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One third of the World's entire food production is lost or wasted every year. Biohydrogen production offers a possibility to re-use this resource; in particular, bread and bakery products wastes, due to their composition (up to 70% of carbohydrates, mostly starch), represent an appropriate source of nutrients for microorganisms. The aim of this work was to convert bread wastes into hydrogen with a sequential system composed of lactic fermentation and photofermentation, with a minimum number of treatments to the substrate. The best results were provided by Lactobacillus amylovorus DSM 20532, followed by photofermentation by Rhodopseudomonas palustris 42OL, supplemented with ferric citrate and magnesium sulfate. The process led to 3.1 mol H 2 mol −1 glucose, among the highest yields obtained on starch containing substrates, with an energy recovery of 54 MJ t −1 dry waste. This study promotes the re-use of energy-containing food wastes for improving circular economy. [ABSTRACT FROM AUTHOR]

The ability of Rhodopseudomonas palustris cells to rapidly acclimate to high light irradiance is an essential issue when cells are grown under sunlight. The aim of this study was to investigate the photo-acclimation process in Rhodopseudomonas palustris 42OL under different culturing conditions: (i) anaerobic (AnG), (ii) aerobic (AG), and (iii) under H 2 -producing (HP) conditions both at low (LL) and high light (HL) irradiances. The results obtained clearly showed that the photosynthetic unit was significantly affected by the light irradiance at which Rp. palustris 42OL was grown. The synthesis of carotenoids was affected by both illumination and culturing conditions. At LL, lycopene was the main carotenoid synthetized under all conditions tested, while at HL under HP conditions, it resulted the predominant carotenoid. Oppositely, under AnG and AG at HL, rhodovibrin was the major carotenoid detected. The increase in light intensity produced a deeper variation in light-harvesting complexes (LHC) ratio. These findings are important for understanding the ecological distribution of PNSB in natural environments, mostly characterized by high light intensities, and for its growth outdoors. [ABSTRACT FROM AUTHOR]

The ability of coping with the damaging effects of high light intensity represents an essential issue when purple non-sulfur bacteria (PNSB) are grown under direct sunlight for photobiological hydrogen production. This study was aimed at investigating whether H 2 photo-evolution could represent, for Rhodopseudomonas palustris 42OL, a safety valve to dissipate an excess of reducing power generated under high light intensities. The physiological status of this strain was assessed under anaerobic (AnG) and aerobic (AG) growing conditions and under H 2 -producing (HP) conditions at low and high light intensities. The results obtained clearly showed that F v /F m ratio was significantly affected by the light intensity under which R. palustris 42OL cells were grown, under either AnG or AG conditions, while, under HP, it constantly remained at its highest value. The increase in light intensity significantly increased the H 2 production rate, which showed a positive correlation with the maximum electron transfer rate ( r ETR max ). These findings are important for optimization of hydrogen production by PNSB under solar light. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris strain 42OL was isolated in 1973 from a sugar refinery waste treatment pond. The strain has been prevalently used for hydrogen production processes using a wide variety of waste-derived substrates, and cultured both indoors and outdoors, either freely suspended or immobilized. R. palustris 42OL was suitable for many other applications and capable of growing in very different culturing conditions, revealing a wide metabolic versatility. The analysis of the genome sequence allowed to identify the metabolic pathways for hydrogen and poly-β-hydroxy-butyrate production, and confirmed the ability of using a wide range of organic acids as substrates. [ABSTRACT FROM AUTHOR]

Abstract: Research on photobiological H2 production processes is pointing towards the use of low cost substrates as sources of reduced carbon for H2 generation. Those substrates (either wastewaters or effluents derived from other fermentation processes) are often rich not only in carbon, but also in fixed nitrogen. is an inhibitor of nitrogenase-mediated H2 production in purple non sulfur bacteria. A Rhodopseudomonas palustris mutant strain (NifA*), which constitutively expresses nitrogenase genes, was utilized in order to test the use of containing fermentation products for photobiological production of H2. The strain was grown on both synthetic and waste-derived containing media. The nifA* mutant produced H2 in the presence of high concentrations of , both in a synthetic medium and in a real vegetable waste-derived medium resulting in higher H2 levels than the wild-type strain. Thus, this study demonstrates that the NifA* strain is well suited to overcome the effects of inhibitory naturally occurring as it converts agricultural waste into biofuel. [Copyright &y& Elsevier]

Abstract: Sunlight represents an important choice for low cost photosynthetic cultures irradiation, especially in up-scaled processes. The aim of this study was the assessment of the hydrogen production performances of Rhodopseudomonas palustris strain 42OL cultivated outdoors, under sunlight, in a 50L tubular photobioreactor. Moreover, bacteriochlorophyll a fluorescence was used for the first time as a tool for monitoring the physiological status of Rp. palustris mass cultures. The maximum H2 production rate of 27.2mlL−1 h−1, and the mean rate per illuminated surface of 3.54±1.53Lm−2 d−1 obtained resulted the highest so far reported for outdoor experiments carried out with purple bacteria in tubular photobioreactors of comparable dimensions. The in-situ measurement of bacteriochlorophyll a fluorescence (F v/F m) showed that the photosystem was unaffected by changing light irradiance during the day and remained fully active over the whole period of hydrogen production. [Copyright &y& Elsevier]