Name: Shayna Keller
Date: 08/01/2024
Time (EST/EDT): 11:00 am
Remote Information: email: mees@umd.edu

Committee Chair: Dr. Judith O'Neil
Committee Members: Dr. Judith O'Neil Dr. Jeffrey Cornwell Dr. Jacob Cram

Title: Investigating Microbial Diversity and Ecophysiology of Filamentous
Cyanobacteria on the Susquehanna Flats, Chesapeake Bay

Abstract: The Susquehanna Flats is a biodiverse and resilient submerged
aquatic vegetation (SAV) bed just below the mouth of the Susquehanna River in
the Chesapeake Bay. The Susquehanna River, the largest tributary of the
Chesapeake Bay, discharges more water than all other tributaries in the Bay
combined. This makes the SAV bed at the Susquehanna Flats important for
nutrient removal of the water discharged into the headwaters of the Bay. The
Susquehanna Flats is also a unique part of the oligohaline portion of the
Chesapeake Bay as it is one of the most prolific and diverse SAV beds that make
up ~8% of SAV in the Chesapeake Bay. The SAV bed was devastated by Hurricane
Agnes in 1972 and did not reappear until the early 2000s when an extended dry
period and long-term reductions in nutrient loading facilitated its resurgence.
Since then, it has recovered to be the most abundant and biodiverse SAV bed
within the upper Chesapeake Bay. However, a nitrogen fixing filamentous
cyanobacteria, morphologically identified as Microseira (Lyngbya) wollei (M.
wollei), has seasonally bloomed at the Susquehanna Flats since the early 2000s.
Over the ensuing decade, anecdotal evidence suggested an overall increase of
cyanobacteria on the SAV beds on the Susquehanna Flats, which raised concerns
about the impact of this growth on the resilience of the recovering SAV bed.
Despite the consistent summer blooms, the filamentous cyanobacterial mats and
its microbiome at the Susquehanna Flats has not been molecularly identified and
its characteristics have not been investigated to date. Additionally, new DNA
sequencing technology has become more readily available, and the identification
and taxonomy of the cyanobacteria family Oscillatoriaceae, of which M. wollei
is a part of, has become more refined and organized. Due to this, molecularly
identifying the filamentous cyanobacterial mats and investigating its
microbiome has become much easier with current methods that can provide
detailed taxonomic information that can help implement management strategies.
Using PacBio long-read amplicon sequencing on the 16S genes of and Illumina
short-read amplicon sequencing on the nifH genes of the filamentous
cyanobacteria mats and a newly observed mucilaginous cyanobacteria mat
collected at the Susquehanna Flats, the host organisms and microbial
compositions were revealed. The results indicate that the dominant filamentous
cyanobacterial mat host is M. wollei and these mats contain a complex microbial
community. The host of a newly observed mucilaginous mats was revealed to be a
novel strain of Phormidium sp. To understand the basic nutrient requirements
and preferences of the M. wollei at the Susquehanna Flats, nutrient bioassay
growth and nitrogen fixation experiments were initiated to assess its growth
and nitrogen fixation qualities. Samples received nutrient treatments of
nitrate, phosphate, nitrate + phosphate, and ammonium compared to the growth of
control samples that did not receive nutrient treatments in the summers of 2022
and 2023. The results demonstrated that M. wollei has variable growth rates,
with higher rates in the mid to late part of the summer season, with
significant stimulations with addition of nitrogen and phosphorus. In terms of
nitrogen fixation, rates were higher in the beginning of the season, with
significant stimulation with phosphorus additions. It is likely that lower
rates measured at the end of the season, were due to the increased availability
of regenerated nitrogen within the system. More detailed investigation of the
seasonal nutrient dynamics are warranted to fully understand the dynamics
between these cyanobacterial mats and the SAV beds.