Iron starvation leads to oxidative stress in Anabaena sp. strain PCC 7120

Abstract

We establish here that iron deficiency causes oxidative stress in the cyanobacterium Anabaena sp. strain PCC 7120. Iron starvation leads to a significant increase in reactive oxygen species, whose effect can be abolished by treatment with the antioxidant tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl). Oxidative stress induced by iron starvation could be a common feature of photosynthetic bacteria.

FIG. 1.

Oxidative stress under conditions of iron deficiency in Anabaena sp. strain PCC 7120. (A) ROS generated by Anabaena sp. strain PCC 7120 cells were analyzed after reaction with 2,7-DCFH-DA. The fluorescence intensity was normalized to the optical densities of the samples. Resulting values are presented in arbitrary units. Bars: 1, iron-replete cells; 2, iron-depleted cells; 3, cells treated with methyl viologen. (B) Lipid peroxidation state under oxidative stress induced by iron starvation. Thermoluminescence was measured with cells grown in the presence of iron (black line) or absence of iron (gray line). Experiments were done twice with similar results.

FIG. 2.

Effect of tempol on isiA expression. (A) RT-PCR analysis of isiA, feoB, and rnpB. Total RNAs were isolated from cells grown in the presence of iron (lane 1), in the absence of iron (lane 2), or in absence of iron and supplemented with 10 mM tempol (lane 3). One microgram of RNA was used in each experiment. Samples were collected at the exponential phase of the PCR. All experiments were repeated twice with similar results obtained. (B) Absorption spectra for cell suspensions with iron (+ iron), without iron (− iron), or without iron but in the presence of tempol (− iron + tempol). The gray arrow indicates a shift of the 680-nm chlorophyll a absorption peak.

FIG. 3.

Oxidative stress under conditions of iron deficiency in E. coli. (A) ROS generated by E. coli DH5α cells were analyzed by using the fluorescent probe 2,7-DCFH-DA. The fluorescence intensity was normalized to the optical densities of the samples. Resulting values are presented in arbitrary units. Bars: 1, iron-replete cells; 2, iron-depleted cells; 3, cells treated with H₂O₂. (B) RT-PCR analysis of feoB and rpoA mRNAs. Cells were grown normally (lanes 1 and 3) or under conditions of iron limitation (lanes 2 and 4). One microgram of RNA was used in each experiment. Samples were collected at the exponential phase of the PCR. All RT-PCR experiments were repeated twice, with similar results obtained.