Publication Date

2024

Document Type

Dissertation/Thesis

First Advisor

Swingley, Wesley D.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences

Abstract

Photosynthesis is one of the most abundant metabolic systems on Earth, and specifically, oxygenic photosynthesis primed the planet for complex, multicellular life. The hallmark of modern oxygenic photosynthesis is the photopigment chlorophyll a found in nearly all oxygenic phototrophs as their primary photopigment in their photosynthesis pathways. There are also many organisms that tap into a variety of chlorophylls to extend the energetic limits of photosynthesis, which are largely found as accessory pigments. One genus of cyanobacteria, Acaryochloris, has garnered attention for the ability to undergo photosynthesis by harnessing the far-red part of the visible light spectrum using chlorophyll d as their primary light-harvesting pigment instead of chlorophyll a. Since chlorophyll d-containing Acaryochloris organisms follow this novel process of oxygenic photosynthesis that is not fully characterized, the objective of this study was to pinpoint in vitro biochemical approaches at ascertaining chlorophyll d biosynthesis.

The main aims of this research were to establish whether adding greater concentrations of chlorophyll a may be directly converted to chlorophyll d and to understand the biochemical conditions necessary to produce chlorophyll d. To investigate these areas, three strains of Acaryochloris (MBIC 11017, CCMEE 5410, and RCC 1774) were cultured under white and farred light with pure chlorophyll a extract to promote conversion to chlorophyll d. Strains MBIC 11017 and CCMEE 5410 utilize chlorophyll d as the primary photopigment along with trace amounts of chlorophyll a as accessory pigments in their photosystems. Conversely, the more distantly-branching strain RCC 1774 utilizes chlorophyll a as a primary pigment and chlorophyll b as an accessory. Strain RCC 1774 functioned as a control and nearest non-chlorophyll d relative that does not thrive in far-red light conditions but thrives in white light conditions like most other oxygenic phototrophs. All three strains were cultured in a medium containing extracted chlorophyll a under both normal growth conditions as well as in a medium modified to include sulfhydryl groups and proton sources that increase the likelihood of facilitating chlorophyll d synthesis via the chemical environment.

The results indicated that there was modest conversion of chlorophyll a to chlorophyll d in unmodified medium. However, the conversion of chlorophyll a to chlorophyll d in the modified growth medium chemically facilitated greater chlorophyll d synthesis in Acaryochloris strains, and there were hints to potential enzymatic participation, such as the elusive chlorophyll d synthase. The inference of this enzyme stems from the synthesis producing more intermediate pigments such as chlorophyllides. These intermediate pigments are known as key components to the biosynthesis of other chlorophyll molecules from chlorophyll a, which provide support for a combination chemically and enzymatically mediated biosynthesis. Future genomic and transcriptomic analyses will hopefully follow on from the clues found in this investigation to identify key genes in chlorophyll d biosynthesis.

Extent

85 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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