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. 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. 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.

中文翻译：

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透明聚乙烯醇冷冻凝胶作为光养细菌连续生产生物氢的固定基质。

光养紫色无硫细菌 (PNSB) 因其通过光发酵各种有机废物产生生物氢形式的宝贵清洁能源的能力而受到关注。为了使这些光养生物过程向商业可行性成熟，需要开发合适的固定化材料，以允许从稳定的催化生物质池连续生产，其中能量不会转向生物质积累，并实现最佳的氢气生产速率。在这里，描述了透明聚乙烯醇 (PVA) 冷冻凝胶珠在固定沼泽红假单胞菌以长期生产氢气中的应用。PVA 冷冻凝胶特性的特征和证明非常适合连续光发酵的目的。最后，说明了材料的长期生物相容性分析。添加甘油助溶剂可在通常不透明的 PVA 冷冻凝胶中产生良好的透光性能，特别适合 PNSB 的近红外光要求。材料表征显示出高机械弹性、低底物扩散阻力以及材料和固定过程的高生物相容性。透明冷冻凝胶中的甘油助溶剂通过增强物理相互作用提供了额外的好处，以至于只需要一个单一的冻融循环就可以形成耐用的冷冻凝胶，从而将实用性扩展到光养生物过程之外。相比之下，传统的 PVA 冷冻凝胶需要多个循环，这会损害被困生物的生存能力。间歇式光生物反应器中固定化沼泽红假单胞菌的产氢研究表明，比浮游培养物持续更长的特定产氢速率。连续培养从固定化细菌中产生了至少 67 天的氢气生产，证明了 PVA 冷冻凝胶固定化对于长期光养生物过程的适用性。固定在冷冻凝胶中的成像生物显示出 PVA 冷冻凝胶的整体结构，并在长期固定后显示出一个活的、稳定的、光发酵的群体。透明 PVA 冷冻凝胶作为光养细菌的固定基质提供了理想的特性，并提供了一种低成本的光生物反应器技术，用于进一步将废物中的生物氢作为可持续能源，