Effects and mechanism of riboflavin on the growth of Alcaligenes faecalis under bias conditions.

Some microorganisms can utilize photoelectrons and electrode electrons. Exogenous electrons generate enough energy for growth, and electron shuttles may accelerate this process. This research data supported photoelectron-responsive microorganism Alcaligenes faecalis was effected by the growth metabolism due to bias and electron shuttle riboflavin (RF) with an adaptive screening voltage under oligotrophic conditions. A slight change was observed in the redox property of RF. RF played the role of an electron shuttle. Microbial extracellular metabolites could bind additional nicotinamide adenine dinucleotide (NADH) species with RF. The intracellular protein content in the group of RF-Bias was 1.94, 1.93 and 4.02 times higher than those in the RF, bias and control groups, respectively, while the corresponding intracellular contents of humus were 1.10, 0.93 and 1.42 times higher. The content of CoA in RF-Bias, RF and bias increased to 116.0%, 108.5% and 103.8%, respectively. The organic acids of the RF-Bias group in the Krebs cycle are more advanced than those of other groups. Overall, in the Krebs cycle, RF and bias facilitated the growth and metabolism of A. faecalis. Finally, a mechanism was proposed, showing that the electron transfer chain and the Krebs cycle are stimulated by RF and bias.

Effects of riboflavin and AQS as electron shuttles on U(vi) reduction and precipitation by Shewanella putrefaciens.

Understanding the mechanisms for electron shuttles (ESs) in microbial extracellular electron transfer (EET) is important in biogeochemical cycles, bioremediation applications, as well as bioenergy strategies. In this work, we adapted electrochemical techniques to probe electrochemically active and redox-active Shewanella putrefaciens. This approach detected flavins and humic-like substances of Shewanella putrefaciens, which were involved in electron transfer to the electrode. A combination of three-dimensional excitation-emission (EEM) florescence spectroscopy methods identified a mixture of riboflavin and humic-like substances in supernatants during sustained incubations. The reductive behaviour of U(vi) by Shewanella putrefaciens in the presence of riboflavin (RF) and anthraquinone-2-sulfonate (AQS) was also investigated in this study. The results indicated that RF and AQS significantly accelerated electron transfer from cells to U(vi), thus enhancing reductive U(vi). The precipitate was further evidenced by SEM, FTIR, XPS and XRD, which demonstrated that chernikovite [H2(UO2)2(PO4)2·8H2O] became the main product on the cell surface of S. putrefaciens. In a contrast, U(iv) mainly existed amorphously on the cell surface of S. putrefaciens with added RF and AQS. This work has significant implications in elucidating RF and AQS as electron shuttles that are efficient in reduction of uranium in geological environments.

Programmed gradient descent biosorption of strontium ions by Saccaromyces cerevisiae and ashing analysis: A decrement solution for nuclide and heavy metal disposal.

One of the waste disposal principles is decrement. The programmed gradient descent biosorption of strontium ions by Saccaromyces cerevisiae regarding bioremoval and ashing process for decrement were studied in present research. The results indicated that S. cerevisiae cells showed valid biosorption for strontium ions with greater than 90% bioremoval efficiency for high concentration strontium ions under batch culture conditions. The S. cerevisiae cells bioaccumulated approximately 10% of strontium ions in the cytoplasm besides adsorbing 90% strontium ions on cell wall. The programmed gradient descent biosorption presented good performance with a nearly 100% bioremoval ratio for low concentration strontium ions after 3 cycles. The ashing process resulted in a huge volume and weight reduction ratio as well as enrichment for strontium in the ash. XRD results showed that SrSO4 existed in ash. Simulated experiments proved that sulfate could adjust the precipitation of strontium ions. Finally, we proposed a technological flow process that combined the programmed gradient descent biosorption and ashing, which could yield great decrement and allow the supernatant to meet discharge standard. This technological flow process may be beneficial for nuclides and heavy metal disposal treatment in many fields.

Biosorption of strontium from simulated nuclear wastewater by Scenedesmus spinosus under culture conditions: adsorption and bioaccumulation processes and models.

Algae biosorption is an ideal wastewater treatment method when coupled with algae growth and biosorption. The adsorption and bioaccumulation of strontium from simulated nuclear wastewater by Scenedesmus spinosus were investigated in this research. One hundred mL of cultured S. spinosus cells with a dry weight of 1.0 mg in simulated nuclear wastewater were used to analyze the effects on S. spinosus cell growth as well as the adsorption and bioaccumulation characters under conditions of 25 ± 1 °C with approximately 3,000 lux illumination. The results showed that S. spinosus had a highly selective biosorption capacity for strontium, with a maximum bioremoval ratio of 76%. The adsorbed strontium ion on cell walls was approximately 90% of the total adsorbed amount; the bioaccumulation in the cytoplasm varied by approximately 10%. The adsorption quantity could be described with an equilibrium isotherm. The pseudo-second-order kinetic model suggested that adsorption was the rate-limiting step of the biosorption process. A new bioaccumulation model with three parameters was proposed and could give a good fit with the experiment data. The results suggested that S. spinosus may be a potential biosorbent for the treatment of nuclear wastewater in culture conditions.