Obligate Microbial Communities Associated with the Toxic Diatom Pseudo-Nitzschia australis Genome? Implications for Genome Assemblies

Date of Award


Degree Type


Degree Name

Master of Science in Biology



Chief Instructor

Deborah Robertson

Second Reader

John Gibbons

Third Reader

G. Jason Smith


Initial genomic sequencing of the diatom isolate Pseudo-nitzschia australis HAB200 revealed "contamination" of the diatom genome with bacterial sequences. This study examined potential impacts bacterial associations have on the diatom genome assembly. P. australis paired-end MiSeq and PacBio sequences were mapped to different bacterial reference genomes. Surprisingly, P. australis reads mapped to entire bacterial genomes despite three months of treatment with Provasoli's antibiotics prior to DNA isolation. Both MiSeq and PacBio reads mapped to approximately 80% of Rhodobacteraceae bacterium HTCC2083 genome suggesting that this species associates with P. australis. P. australis mapped best to the genomes of bacteria belonging to the Roseobacter clade. Removing mapped bacterial reads slightly reduced the estimated genome size of P.autralis but the genome remains larger than any previously published diatom genome. The presence of entire microbial genomes may reveal an evolved obligate symbiotic relationship between bacteria and diatoms.