The son-killer microbe Arsenophonus nasoniae is a widespread associate of the parasitic wasp Nasonia vitripennis in Europe

Bacterial effectors mediate kinase reprogramming through mimicry of conserved eukaryotic motifs

Bacteria have evolved numerous biochemical processes that underpin their biology and pathogenesis. The small, non-enzymatic bacterial (Salmonella) effector SteE mediates kinase reprogramming, whereby the canonical serine/threonine host kinase GSK3 gains tyrosine-directed activity towards neosubstrates, promoting Salmonella virulence. Yet, both the mechanism behind the switch in GSK3's activity and the diversity of this phenomenon remain to be determined. Here we show that kinase reprogramming of GSK3 is mediated by putative homologues from diverse Gram-negative pathogens. Next, we identify both the molecular basis of how SteE targets GSK3 and uncover that the SteE-induced tyrosine activity conferred on GSK3 requires an L/xGxP motif. This motif, found in several CMGC kinases that undergo auto-tyrosine phosphorylation, was previously shown to mediate GSK3 autophosphorylation on a tyrosine. Together, we suggest that the SteE family of intrinsically disordered proteins mediates kinase reprogramming via several short linear motifs that each appear to mimic eukaryotic signalling motifs. With this insight comes the potential for the rationale design of synthetic reprogramming proteins.

The Honeybee Associate Galleria mellonella Can Acquire Arsenophonus apicola Through Oral and Parenteral Infection Routes

Members of the genus Arsenophonus are classically considered to be vertically transmitted endosymbiotic associates of invertebrates. Acquisition of Arsenophonus apicola by Apis mellifera honeybees through social and environmental pathways raises the possibility that this species can infect a broader range of host species. In this study, we tested whether a natural inhabitant of bee hives, the wax moth Galleria mellonella, was a suitable host for A. apicola. We first demonstrated A. apicola colonised G. mellonella larvae following injection at doses as low as 104 CFU. A similar capacity of A. apicola to infect G. mellonella orally was evidenced, impacting waxworm development and mortality. Microscopy indicated that A. apicola crossed from gut to hemocoel in the G. mellonella crop, inducing melanisation. PCR screening of Galleria individuals in an apiary sample confirmed exposure of Galleria in the hive context. We conclude that A. apicola is capable of infecting and damaging hive associates. These findings raise two onward avenues of research: first, to investigate whether A. apicola's presence could protect hives against Galleria infestations, and second, to utilise model insect G. mellonella for immunity research to uncover the interplay between A. apicola and insect host defences whilst elucidating virulence factors utilised by A. apicola during infection.

Genome dynamics across the evolutionary transition to endosymbiosis

Endosymbiosis-where a microbe lives and replicates within a host-is an important contributor to organismal function that has accelerated evolutionary innovations and catalyzed the evolution of complex life. The evolutionary processes associated with transitions to endosymbiosis, however, are poorly understood. Here, we leverage the wide diversity of host-associated lifestyles of the genus Arsenophonus to reveal the complex evolutionary processes that occur during the transition to a vertically transmitted endosymbiotic lifestyle from strains maintained solely by horizontal (infectious) transmission. We compared the genomes of 38 strains spanning diverse lifestyles from horizontally transmitted pathogens to obligate interdependent endosymbionts. Among culturable strains, we observed those with vertical transmission had larger genome sizes than closely related horizontally transmitting counterparts, consistent with evolutionary innovation and the rapid gain of new functions. Increased genome size was a consequence of prophage and plasmid acquisition, including a cargo of type III effectors, alongside the concomitant loss of CRISPR-Cas genome defense systems, enabling mobile genetic element expansion. Persistent endosymbiosis was also associated with loss of type VI secretion, which we hypothesize to be a consequence of reduced microbe-microbe competition. Thereafter, the transition to endosymbiosis with strict vertical inheritance was associated with the expected relaxation of purifying selection, gene pseudogenization, metabolic degradation, and genome reduction. We argue that reduced phage predation in endosymbiotic niches drives the loss of genome defense systems driving rapid genome expansion upon the adoption of endosymbiosis and vertical transmission. This remodeling enables rapid horizontal gene transfer-mediated evolutionary innovation and precedes the reductive evolution traditionally associated with adaptation to endosymbiosis.

Ecological determinants of prevalence of the male-killing bacterium Arsenophonus nasoniae

Male-killing bacteria are found in a broad range of arthropods. Arsenophonus nasoniae is a male-killing bacterium, causing a 80% reduction of the male progeny in infected Nasonia vitripennis wasps. Although the discovery of A. nasoniae dates from the early 80's, knowledge about the biology and ecology of this endosymbiont is still scarce. One of these poorly studied features is the ecological factors underlying A. nasoniae incidence on its Nasonia spp. hosts in different geographical locations. Here, we studied the prevalence of A. nasoniae in Iberian wild populations of its host N. vitripennis. This wasp species is a common parasitoid of the blowfly Protocalliphora azurea pupae, which in turn is a parasite of hole-nesting birds, such as the blue tit (Cyanistes caeruleus). We also examined the effects of bird rearing conditions on the prevalence of A. nasoniae through a brood size manipulation experiment (creating enlarged, control and reduced broods). Both the wasp and bacterium presence were tested through PCR assays in blowfly pupae. We found A. nasoniae in almost half (47%) of nests containing blowflies parasitized by N. vitripennis. The prevalence of A. nasoniae was similar in the two geographical areas examined (central Portugal and southeastern Spain) and the probability of infection by A. nasoniae was independent of the number of blowfly pupae in the nest. Experimental manipulation of brood size did not affect the prevalence of A. nasoniae nor the prevalence of its host, N. vitripennis. These results suggest that the incidence of A. nasoniae in natural populations of N. vitripennis is high in the Iberian Peninsula, and the infestation frequency of nests by N. vitripennis carrying A. nasoniae is spatially stable in this geographical region independently of bird rearing conditions.