Culture-independent analysis of the bacterial community shifts in a macroalgal disease

Throughout their evolution, marine sessile eukaryotes have formed intimate relationships with microorganisms that are fundamental for their functioning. Delisea pulchra is a temperate red macroalga that is affected by a bleaching disease that increase in frequency during summer, when seawater temperature rises and the algal’s chemical defenses are reduced. The role of bacteria in the disease has been implied by difference in the microbial community composition between healthy and bleached algae and by two bacterial strains that can cause bleaching in vitro. In the present thesis, deep-sequencing of the 16S rRNA gene detected operational taxonomic units (OTUs) matching with 100% identity and coverage to both in vitro pathogens in two natural disease events. The OTU analysis further revealed that members of the families Rhodobacteraceae and Flavobacteraceae strongly contribute to the difference in microbial communities between healthy and diseased algae and therefore these groups have been postulated to contain potential pathogens and/or scavengers. The differences in microbial communities of two more disease events were analysed through metagenomic sequencing. Reconstruction of 16S rRNA gene sequences revealed a large variability of the OTUs enriched in bleached algae between bleaching events and individual algae. A comparison of the functional gene profiles revealed statistically significant differences and, in contrast to the high OTU variability, a consistent set of function that was enriched in bleached samples. Genome reconstruction showed that no single, “bleaching-enriched” genome possesses most of the functions enriched in bleached algae. These observations are consistent with a model in which disease is caused by a polymicrobial consortium of opportunistic pathogens. Experiments in a flow-through aquarium showed that a temperature increase to the highest levels observed in the field produced no consistent outcome on the frequency of bleaching, indicating that temperature alone is not a major driver of the disease. These experiments also revealed that the aquarium conditions can generate significant changes in the microbial communities associated with D. pulchra, which is consistent with the notion of an adaptive response by the algal holobiont. Altogether, this thesis contributes to our understanding of the role that bacteria play in marine diseases.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2015

Author dc:creator

• Zozaya Valdes, Enrique

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/18866

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/55767