Simultaneous enumeration of Phaeodactylum tricornutum (MLB292) and bacteria growing in mixed communities

Abstract

Diatoms play a decisive role in global primary production, have a key role in the marine food web, and serve as food for the industrial culture of aquatic animals. In addition, species of diatoms have been chosen as tools for measuring sea water quality and for bioassay procedures. Among them, Phaeodactylum tricornutum (Bohlin) Lewin, 1958, represents a good biological model due to its ease of handling and also to its physiological, genetic and growth characteristics. We investigated the use of the Epifluorescence Microscopy (EPM) to visualize and enumerate P. tricornutum cells and bacteria in cultures containing botfi kinds of microorganisms. The cell suspension was filtered, stained with SYBR Green and analyzed by EPM. P. tricornutum can be enumerated using EPM with comparable accuracy as using a hemocytometer. The same kind of growth curve is obtained with either method. EPM is an advantageous alternative to the classic light microscope counting method; it allows the simultaneous enumeration off! tricornutum and bacteria in a single sample, measuring red autofluorescence and green fluorescence respectively. Moreover, the methodology is suitable for dynamic studies performed to determine the growth dependence between P. tricornutum and bacteria. Another advantage of this technique is that different shapes, sizes and physiological stages of the microbiological communities can be observed.