) transmitted. The results of the feeding experiments were all negative: none of the spiroplasmas persisted in the gut or appeared in the haemolymph. None of the flies which had been fed the spiroplasma suspension displayed any pathology.

Pathogenicity of mollicutes for insects: possible use in biological control

Acholeplasmas, spiroplasmas and other non-helical sterol-requiring mycoplasmas of unknown phylogenetic affinity inhabit insects. Of these, only spiroplasmas are known to be pathogenic. Group I-2 spiroplasmas, or Spiroplasma apis, especially in combination with other organisms, reduce honey-bee longevity. Plant pathogenic mycoplasma-like organisms are often found intracellularly in insects. Spiroplasmas are found predominantly in the gut lumen or haemolymph (or both) of their insect hosts. Pathogenicity of mycoplasmas is usually altered by extended passage in unusual hosts, in only one of two alternate hosts, or in culture media. Enhancement of experimental pathogenicity may occur with extended cultural passages, but maintenance of natural pathogenicity must be accomplished by continuous exposure to the usual host. Recent data provide new information on the ecology of pathogenicity. Spiroplasmas from unique habitats also tend to be unique. Spiroplasmas isolated from flowers appear to be adapted to insect species that frequent floral surfaces. Group IV spiroplasmas have been isolated from members of 4 holometabolous insect orders (including Lepidoptera), all of which visit flowers. Social or predatory insects, or insects with an "aggregation" phase in their life histories, also appear to be prone to spiroplasma infection. Some insect species which harbor spiroplasmas also carry infections of other mollicutes, some of which involve the haemolymph. Appearance of spiroplasmas in adult insects in nature is strongly affected by seasonality. Extensive tests of the host ranges of the new insect mollicutes will be required before their suitability for biological control can be evaluated.