Highlights

• 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 toxin production in more toxic strains occured 6–13 days later than less toxic strains which peaked at day 13 during exponential growth phase.
• 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.