Physical properties and heavy metal uptake of encapsulated Escherichia coli expressing a metal binding gene (NCP)

Abstract

A recombinant Escherichia coli expressing the Neurospora crassa metallothionein gene (NCP) has previously been shown to remove low levels of Cd and other metals from solution. For further development as a biosorbent, the encapsulation of the NCP is investigated by various matrices. The NCP was encapsulated in alginate, chitosan-alginate or kappa-carrageenan, and its physical properties characterized. Results indicated that encapsulation in alginate resulted in fragile beads, whereas encapsulation in kappa-carrageenan or chitosan-alginate provided more physical and chemical integrity to the beads. Maximal heavy metal removal by cells encapsulated in carrageenan occurred within 3 h, while a gradual increase in removal was observed up to 24 h for cells encapsulated in chitosan-alginate. Metal removal by cells encapsulated in alginate beads was lower than those encapsulated in carrageenan or chitosan-alginate.

Random UV-C mutagenesis ofScheffersomyces(formerlyPichia)stipitisNRRL Y-7124 to improve anaerobic growth on lignocellulosic sugars

“…Following a modified procedure of Bang and Pazirandeh [7], the cell pellet was suspended and fixed in 2.5% glutaraldehyde prepared in 100 mM cacodylate buffer, pH 7.2, for 1 h on ice. To remove any remaining glutaraldehyde, the cells were rinsed with the buffer twice and then with distilled water once, allowing several minutes for each step.…”

“…The cells were dehydrated in successive gradations of ethanol (50, 70, 80 and 100%; 15 min each treatment), mounted on the aluminum stub, and placed in the desiccator to dry overnight or until needed. The samples were subjected to SEM and analysis (Zeiss Supra 40 VP; Carl Zeiss, Jena, Germany) [7]. …”