Australia’s Saccostrea glomerata (Sydney rock oyster) aquaculture industry annually contributes $107 million AUD to the economy. In 1910, the industry thrived, however, the 1960s saw to an outbreak of Queensland Unknown (QX) disease in Queensland. QX disease, caused by Marteilia sydneyi , leads to up to 90% mortality in cultivated and wild S. glomerata stock. This parasite remains the most limiting factor in Australian S. glomerata aquaculture, continually threatening its commercial viability.
M. sydneyi is an ascetosporean parasite, and several species within the Marteilia genus parasitize bivalve molluscs relied upon for aquaculture worldwide. Ostrea edulis (European flat oyster) and Mytilus edulis (European mussel) are two aquaculture species farmed extensively that have suffered recurrent outbreaks of disease and mass mortality due to another Ascetosporean parasite, Marteilia refringens. Despite the World Organisation for Animal Health listing M. sydneyi as a notifiable pathogen and its significant economic impact, there is minimal information available about the parasite. Currently, only two genomes are published for parasites within Ascetosporea, neither of which belongs to Paramyxida, to which M. sydneyi belongs. Despite the substantial economic impact M. sydneyi has on S. glomerata aq
uaculture in Queensland and New South Wales, very little is known about its lifecycle, evolutionary history, metabolism, and its interactions with its environment.
Figure 0 : M. sydneyi infected S. glomerata digestive gland smear . Blue cells indicate M. sydneyi infection.
In efforts to fill this gap, we identified infected and non-infected oysters, extracted RNA from the digestive glands, and sequenced their transcriptomes. Sequences likely originating from M. sydneyi were identified by subtracting transcripts that originated from the host, followed by homology-based bioinformatic analyses. To better understand the parasite, we are also working on generating a draft genome for M. sydneyi by utilizing long-read Nanopore DNA sequencing and PacBio HiFi sequencing. Generating cutting-edge genomic resources will allow us to identify candidate genes for the development of much-needed diagnostic assays.
As well as generating transcriptomic and genomic data for M. sydneyi, we have compared gene expression between infected and non-infected S. glomerata , enabling us to understand the molecular responses of the host oyster to infection. Overall, this research allows us to address the many unknowns surrounding the parasite, leading to new avenues for mitigation of the negative impacts it causes.