Isolation of Squarebop I bacteriorhodopsin from biomass of coastal salterns

Squarebop I bacteriorhodopsin is a light-activated proton pump present in the membranes of the archeon Haloquadratum walsbyi, a square-shaped organism representing 50–60% of microbial population in the crystallizer ponds of the coastal salterns.Here we describe: (1) the operating mode of a bioreactor designed to concentrate the saltern biomass through a microfiltration process based on polyethersulfone hollow fibers; (2) the isolation of Squarebop I bacteriorhodopsin from solubilized biomass by means of a single chromatographic step; (3) tightly bound lipids to the isolated and purified protein as revealed by MALDI-TOF/MS analysis; (4) the photoactivity of Squarebop I bacteriorhodopsin isolated from environmental samples by flash spectroscopy.Yield of the isolation process is 150 μg of Squarebop I bacteriorhodopsin from 1 l of 25-fold concentrated biomass. The possibility of using the concentrated biomass of salterns, as renewable resource for the isolation of functional bacteriorhodopsin and possibly other valuable bioproducts, is briefly discussed.

► Squarebop I isolation from solubilized biomass by one chromatographic step.
► Functional bacteriorhodopsin and lipids extracted at a reasonable yield.
► Microfiltration process designed to concentrate saltern biomass.
► Saltern biomass as source for archaeal retinal-proteins.