Effects of heavy metals on Cyanothece sp. CCY 0110 growth, extracellular polymeric substances (EPS) production, ultrastructure and protein profiles.

The effects of several heavy metals on the growth/survival, EPS production, ultrastructure and protein profiles of the highly efficient extracellular polymeric substances (EPS)-producer cyanobacterium Cyanothece sp. CCY 0110 were evaluated. Our results clearly show that each heavy metal affects the cells in a particular manner, triggering distinctive responses. Concerning chronic exposure, cells were more affected by Cu(2+) followed by Pb(2+), Cd(2+), and Li(+). The presence of metal leads to remarkable ultrastructural changes, mainly at the thylakoid level. The comparison of the proteomes (iTRAQ) allowed to follow the stress responses and to distinguish specific effects related to the time of exposure and/or the concentration of an essential (Cu(2+)) and a non-essential (Cd(2+)) metal. The majority of the proteins identified and with fold changes were associated with photosynthesis, CO2 fixation and carbohydrate metabolism, translation, and nitrogen and amino acid metabolism. Moreover, our results indicate that during chronic exposure to sub-lethal concentrations of Cu(2+), the cells tune down their metabolic rate to invest energy in the activation of detoxification mechanisms, which eventually result in a remarkable recovery. In contrast, the toxic effects of Cd(2+) are cumulative. Unexpectedly, the amount of released polysaccharides (RPS) was not enhanced by the presence of heavy metals. BIOLOGICAL SIGNIFICANCE: This work shows the holistic effects of different heavy metals on the cells of the highly efficient EPS-producer the cyanobacterium Cyanothece sp. CCY 0110. The growth/survival, EPS production, ultrastructure, protein profiles and stress response were evaluated. The knowledge generated by this study will contribute to the implementation of heavy-metal removal systems based on cyanobacteria EPS or their isolated polymers.

Comparative eco-toxicities of nano-ZnO particles under aquatic and aerosol exposure modes.

The antimicrobial activity of ZnO nanoparticles (NPs) was investigated under aquatic and aerosol exposure modes. ZnO NPs in aquatic media aggregated to micrometer-sized particles and did not interact with microorganisms effectively. Hence, the inhibition of microbial growth by nano-ZnO NPs (e.g., Mycobacterium smegmatis and Cyanothece 51142) in aquatic media was mainly attributable to dissolved zinc species. Shewanella oneidensis MR-1 and Escherichia coli were able to produce large amounts of extracellular polymeric substances, and their growth was not inhibited by ZnO NPs in aquatic media, even at high concentrations (>40 mg/L). On the other hand, when ZnO NPs were electrosprayed onto an E. coli biofilm so that NPs could be directly deposited onto the cell surface, the aerosol exposure dramatically reduced cellular viability. For example, an electrospray of ZnO NPs (20 nm) reduced the total number of viable E.coli cells by 57% compared to the control case, in which we electrosprayed only the buffer solution. However, electrospraying large-sized ZnO particles (480 nm) or nonsoluble TiO(2) NPs (20 nm) caused much less lethality to E. coli cells. The above observation implies that the aerosol method of exposing ZnO NPs to biological systems appears to have a much higher antimicrobial activity, and thus may lead to practical applications of employing a novel antimicrobial agent for airborne disease control.