Genetic fingerprints of microalgal culture strains: amplified fragment length polymorphism (AFLP) for investigations below the species level

Abstract

The aim of the present thesis was to analyse microalgal culture strains at the level below species. This was important to improve the abilities of service culture collections of algae to preserve biodiversity more efficiently and to provide their user community with correctly identified and clean organisms. As examples commonly used microalgal strains of great value in applied research were investigated with genetic fngerprints provided by the AFLP (amplified fragment length polymorphism) method. Using AFLP different strains of the same species (Chlorella vulgaris) could be discriminated and a genetic signature was obtained for each isolate. This intra-specific genomic variation may also correspond to differences in physiological/biochemical properties and, therefore, advocates to carefully record which isolate has been used in any experiment or applied research. The method was found sensitive enough to even clearly distinguish between phenotypically different mutants of the same species, Parachlorella kessleri, and their corresponding wildtype strain. Normally, AFLP analyses are not reliable for contaminated organisms, because the resulting fragments cannot be assigned with certainty to the organism in study or to the contamination. However, by comparing banding patterns generated from cultures with differing ratios of algae and contaminating bacteria, it was demonstrated here, that also non-axenic cultures can be investigated with AFLP. In addition, the AFLP technique was found to be well suited to detect viral infections in cultures of microalgae. Cryopreservation has become the method of choice for the long-term preservation of microalgae as it should theoretically guarantee genetically stable cultures over several decades. However, the genetic integrity of microalgae after cryopreservation has not been investigated at the molecular level to date and was assessed here using AFLP.