Arthurita Venter

A preliminary survey of the diversity of soil algae and cyanoprokaryotes on mafic and ultramafic substrates in South Africa

Despite a large body of work on the serpentine-substrate effect on vascular plants, little work has been undertaken to describe algal communities found on serpentine soils derived from peridotite and other ultramafic rocks. We report a preliminary study describing the occurrence of algae and cyanoprokaryotes on mafic and ultramafic substrates from South Africa. Results suggest that slope and aspect play a key role in species diversity and community composition and, although low pH, nutrients and metal content do not reduce species richness, these edaphic features also influence species composition. Further, typical soil genera such as Leptolyngbya, Microcoleus, Phormidium, Chlamydomonas, Chlorococcum and Hantzschia were found at most sites. Chroococcus sp., Scytonema ocellatum, Nostoc linckia, Chlorotetraedron sp., Hormotilopsis gelatinosa, Klebsormidium flaccidium, Pleurococcus sp. and Tetracystis elliptica were unique to one serpentine site. The preliminary survey provides directions for future research on the serpentine-substrate effect on algal and cyanoprokaryote diversity in South Africa.

Photosynthetic differences between Microcystis aeruginosa and Oscillatoria simplicissima in relation to species succession in the Vaal River, South Africa

In 1991 Oscillatoria simplicissima replaced Microcystis aeruginosa in the Vaal River, South Africa. This study explored the reason for this succession by looking at the photosynthetic performance of these two cyanoprokaryotes at different temperatures, light intensities and N:P ratios. Microcystis aeruginosa showed higher growth rates and chlorophyll a concentrations than O. simplicissima for most treatments, except the N-deficient treatments. It seems that M. aeruginosa can maintain growth under a range of different conditions and can keep forming mass occurrences, but has high light requirements for photosynthesis and maintenance and can tolerate a much higher light intensity without experiencing photo-inhibition. Oscillatoria simplicissima, on the other hand, is able to harvest available light more efficiently at 25 °C and 15 μmol m2 s-1, experiences less damage or loss at antenna level and retains more of its electron transport capabilities than Microcystis, giving it a competitive edge over M. aeruginosa under these environmental conditions.

Biological crusts of serpentine and non-serpentine soils from the Barberton Greenstone Belt of South Africa

Climate and geography can influence biological soil crust (BSC) community composition, but local heterogeneity in variables such as soil characteristics or microclimate gradients can also impact cryptogamic diversity. Heavy metals and nutrient imbalances in serpentine soils are known to influence the distributions of higher plants, but cryptogamic species appear to be more tolerant of substrate. The aim of this study was to compare the cryptogamic composition of serpentine and non-serpentine soils by using integrative taxonomy, which combines morphological and DNA barcoding data, to determine how soil characteristics in combination with rainfall can influence BSC community composition. Samples from serpentine and non-serpentine soils were enumerated and total genomic DNA was isolated from the soil samples. Analyses of the 16S rRNA gene and ITS sequences were done using the quantitative insights into microbial ecology (QIIME) workflow to determine which eukaryotic microorganisms were present in the samples. Sixty genera from the Cyanophyceae (38), Chlorophyceae (10), Bacillariophyceae (6), Eustigmatophyceae (4), Trebouxiophyceae (1) and Xanthophyceae (1) classes were detected with this approach. Results confirm that algae and cyanobacteria are tolerant of most substrates and can even colonize environments with high levels of heavy metal and nutrient imbalances, if moisture is present. Genera such as Acaryochloris, Annamia, Brasilonema, Chrocosphaera, Halomicronema, Planktothricoides, Rubidibacter, and Toxopsis are reported for the first time for South African soil.

Diel fluctuations of phosphatase and nitrate reductase activities in vitro and in situ in the Vaal River (South Africa)

Rivers are dynamic systems that are spatially and temporally subjected to physical and biological variation. Temperature, pH, and concentrations of dissolved oxygen and inorganic nitrogen (N) and phosphorus (P) have been shown to tluctuate between extremes of night and day in the Vaal River in South Africa (PIETERSE & Roos 1992). Microorganisms must be able to respond to environmental changes and rapidly adjust their metabolism to ambient conditions to efficiendy utilise available resources. N and P occur in different forms in the aquatic environment, but only a few are readily available for phytoplanktonic utilisation. Nitrate reductase (NR) and phosphatases are enzymes that transform nitrateand phosphate-containing compounds, respectively, into bioavailable forms. These enzymes are, therefore, an essential part of regeneration mechanisms in nutrient recycling processes. A considerable amount of ecological data currendy exist concerning the variation in environmental variables and nutrient levels in relation to growth responses in aquatic environments. There is, however, still a paucity in our understanding of how environmental variables impact on basic physiological mechanisms. Furthermore, although physiologists have studied differem pathways of algal metabolism, it has not been done with those species common in aquatic environments. Physiological differences between species may lead to a competitive advantage of some species, and may thus pardy explain the development o f mass occurrences o f certain harmful species. During this study, the observations made illustrate the diel variation of phosphatase activities in si tu and the interrelationships between environmental variables and phosphatase activities, as well as the extremes between which both can tluctuate during a diel cycle. Two bloom-forming species, Chlamydomas incerta and Oscillatoria simplicissima, have been used in vitro to investigate the occurrence of an imernally controlled diel cycle in enzyme activity. Materials and methods