Biology subjects

Gates, C.

Publications and source records attributed to Gates, C..

4 recordsLinked to original sources

bioRxiv2026

Interactions of Phototropism and Gravitropism in Cyanobacteria

While gene expression in bacteria has been shown to be affected by near-zero or extremely high gravity, a mechanism has not been established to date. In larger organisms, gravity-sensing mechanisms usually rely on a dense body applying directional pressure which can be detected by the cell. Herein we demonstrate a means of observing the effect of gravity on cyanobacteria by differential expression of native pigments in response to both gravity and light. We observe that in the cyanobacterium Synechococcus sp. PCC 7002, the distribution of pigmentation within the cell, and across cell colonies, is regulated by combined directional sensing of incoming light, adhesion to a surface via extracellular matrix, and applied external force, including the normal force of gravity applied to the cell. Cells grown on a substrate orient their thylakoids on the cell faces proximal and distal to the substrate and locate both chlorophyll and phycobilins in both of these membrane regions; phycobilins are primarily targeted to the membrane region nearest to the light source, while chlorophyll is preferentially expressed in the region opposite the overall external force applied to the cell. The mechanism for distribution of pigments appears to be regulated by presence of polyphosphate bodies within the cell, and removal of polyphosphate negates the cells ability to sense external forces. Furthermore, colonial morphology is affected by application of force, with cells responding to the secretions of other cells along a gradient along the expected response to shading. These results represent a critical step toward understanding basal phototrophic regulatory mechanisms of light use and demonstrate the first known intracellular directional gravity response mechanism in a prokaryote. Statement of SignificanceTo date, no directionally sensitive gravity response mechanism has been observed in any prokaryote. We demonstrate the first evidence of a directional response to external force in a cyanobacterium. This pigment distribution force-directed response interacts with the conventional response to directional light. Furthermore, the cells appear to be able to respond to the presence of other cells above them via intercellular signaling which is not simply due to shading by light.

biophysics↗

bioRxiv2025

Adaptation of the Chlorella photosynthetic electron transport chain to environmental light conditions

In photosynthetic organisms, the process of photosystem II-cyclic electron flow (PSII-CEF) protects against degradation of the active D1 protein subunit of photosystem II in high light environments. By comparing the photophysiology of the extreme-light (2000 {micro}Ein/m2/s) desert alga Chlorella ohadii to the low-light (20 {micro}Ein/m2/s) aquatic alga Chlorella sp. NIES 642, we can monitor how natural adaptations resulting in differing levels of PSII-CEF affect the photosynthetic electron transport chain. Modeling of chlorophyll fast repetition rate fluorometry shows distinct backward transitions of the Kok cycle in C. ohadii, which are absent in NIES 642. Increase in PSII-CEF also has a positive effect on the occurrence of miss parameters in the water oxidizing complex. Fluorescent Q A- reoxidation kinetics detail that the majority of reaction centers in C. ohadii are performing electron transfer to oxidized QB under saturating light conditions. A combination of kinetic observations excludes plastocyanin as a potential external electron carrier in the mechanistic path of PSII-CEF and suggests that photosystem I-cyclic electron flow works in tandem with PSII-CEF. The combination of these two alternative flow mechanisms expedite electron transfer downstream of PSII and optimize ATP production, respectively. Utilizing 77K spectrofluorometry, congruent photosystem stoichiometry is found between both Chlorella species, despite a 100-fold growth light intensity difference. Electrochromic shift measurements show that C. ohadii has diminished changes to both trans-membrane potential and {Delta}pH during operation of photosynthesis compared to NIES 642, and that excess addition of N,N-dicyclohexylcarbodiimide to Chlorella cells has an inhibitory effect on the photosynthetic electron transport chain.

biochemistry↗

bioRxiv2022

Kinetics and targeting of Vipp1 aggregation in cyanobacteria

The kinetics of regulation of vesicle-inducing protein in plastids (Vipp1), an essential protein in all oxygenic phototrophs, are not completely understood. Vipp1 is responsible for both membrane maintenance and damage repair processes, aggregating at sites of damage (proton leakage) or physical strain (responding to presence of anionic lipids). Herein we spatiotemporally resolve exchange between inactive cytoplasmic Vipp1 and these two functionalities. We demonstrate that Vipp1 can be aggregated to a specific site in the thylakoid membrane by laser damage, but this behavior appears to be mediated by a rapidly resolved secondary process, as cytoplasmic Vipp1 is rendered unresponsive to nearby damage on a time scale three orders of magnitude faster than the aggregation process itself. One Sentence SummaryVipp1 aggregation to points on the thylakoid is induced in response to specific damage and repair kinetics are observed.

biochemistry↗

bioRxiv2020

Proximity-based proteomics reveals the thylakoid lumen proteome in the cyanobacterium Synechococcus sp. PCC 7002

Cyanobacteria possess unique intracellular organization. Many proteomic studies have examined different features of cyanobacteria to learn about the structure-function relationships between the intracellular structures of cyanobacteria and their roles in cells. While these studies have made great progress in understanding cyanobacterial physiology, the previous fractionation methods used to purify cellular structures have limitations; specifically, certain regions of cells cannot be purified with existing fractionation methods. Proximity-based proteomics techniques were developed to overcome the limitations of biochemical fractionation for proteomics. Proximity-based proteomics relies on spatiotemporal protein labeling followed by mass spectrometry of the labeled proteins to determine the proteome of the region of interest. We have performed proximity-based proteomics in the cyanobacterium Synechococcus sp. PCC 7002 with the APEX2 enzyme, an engineered ascorbate peroxidase. We determined the proteome of the thylakoid lumen, a region of the cell that has remained challenging to study with existing methods, using a PsbU-APEX2 gene fusion. This study demonstrates the power of APEX2 as a tool to study the cell biology of intracellular features of cyanobacteria with enhanced spatiotemporal resolution.

biochemistry↗