HCNSO Student Theses and Dissertations

Defense Date


Document Type


Degree Name

M.S. Marine Biology

First Advisor

Dr. Jose Lopez

Second Advisor

Dr. Patricia Blackwelder

Third Advisor

Dr. Tamara Frank


The pelagic tunicate, Pyrosoma atlanticum, is known for its brilliant bioluminescence, but the mechanism causing this bioluminescence has not been fully characterized. This study identifies the bacterial bioluminescent symbionts of P. atlanticum collected in the northern Gulf of Mexico using various methods such as electron microscopy, light microscopy, and molecular genetics. The bacteria are localized within a specific pyrosome light organ. Bioluminescent symbiotic bacteria of Vibrionaceae composed >50% of taxa in tunicate samples (n=13), which was shown by utilizing current molecular genetics methodologies. While searching for bacterial lux genes in 2 tunicate samples, we also serendipitously generated a draft tunicate mitochondrial genome which was used for P. atlanticum pyrosome identification. Furthermore, a total of 396K MiSeq16S rRNA reads provided pyrosome microbiome profiles to determine bacterial symbiont taxonomy. After comparing with the Silva rRNA database, a 99% sequence identity matched a Photobacterium sp. R33-like bacterium (referred to as Photobacterium-Pa1) as the most abundant bacteria within P. atlanticum samples. Specifically-designed 16S rRNA V4 probes for fluorescence in situ hybridization (FISH) verified the Photobacterium-Pa1 location around the periphery of each pyrosome luminous organ. Scanning and transmission electron microscopy (SEM, TEM respectively) confirmed a rod-like bacterial presence which also appears intracellular in the light organs. This intracellular bacterial localization may represent a bacteriocyte formation reminiscent of other invertebrates.