Aquatic Hemiptera in Southwest Cameroon: Biodiversity of Potential Reservoirs of Mycobacterium ulcerans and Multiple Wolbachia Sequence Types Revealed by Metagenomics

Abstract

Buruli ulcer (BU), caused by Mycobacterium ulcerans, is a neglected tropical disease associated with freshwater habitats. A variety of limnic organisms harbor this pathogen, including aquatic bugs (Hemiptera: Heteroptera), which have been hypothesized to be epidemiologically important reservoirs. Aquatic Hemiptera exhibit high levels of diversity in the tropics, but species identification remains challenging. In this study, we collected aquatic bugs from emerging foci of BU in the Southwest Region of Cameroon, which were identified using morphological and molecular methods. The bugs were screened for mycobacterial DNA and a selection of 20 mycobacteria-positive specimens from the families Gerridae and Veliidae were subjected to next-generation sequencing. Only one individual revealed putative M. ulcerans DNA, but all specimens contained sequences from the widespread alpha-proteobacterial symbiont, Wolbachia. Phylogenetic analysis placed the Wolbachia sequences into supergroups A, B, and F. Circularized mitogenomes were obtained for seven gerrids and two veliids, the first from these families for the African continent. This study suggests that aquatic Hemiptera may have a minor role (if any) in the spread of BU in Southwest Cameroon. Our metagenomic analysis provides new insights into the incursion of Wolbachia into aquatic environments and generated valuable resources to aid molecular taxonomic studies of aquatic Hemiptera.

The Microbiome of Neotropical Water Striders and Its Potential Role in Codiversification

“…These taxa have also been previously associated with both aquatic and terrestrial insects [ 46 , 47 , 48 , 49 , 50 , 51 ], suggesting that they are a common component of the microbiome of insects in general, and play important functional roles in their insect hosts [ 3 , 6 , 46 , 52 ]. For example, a recent study found that the genus Wolbachia is widespread in aquatic Hemipteran, including Gerridae, from Southwest Cameroon [ 53 ]. In addition, the genera Wolbachia and Spiroplasma are known to influence host ecology and evolution [ 1 , 3 , 6 , 53 ], and could be involved in diversification in water striders (see below).…”

“…For example, a recent study found that the genus Wolbachia is widespread in aquatic Hemipteran, including Gerridae, from Southwest Cameroon [ 53 ]. In addition, the genera Wolbachia and Spiroplasma are known to influence host ecology and evolution [ 1 , 3 , 6 , 53 ], and could be involved in diversification in water striders (see below).…”

“…Wolbachia has also been implicated in reproductive isolation and speciation in insects [ 78 , 84 , 85 ]. On the other hand, Spiroplasma is associated with male-killing [ 47 , 53 , 86 ]. Although more work is need to assess the evolutionary consequences of host-microbiome interaction in water striders, our results suggest the possibility that some bacterial taxa, such as Wolbachia and Spiroplasma, are involved in codiversification in water striders.…”

Evidence of new strains of Wolbachia symbiont colonising semiaquatic bugs (Hemiptera: Gerroidea) in mangrove environment of the Lesser Antilles

“…Of all the studies carried out, very few have been conducted on aquatic insects and even fewer on marine insects. However, two recent studies conducted in Cameroon [ 18 ] and Panama [ 19 ] looking for the bacterial community in the Gerridae and Veliidae found Wolbachia in these taxa.…”

“…Few recent studies demonstrated the presence of Wolbachia in semiaquatic bugs. In Cameroon, Esemu et al (2019) detected Wolbachia in freshwater insects that represent a potential reservoir for the bacterium Mycobacterium ulcerans MacCallum, 1948 causing Buruli ulcer. This research focused on nine species of the Gerridae Leach, 1815 and Veliidae Amyot & Serville, 1843 families including the three genera Limnogonus, Microvelia, and Rhagovelia [18].…”