Achievements

Developing a test to detect oyster pathogens deployable in the field presented two challenges: i) selecting the most relevant pathogens regarding their impact on oyster production and ii) developing a cheap and user-friendly procedure operable by farmers with minimal training and equipment. To succeed in this endeavor, we kept tight communication with oyster farmers, syndicates and researchers in the domain. These discussions reoriented our focus from OshV1 to V.aestuarianus when we realized that farmers have adapted their production methods to cope with OshV1 infections, while V.aestuarianus outbreaks lead to 80% mortality in adult oysters. Moreover, we surveyed oyster farmers and spent time with one of them to grasp how much they are interested in self-testing their oyster beds, and how much they would be ready to invest (money- and time-wise) for that. These interactions strongly oriented our project towards the development of a simple paper-based test.

We propose a kinetic model describing the evolution of the molecular species involved in the enzymatic activity of LwCas13a. We developed a system of ordinary differential equations (ODEs) and solved that numerically, without making use of the Michaelis-Menten assumptions used in the literature. We were interested in the amount of Cas collateral activity (probe activation) as a function of time, which is proportional to the fluorescence intensity in our plate reader experiments. The model could nicely fit the data, and we could infer rate constants of the molecular reactions involved. Remarkably, we were able to quantify how the parameters are affected by the mismatch (Hamming distance) between guides and targets. We were also able to evaluate the guide-target binding rate constant, the specific and collateral activity for different guides/targets. We could estimate the order of magnitude of all rate constants, understand the limiting steps and timescales of the process.

Given the urgent need expressed by oyster farmers for a user-friendly and cheap oyster pathogens test, we developed a business plan to push our project from proof-of-principle stage to a commercially distributed product. Our business plan meets the cost and simplicity specifications and we propose to introduce a first-generation test on the market in 2024. It will cost 5€, take 1 hour to perform with a saucepan, a thermometer and a clock as sole equipment required. We will release a smartphone application to bring the result evaluation from qualitative to quantitative. Concomitantly we will launch a participative science project, automatically fed by results from the app. The goal is to understand how pathogens spread in space and time. This knowledge can help farmers to adapt their production methods. In parallel, we will progressively expand our market, propose tests to detect a larger spectrum of infections and address other aquaculture organisms.