[Eoas-seminar] Oceanography Thesis Defense - Kaitlin Dombroski, 11/05/24 at 10:15AM, EOAS 2061

[eoas-seminar at lists.fsu.edu]

Oceanography Seminar

Kaitlin Dombroski
M.S. Biological Oceanography Candidate
Major Professor: Dr. Olivia U. Mason

Time and Date: 10:15 AM on November 5, 2024
Location: EOAS 2061

TITLE:  Dissolved oxygen concentrations influence microbial diversity, abundance, and dominant players in an oxygen minimum zone​

 ABSTRACT: The expansion of global oxygen minimum zones (OMZs) has a profound influence on the resident macrofauna. Less obvious is the influence of low oxygen on the diversity and abundance of planktonic microbes. Given the role that microbes play in regulating marine biogeochemical cycles, changes in community structure are ecologically consequential. Here we analyzed microbial community structure in relationship to oxygen in the northern Benguela Upwelling System (nBUS) OMZ. Analysis of 16S rRNA gene sequence (iTag) data revealed that oxygen was a primary driver influencing microbial community structure and diversity, with the highest diversity observed in the dysoxic samples, and the lowest in the suboxic samples. Differences in diversity were primarily due to changes in community evenness in relationship to oxygen. For example, evenness decreased in suboxic samples due to oscillations in the abundance of microbial groups such as SUP05 in the class Gammaproteobacteria, which significantly increased in abundance as oxygen decreased. Due to the significant relationship between SUP05 and oxygen concentrations, we analyzed all publicly available, medium to high quality genomes of SUP05 and their close relatives from the family Thioglobaceae (217 genomes total). These genomes were from microbes sampled in the nBUS and more broadly in global OMZs. Genome annotation revealed that SUP05 encodes carbon fixation, sulfur oxidation and denitrification. Importantly, few have the genetic machinery to carry out complete denitrification, as most lacked the final enzyme that converts nitrous oxide (N₂O), to nitrogen gas (N₂), suggesting that as OMZs expand in size and severity along with a concomitant increase in SUP05 abundances, this group may be become an important source of nitrous oxide through incomplete denitrification. Together, the data revealed that oxygen is an important regulator of microbial communities and their diversity, and that as OMZs expand and SUP05 abundances increase, their role in biogeochemical cycles will become more important, particularly as a potential source of greenhouse gases.
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