Two Bacterial Genera, Sodalis and Rickettsia, Associated with the Seal Louse Proechinophthirus fluctus (Phthiraptera: Anoplura)

Abstract

Roughly 10% to 15% of insect species host heritable symbiotic bacteria known as endosymbionts. The lice parasitizing mammals rely on endosymbionts to provide essential vitamins absent in their blood meals. Here, we describe two bacterial associates from a louse, Proechinophthirus fluctus, which is an obligate ectoparasite of a marine mammal. One of these is a heritable endosymbiont that is not closely related to endosymbionts of other mammalian lice. Rather, it is more closely related to endosymbionts of the genus Sodalis associated with spittlebugs and feather-chewing bird lice. Localization and vertical transmission of this endosymbiont are also more similar to those of bird lice than to those of other mammalian lice. The endosymbiont genome appears to be degrading in symbiosis; however, it is considerably larger than the genomes of other mammalian louse endosymbionts. These patterns suggest the possibility that this Sodalis endosymbiont might be recently acquired, replacing a now-extinct, ancient endosymbiont. From the same lice, we also identified an abundant bacterium belonging to the genus Rickettsia that is closely related to Rickettsia ricketsii, a human pathogen vectored by ticks. No obvious masses of the Rickettsia bacterium were observed in louse tissues, nor did we find any evidence of vertical transmission, so the nature of its association remains unclear. IMPORTANCE Many insects are host to heritable symbiotic bacteria. These heritable bacteria have been identified from numerous species of parasitic lice. It appears that novel symbioses have formed between lice and bacteria many times, with new bacterial symbionts potentially replacing existing ones. However, little was known about the symbionts of lice parasitizing marine mammals. Here, we identified a heritable bacterial symbiont in lice parasitizing northern fur seals. This bacterial symbiont appears to have been recently acquired by the lice. The findings reported here provide insights into how new symbioses form and how this lifestyle is shaping the symbiont genome.

Feather mites play a role in cleaning host feathers: New insights fromDNAmetabarcoding and microscopy

“…Lack of a stable "microbiome" across different individuals of a given species has been found in other organisms with a nutritionally broad diet (Shapira, 2016). In contrast, species with highly biased diets, such as lice feeding on bird feathers (mainly keratin) or termites feeding on dead wood (mainly cellulose), typically have permanent and relatively stable endosymbiotic bacteria which provide them essential vitamins or other nutritional supplements (Puchta, 1955;Ohkuma, 2008;Perotti, Kirkness, Reed, & Braig, 2009;Boyd et al, 2016; but see Hammer et al, 2017). Thus, our results suggesting the lack of a stable microbiome at the mite species level add support to the hypothesis of a generalist fungivore-microbivore- (2014) and Denef, Fujimoto, Berry, and Schmidt (2016) [Colour figure can be viewed at wileyonlinelibrary.com] detritivore diet for the feather mites reported here, instead of these resources being taken as a by-product of a diet based mostly on uropygial oil (Engel & Moran, 2013;Sanders et al, 2017;Shapira, 2016).…”

Grandeur Alliances: Symbiont Metabolic Integration and Obligate Arthropod Hematophagy

“…Interestingly, the absence of Wigglesworthia within tsetse results in the loss of Sodalis in subsequent generations [93]. Lastly, the identification of Sodalis -like bacteria have been described in numerous insect species including various Hemiptera, Diptera, Coleoptera and Phithiraptera [94-101], although little is known concerning genome modifications following establishment within these very different hosts [102, 103]. …”

A new symbiotic lineage related toNeisseriaandSnodgrassellaarises from the dynamic and diverse microbiomes in sucking lice

“…Correspondingly, each of these lineages has been found in two to four related host species as a result of co-phylogenetic processes. The fourth lineage, the Sodalis-like symbiont from Proechinophthirus fluctus, possesses a significantly larger genome exceeding 2 Mbp, and GC content 50%, which the authors interpret as possible evidence of recent replacement of a more ancient and now extinct endosymbiont (Boyd et al 2016). The diversity and distribution of the known symbionts in sucking lice thus indicate that this insect group has been undergoing particularly dynamic acquisition, loss, and replacement of symbionts.…”

“…(Light et al 2010), are the most ancient and diversified group. Accordingly, they possess a high diversity of symbiotic bacteria , Boyd et al 2014, Boyd et al 2016, Fukatsu et al 2009, Hypsa and Krizek 2007. Depending on interpretation, the 16S rRNA gene-based phylogenies for the available taxa suggest 5-6 independent symbiotic lineages.…”