No abstract

A simple photocatalytic hydrogen-evolving system is reported based on intermolecular electron transfer using isolated Photosystem I (PSI) reaction centers as the photoactive element. The system is composed of platinized PSI covalently linked to plastocyanin (PC). Water-soluble sodium ascorbate is the electron donor. PC was attached to PSI by formation of peptide bonds with the cross-linking reagent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride. Compared to the unlinked proteins, cross-linking of PC and PSI resulted in a substantial increase in light-driven reduction of hexachloroplatinate ions (PtCl6 2- + 4e - → Pt↓ + 6Cl-). Hydrogen photoevolution by cross-linked PC−platinized PSI was increased 3-fold both in initial rate and total yield. Analysis of the reaction indicates that covalent linkage of PC to PSI results in a greater rate of total electron throughput from sodium ascorbate to light-activated hydrogen evolution. In addition, although photocatalytic hydrogen-evolving activity was easily demonstrated in the cross-linked system, the native pathway of electron flow yielding enzymatic NADP+ reduction activity was not observed upon addition of the natural PSI electron-accepting system, ferredoxin plus ferredoxin:NADP+ oxidoreductase.

Aim:  The purpose of this study was to analyse the effects of different culture parameters on Gluconacetobacter hansenii (ATCC 10821) to determine which conditions provided optimum cellulose growth. Methods and Results:  Five culture factors were investigated: carbon source, addition of ethanol, inoculation ratio, pH and temperature. jmp Software (SAS, Cary, NC, USA) was used to design this experiment using a fractional factorial design. After 22 days of static culture, the cellulose produced by the bacteria was harvested, purified and dried to compare the cellulose yields. The results were analysed by fitting the data to a first‐order model with two‐factor interactions. Conclusions:  The study confirmed that carbon source, addition of ethanol, and temperature were significant factors in the production of cellulose of this G. hansenii strain. While pH alone does not significantly affect average cellulose production, cellulose yields are affected by pH interaction with the carbon source. Culturing the bacteria on glucose at pH 6·5 produces more cellulose than at pH 5·5, while using mannitol at pH 5·5 produces more cellulose than at pH 6·5. The bacteria produced the most cellulose when cultured on mannitol, at pH 5·5, without ethanol, at 20°C. Inoculation ratio was not found to be a significant factor or involved in any significant two‐factor interaction. Significance and Impact of the Study:  These findings give insight into the conditions necessary to maximize cellulose production from this G. hansenii strain. In addition, this work demonstrates how the fractional factorial design can be used to test a large number of factors using an abbreviated set of experiments. Fitting a statistical model determined the significant factors as well as the significant two‐factor interactions.

It was previously discovered that the unique structure and chemistry of bacterial cellulose (BC) permits the formation of calcium-deficient hydroxyapatite (CdHAP) nanocrystallites under aqueous conditions at ambient pH and temperature.In this study, BC was chemically modified via a limited periodate oxidation reaction to render the composite degradable and thus more suitable for bone regeneration. While native BC does not degrade in mammalian systems, periodate oxidation yields dialdehyde cellulose which breaks down at physiological pH. The composite was characterized by tensile testing, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. X-ray diffraction showed that oxidized BC retains its structure and could biomimetically form CdHAP. Degradation behavior was analyzed by incubating the samples in simulated physiological fluid (pH 7.4) at 37°C under static and dynamic conditions. The oxidized BC and oxidized BCCdHAP composites both lost significant mass after exposure to the simulated physiological environment. Examination of the incubation solutions by UV-Vis spectrophotometric analysis demonstrated that, while native BC released only small amounts of soluble cellulose fragments, oxidized cellulose releases carbonyl containing degradation products as well as soluble cellulose fragments. By entrapping CdHAP in a degradable hydrogel carrier, this composite should elicit bone regeneration then resorb over time to be replaced by new osseous tissue.