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  • 1. Albers, Eva
    et al.
    Johansson, Emma
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Processum.
    Franzén, Carl Johan
    Larsson, Christer
    Selective suppression of bacterial contaminants by process conditions during lignocellulose based yeast fermentations2011In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 4, article id Art no 59Article in journal (Refereed)
    Abstract [en]

    Background: Contamination of bacteria in large-scale yeast fermentations is a serious problem and a threat to the development of successful biofuel production plants. Huge research efforts have been spent in order to solve this problem, but additional ways must still be found to keep bacterial contaminants from thriving in these environments. The aim of this project was to develop process conditions that would inhibit bacterial growth while giving yeast a competitive advantage. Results: Lactic acid bacteria are usually considered to be the most common contaminants in industrial yeast fermentations. Our observations support this view but also suggest that acetic acid bacteria, although not so numerous, could be a much more problematic obstacle to overcome. Acetic acid bacteria showed a capacity to drastically reduce the viability of yeast. In addition, they consumed the previously formed ethanol. Lactic acid bacteria did not show this detrimental effect on yeast viability. It was possible to combat both types of bacteria by a combined addition of NaCl and ethanol to the wood hydrolysate medium used. As a result of NaCl + ethanol additions the amount of viable bacteria decreased and yeast viability was enhanced concomitantly with an increase in ethanol concentration. The successful result obtained via addition of NaCl and ethanol was also confirmed in a real industrial ethanol production plant with its natural inherent yeast/bacterial community. Conclusions: It is possible to reduce the number of bacteria and offer a selective advantage to yeast by a combined addition of NaCl and ethanol when cultivated in lignocellulosic medium such as wood hydrolysate. However, for optimal results, the concentrations of NaCl + ethanol must be adjusted to suit the challenges offered by each hydrolysate. © 2011 Albers et al; licensee BioMed Central Ltd.

  • 2.
    Björkmalm, Johanna
    et al.
    RISE - Research Institutes of Sweden, Built Environment, Energy and Circular Economy.
    Byrne, Eoin
    Lund University, Sweden.
    van Niel, Ed
    Lund University, Sweden.
    Willquist, Karin
    RISE - Research Institutes of Sweden, Built Environment, Energy and Circular Economy.
    A non-linear model of hydrogen production by Caldicellulosiruptor saccharolyticus for diauxic-like consumption of lignocellulosic sugar mixtures2018In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 11, article id 175Article in journal (Refereed)
    Abstract [en]

    Background

    Caldicellulosiruptor saccharolyticus is an attractive hydrogen producer suitable for growth on various lignocellulosic substrates. The aim of this study was to quantify uptake of pentose and hexose monosaccharides in an industrial substrate and to present a kinetic growth model of C. saccharolyticus that includes sugar uptake on defined and industrial media. The model is based on Monod and Hill kinetics extended with gas-to-liquid mass transfer and a cybernetic approach to describe diauxic-like growth.

    Results

    Mathematical expressions were developed to describe hydrogen production by C. saccharolyticus consuming glucose, xylose, and arabinose. The model parameters were calibrated against batch fermentation data. The experimental data included four different cases: glucose, xylose, sugar mixture, and wheat straw hydrolysate (WSH) fermentations. The fermentations were performed without yeast extract. The substrate uptake rate of C. saccharolyticus on single sugar-defined media was higher on glucose compared to xylose. In contrast, in the defined sugar mixture and WSH, the pentoses were consumed faster than glucose. Subsequently, the cultures entered a lag phase when all pentoses were consumed after which glucose uptake rate increased. This phenomenon suggested a diauxic-like behavior as was deduced from the successive appearance of two peaks in the hydrogen and carbon dioxide productivity. The observation could be described with a modified diauxic model including a second enzyme system with a higher affinity for glucose being expressed when pentose saccharides are consumed. This behavior was more pronounced when WSH was used as substrate.

    Conclusions

    The previously observed co-consumption of glucose and pentoses with a preference for the latter was herein confirmed. However, once all pentoses were consumed, C. saccharolyticus most probably expressed another uptake system to account for the observed increased glucose uptake rate. This phenomenon could be quantitatively captured in a kinetic model of the entire diauxic-like growth process. Moreover, the observation indicates a regulation system that has fundamental research relevance, since pentose and glucose uptake in C. saccharolyticus has only been described with ABC transporters, whereas previously reported diauxic growth phenomena have been correlated mainly to PTS systems for sugar uptake.

  • 3.
    Byrne, Eoin
    et al.
    Lund University, Sweden.
    Kovacs, Krisztyna
    Lund University, Sweden.
    Van Niel, Ed W. J.
    Lund University, Sweden.
    Willquist, Karin
    RISE - Research Institutes of Sweden, Built Environment, Energy and Circular Economy.
    Svensson, Sven-Erik
    SLU Swedish University of Agricultural Sciences, Sweden.
    Kreuger, Emma
    Lund University, Sweden.
    Reduced use of phosphorus and water in sequential dark fermentation and anaerobic digestion of wheat straw and the application of ensiled steam-pretreated lucerne as a macronutrient provider in anaerobic digestion2018In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 11, no 1, article id 281Article in journal (Refereed)
    Abstract [en]

    Background: Current EU directives demand increased use of renewable fuels in the transportation sector but restrict governmental support for production of biofuels produced from crops. The use of intercropped lucerne and wheat may comply with the directives. In the current study, the combination of ensiled lucerne (Medicago sativa L.) and wheat straw as substrate for hydrogen and methane production was investigated. Steam-pretreated and enzymatically hydrolysed wheat straw [WSH, 76% of total chemical oxygen demand (COD)] and ensiled lucerne (LH, 24% of total COD) were used for sequential hydrogen production through dark fermentation and methane production through anaerobic digestion and directly for anaerobic digestion. Synthetic co-cultures of extreme thermophilic Caldicellulosiruptor species adapted to elevated osmolalities were used for dark fermentation. Results: Based on 6 tested steam pretreatment conditions, 5 min at 200 °C was chosen for the ensiled lucerne. The same conditions as applied for wheat straw (10 min at 200 °C with 1% acetic acid) would give similar sugar yields. Volumetric hydrogen productivities of 6.7 and 4.3 mmol/L/h and hydrogen yields of 1.9 and 1.8 mol/mol hexose were observed using WSH and the combination of WSH and LH, respectively, which were relatively low compared to those of the wild-type strains. The combinations of WSH plus LH and the effluent from dark fermentation of WSH plus LH were efficiently converted to methane in anaerobic digestion with COD removal of 85-89% at organic loading rates of COD 5.4 and 8.5 g/L/day, respectively, in UASB reactors. The nutrients in the combined hydrolysates could support this conversion. Conclusions: This study demonstrates the possibility of reducing the water addition to WSH by 26% and the phosphorus addition by 80% in dark fermentation with Caldicellulosiruptor species, compared to previous reports. WSH and combined WSH and LH were well tolerated by osmotolerant co-cultures. The yield was not significantly different when using defined media or hydrolysates with the same concentrations of sugars. However, the sugar concentration was negatively correlated with the hydrogen yield when comparing the results to previous reports. Hydrolysates and effluents from dark fermentation can be efficiently converted to methane. Lucerne can serve as macronutrient provider in anaerobic digestion. Intercropping with wheat is promising.

  • 4. Jönsson, Leif J.
    et al.
    Alriksson, Björn
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Processum.
    Nilvebrant, Nils-Olof
    Bioconversion of lignocellulose: Inhibitors and detoxification2013In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 6, no 1, article id Art no 16Article in journal (Refereed)
    Abstract [en]

    Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts. © 2013 Jonsson et al.; licensee BioMed Central Ltd.

  • 5.
    Pawar, Sudhanshu S.
    et al.
    RISE. Lund University, Sweden.
    Vongkumpeang, Thitiwut
    Lund University, Sweden.
    Grey, Carl
    Lund University, Sweden.
    van Niel, Ed W. J.
    Lund University, Sweden.
    Biofilm formation by designed co-cultures of Caldicellulosiruptor species as a means to improve hydrogen productivity2015In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 8, no 1, article id 19Article in journal (Refereed)
    Abstract [en]

    Background: Caldicellulosiruptor species have gained a reputation as being among the best microorganisms to produce hydrogen (H2) due to possession of a combination of appropriate features. However, due to their low volumetric H2 productivities (Q H2), Caldicellulosiruptor species cannot be considered for any viable biohydrogen production process yet. In this study, we evaluate biofilm forming potential of pure and co-cultures of Caldicellulosiruptor saccharolyticus and Caldicellulosiruptor owensensis in continuously stirred tank reactors (CSTR) and up-flow anaerobic (UA) reactors. We also evaluate biofilms as a means to retain biomass in the reactor and its influence on Q H2. Moreover, we explore the factors influencing the formation of biofilm. Results: Co-cultures of C. saccharolyticus and C. owensensis form substantially more biofilm than formed by C. owensensis alone. Biofilms improved substrate conversion in both of the reactor systems, but improved the Q H2 only in the UA reactor. When grown in the presence of each other's culture supernatant, both C. saccharolyticus and C. owensensis were positively influenced on their individual growth and H2 production. Unlike the CSTR, UA reactors allowed retention of C. saccharolyticus and C. owensensis when subjected to very high substrate loading rates. In the UA reactor, maximum Q H2 (approximately 20 mmol∈·∈L-1∈ ·∈h-1) was obtained only with granular sludge as the carrier material. In the CSTR, stirring negatively affected biofilm formation. Whereas, a clear correlation was observed between elevated (>40 μM) intracellular levels of the secondary messenger bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) and biofilm formation. Conclusions: In co-cultures C. saccharolyticus fortified the trade of biofilm formation by C. owensensis, which was mediated by elevated levels of c-di-GMP in C. owensensis. These biofilms were effective in retaining biomass of both species in the reactor and improving Q H2 in a UA reactor using granular sludge as the carrier material. This concept forms a basis for further optimizing the Q H2 at laboratory scale and beyond. © 2015 Pawar et al.; licensee BioMed Central.

  • 6.
    Peciulyte, Ausra
    et al.
    Chalmers University of Technology, Sweden.
    Karlström, Katarina
    RISE, Innventia.
    Larsson, Per Tomas
    RISE, Innventia. KTH Royal Institute of Technology, Sweden.
    Olsson, Lisbeth
    Chalmers University of Technology, Sweden.
    Impact of the supramolecular structure of cellulose on the efficiency of enzymatic hydrolysis2015In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 8, no 1, article id 56Article in journal (Refereed)
    Abstract [en]

    Background: The efficiency of enzymatic hydrolysis is reduced by the structural properties of cellulose. Although efforts have been made to explain the mechanism of enzymatic hydrolysis of cellulose by considering the interaction of cellulolytic enzymes with cellulose or the changes in the structure of cellulose during enzymatic hydrolysis, the process of cellulose hydrolysis is not yet fully understood. We have analysed the characteristics of the complex supramolecular structure of cellulose on the nanometre scale in terms of the spatial distribution of fibrils and fibril aggregates, the accessible surface area and the crystallinity during enzymatic hydrolysis. Influence of the porosity of the substrates and the hydrolysability was also investigated. All cellulosic substrates used in this study contained more than 96% cellulose. Results: Conversion yields of six cellulosic substrates were as follows, in descending order: nano-crystalline cellulose produced from never-dried soda pulp (NCC-OPHS-ND)∈>∈never-dried soda pulp (OPHS-ND)∈>∈dried soda pulp (OPHS-D)∈>∈Avicel∈>∈cotton treated with sodium hydroxide (cotton∈+∈NaOH)∈>∈cotton. Conclusions: No significant correlations were observed between the yield of conversion and supramolecular characteristics, such as specific surface area (SSA) and lateral fibril dimensions (LFD). A strong correlation was found between the average pore size of the starting material and the enzymatic conversion yield. The degree of crystallinity was maintained during enzymatic hydrolysis of the cellulosic substrates, contradicting previous explanations of the increasing crystallinity of cellulose during enzymatic hydrolysis. Both acid and enzymatic hydrolysis can increase the LFD, but no plausible mechanisms could be identified. The sample with the highest initial degree of crystallinity, NCC-OPHS-ND, exhibited the highest conversion yield, but this was not accompanied by any change in LFD, indicating that the hydrolysis mechanism is not based on lateral erosion

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