Towards the Development of an Algae-Bacteria Pest Model: Enrichment of Oligoflexales Bacteria in Nannochloropsis oceanica Cultures with Different Starting Microbiomes

In 2018, a novel predatory bacterium named FD111 was identified, which could infect and significantly damage Nannochloropsis sp. in open pond cultures. Further research on this pest was hindered due to difficulties in cultivating it in laboratory conditions, making it tough to study its infection mechanisms and develop strategies for algal crop protection and Integrated Pest Management (IPM). After multiple attempts, a FD111-like bacterium pest was successfully resurrected using both a lab strain and a field-adapted strain of Nannochloropsis oceanica. The algae culture showed signs of deterioration after three days of infection, with a significant decrease in photosynthetic efficiency and bleaching of the culture. With the use of transmission electron microscope, a life cycle for FD111-like bacterium in N. oceanica was proposed, showing infection and reproduction mechanisms akin to earlier findings, albeit with slight differences in morphology. The FD111-like bacterium appeared to have a rod shape and flagella, which differed from the hook shape described in the only existing publication. Metagenomic sequencing identified the presence of three distinct sequences belonging to the Pseudobacteriovorax genus, within Oligoflexales order in the co-culture, suggesting multiple strains of FD111-like bacterium may be present. Future research will aim to obtain an isolate of the FD111 bacterium, gain deeper insights into its infection mechanisms, and develop protective strategies.