Biological contaminant detection in industrial microalgal cultures

• Autor(a) principal: José, Mélissa
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/19579
• topic: Tisochrysis lutea; Phaeodactylum tricornutum; Culturas de microalgas industriais; Contaminantes biológicos; Métodos moleculares

Biological contamination is one of the greatest limitations in the industrial cultivation microalgae, since the productivity is reduced within a few hours upon detection. The determination and quantification of different biological contaminants is a difficult task, and techniques have been developed aiming to control or eliminate them. Molecular approaches are the most specific/sensitive, allowing for their detection at an early stage. Once the contaminant is detected, mitigation strategies involving the manipulation of environmental/abiotic factors, such as the addition of chemical compounds, are used. In this thesis, molecular methods were developed and used to identify harmful biological contaminants in industrial microalgal cultures focusing on eukaryotic taxa. Samples from contaminated cultures of T. lutea and P. tricornutum were taken to extract DNA and sequenced using NGS technology. The data obtained was analysed using bioinformatic and phylogenetic tools to identify the possible contaminants collapsing the cultures. For the contaminated cultures of T. lutea, the most likely candidate causing the culture collapse was the "golden alga" Paraphysomonas (Chrysophyceae). One primer pair was designed and optimized, and the limit of detection (LOD) was tested, corresponding to an LOD = 0.0049% relative abundance. The Paraphysomonas life cycle was studied, and several mitigation strategies were tested. Salinity of 60 ppt and GeO2 at 1 mg/L showed to be promising, with the ability to control the development of this chrysophyte without harming T. lutea. Concerning the contaminated cultures of P. tricornutum, the Heterolobosea contaminant (Excavata) showed to be the main cause of the culture collapse. Three robust primer pairs were designed with promising results under standard PCR conditions. The life cycle of Heterolobosea contaminant was studied, and only one mitigation strategy was tested (pH at 10). However, the treatment did not show the ability to control the development of this heterolobosean contaminant, and no further mitigations were tested.