A dual compartment cuvette system for correcting scattering in whole-cell absorbance spectroscopy of photosynthetic microorganisms

• Published in: Photosynthesis research 2022-01, Vol.151 (1), p.61-69
• Main Authors: Hervey, John R. D., Bombelli, Paolo, Lea-Smith, David J., Hulme, Alan K., Hulme, Nathan R., Rullay, Atvinder K., Keighley, Robert, Howe, Christopher J.
• Format: Article
• Language: English
• Subjects: Absorbance; Absorption spectroscopy; Algae; Aquatic microorganisms; Biochemistry; Biomedical and Life Sciences; Cell size; Chromophores; Cyanobacteria; Cytology; Life Sciences; Light; Light scattering; Microorganisms; Photons; Photosynthesis; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; Scattering, Radiation; Spectrophotometry; Spectrum Analysis; Sulfur; Sulfur compounds; Technical Communication; Titanium dioxide
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-021-00866-8

Absorption spectroscopy is widely used to determine absorption and transmission spectra of chromophores in solution, in addition to suspensions of particles, including micro-organisms. Light scattering, caused by photons deflected from part or all of the cells or other particles in suspension, results in distortions to the absorption spectra, lost information and poor resolution. A spectrophotometer with an integrating sphere may be used to alleviate this problem. However, these instruments are not universally available in biology laboratories, for reasons such as cost. Here, we describe a novel, rapid, and inexpensive technique that minimises the effect of light scattering when performing whole-cell spectroscopy. This method involves using a custom made dual compartment cuvette containing titanium dioxide in one chamber as a scattering agent. Measurements were conducted of a range of different photosynthetic micro-organisms of varying cell size and morphology, including cyanobacteria, eukaryotic microalgae and a purple non-sulphur bacterium. A concentration of 1 mg ml −1 titanium dioxide, using a spectrophotometer with a slit width of 5 nm, produced spectra for cyanobacteria and microalgae similar (1–4% difference) to those obtained using an integrating sphere. The spectrum > 520 nm was similar to that with an integrating sphere with the purple non-sulphur bacterium. This system produced superior results to those obtained using a recently reported method, the application of the diffusing agent, Scotch™ Magic tape, to the side of the cuvette. The protocol can be completed in an equivalent period of time to standard whole-cell absorbance spectroscopy techniques, and is, in principle, suitable for any dual-beam spectrophotometer.