Can intracellular organelle organization shape microbial motility across scales?

Di Nezio, Francesco and Ghoshal, Arkajyoti and Ong, Irvine and Dhar, Jayabrata and Buetti-Dinh, Antoine and Storelli, Nicola and Tonolla, Mauro and Sengupta, Anupam (2022) Can intracellular organelle organization shape microbial motility across scales? In: 18th International Symposium on Microbial Ecology, 14-19.08.2022, Lausanne.

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Abstract

Anoxygenic phototrophic sulfur bacteria are common inhabitants of water bodies characterized by euxinic conditions. Meromictic lakes, with their permanently stratified waters, are favourable environments to support the growth of these microorganisms. Recently, it has been demonstrated that high concentration of the motile purple sulfur bacterium Chromatium okenii, mediated by positive phototaxis and negative aerotaxis, can lead to enhancement of local fluid density that ultimately triggers convective instabilities known as bioconvection. However, while cellular phenotype and specific gravity have been linked to such instabilities, the role played by intracellular inclusions and their localization has not been investigated yet. This work aims at understanding how the spatio-temporal organization of sulphur globules – transient inclusions formed by sulfur bacteria during photosynthesis - influences the swimming properties of C. okenii over different physiological growth stages. Using precise microfluidic confinements, microscale imaging and quantitative analysis, cell motility, and the growth and distribution of sulphur globules were monitored over ecologically-relevant physiological conditions, such as physical (light) and chemical (oxygen and sulphide) gradients. A data-based mathematical model was developed to elucidate the effect of size and coordinates of sulphur globules on the swimming speed and stability of C. okenii. The results of this work show how sulphur globules organization ultimately enables optimal trade-offs between (positive) phototaxis and (negative) aerotaxis in purple sulphur bacteria , establishing intracellular organelle distribution as a key determinant of microbial migration, thus providing a mechanistic basis for the commonly observed large-scale C. okenii bioconvection under natural settings.

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