Growth and anatoxin-a production of Microcoleus (Cyanobacteria) strains from streams in California, USA

• Four toxic and two non-toxic monoclonal strains of cyanobacterium Microcoleus were isolated from streams in California and grown in batch culture for 49 days. • The four toxic strains were molecularly identified as Microcoleus anatoxicus , which expands its known distribution throughout coastal and inland watersheds in northern California. • Maximum anatoxin-a and dihydroanatoxin production occurred during the exponential growth phase. • Maximum toxin production in more toxic strains peaked 6-13 days later than less toxic strains, with a persistently higher fraction of extracellular toxins. • Peak toxin concentrations corresponded with reduced growth rates for all M. anatoxicus strains and were followed by quick recovery of cell division. • More toxic strains achieved faster maximum growth rates than the less toxic and non-toxic strains under luxurious nutrient culture conditions. • Significant intraspecific variation in toxin and growth rate responses of M. anatoxicus strains from wide geographical range may represent challenges for harmful algal blooms mitigation. Benthic cyanobacterial proliferations are an emerging concern globally due to their potential for toxin production and subsequent negative environmental and health impacts. Microcoleus is a common mat-forming genus reported to produce potent neurotoxin, anatoxin-a, ingestion of which has been associated with animal mortalities. Six different unialgal monoclonal strains of Microcoleus were isolated from streams in California and grown in batch culture for 49 days. The four toxic strains were identified using a polyphasic approach as belonging to the species Microcoleus anatoxicus , which expands its known distribution throughout the Klamath River and Rock Creek watersheds in northern California. The non-toxic strains from the Eel River belonged to Microcoleus sp. 1. Maximum toxin production occurred during the exponential growth phase, and peaked 6-13 days later in more toxic strains, with a persistently higher fraction of extracellular toxins compared to less toxic strains, which had maximum toxin concentrations at day 13. The proposed mechanism of toxin release into culture medium was through damage to the cell walls of unhealthy filaments. Peak toxin production was energetically expensive for all M. anatoxicus strains, evidenced by reduced specific growth rates at the time of peak toxin production, followed by quick recovery of cell division. Despite this, more toxic strains achieved faster maximum growth rates than the less toxic and non-toxic strains under luxurious nutrient culture conditions. Differential toxin and growth rate responses of M. anatoxicus strains from wide geographical ranges under the same laboratory-controlled conditions suggest high intraspecific variation, which may represent challenges for harmful algal blooms mitigation. More toxic strains have the potential to proliferate and consistently release extracellular anatoxins into the environment. This study provides a baseline to understanding the growth and toxin kinetics of two commonly occurring Microcoleus species in northern California which may help benthic harmful cyanobacteria management.