Photoadaptation rates of Synechococcus WH7803 cultures at two iron concentrations

The marine cyanobacterium Synechococcus WH7803 adapts to changes in light intensity by changing its photosynthetic physiology. This work is a study of the rate of photoadaptation of Synechococcus WH7803 in laboratory cultures. Cultures were shifted from constant 8 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light to constant 80 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light, from constant 80 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light to constant 8 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light and from different light regimes to a single fluctuating light regime. The response of high iron cultures grown in modified aquil culture medium at 5*10{dollar}sp{lcub}-6{rcub}{dollar}M Fe was compared with the response of low iron cultures grown in modified aquil medium at 1*10{dollar}sp{lcub}-6{rcub}{dollar}M Fe. Cultures were assayed every 2 days for at least 10 days, assaying cell population density by fluorescence microscopy, chlorophyll a by spectrophotometry of acetone extracts, total protein by the bicinchoninic acid method, and photosynthesis vs. irradiance (P vs. I) response by {dollar}rm Hsp{lcub}14{rcub}COsb3sp-{dollar} uptake at 10 light intensities. Iron nutrition did not strongly affect the rate of photoadaptation as determined from the slopes of P vs. I curves as light approaches zero (the parameter called alpha). The rate of chlorophyll a synthesis was the parameter most strongly affected by iron nutrition, slowing in restricted iron medium. Based on alpha per cell, the adaptation time to the shift from constant 8 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light to constant 80 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light was less than 2 days. Based on other culture parameters the time to complete adaptation may be closer to 8 days. Based on alpha per cell, the adaptation time to the shift from constant 80 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light to constant 8 {dollar}rmmu Emsp{lcub}-2{rcub}ssp{lcub}-1{rcub}{dollar} light was on the order of 2 days. Based on other culture parameters the time to complete adaptation may exceed 10 days.