The Physiological Characteristics of Oscillatoria simplicissima.

Abstract

Oscillatoria simplicissima is a blue-green alga that was first observed in the Vaal River in 1984. It replaced Microcystis aeruginosa and became dominant after an increase in the organic phosphorussupply in the Loch Vaal catchment area to form algal blooms of great intensity. Although this blue-green alga is presumably non-toxic in small concentrations, the magnitude of its blooms causes many problems in the Vaal River during summer seasons. The blooms are responsible for musty odours and colour changes in the water that prevent recreational activities, which have economic implications for the holiday resorts in the area. Little was known about the physiology and growth requirements of 0. simplicissima. Therefore the aim of this study was to isolate this blue-green alga in order to determine its growth requirements and to study its physiological characteristics. The morphological characteristics of 0. simplicissima were also investigated and compared to 0. rubescens in order to determine if they are variants of the same species. Unialgal cultures of 0. simplicissima were isolated from a water sample collected from the Vaal River. Optimum growth and maximum uptake of radioactive carbon of 0. simplicissima occurred at 28 °C and 10 μmol m· 2 s· 1. Temperatures higher than 36 °C and lower than 24 °C and light intensities higher than 20 μmol m· 2 s· 1 and lower than 10 μmol m· 2 s· 1 adversely affected growth of 0. simplicissima in batch cultures. Chlorophyll-a fluorescence results confirmed that high light intensity adversely affects electron transport in photosystem II and therefore photosynthesis. 0. simplicissima grew the best in an alkaline growth medium with 45.16 mg/1 NO 3-N, 8.16 mg/I PO4- P, 7.5 mg/I Mg2 +, 10 mg/1 ca2 +, 5 mg/I carbon with Na2CO3 as C-source, 2 mg/I Fe2 + and citric acid as chelating agent. Nitrate reductase activity of 0. simplicissima grown in continuous light exhibits a circadian rhythm, but alkaline phosphatase does not exhibit any diurnal rhythm. 0. simplicissima and 0. rubescens have morphological characteristic in common such as thylakoids with phycobilisomes, gas vesicles and inclusion bodies. Morphological differences exist such as the colour of the filaments and the arrangements of the thylakoids. Based on the physiological and morphological differences the conclusion can be made that these organisms are different species.