1-naphthalenesulfonic acid and sulfate as sulfur sources for the green ALGA Scenedesmus obliquus

Abstract

The green alga Scenedesmus obliquus was grown in batch cultures either with sulfate or 1-naphthalenesulfonic acid (1-NS) or both compounds as sulfur source. Growth rates, pigment content and elimination rates of the sulfur compounds were dependent on the initial concentrations of the sulfur sources ( K S-value for sulfate = 9.9 μM; K S-value for 1-NS = 46 μM). Threshold concentrations for uptake were 6.3 μM for sulfate and 38.2 μM for 1-NS. When 0.014–0.140 mM of sulfate was added to the medium containing 0.217 mM of 1-NS, the amount of 1-NS eliminated after 5 d was reduced in proportion to the sulfate dosage. The calculated sulfur elimination rates and those obtained using 35S-labeled compounds agreed with one another to a large extent. The carbon of 14C-labeled 1-NS did not accumulate in the biomass. When cultivating Scenedesmus obliquus with sulfate and 1-naphthalenesulfonic acid (1-NS) as sulfur sources in a turbidostat the maximum growth rate of Scenedesmus obliquus wasμ = 0.107h −1with sulfate at a preset biomass concentration of 85 mg dm/1 and a maximal elimination of about 70% was determined at a biomass concentration of 1510 mg dm/l. Growth and elimination rate were reduced when 1-NS was supplied as the sulfur source in the medium. The maximum growth rate was onlyμ = 0.004h −1and 1-NS elimination reached 14%. Additional batch experiments showed that small amounts of sulfate had a great influence on growth and on elimination of 1-NS. Pulse addition of sulfate to a continuous culture with 1-NS as sulfur source increased the growth rate 20 times and the elimination rate of 1-NS 15 times.