Effects of monosulfuron-ester on metabolic processes of nitrogen-fixing cyanobacteria Anabaena flos-aquae and Anabaena azotica

Abstract Presence of the relatively new sulfonylurea herbicide monosulfuron-ester at 0.03-300 nmol/L affected the growth of two non-target nitrogen-fixing cyanobacteria (Anabaena flos-aquae and Anabaena azotica) and substantially inhibited in vitro Acetolactate synthase activity, with IC50 of 3.3 and 101.3 nmol/L for A. flos-aquae and A. azotica, respectively. Presenting in 30-300 nmol/L, it inhibited protein synthesis of the cyanobacteria with less amino acids produced as its concentration increased. Our findings support the view that monosulfuron-ester toxicity in both nitrogen-fixing cyanobacteria is due to its interference with protein metabolism via inhibition of branch-chain amino acid biosynthesis, and particularly Acetolactate synthase activity.

Iron induced metabolic changes in the diazotrophic cyanobacterium Anabaena PCC 7120.

Iron induced changes in growth, N2-fixation, CO2 fixation and photosynthetic activity were studied in a diazotrophic cyanobacterium Anabaena PCC 7120. Iron at 50 microM concentration supported the maximum growth, heterocyst frequency, CO2 fixation, photosystem I (PS I), photosystem II (PS II) and nitrogenase activities in the organism. Higher concentration of iron inhibited these processes. Chl a and PS II activities were more sensitive to iron than the protein and PS I activity.

Influence of clay minerals on selenium toxicity to algae

In this study, selenite was found to be acutely toxic to the fresh water algae Anabaena constricta and Chlorella ellipsoidea. However, the latter was more tolerant. Severe reduction in chlorophyll a content was significant reaching 65.2%, 61.4% for Anabaena and Chlorella respectively at 30mg L[-1] Se after 24 hrs incubation. The EC50 values were: 138 mg SeL-1, 141 mg Se L[-1] at one day; 120 mg Se L[-1], 126 mg Se L[-1] at 3 days; 91 mg Se L[-1], 100 mg Se L[-1] at 5 days and 67 mg Se L[-1], 70 mg Se L[-1] at 7 days for Anabaena and Chlorella, respectively. Addition of the clay minerals kaolinite and bentonite decreased selenite toxicity considerably, bentonite was more effective. The EC50 values for combined effect of selenium and either kaolinite or bentonite in reducing growth after 7 days incubation were 76,83 mg Se L[-1] for Anabaena and 73, 81 mg Se L[-1] for Chlorella. Phosphorus uptake by Chlorella was enhanced and went parallel with a concomitant elevation in pH values of the medium with increasing selenite concentrations, and observation which was controversely to that exhibited in Anabaena cultures. Acid and alkalize phosphatase activity decreased in both organisms with increasing Se concentrations