Life at high temperature observed in vitro upon laser heating of gold nanoparticles

Studying microorganisms at high temperatures is challenging on conventional optical microscopes. Here, the authors introduce the concept of microscale laser heating over the full field of view by using gold nanoparticles as light absorbers, and study thermophile species up to 80 degrees C. Thermophiles are microorganisms that thrive at high temperature. Studying them can provide valuable information on how life has adapted to extreme conditions. However, high temperature conditions are difficult to achieve on conventional optical microscopes. Some home-made solutions have been proposed, all based on local resistive electric heating, but no simple commercial solution exists. In this article, we introduce the concept of microscale laser heating over the field of view of a microscope to achieve high temperature for the study of thermophiles, while maintaining the user environment in soft conditions. Microscale heating with moderate laser intensities is achieved using a substrate covered with gold nanoparticles, as biocompatible, efficient light absorbers. The influences of possible microscale fluid convection, cell confinement and centrifugal thermophoretic motion are discussed. The method is demonstrated with two species: (i) Geobacillus stearothermophilus, a motile thermophilic bacterium thriving around 65 degrees C, which we observed to germinate, grow and swim upon microscale heating and (ii) Sulfolobus shibatae, a hyperthermophilic archaeon living at the optimal temperature of 80 degrees C. This work opens the path toward simple and safe observation of thermophilic microorganisms using current and accessible microscopy tools.

Automated summary

In this article, the authors introduce a method for studying thermophilic microorganisms at high temperatures using microscale laser heating with gold nanoparticles as light absorbers. The method is demonstrated with two species and offers a simple and safe way to observe thermophiles using current microscopy tools.