Tetracycline reduces feeding and reproduction of the parthenogenetic springtail, Folsomia candida

Wolbachia: Advancing into a Second Century

Wolbachia pipientis had its scientific debut nearly a century ago and has recently emerged as a target for therapeutic treatment of filarial infections and an attractive tool for control of arthropod pests. Wolbachia was known as a biological entity before DNA was recognized as the molecule that carries the genetic information on which life depends, and before arthropods and nematodes were grouped in the Ecdysozoa. Today, some investigators consider Wolbachia the most abundant endosymbiont on earth, given the numbers of its hosts and its diverse mutualistic, commensal, and parasitic roles in their life histories. Recent advances in molecular technologies have revolutionized our understanding of Wolbachia and its associated reproductive phenotypes. New models have emerged for its investigation, and substantial progress has been made towards Wolbachia-based interventions in medicine and agriculture. Here I introduce Wolbachia, with a focus on aspects of its biology that are covered in greater detail in subsequent chapters.

Paraquat is toxic to the soil-dwelling arthropod, Folsomia candida (Collembola: Isotomidae), and has potential effects on its Wolbachia endosymbiont

The springtail, Folsomia candida, is a soil arthropod commonly used to evaluate environmental toxins. Conflicting data on the toxicity of the herbicide paraquat prompted re-evaluation of its effects on F. candida survival and reproduction. Paraquat has an LC₅₀ of about 80 μM when tested in the absence of charcoal; charcoal, often used in test arenas to facilitate visualization of the white Collembola, has a protective effect. Survivors of paraquat treatment fail to resume molting and oviposition, suggesting an irreversible effect on the Wolbachia symbiont that restores diploidy during parthenogenetic reproduction of this species.

Wolbachia springs eternal: symbiosis in Collembola is associated with host ecology

Wolbachia are endosymbiotic alpha-proteobacteria infecting a wide range of arthropods and nematode hosts with diverse interactions, from reproductive parasites to obligate mutualists. Their taxonomy is defined by lineages called supergroups (labelled by letters of the alphabet), while their evolutionary history is complex, with multiple horizontal transfers and secondary losses. One of the least recently derived, supergroup E, infects springtails (Collembola), widely distributed hexapods, with sexual and/or parthenogenetic populations depending on species. To better characterize the diversity of Wolbachia infecting springtails, the presence of Wolbachia was screened in 58 species. Eleven (20%) species were found to be positive, with three Wolbachia genotypes identified for the first time in supergroup A. The novel genotypes infect springtails ecologically and biologically different from those infected by supergroup E. To root the Wolbachia phylogeny, rather than distant other Rickettsiales, supergroup L infecting plant-parasitic nematodes was used here. We hypothesize that the ancestor of Wolbachia was consumed by soil-dwelling nematodes, and was transferred horizontally via plants into aphids, which then infected edaphic arthropods (e.g. springtails and oribatid mites) before expanding into most clades of terrestrial arthropods and filarial nematodes.

Identifying the Role of Elevation, Geography, and Species Identity in Structuring Turtle Ant (Cephalotes Latreille, 1802) Bacterial Communities

Bacterial communities in animals are often necessary for hosts to survive, particularly for hosts with nutrient-limited diets. The composition, abundance, and richness of these bacterial communities may be shaped by host identity and external ecological factors. The turtle ants (genus Cephalotes) are predominantly herbivorous and known to rely on bacterial communities to enrich their diet. Cephalotes have a broad Neotropical distribution, with high diversity in the South American Cerrado, a geologically and biologically diverse savanna. Using 16S rRNA amplicon sequencing, we examined the bacterial communities of forty-one Cephalotes samples of sixteen different species collected from multiple locations across two sites in the Cerrado (MG, Brazil) and compared the bacterial communities according to elevation, locality, species, and species group, defined by host phylogeny. Beta diversity of bacterial communities differed with respect to all categories but particularly strongly when compared by geographic location, species, and species group. Differences seen in species and species groups can be partially explained by the high abundance of Mesorhizobium in Cephalotes pusillus and Cephalotes depressus species groups, when compared to other clades via the Analysis of Composition of Microbiome (ANCOM). Though the Cephalotes bacterial community is highly conserved, results from this study indicate that multiple external factors can affect and change bacterial community composition and abundance.

DNA recombination and repair in Wolbachia: RecA and related proteins

Wolbachia is an obligate intracellular bacterium that has undergone extensive genomic streamlining in its arthropod and nematode hosts. Because the gene encoding the bacterial DNA recombination/repair protein RecA is not essential in Escherichia coli, abundant expression of this protein in a mosquito cell line persistently infected with Wolbachia strain wStri was unexpected. However, RecA's role in the lytic cycle of bacteriophage lambda provides an explanation for retention of recA in strains known to encode lambda-like WO prophages. To examine DNA recombination/repair capacities in Wolbachia, a systematic examination of RecA and related proteins in complete or nearly complete Wolbachia genomes from supergroups A, B, C, D, E, F, J and S was undertaken. Genes encoding proteins including RecA, RecF, RecO, RecR, RecG and Holliday junction resolvases RuvA, RuvB and RuvC are uniformly absent from Wolbachia in supergroup C and have reduced representation in supergroups D and J, suggesting that recombination and repair activities are compromised in nematode-associated Wolbachia, relative to strains that infect arthropods. An exception is filarial Wolbachia strain wMhie, assigned to supergroup F, which occurs in a nematode host from a poikilothermic lizard. Genes encoding LexA and error-prone polymerases are absent from all Wolbachia genomes, suggesting that the SOS functions induced by RecA-mediated activation of LexA do not occur, despite retention of genes encoding a few proteins that respond to LexA induction in E. coli. Three independent E. coli accessions converge on a single Wolbachia UvrD helicase, which interacts with mismatch repair proteins MutS and MutL, encoded in nearly all Wolbachia genomes. With the exception of MutL, which has been mapped to a eukaryotic association module in Phage WO, proteins involved in recombination/repair are uniformly represented by single protein annotations. Putative phage-encoded MutL proteins are restricted to Wolbachia supergroups A and B and show higher amino acid identity than chromosomally encoded MutL orthologs. This analysis underscores differences between nematode and arthropod-associated Wolbachia and describes aspects of DNA metabolism that potentially impact development of procedures for transformation and genetic manipulation of Wolbachia.