Influences of iron and humic acid on the growth of the cyanobacterium Anabaena circinalis

Fe may play a key role in the growth of cyanobacteria, which sometimes cause water blooms in eutrophic water environments. Humic acid (HA) is also considered to be a controlling factor in algal growth, as HA is abundant around water basins and has a variety of chemical functions, including Fe-chelation and catalysis. To evaluate the influence of iron depletion and the presence of HA on the growth of Anabaena circinalis, a water bloom-forming cyanobacterium, ex situ cultivation experiments were performed using chemically defined media. The data were analyzed to characterize the effects of Fe and HA on cell growth. A Fe concentration of 10−8 to 10−7 M was the threshold for growth of the cyanobacterium. HA may have toxic effects (at [HA] > 0.01 mg C l−1) and may reduce Fe bioavailability (at [HA] ≥ 0.1 mg C l−1), which delays and/or decreases the growth of the cyanobacterium.