Rapid isolation of culturable microalgae from a tropical shallow lake system

Microalgae diversity is constantly being studied and explored for biotechnological uses. The shallow lake system of Lençois Maranhenses (SLLM) is a unique coastal ecosystem in northeast Brazil found interspersed in a field of sand dunes. Organisms in these tropical lakes are constantly exposed to high temperatures and solar irradiance. Yet, little is known about the diversity of culturable microalgae in this aquatic ecosystem. This study reports the use of flow cytometry with fluorescence-activated cell sorting (FACS) to isolate single microalgae cells/coenobia from five lakes in SLLM, accessing the efficiency of this isolation technique with two types of culture media. To retrieve the highest diversity of culturable microalgae, planktonic, benthic, and epiphytic samples were collected and processed by FACS. The diversity of microalgae in natural lake communities was described by morphology-based taxonomy. Isolates of the most abundant phylum established in cultures (Chlorophyta) were characterized by gene sequencing (18S rDNA). A total of 3072 microalgal cells/coenobia were sorted into 96-well plates. From these, 945 wells presented algal growth (31% success rate). Based on morphological diversity and adaptability to culture conditions, a set of 171 strains were selected to be incorporated in a culture collection. Microalgae present in the lakes belonged to six phyla, with four of them represented in the cultured strains. Our sampling strategy coupled with FACS isolation retrieved a fairly large number and diversity of microalgal strains with minimum isolation effort from a unique coastal environment. The monoclonal cultures established in this study offer new opportunities for basic and applied research on microalgae biotechnology. Graphical abstract ᅟ