Emergent functional traits in aquatic microorganisms
Microorganisms are indispensable in holding our ecosystem in balance. Owing to the aquatic nature of their habitats, most microbes are frequently exposed to fluid flow, which at the scale of a single cell, is a complex biophysical interplay between fluid mechanical stimuli and phenotypic traits of a cell. In this talk I will discuss two recent examples that elucidate how external stimuli cross-talk with phenotypic traits, thereby triggering emergent microbial functions. In the first case, we will see how Chromatium okenii, a 10 μm long purple sulphur bacterium, is capable of mixing a meter thick layer of water in the Swiss Alpine lake, Lago di Cadagno. By changing the local fluid density, C. okenii is able to trigger convection rolls, creating a sustained well-mixed layer within the meromictic lake. Using in-situ measurements, laboratory experiments and simulations we found that bio-convection, so far observed mainly under laboratory settings, can induce mixing of nutrients within a stratified natural water body. In the second instance, we will examine how motile phytoplankton – one of the most important photosynthetic organisms in oceans – can rapidly switch morphology in response to turbulence-like cues, and exploit it to diversify their migration strategy. Quantitative imaging on Heterosigma akashiwo, together with a model of cell mechanics, revealed that a minute sub-micron change in the morphology is sufficient to invert the cells’ preferential swimming direction. Interestingly, in both instances, phenotypic traits couple with fluid flow, to elicit important eco-physiological attributes at the scale of microbial populations. I will conclude by highlighting why our ability to quantify biophysical traits, and establishing a link to corresponding biological functions, will be critical in deciphering microbial behaviour, more so during rapidly shifting patterns that we encounter in our environment today.
Host: Hans-Peter Grossart