Transparent polyvinyl-alcohol cryogel as immobilisation matrix for continuous biohydrogen production by phototrophic bacteria

Abstract

Background Phototrophic purple non-sulfur bacteria (PNSB) have gained attention for their ability to produce a valuable clean energy source in the form biohydrogen via photofermentation of a wide variety of organic wastes. For maturation of these phototrophic bioprocesses towards commercial feasibility, development of suitable immobilisation materials is required to allow continuous production from a stable pool of catalytic biomass in which energy is not diverted towards biomass accumulation, and optimal hydrogen production rates are realised. Here, the application of transparent polyvinyl-alcohol (PVA) cryogel beads to immobilisation of Rhodopseudomonas palustris for long-term hydrogen production is described. PVA cryogel properties are characterised and demonstrated to be well suited to the purpose of continuous photofermentation. Finally, analysis of the long-term biocompatibility of the material is illustrated. Results The addition of glycerol co-solvent induces favourable light transmission properties in normally opaque PVA cryogels, especially well-suited to the near-infrared light requirements of PNSB. Material characterisation showed high mechanical resilience, low resistance to diffusion of substrates and high biocompatibility of the material and immobilisation process. The glycerol co-solvent in transparent cryogels offered additional benefit by reinforcing physical interactions to the extent that only a single freeze–thaw cycle was required to form durable cryogels, extending utility beyond only phototrophic bioprocesses. In contrast, conventional PVA cryogels require multiple cycles which compromise viability of entrapped organisms. Hydrogen production studies of immobilised Rhodopseudomonas palustris in batch photobioreactors showed higher specific hydrogen production rates which continued longer than planktonic cultures. Continuous cultivation yielded hydrogen production for at least 67 days from immobilised bacteria, demonstrating the suitability of PVA cryogel immobilisation for long-term phototrophic bioprocesses. Imaged organisms immobilised in cryogels showed a monolithic structure to PVA cryogels, and demonstrated a living, stable, photofermentative population after long-term immobilisation. Conclusion Transparent PVA cryogels offer ideal properties as an immobilisation matrix for phototrophic bacteria and present a low-cost photobioreactor technology for the further advancement of biohydrogen from waste as a sustainable energy source, as well as development of alternative photo-bioprocesses exploiting the unique capabilities of purple non-sulfur bacteria.

Facile Fabrication of Transparent and Opaque Albumin Methacryloyl Gels with Highly Improved Mechanical Properties and Controlled Pore Structures

“…In contrast, the macroporous structure of BSAMA cryogels ( Figure 3 ) was clearly visible. The opaque cryogels clearly demonstrated macroporosity resulting from phase separation [ 53 ]. The porous morphology and mean pore diameter of 10% BSAMA cryogels from CLSM results were close to those from SEM results.…”

Polymeric Materials Used for Immobilisation of Bacteria for the Bioremediation of Contaminants in Water

“…A production of lactic, fumaric and succinic acids by various microbial cells (filamentous fungi Rhizopusoryzae (F-814, F-1127) and bacteria Actinobacillus succinogenes B-10111) immobilised into PVA cryogels revealed higher yields than non-immobilised cells [50]. The macroporous cryogels revealed enhanced efficacy with various cell types compared to polymeric matrices available at the time such as pAAm, Alg, hydroxymethylmethacrylate (HEMA), humic acid particles cross-linked by triglycidylpropane derivative within gum Arabic, and carrageenan [51][52][53][54]. Currently used carriers can be classified as organic carriers, inorganic carriers, and composite carriers regarding their chemical composition.…”

Investigating and modeling the effect of light intensity on Rhodopseudomonas palustris growth

“…Van Niels medium was used in all experiments. This medium was developed through the adjustment of the Van Niels Yeast Broth (van Niel, 1944) through the addition of glycerol as the main carbon source (du Toit & Pott, 2020). Table 1 provides a summary of the adjusted Van Niels medium along with the concentrations of each component.…”

“…An important, an increasingly researched application is its ability to produce a clean source of energy in the form of hydrogen (du Toit & Pott, 2020; Hallenbeck & Ghosh, 2009; Pott et al, 2013; Ross & Pott, 2020) and biopolymers such as polyhydroxybutyrate (PHB) as an alternative to petroleum‐based plastics (Brown et al, 2020; Z. Li et al, 2016). The bacterial biomass has also been used as an animal feedstock and biofertilizer due to its high protein concentration (Carlozzi & Sacchi, 2001).…”