Growth competition between Halobacterium salinarium strain PHH1 and mutants affected in gas vesicle synthesis

Abstract

To investigate the role of the buoyancy provided by gas vesicles in the facultative anaerobe Halobacterium salinarium PHHl, the growth of a gasvacuolate (Gv' ) strain in competition with two gas-vesicle-def ective ( G e mutants was examined. The Gv+ strain synthesized gas vesicles throughout its growth cycle, and floated up to form a thick surface scum during the exponential growth phase in static culture. Mutant GvM produced significantly fewer gas vesicles than the Gv+ strain in corresponding stages of growth, although in late stationary phase a small proportion of cells floated up to the surface of static cultures. Mutant Gvd& had a much lower gas vesicle content in shaken culture and produced negligible amounts of gas vesicles in static culture. The Gv+ and the two G f l strains grew equally well in shaken cultures, but in static cultures, where steep vertical gradients of oxygen concentration were established, Gvdefl was outgrown by the Gv* strain. Gd* outcompeted the Gv+ strain in shallow static cultures, perhaps because Gvdefz carried a smaller protein burden, which offset the benefits of buoyancy. This selection for Gvdefz was lost in deeper static cultures, although it could be restored by aerating static cultures from below. The results support the hypothesis that the role of buoyancy in halobacteria is to maintain cells at the more aerated surface of brine pools.

Regulatory Multidimensionality of Gas Vesicle Biogenesis inHalobacterium salinarumNRC-1

“…We note that Walsby and coworkers [7, 17] have also shown light scattering by intracellular GV in Halobacterium salinarum strains. To quantify the influence of intracellular GV on scattering in Halobacterium salinarum NRC-1, we first isolated and grew a spontaneous and stable gas-vesicle minus (GV − ) mutant of Halobacterium salinarum NRC-1.…”

Halophilic Microorganisms and their Environments

“…In shallow static cultures the mutant won the competition. This was explained by its smaller protein burden, i.e., the wild type wasted much energy to produce gas vesicles that were unnecessary under the conditions employed (Beard et al, 1997). The idea that gas vesicles may also be effective as a shield against harmful UV radiation was not confirmed in laboratory experiments (Simon, 1980).…”

High production of bacteriorhodopsin from wild type Halobacterium salinarum

“…This is in accordance with the findings of previous studies that quantified the mRNA level from the bacteriorhodopsin gene of wild-type H. salinarum under conditions in which oxygen levels were steadily depleted. The bacteriorhodopsin transcript levels increased in response to the steadily-decreasing oxygen level for the first 48 h (Beard et al 1997;Mül-ler and DasSarma 2005;Schmid et al 2007;Shand and Betlach 1991).…”