Australian Seafood Cooperative Research Center

RNA interference (RNAi) mediated by double stranded RNA (dsRNA) has emerged as one of the most promising techniques to study gene function of non-model protozoan parasites. We have previously demonstrated that bacterially expressed dsRNA delivered by immersion elicited successful knockdown in Neoparamoeba pemaquidensis, the non-infective species closely related to the causative agent of salmonid amoebic gill disease (AGD). However, considering that amoebae naturally feeds on microorganisms, direct ingestion of bacteria designed to express dsRNA could allow rapid and low-cost analysis of gene function on a large-scale. Therefore, the main objective of this study was to investigate whether ingestion of bacteria-expressing dsRNAs would also induce suppression of N. pemaquidensis β-actin and EF1α. Despite effective bacterial uptake, no significant variation in EF1α relative copy number was triggered by dsRNA ingestion. β-actin, on the other hand, presented similar silencing efficiency to what was observed in our previous soaking study. However, the observed RNAi response was delayed by at least 72 h. The present work provides evidence that delivery of bacterially expressed dsRNA through feeding can be successfully achieved in N. pemaquidensis, albeit not as efficiently as by soaking. Therefore, further investigation is required to develop more efficient and specific RNAi delivery systems in Neoparamoeba species. To our knowledge, this is the first time that RNAi-mediated knockdown through ingestion was attempted to manipulate gene function of a marine amoeba.

SummaryAtlantic Salmon (AS) and Yellowtail Kingfish (YTK) are two major commercial fish species in Australia. During food processing, waste material of 40–50% of the whole AS and YTK is generated, including the head, skin, frame, belly flap and viscera. This material is usually discarded even though it is rich in protein and fat. The aim of this study was to characterise the composition of these wastes for their potential applications. The contents of protein and fat in these wastes are 10–20% and 20–30%, respectively. Profiles of amino acids, fatty acids and minerals showed they are good sources of essential amino acids (20–30% of total amino acids), omega‐3 fatty acids (about 20% of total fatty acids) and various elements. For example, AS viscera is high in zinc (740 mg kg−1). Molecular weight distribution of the protein was mainly between 25 and 250 kDa. The potential commercial applications of these wastes are discussed on the basis of these analyses.