Microgravity

Real-time, In Situ Fluorescence And Optical Density Measurements Of Liquid Cultures In Simulated Microgravity

By Keith Cowing

Status Report

biorxiv.org

March 30, 2026

Filed under biochemistry, biophysics, biorxiv.org, Cell Spinpod, Escherichia coli, genomics, Gravitational biology, ISS, microbiology, Microgravity, Saccharomyces cerevisiae, Spectroscopy

Real-time, In Situ Fluorescence And Optical Density Measurements Of Liquid Cultures In Simulated Microgravity — A) A close-up, exploded view of the spinpod optical system and diagram of operations. To take fluorescence measurements, excitation light first passes through a bidirectional optical probe from the LED light source to illuminate liquid cultures encased in a spinpod. Fluorescence emission then returns through the optical probe to the spectrometer for measurement, through a longpass filter that reduces signal from the excitation wavelength. To take optical density measurements, a red LED mounted toward the optical probe but on the opposite side of the spinpod illuminates the spinpod (“OD illumination hardware”). This light passes through the spinpod and to the spectrometer without filtering. The spinpod is housed in two joined Carrier Extenders with additional Carrier Extenders placed inline as spacers. B) Photograph of the system diagrammed in panel A; optical probe is in front. Tape has been applied to the outside of carrier extenders to shield the optical path from external light. C) and D) Rear and front close-up views, respectively, of the OD illumination hardware. — biorxiv.org

As human space exploration expands to the Moon, Mars, and beyond, there is a growing need to study the effects of altered gravity on the microbial systems that we will bring with us for life support.

Because spaceflight experiment opportunities are rare and resource-intensive, most space biology experiments are conducted using ground-based simulators. The most common microgravity simulator for microbial experiments, the rotating wall vessel, can approximate the low-shear and low-turbulence conditions that characterize microgravity.

However, current designs do not allow for real-time measurement of growth or metabolic activity during rotation: experiments require destructive sampling or disruption of the microgravity simulation conditions.

Here, we describe the development of an in situ spectroscopy system compatible with the Cell Spinpod rotating wall vessel, which enables measurement of both optical absorbance and fluorescence with high temporal resolution, producing growth curves similar to those from an off-the-shelf plate reader. These results are validated using two common microbial hosts: Escherichia coli and Saccharomyces cerevisiae.

The Spinpod Optical System has the potential to diversify the types of microbiology experiments possible in simulated microgravity, allowing the measurement of not only growth curve parameters but also metabolic activity, gene expression, or community dynamics. It thus has the potential to improve the quality of experiments seeking to characterize microbial responses to spaceflight conditions.

Real-time, in situ fluorescence and optical density measurements of liquid cultures in simulated microgravity, biorxiv.org (open access)

Astrobiology, Tricorder,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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