Sulphide Resistance in the Cyanobacterium Microcystis aeruginosa: a Comparative Study of Morphology and Photosynthetic Performance Between the Sulphide-Resistant Mutant and the Wild-Type Strain

摘要

The cyanobacterium Microcystis aeruginosa is a mesophilic freshwater organism, which cannot tolerate sulphide. However, it was possible to isolate a sulphide-resistant (S (r) ) mutant strain that was able to survive in a normally lethal medium sulphide. In order to evaluate the cost of the mutation conferring sulphide resistance in the S (r) strain of M. aeruginosa, the morphology and the photosynthetic performance were compared to that found in the wild-type, sulphide-sensitive (S (s) ) strain. An increase in size and a disrupted morphology was observed in S (r) cells in comparison to the S (s) counterpart. Phycoerythrin and phycocyanin levels were higher in the S (r) than in the S (s) cells, whereas a higher carotenoid content, per unit volume, was found in the S (s) strain. The irradiance-saturated photosynthetic oxygen-production rate (GPR (max)) and the photosynthetic efficiency (measured both by oxygen production and fluorescence, alpha (GPR) and alpha (ETR)) were lower in the S (r) strain than in the wild-type. These results appear to be the result of package effect. On the other hand, the S (r) strain showed higher quantum yield of non-photochemical quenching, especially those regulated mechanisms (estimated throughout q (N) and Y(NPQ)) and a significantly lower slope in the maximum quantum yield of light-adapted samples (F (v) '/F (m) ') compared to the S (s) strain. These findings point to a change in the regulation of the quenching of the transition states (q (T) ) in the S (r) strain which may be generated by a change in the distribution of thylakoidal membranes, which somehow could protect metalloenzymes of the electron transport chain from the lethal effect of sulphide.