In the mesophilic cyanobacterium Synechococcus elongatus PCC 7942, iron starvation induces the expression of a number of proteins, including IdiA and IsiA. Whereas IdiA protects photosystem (PS) II under mild iron limitation against oxidative stress in a yet unknown way, prolonged iron starvation leads to the formation of the PS I-IsiA supercomplex. Transcription of idiA is positively regulated by IdiB under iron starvation, and Fur represses transcription of isiAB under iron-sufficient growth conditions. In this report, data are presented suggesting a strong interrelationship between iron homeostasis and oxidative stress in S. elongatus PCC 7942, and showing that transcription of major iron-regulated genes, such as isiA, isiAB, idiA, idiB, mapA, and irpA, is induced by oxidative stress within a few minutes by treatment of cells with hydrogen peroxide or methylviologen. The overall results suggest that isiA/isiAB as well as idiB transcription in response to oxidative stress might be controlled by a transcriptional repressor possibly of the PerR-type. This fact also explains the observed cross-talk between IdiB- and Fur-mediated transcriptional regulation of gene expression and for the role of H(2)O(2) as a superior trigger coordinating expression of iron-regulated genes under iron starvation and oxidative stress. Measuring 77 K chlorophyll a fluorescence, it is shown that hydrogen peroxide treatment causes a transient short-term modification of PS II and PS I most likely leading to increased cyclic electron transport around PS I. In this context, the intriguing observation was made that idiB is transcribed as part of an operon together with a gene encoding a potential [2Fe-2S]-protein. This protein has similarity to [Fe-S]-proteins involved in the electron transport activity of the NDH I complex in eubacteria. Since the NDH I complex is involved in cyclic electron transport activity around PS I in cyanobacteria and both adaptation to iron starvation and adaptation to oxidative stress lead to an enhanced cyclic electron transport activity around PS I, this potential [Fe-S]-protein might participate in the overall adaptational response to iron starvation and/or oxidative stress in Synechococcus.

The land snailEobania vermiculatais an important crop pest causing considerable damage in agriculture. The aim of the present work is to evaluate the possibilities of using silver nanoparticles (AgNPs) to control the land snail. The AgNPs have been synthesized biologically using white radish (Raphanus sativusvar.aegyptiacus). The biosynthesis was regularly monitored by UV-Vis spectroscopy. X-ray diffraction spectra revealed peaks of crystalline nature of AgNPs and the transmission electron micrographs further confirmed the size of the synthesized nanoparticles ranging from 6 to 38 nm. The exposure of the snails and soil matrix to AgNPs in a laboratory experiment reduced the activity and the viability of the land snail (20% of AgNPs treated snails died) as well as the frequency of fungal population in the surrounding soil. Moreover histology and ultrastructure alterations have been found in both kidney and the digestive gland of AgNPs treated land snails. The synergistic effect of synthesized AgNPs as antifungal was evaluated and clearly revealed that AgNPs can be effectively used against various plant pathogenic fungi. The present study results may open a new avenue to use the snail as bioindicator organism of environmental pollution.

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