Honors College

Document Type

Honors Thesis

Publication Date

Fall 2019


Marine macroalgae host a diverse microbiota. Bacteria are the most prominent group, and relationships between the algae and bacteria are complex and dynamic. The goal of this project was to examine the distribution and ASV diversity of Bacteria associated with Porphyra umbilicalis with special focus on some isolates, including studies of their temperature dependence and consideration of how they may affect Porphyra. Previous studies showed that some bacteria are required for normal algal morphology and growth. Porphyra umbilicalis is an abundant red macroalga found in the intertidal zone and is an important food for invertebrates. Because of its significance in intertidal communities across the North Atlantic rocky shore, it is important to understand its microbial associations.

The biodiversity of the microbiota of P. umbilicalis samples collected from four trans-Atlantic locations in the winter of 2016 were compared using amplicon sequence variants (ASVs) derived following DNA extraction from sequencing of the V4 hypervariable region of the 16S rDNA. Bacteria were isolated from germlings of P. umbilicalis spread on agar plates. PCR of nearly full length 16S rDNA gene sequences identified these bacteria. Temperature optima for growth of six of the 21 isolates were examined. The microbiota of P. umbilicalis differed significantly across all four locations and regional specificity was found on the thallus between bacteria on the holdfast versus blade margin of bacterial communities on the plants. Growth experiments showed variability in the effects of temperature on growth of different isolates.