Towards defining global ecotypes of the toxic cyanobacterium Raphidiopsis raciborskii

Abstract

ABSTRACT Raphidiopsis raciborskii is a harmful bloom-forming cyanobacterium with strains that vary in ecophysiology within and between populations around the world. Understanding the extent of intraspecific diversity of strains is needed to design laboratory experiments that capture the breadth of responses the species has to abiotic and biotic interactions; therefore, choice of strains is a critical consideration for experimental design. In this paper, we identified major ecotypes of 12 R. raciborskii strains from three continents, characterizing their morphology via microscopic cell measurements; physiology via growth rates under nitrogen-replete and -free conditions; and genetic variation, via multiplex randomly amplified polymorphic DNA PCR (i.e., DNA fingerprinting). Euclidean distance plots based on morphological and physiological measurements showed three groupings of strains defined as the major ecotypes. Best groupings were obtained using a selection of both morphological and physiological traits. Ecotype groupings did not correlate with geographic location, implying that understanding the ecology of the species does not require in-depth local knowledge of the strains. This study indicates that general average physiology of the global species could be characterized, indicating the existence of major ecotypes across populations.