Research Article: Effects of short-time alkaline pretreatment on growth and photosynthesis efficiency of endemic cyanobacterium Fischerella sp. FS ۱۸.

Alkaline pH is one of the most important problems of our aquatic habitat. We used Stigonematalean native cyanobacterium Fischerella sp. FS ۱۸ as our model strain, andstudied it under different alkaline pHs (۷, ۹ and rarely ۱۱) under two different – short and long- time treatments (۲۴ and ۹۶ hours after inoculation). Spectroscopic results showed that both alkalinity and time affected growth rate, phycobilisome and chlorophyll production. Response surface plot analysis of distribution showed that the pH borders between ۸.۵ to  ۹ would be critical at ۲۴ hours after inoculation reaching to the highest rates of phycobilisomes. Spectrofluorimetric analysis showed that the highest photosystem I/ photosystem II may be seen at ۲۴ hours at pH۹. Photosynthesis- Irradiance curves showed that the highest rate of maximum photosynthesis belonged to pH۹ in the short time treatment (۲۴ hours). Increasing the time (۹۶ hours) decreased the maximum amount of oxygen liberation significantly. Moving from the optimum conditions (even slightly) caused a sharp decline in the amount of alpha. The slope of decline was steep until near neutral and longtime condition.  Decreasing the time, and at the same time increasing alkalinity (alkaline pH) caused higher activity of photosystems especially photosystem I which lead to higher reductant production and cyclic electron flow operation. Distinct borders of pH (۸.۵-۹) at ۲۴ hours caused considerably high growth and matter production. This was naturally true for phycocyanin, phycoerythrin and the other economically important matters.  

Keywords:

Alkalinine pH , Cyanobacteria , Ecophysiology , Fischerella sp. FS ۱۸ , Time , Ultrastructure