Photosynthesis and respiration of a diatom biofilm cultured in a new gradient growth chamber

Abstract

A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O-2 diffusion fluxes from concentration profiles of O-2. Profiles of O-2, pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O-2 were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O-2 from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 mu-Einst m-2 s-1 and 2.4 mM HCO-3- was limited by the supply of inorganic carbon. Exposure to light above 360 mu-Einst m-2 s-1 stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O-2. Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O-2. High concentrations of O-2 in the liquid medium decreased the net outflux of O-2 with little effect on the gross photosynthesis. The effects of inorganic carbon and O-2 on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity.