PROTECTIVE EFFECTS OF Pandanus tectorius LEAF EXTRACT AGAINST BIOTIC AND ABIOTIC STRESSORS INGNOTOBIOTIC Artemia TEST SYSTEM

Abstract

This thesis work investigated a more sustainable and environmentally friendly approach to replacing chemical-based alternatives for improving abiotic stress tolerance and preventing shrimp diseases in aquaculture. The efficacy of methanolic Pandanus tectorius leaf extract (PLE) as a natural alternative for increasing shrimp tolerance to lethal abiotic stressors (i.e., temperature at 42°C for 15 min, pH 5.3 for 24 h, and salinity at 100 g/L for 48 h), and Vibrio campbellii (10⁶ cells/mL), the latter of which causes Vibriosis, was examined. Artemia franciscana brine shrimp was used as the model organism in this study because it can be hatched axenically and grown in gnotobiotic systems. These systems provide conditions for precise evaluation of the prophylactic and metaphylactic effects of specific compounds or extracts, and the impact on host-environment or host-microbe interactions. The application of PLE increased Artemia's tolerance to abiotic stresses and Vibrio challenge at the series of doses (1 g/L - 6 g/L) during pretreatment. Tolerance can also be achieved by exposing the Artemia to methanolic PLE during the challenge in continuous exposure at 0.2 g/L. Methanolic PLE was found to be non-toxic to Artemia up to 6 g/L during pretreatment and 1 g/L during continuous exposure. It also increased the expression of genes necessary for maintaining the structural integrity of the exoskeleton against abiotic stresses, and innate immune genes (hsp70, hsp60, hsp90, hmgb1, proPO, and tgase) that protect against Vibrio. The upregulation of heat shock proteins and other immune genes following methanolic PLE exposure, as demonstrated by qPCR and transcriptomic analysis, as well as their potential roles and mechanistic actions in contributing to protection, were discussed. Moreover, it was revealed that methanolic PLE inhibited virulence factors such as enzyme activities (i.e., caseinase, lipase, phospholipase), swimming and swarming motilities, Vibrio colonisation in Artemia, and bacterial growth significantly. This study added to our understanding of the molecular basis of stress responses in shrimp, as well as the potential of methanolic PLE as a stress and bacterial disease control strategy. Further research should focus on optimizing methanolic PLE dosage, application methods, and its long-term effects on Artemia.