Investigations on the photosynthetic sulfur bacterium Chlorobium phaeobacteroides causing seasonal blooms in Lake Kinneret

Abstract

Between May and December, the annual stratification period in Lake Kinneret, sulfide is formed and accumulates in the hypolimnion. In July–August a large population (up to 10⁶ cells/mL) of green, photosynthetic, sulfur bacteria develops at the boundary of the oxidative and reductive zones of the water column lasting for 3–8 weeks. These bacteria were isolated from the lake and identified as Chlorobium phaeobacteroides. Optimal growth conditions included 160 mg S⁼L⁻¹ and light intensities of 5–0 μEinstein (μE) m⁻²s⁻¹. Glucose and acetate augmented growth when added to the mineral medium. The lowest light intensity which still supported growth was 0.3 μE m⁻²s⁻¹ when acetate was present and 1.0 μE m⁻²s⁻¹ when no organic substrate was present. Under complete darkness, either with or without organic substrate, the bacteria die. Photosynthetic activity was higher when no organic compound was added to the medium. Uptake of acetate was light-dependant.In the lake the photosynthetic activity of the bacteria is low because of the limited light intensity (0.3 μE m⁻²s⁻¹) at the bloom layer. It is suggested that the appearance and the disappearance of the bloom are caused by the influence of the daily internal seiche.