Methods to quantify biological contaminants in microalgae cultures

Microalgae cultivation processes are becoming increasingly used for food and feed production and for wastewaters treatment. Large part of laboratory experiments and industrial processes are carried out with microalgae cultivated in non-aseptic environments containing biological contaminants as bacteria, fungi, viruses and grazers. Such contaminants can significantly influence microalgae growth through interactions such as competition, parasitism, predation and mutualism. Accurate and selective quantification of contaminants and microalgae in terms of cell and biomass concentration and of elemental composition is fundamental to understand how and how much such interactions affect microalgae growth and the quality of the produced biomass. In this work a review is made about the main analytical methods that have been employed, and that might be potentially used in the future, to quantify microalgae and their biological contaminants in heterogeneous samples. Large part of data available about biological contaminants in microalgae cultures come from cell concentration analysis or from qualitative methods. Bacteria and grazers have been the mostly investigated contaminants, while less attention has been given to viruses and fungi. Flow cytometry and DNA analysis are two of the most powerful and promising techniques for cell concentration measurement, however relevant work is still required for protocols optimization, in particular to attain quantitative and reproducible methods. Biomass concentration and elemental composition of contaminants inside microalgae cultures has been scarcely investigated. For this aim, different innovative techniques for single cell mass and elemental composition analysis have been described, focusing on their potential application for microalgae samples.