Microfluidic growth chambers with optical tweezers for full spatial single-cell control and analysis of evolving microbes.

Single-cell analysis in microfluidic systems has opened up new possibilities in biotechnological research enabling us to deal with large eukaryotic cells and even small bacteria. In particular, transient investigations in laminar flow or diffusive environments can be performed to unravel single cell behaviour. Up to now, most systems have been limited with respect to precise cell inoculation and sampling methods. Individual cell selection and manipulations have now been made possible by combining laser tweezers with microfluidic cell cultivation environments specifically tailored for micrometre-sized bacteria. Single cells were optically seeded into various micrometre-sized growth sites arranged in parallel. During cultivation, single-cell elongation, morphology and growth rates were derived from single cells and microcolonies of up to 500 cells. Growth of irradiated bacteria was not impaired by minimizing the exposed laser dosage as confirmed by exceptional growth rates. In fact, Escherichia coli exhibited doubling times of less than 20min. For the first time, a filamentous Escherichia coli WT (MG1655) was safely relocated from its growing microcolony by laser manipulations. The cell was transferred to an empty cultivation spot allowing single-cell growth and morphology investigations. Contrary to previous discussions, the filamentous E. coli exhibited normal cell morphology and division after a few generations. This combination of optical tweezers and single-cell analysis in microfluidics adds a new degree of freedom to microbial single-cell analysis.