2018_EJRNL_PP_JOCELYN_DUNSTAN_1.pdf
Terbatas  Ratnasari
» Gedung UPT Perpustakaan
Terbatas  Ratnasari
» Gedung UPT Perpustakaan
We report a novel form of convection in suspensions of the bioluminescent marine bacterium
Photobacterium phosphoreum. Suspensions of these bacteria placed in a chamber
open to the air create persistent luminescent plumes most easily visible when observed
in the dark. These flows are strikingly similar to the classical bioconvection pattern
of aerotactic swimming bacteria, which create an unstable stratification by swimming
upwards to an air-water interface, but they are a puzzle since the strain of P. phosphoreum
used does not express flagella and therefore cannot swim. When microspheres were used
instead of bacteria, similar flow patterns were observed, suggesting that the convective
motion was not driven by bacteria but instead by the accumulation of salt at the airwater
interface due to evaporation of the culture medium. Even at room temperature and
humidity, and physiologically relevant salt concentrations, the water evaporation was found
to be sufficient to drive convection patterns. To prove this hypothesis, experiments were
complemented with a mathematical model that aimed to understand the mechanism of
plume formation and the role of salt in triggering the instability. The simplified system
of evaporating salty water was first studied using linear stability analysis, and then with
finite element simulations. A comparison between these three approaches is presented.
While evaporation-driven convection has not been discussed extensively in the context of
biological systems, these results suggest that the phenomenon may be broadly relevant,
particularly in those systems involving microorganisms of limited motility.