Browsing by Author "Dames, Nicole Rebecca"

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    Linking the occurrence of marine yeasts with elemental concentrations in mussels from Saldana Bay and Langebaan Lagoon
    (Stellenbosch : Stellenbosch University, 2015-12) Dames, Nicole Rebecca; Botha, Alfred; Bezuidenhout, Jacques; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Marine mussels are known to form symbioses with bacteria, however, little is known about their interactions with yeasts, especially within polluted environments. The occasional occurrence of pollution, including elevated levels of trace elements, in the Saldanha Bay area situated along the South Western Coast of South Africa, presented an opportunity to discover potential links between the presence of yeasts and elevated trace element levels in mussel tissue. Four sampling sites were selected in and around Saldanha Bay and Langebaan Lagoon, from which mussel and seawater samples were collected over a period of one year. While physical parameters regarding mussel size were noted for each of the mussel samples, culturable yeasts in these and in the seawater were isolated and enumerated on two different media. Yeast isolates were identified using molecular techniques. The mussel samples were also analysed using inductively coupled plasma mass spectrometry (ICP-MS) analysis to determine the trace elemental content of the mussel tissue. Representatives of several yeast genera were isolated from the mussels, namely Candida, Cryptococcus, Debaryomyces, Metschnikowia, Meyerozyma and Yarrowia. However, the most frequently isolated yeast species was Rhodotorula mucilaginosa. A notably higher number of yeast and yeast-like species were isolated from the seawater than from the mussel tissue and we therefore contend that the mussels select specific yeast strains from the seawater for ingestion. The most frequently occurring yeast species in seawater were Cryptococcus magnus, Meyerozyma guilliermondii, Rhodosporidium diobovatum, R. mucilaginosa and Rhodotorula taiwanensis. The mussels grown in mussel farms (Site 1 and 4) were significantly (p ≤ 0.05) larger than those at Site 2 and 3, while no significant difference was observed between sites with regard to trace element levels. It was found that the concentrations of iron (Fe), zinc (Zn) and aluminium (Al) were the highest across all four sites. Subsequent Pearson’s correlation analyses revealed significant positive correlations between mussel mass and the numbers of Candida zeylanoides and Candida takamatsuzukensis in mussel tissue, indicating that these species may be a nutrient source for mussels. In contrast, a significant negative correlation (p > 0.05) was observed between mussel length and R. mucilaginosa colony counts in the mussel tissue, indicating that an association may exist between this yeast and juveniles mussels in the Saldanha Bay area. Further analyses revealed negative correlations between mussel size and some trace element concentrations (i.e. Al, Fe, mercury (Hg) and nickel (Ni)), pointing to a potential toxic effect of these elements on mussel health. Moreover, the numbers of R. mucilaginosa and Metschnikowia bicuspidata as enumerated on at least one of the culture media, showed positive correlations with levels of arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), Fe, Hg, Ni and Zn in the mussel tissue. The results indicated that the yeasts are more prehaps readily taken up by the mussels in the presence of these metallic cations. In conclusion, this pioneering study revealed that a number of different symbioses might exist between marine yeasts and mussels, and that these symbioses may be influenced by elevated trace element levels associated with pollution.