Award Date

May 2025

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Committee Member

Nicole Pietrasiak

Second Committee Member

Brian Hedlund

Third Committee Member

Aude Picard

Fourth Committee Member

Elisabeth Hausrath

Number of Pages

127

Abstract

Cyanobacteria are photosynthetic microbes with essential roles in Earth’s ecosystems. The secretion of long–chain polysaccharides, known as exopolysaccharides (EPS), is a key trait facilitating cyanobacterial adaptation to diverse ecosystems. Genomics studies have shown that aquatic cyanobacteria harbor multiple gene copies encoding EPS export proteins, likely conferring a selective advantage in lakes or oceans. In addition, physiological experiments showed that nutrient limitation in aquatic habitats influences EPS production, affecting cyanobacterial fitness. However, whether terrestrial cyanobacteria also harbor multiple EPS-related genes and how nutrient limitation impacts their EPS production is not well understood.In the first chapter of my thesis, we investigated the variability in EPS gene copy numbers in genomes of aquatic and terrestrial cyanobacteria. We were further interested in exploring the factors influencing this variability. Our comparative genomic analysis revealed that soil cyanobacteria harbor more EPS-related gene copies than their freshwater counterparts. Historical horizontal gene transfer and gene loss, rather than gene duplication, may be the main factor of this variation in gene copy number. A high number of EPS-related gene copies might influence EPS structure and length, which may provide a selective advantage in highly dynamic environments such as soils. In the second chapter, we evaluated how phosphorus (P), an essential nutrient, affects the EPS production in soil cyanobacteria. Physiological experiments in the second chapter demonstrated that phosphorus limitation, in the form of a reduction in available phosphate, limits both biomass and total EPS content in soil cyanobacteria cultures. However, the EPS-to-biomass ratio remained consistent. Although the production of EPS is energetically expensive, our findings showed that soil cyanobacteria still produce EPS under P limitation. Suggesting that EPS is an important trait for cyanobacterial survival and might influence biofilm formation under P limitation. While our comparative genomics analysis indicated the presence of multiple EPS-related gene copies in soil cyanobacteria, the functional role of these multiple copies under nutrient limitation remains unclear. Our physiological analysis did not show an increase in EPS production under P limitation, nor did they indicate a complete shutdown of EPS synthesis. Future research should investigate potential structural modifications of EPS under P limitation. These modifications may provide a selective advantage for cyanobacterial survival and therefore impact on soil ecosystem function.

Keywords

comparative genomics; cyanobacteria; exopolysaccharides; phosphorus limitation

Disciplines

Genetics | Medical Physiology | Microbiology | Physiology

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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