Nutrient-induced fluorescence transients in diatom-bacteria biofilms suggested the possible application of marine biofilms in monitoring nutrient disturbance

Abstract

The phenomenon of nutrient-induced fluorescence transients (NIFTs) in algae has shown potential in indicating nutrient disturbance in water. However, it has only been reported in green algae with a narrow detection range. Marine biofilms, a type of microorganism aggregate with significant application potential, have been less investigated in relation to their NIFTs phenomenon. In the present study, we conducted a bioassay lasting 36 h to test the utilization of different nutrients by diatom-bacteria marine biofilms through detecting the effective quantum yield [Y(II)]. We found that the biofilms selectively utilized nitrate, ammonium, inorganic and organic phosphate, while not utilizing glycine and urea. Among the nutrients that could be used by the biofilms, only ammonium induced a significant NIFTs phenomenon. We observed a linear relationship between fluorescence changes during the ammonium-induced NIFTs and ammonium concentrations in both nitrogen-limited and phosphorus-limited biofilm cultures. Notably, a final concentration of 500 μM ammonium triggered significant increases in fluorescence compared to lower concentrations. Our study suggests that nutrient-limited marine biofilms have potential to monitor ammonium disturbance in water, with the significant increases in biofilm fluorescence serving as an alarm for ammonium input.