Low-temperature motility

Antarctic sea ice bacteria seen swimming at +4C under light microscopy.

Can bacteria swim toward chemicals at low temperature?

Motility (swimming) is an important behavior common to many marine bacteria. It allows bacteria to move around in their environment, using "taxis" (motility in response to a gradient) to discover food sources (chemotaxis), optimal salinities (halotaxis), or a surface to live on (thigmotaxis). Much work has been done characterizing bacterial motility in warmer marine environments, showing robust motility often with characteristic patterns of movement. However, despite the fact that most of the ocean is cold (<5C), we know very little about how temperature impacts bacterial motility.  

 A figure from Showalter and Deming, 2018, showing taxis of the model marine psychrophile  Colwellia psychrerythraea &nbsp;strain 34H across a temperature profile. Interestingly, the organism retains chemotaxic ability beyond its maximum growth temperature (~18C).

A figure from Showalter and Deming, 2018, showing taxis of the model marine psychrophile Colwellia psychrerythraea strain 34H across a temperature profile. Interestingly, the organism retains chemotaxic ability beyond its maximum growth temperature (~18C).

My master's thesis asked fundamental questions about bacterial chemotaxis and halotaxis in low temperatures. What are the temperature limits of bacterial taxis? How might temperature impact movement toward chemicals or salt gradients?

We showed, using a model marine psychrophile, that bacteria are capable of chemotaxis at subzero temperatures (observed down to -8C, a world record for chemotaxis) and also demonstrated halotaxis and chemohalotaxis. Results were published in the journal Environmental Microbiology Reports, available here.

Motility and taxis in natural sea ice

In addition to using traditional methods to investigate the taxis of a model organism in the laboratory, we collaborated with colleagues at Portland State University and Caltech/NASA JPL to investigate motility and taxis of natural sea ice communities. The digital holographic microscope, or DHM, allows us to see motility at near in situ conditions because of its fieldability in extreme environments.

Using sea ice brines taken from Nuuk, Greenland, we found that bacteria swim in sea ice brines at near in situ conditions and demonstrate chemotaxic behavior near these conditions, as well. The results are available in Plos One.