Messbauer spectroscopy of cyanobacteria Synechocystis sp. PCC 6803 devoid of photosystem I and containing inactive phycobilisomes

Messbauer spectra of the psaAB mutant of Synechocystis sp. PPC 6803 devoid of photosystem I grown in a ⁵⁷Fe-containing medium were measured. The spectrum is a broadened dublet whose size (about 20%) and parameters (isomeric shift δ = 0.3 mm/s and quadrupole splitting Δ = 0.8 mm/s) suggest the presence of abundant nanoclusters of Fe³⁺ oxides in a superparamagnetic state tightly bound to the membrane. Treatment of cells with EDTA was accompanied by a substantial (tenfold) decrease in the amount of iron nonspecifically bound to the membrane and the appearance of Fe²⁺ localized, probably, inside cells and/or cell membranes. In addition, the spectrum of washed cells exhibited superfine magnetic splitting due to iron oxide clusters greater in size than nanoclusters present in the membrane prior to EDTA treatment.