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Symbiotic bacteria in midges: understanding their role in determining vector competence and transmission of viruses

Periodic Reporting for period 1 - MIDGESYM (Symbiotic bacteria in midges: understanding their role in determining vector competence and transmission of viruses)

Reporting period: 2015-08-01 to 2017-07-31

The health of livestock is commonly impacted by viruses acquired from midge vectors, causing considerable economic losses across the EU. The control of midges/midge vector competence thus represents a pressing concern. Recent research demonstrated inherited symbionts can alter the vector competence of their insect host, and thus represent viable means of interrupting pathogen transmission in natural populations. However, reduction of vector competence has only been considered for Wolbachia symbiont infections, and for viruses of importance to human health. Midges, in contrast, are commonly infected with a Cardinium heritable symbiont with unknown properties.

In this project we will use genomic transcriptomic and field approaches to establish tools for understanding this symbiont, and determine whether the symbiont affects host immune system activity and vector competence following exposure to an infected blood meal.

In particular we aim:

a) To establish draft genome sequence for Cardinium symbiont, to investigate potential properties of this symbiont.
b) Characterize any other symbionts in this economically important group
c) Establish the impact of symbionts on host gene expression, particularly related to immune function.

This proposal will thus provide both fundamental understanding of a poorly studied symbiont in an important host group, and, more practically, evaluate whether alteration of symbiont presence is a viable means of interrupting the transmission of Schmallenberg virus, a cause of serious economic loss in the EU livestock sector. The project will additionally provide training in a range of technical and transferable skills necessary for research leadership.
1. We have obtained a draft genome sequence for the Cardinium symbiont of the biting midge, C. newsteadi. This represents the first genome sequence of Cardinium from the midge clade. Data indicate that the midge symbiont is in fact a basal lineage in the genus Cardinium, contrary to previous views. The genome sequence provides insight into the potential biological importance of the symbiont to the mideg.

2. We detected the first observation of a torix group Rickettsia in the biting midge C.newsteadi. This is a potential important modulator of midge biology. We have completed a draft genome sequence for the symbiont which provides insight into biological function. Further, we have demonstrated that 40% of biting midge species carry Rickettsia infections, with all individuals of many species being infected.

3. We have demonstrated the Rickettsia is a vertically transmitted symbiont of the midge, and also infects midgut tissue. Its biological role will be the subject of further exploration.

4. We have additionally obtained draft genome sequence of Rickettsia from other midge species, and other aquatic invertebrates, to assess the potential diversity of interactions that exist.
We have completed the sequence of the genome of two potentially important modifiers of biting midge biology. These data are important because they may underpin novel mechanisms by which to control the arboviral diseases of livestock that are vectored by midges.

Potential impacts include:
i) potential discovery of a novel veterinary pathogen - Rickettsia have pathogenic properties in some cases and merit evaluation.
ii) discovery of a new potential modulator of vector competence/vector biology
Rickettsia bacteria (in red) inside the ovaries of the biting midge C. newsteadi (blue-DNA)