Publications

4618

Abstract The African citrus triozid (ACT), Trioza erytreae (Del Guercio, 1918) (Hemiptera: Triozidae), is a significant pest of citrus in southern Africa serving as a vector of African citrus greening disease associated with the phloem-limited gram-negative bacterium “Candidatus Liberibacter africanus” (CLaf). ACT can also vector another Liberibacter species, “Ca. Liberibacter asiaticus” (CLas) associated with Asian citrus greening. Given the confirmed presence of CLas on the African continent, efforts to monitor populations of ACT as well as associated liberibacters in citrus environments have been enhanced since 2021. Trapping and active collections in citrus surroundings indicated the presence of two triozid species with similar morphology to ACT and five other triozids which were morphologically distinct. This study aimed to characterise the diversity of triozid species around citrus and determine their association with liberibacter. Morphological characters and nucleotide sequence phylogeny of the mitochondrial cytochrome c oxidase I (COI) gene region supported the distinction of seven triozid species including ACT. CLaf was only detected in ACT. None of the other triozid species had any liberibacter species associated with them. Our results suggest the presence of other triozid species in other African countries, which probably were misidentified as ACT. Our findings highlight the need for a comprehensive taxonomic revision of triozids associated with citrus. Integrating morphological and molecular characters in a revised classification will be essential for accurate identification of ACT. Molecular confirmation is needed for confidence in distinguishing ACT from closely related non-pest species.

Abstract Segmented filamentous bacteria (SFB) describe morphologically similar gut commensals found in mammals, fish and birds. In mice, SFB intimately colonizes the ileal epithelium at the time of weaning and elicits a strong pleiotropic immune activation that fosters colonization resistance while augmenting disease severity in various disease models. SFB is therefore critical in both health and disease but information regarding SFB in humans remains limited. Here, we first identify and characterize a human SFB species with SFB-specific morphology, including the hook-like tip structure that mediates attachment, and unique genome features, including a starch and glycogen degradation module. This species, which we name Anisomitus miae and establish as the nomenclature type for the SFB genus, is common across Africa. We then bioinformatically identify, based on the 16S rRNA gene V3-V4 variable region sequence, four major, and two minor, human SFB lineages in forty-four countries distributed across all six inhabited continents. We provide evidence towards the co-colonization potential of the SFB lineages and their colonization dynamics, including a potent but short-lived colonization peak in children between one to five years of age. This study establishes the presence of multiple SFB species in the human population and SFB as a minor but wide-spread group of commensals in humans.