Partial characterization of extracellular polysaccharides produced by cyanobacterium Arthrospira platensis

Characterization of alginate-like exopolysaccharides isolated from aerobic granular sludge in pilot-plant

To understand functional gel-forming exopolysaccharides in aerobic granular sludge, alginate-like exopolysaccharides were specifically extracted from aerobic granular sludge cultivated in a pilot plant treating municipal sewage. The exopolysaccharides were identified by the FAO/WHO alginate identification tests, characterized by biochemical assays, gelation with Ca(2+), blocks fractionation, spectroscopic analysis as UV-visible, FT-IR and MALDI-TOF MS, and electrophoresis. The yield of extractable alginate-like exopolysaccharides was reached 160+/-4mg/g (VSS ratio). They resembled seaweed alginate in UV-visible and MALDI-TOF MS spectra, and distinguished from it in the reactions with acid ferric sulfate, phenol-sulfuric acid and Coomassie brilliant blue G250. Characterized by their high percentage of poly guluronic acid blocks (69.07+/-8.95%), the isolated exopolysaccharides were capable to form rigid, non-deformable gels in CaCl(2). They were one of the dominant exopolysaccharides in aerobic granular sludge. We suggest that polymers play a significant role in providing aerobic granular sludge a highly hydrophobic, compact, strong and elastic structure.

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.