Biology subjects

Tay, J. W.

Publications and source records attributed to Tay, J. W..

7 recordsLinked to original sources

bioRxiv2025

Calcite Precipitation by a Nitrogen-Fixing Cyanobacterium

Microbiologically induced calcium carbonate precipitation (MICP) is the process through which the metabolic activity of microorganisms causes the precipitation of calcium carbonate, which can result in solidification of sediment. In cyanobacteria, MICP is thought to occur primarily because cells sequester bicarbonate for the photosynthetic process, thereby lowering the pH of the surrounding media. However, these mechanisms are still poorly understood. Here we show direct evidence of MICP caused by the filamentous cyanobacterium Anabaena. Anabaena differentiates into photosynthetic vegetative cells and nitrogen-fixing heterocysts. Using quantitative microscopy, we show that MICP occurs due to two distinct mechanisms: Firstly, mechanical stress on vegetative cells can cause leakage and/or lysis, releasing sequestered bicarbonate into the environment, resulting in formation of new crystals. Secondly, contact between a heterocyst and a calcite crystal seed appears to cause rapid crystal growth. Our results suggest an evolutionary benefit of contact-mediated precipitation to anchor cyanobacteria growing in tidal regions. By providing greater insight into MICP caused by Anabaena, these results could be used to optimize bio-cement production, thereby enabling a green construction material that could assist with carbon sequestration and reducing the impact of climate change.

microbiology↗

bioRxiv2024

Machine Learning Models for Segmentation and Classification of Cyanobacterial Cells

Timelapse microscopy has recently been employed to study the metabolism and physiology of cyanobacteria at the single-cell level. However, the identification of individual cells in brightfield images remains a significant challenge. Traditional intensity-based segmentation algorithms perform poorly when identifying individual cells in dense colonies due to a lack of contrast between neighboring cells. Here, we describe a newly developed software package called Cypose which uses machine learning (ML) models to solve two specific tasks: segmentation of individual cyanobacterial cells, and classification of cellular phenotypes. The segmentation models are based on the Cellpose framework, while classification is performed using a convolutional neural network named Cyclass. To our knowledge, these are the first developed ML-based models for cyanobacteria segmentation and classification. When compared to other methods, our segmentation models showed improved performance and were able to segment cells with varied morphological phenotypes, as well as differentiate between live and lysed cells. We also found that our models were robust to imaging artifacts, such as dust and cell debris. Additionally, the classification model was able to identify different cellular phenotypes using only images as input. Together, these models improve cell segmentation accuracy and enable high-throughput analysis of dense cyanobacterial colonies and filamentous cyanobacteria.

microbiology↗

bioRxiv2022

Asymmetric survival in single-cell lineages of cyanobacteria in response to photodamage

Summary paragraphOxygenic photosynthesis is driven by the coupled action of the light-dependent pigment protein complexes, photosystem I and II, located within the internal thylakoid membrane system. However, photosystem II is known to be prone to photooxidative damage. Thus, photosynthetic organisms have evolved a repair cycle to continuously replace the damaged proteins in photosystem II. However, it has remained difficult to deconvolute the damage and repair processes using traditional ensemble approaches. Here we demonstrate an automated approach using time-lapse fluorescence microscopy and computational image analysis to study the dynamics and effects of photodamage in single cells at sub-cellular resolution in cyanobacteria. By growing cells in a two-dimensional layer, we avoid shading effects, thereby generating uniform and reproducible growth conditions. Using this platform, we analyzed the growth and physiology of multiple strains simultaneously under defined photoinhibitory conditions stimulated by UV-A light. Our results reveal an asymmetric cellular response to photodamage between sibling cells and the generation of an elusive subcellular structure, here named a photoendosome, derived from the thylakoid which could indicate the presence of a previously unknown photoprotective mechanism. We anticipate these results to be a starting point for further studies to better understand photodamage and repair at the single-cell level.

biochemistry↗

bioRxiv2020

CyAn: A MATLAB toolbox for image and data analysis of cyanobacteria

Studies of photosynthetic cyanobacteria are often carried out by growing the bacteria in large volume cultures. However, this results in an uneven amount of light received by the cells due to cell-cell shading. Fluorescence microscopy solves this issue as cells can be grown in a single layer, eliminating shading issues. However, microscopy brings its own challenge as hundreds of cells are imaged at the same time, making it difficult to analyze the resulting data by hand. Here we present CyAn, a toolbox to process and analyze microscope images of cyanobacteria. The toolbox automates cyanobacteria identification in microscope images, tracks moving and dividing cells, and computes relevant biological data such as growth rates. As proof-of-principle, we demonstrate that wild type and mutants can be grown on the same slide and identified using the software, allowing a much more accurate probe into photosynthetic processes that are often masked due to cellular heterogeneity or those requiring precise light control to prevent cell-cell shading.

microbiology↗

bioRxiv2019

Single Cell Analysis Reveals Multiple Requirements for Zinc in the Mammalian Cell Cycle

Despite recognition of the fundamental role of zinc (Zn2+) for growth and proliferation, mechanisms of how Zn2+ deficiency arrests these processes remain enigmatic. We induced subtle intracellular Zn2+ perturbations and tracked asynchronously cycling cells throughout division using fluorescent reporters, high throughput microscopy, and quantitative analysis. We found that Zn2+ deficiency induces quiescence and Zn2+ resupply stimulates cell-cycle reentry. By monitoring single cells after Zn2+ deprivation, we found that depending on where cells were in the cell cycle, they either went quiescent or entered the cell cycle but stalled in S phase. Stalled cells were defective in DNA synthesis and had increased DNA damage levels, suggesting a role for Zn2+ in maintaining genome integrity. Finally, we found that Zn2+ deficiency-induced quiescence does not require the cell-cycle inhibitor p21. Overall, our study provides new insights into when Zn2+ is required during the mammalian cell cycle and the consequences Zn2+ deficiency.

cell biology↗

bioRxiv2019

Multi-generational analysis and manipulation of chromosomes in a polyploid cyanobacterium

Faithful inheritance of genetic material from one generation to the next is an essential process for all life on earth. Much of what is known about microbial DNA replication and inheritance has been learned from a small number of bacterial species that share many common traits. Whether these pathways are conserved across the great diversity of the microbiome remains unclear. To address this question, we studied chromosome dynamics in a polyploid photosynthetic bacteria using single cell, time-lapse microscopy over multi-generation lineages in conjunction with inducible CRISPR-interference and fluorescent chromosome labeling. With this method we demonstrated the long-term consequences of manipulating parameters such as cell growth, cell division, and DNA replication and segregation on chromosome regulation in a polyploid bacterial species. We find that these bacteria are surprisingly resilient to chromosome disruption resulting in continued cell growth when DNA replication is inhibited and even in the complete absence of chromosomes.

molecular biology↗

bioRxiv2018

Q-FADD: A mechanistic approach for modeling the accumulation of proteins at sites of DNA damage by free diffusion

The repair of DNA damage requires the ordered recruitment of many different proteins that are responsible for signaling and subsequent repair. A powerful tool for studying the orchestrated accumulation of these proteins at damage sites is laser microirradiation in live cells, followed by monitoring of the accumulation of the fluorescently labeled protein in question. Despite the widespread use of this approach, there exists no rigorous method for characterizing this process quantitatively. Here we introduce a free diffusion model that explicitly accounts for the unique topology of individual nuclei and quantitatively describes the accumulation of two test proteins, poly-ADP-ribose polymerases 1 and 2. Application of our model to other proteins will yield novel insights into the timing and mechanism of DNA repair.

biochemistry↗