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In this study, a coculture bioprocess was developed with Clostridium strains producing butyric acid and Megasphaera hexanoica producing caproic acid from the butyric acid. The two bacterial strains were each cultivated in two submerged hollow-fiber membrane bioreactors (s-HF/MBRs), separately. Each fermentation broth was filtered through the membrane modules, and the filtered broth was either interchanged on another reactor or obtained sequentially through. Using s-HF/MBRs, the caproic acid concentration increased to 10.08 g L -1 , with the fastest productivity of 0.69 g L -1  h -1 , which higher than that previously reported., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Objective: To produce butyric acid from red algae such as Gelidium amansii in which galactose is a main carbohydrate, microorganisms utilizing galactose and tolerating inhibitors in hydrolysis including levulinic acid and 5-hydroxymethylfurfural (HMF) are required., Results: A newly isolated bacterium, Clostridium sp. S1 produced butyric acid not only from galactose as the sole carbon source but also from a mixture of galactose and glucose through simultaneous utilization. Notably, Clostridium sp. S1 produced butyric acid and a small amount of acetic acid with the butyrate:acetate ratio of 45.4:1 and it even converted acetate to butyric acid. Clostridium sp. S1 tolerated 0.5-2 g levulinic acid/l and recovered from HMF inhibition at 0.6-2.5 g/l, resulting in 85-92% butyric acid concentration of the control culture. When acid-pretreated G. amansii hydrolysate was used, Clostridium sp. S1 produced 4.83 g butyric acid/l from 10 g galactose/l and 1 g glucose/l., Conclusion: Clostridium sp. S1 produces butyric acid from red algae due to its characteristics in sugar utilization and tolerance to inhibitors, demonstrating its advantage as a red algae-utilizing microorganism.

A Gram-stain positive, strict anaerobe, spore-forming, motile rod-shaped bacterial strain with peritrichous flagella, designated YMB-57(T), was isolated from the intestine of a cinereous vulture (Aegypius monachus) in Korea. Strain YMB-57(T) was found to show optimal growth at 37 °C, pH 7.5 and 1.0 % (w/v) NaCl. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain YMB-57(T) belongs to the genus Clostridium and is most closely related to the type strains of Clostridium subterminale (96.9 % sequence similarity), Clostridium thiosulfatireducens (96.7 %) and Clostridium sulfidigenes (96.6 %). The main fermentation end-products identified following growth in PYG medium were acetate, butyrate, ethanol, propanol, carbon dioxide and hydrogen. Peptone was converted to ethanol, and butanol, whereas glucose was fermented to ethanol. The major cellular fatty acids were identified as C16:0, C18:1 ω9c, and C18:1 ω9c DMA and the DNA G+C content was determined to be 34.0 mol%. Phenotypic and phylogenetic differences indicate that strain YMB-57(T) is distinct from other Clostridium species. It is proposed that strain YMB-57(T) be classified as the type strain of a novel species of the genus Clostridium, with the name Clostridium vulturis sp. nov. The type strain is YMB-57(T) (=KCTC 15114(T) = JCM 17998(T)).

Clostridium sp. BS-1 produces hexanoic acid as a metabolite using galactitol and enhanced hexanoic acid production was obtained by in situ extractive fermentation with Clostridium sp. BS-1 under an optimized medium composition. For medium optimization, five ingredients were selected as variables, and among them yeast extract, tryptone, and sodium butyrate were selected as significant variables according to a fractional factorial experimental design, a steepest ascent experimental design, and a Box-Behnken experimental design. The optimized medium had the following compositions in modified Clostridium acetobutyricum (mCAB) medium: 15.5gL(-1) of yeast extract, 10.13gL(-1) of tryptone, 0.04gL(-1) of FeSO4·7H2O, 0.85gL(-1) of sodium acetate, and 6.47gL(-1) of sodium butyrate. The predicted concentration of hexanoic acid with the optimized medium was 6.98gL(-1), and this was validated experimentally by producing 6.96gL(-1) of hexanoic acid with Clostridium sp. BS-1 under the optimized conditions. In situ extractive fermentation for hexanoic acid removal was then applied in a batch culture system with the optimized medium and 10% (v/v) alamine 336 in oleyl alcohol as an extractive solvent. The pH of the culture in the extractive fermentation was maintained at 5.4-5.6 by an acid balance between production and retrieval by extraction. During a 16 day culture, the hexanoic acid concentration in the solvent increased to 32gL(-1) while it was maintained in a range of 1-2gL(-1) in the medium. The maximum rate of hexanoic acid production was 0.34gL(-1)h(-1) in in situ extractive fermentation., (Copyright © 2013. Published by Elsevier Inc.)

Medium compositions favoring butanol and 1,3-propanediol (1,3-PDO) production from glycerol by Clostridium pasteurianum DSM525 were investigated using statistical experimental designs. Medium components affecting butanol and 1,3-PDO production were screened using a fractional factorial experimental design. Among the six tested variables (phosphate buffer, MnSO4·H2O, MgSO4·7H2O, FeSO4·7H2O, (NH4)2SO4, and yeast extract), FeSO4·7H2O, (NH4)2SO4, and yeast extract were found to be significant variables for further optimization of medium using a Box-Behnken design. Optimal butanol (0.98 g/L/h) and 1,3-PDO (1.19 g/L/h) productivities were predicted by the corresponding quadratic model for each product and the models were validated experimentally under optimized conditions. The optimal medium composition for butanol production was significantly different from that for 1,3-PDO production (0.06 vs. 0 g/L for FeSO4·7H2O, 7.35 vs. 0 g/L for (NH4)2SO4, and 5.08 vs. 8.0 g/L for yeast extract), suggesting that the product formation from glycerol by C. pasteurianum DSM525 can be controlled by changing medium compositions., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The production of butanol from thin stillage by Clostridium pasteurianum DSM 525 was evaluated in the paper. At initial pH values ranging from 5.0 to 7.0 C. pasteurianum DSM 525 produced 6.2-7.2 g/L of butanol utilizing glycerol in thin stillage as the main carbon source, with yields of 0.32-0.44 g butanol produced/g glycerol consumed, which are higher than previously reported yields (e.g., 0.14-0.31 g butanol/g glycerol, Biebl, 2001). Lactic acid in the thin stillage acted as a buffering agent, maintaining the pH of the medium within a range of 5.7-6.1. Lactic acid was also utilized along with glycerol, enhancing butanol production (6.5 g/L butanol vs. 8.7 g/L butanol with 0 and 16 g/L lactic acid, respectively). These results demonstrate the feasibility of cost-effective butanol production using thin stillage as a nutrient-containing medium with a pH buffering capacity., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

In a study screening anaerobic microbes utilizing D: -galactitol as a fermentable carbon source, four bacterial strains were isolated from an enrichment culture producing H₂, ethanol, butanol, acetic acid, butyric acid, and hexanoic acid. Among these isolates, strain BS-1 produced hexanoic acid as a major metabolic product of anaerobic fermentation with D: -galactitol. Strain BS-1 belonged to the genus Clostridium based on phylogenetic analysis using 16S rRNA gene sequences, and the most closely related strain was Clostridium sporosphaeroides DSM 1294(T), with 94.4% 16S rRNA gene similarity. In batch cultures, Clostridium sp. BS-1 produced 550 ± 31 mL L⁻¹ of H₂, 0.36 ± 0.01 g L⁻¹ of acetic acid, 0.44 ± 0.01 g L⁻¹ of butyric acid, and 0.98 ± 0.03 g L⁻¹ of hexanoic acid in a 4-day cultivation. The production of hexanoic acid increased to 1.22 and 1.73 g L⁻¹ with the addition of 1.5 g L⁻¹ of sodium acetate and 100 mM 2-(N-morpholino)ethanesulfonic acid (MES), respectively. Especially when 1.5 g L⁻¹ of sodium acetate and 100 mM MES were added simultaneously, the production of hexanoic acid increased up to 2.99 g L⁻¹. Without adding sodium acetate, 2.75 g L⁻¹ of hexanoic acid production from D-galactitol was achieved using a coculture of Clostridium sp. BS-1 and one of the isolates, Clostridium sp. BS-7, in the presence of 100 mM MES. In addition, volatile fatty acid (VFA) production by Clostridium sp. BS-1 from D-galactitol and D: -glucose was enhanced when a more reduced culture redox potential (CRP) was applied via addition of Na₂S·9H₂O.

The microbial production of 1,3-propanediol (1,3-PD) from raw glycerol, a byproduct of biodiesel production, is economically and environmentally advantageous. Although direct use of raw glycerol without any pretreatment is desirable, previous studies have reported that this could cause inhibition of microbial growth. In this study, we investigated the effects of raw glycerol type, different microorganisms, and pretreatment of raw glycerol on the production of 1,3-PD. Raw glycerol from waste vegetable-oil-based biodiesel production generally caused more inhibition of 1,3-PD production and microbial growth compared to raw glycerol from soybean-oil-based biodiesel production. In addition, two raw glycerol types produced from two biodiesel manufacturers using waste vegetable oil exhibited different 1,3-PD production behavior, partially due to different amounts of methanol included in the raw glycerol from the two biodiesel manufacturers. Klebsiella strains were generally resistant to all types of raw glycerol while the growth of Clostridium strains was variably inhibited depending on the type of raw glycerol. The 1,3-PD production of the Clostridium strains using acid-pretreated raw glycerol was significantly enhanced compared to that with raw glycerol, demonstrating the feasibility of using raw glycerol for 1,3-PD production by various microorganisms.

Background: Currently, the most promising microorganism used for the bio-production of butyric acid is Clostridium tyrobutyricum ATCC 25755T; however, it is unable to use sucrose as a sole carbon source. Consequently, a newly isolated strain, Bacillus sp. SGP1, that was found to produce a levansucrase enzyme, which hydrolyzes sucrose into fructose and glucose, was used in a co-culture with this strain, permitting C. tyrobutyricum ATCC 25755T to ferment sucrose to butyric acid. Results: B. sp. SGP1 alone did not show any butyric acid production and the main metabolite produced was lactic acid. This allowed C. tyrobutyricum ATCC 25755T to utilize the monosaccharides resulting from the activity of levansucrase together with the lactic acid produced by B. sp. SGP1 to generate butyric acid, which was the main fermentative product within the co-culture. Furthermore, the final acetic acid concentration in the co-culture was significantly lower when compared with pure C. tyrobutyricum ATCC 25755T cultures grown on glucose. In fedbatch fermentations, the optimum conditions for the production of butyric acid were around pH 5.50 and a temperature of 37°C. Under these conditions, the final butyrate concentration was 34.2±1.8 g/L with yields of 0.35±0.03 g butyrate/g sucrose and maximum productivity of 0.3±0.04 g/L/h. Conclusions: Using this co-culture, sucrose can be utilized as a carbon source for butyric acid production at a relatively high yield. In addition, this co-culture offers also the benefit of a greater selectivity, with butyric acid constituting 92.8% of the acids when the fermentation was terminated. [ABSTRACT FROM AUTHOR]

Lignocellulosic degradation compounds, especially phenolic compounds, inhibit the fermentation of Clostridium strains. In this study, a simple in situ detoxification method using a surfactant was developed for butyric acid production by Clostridium tyrobutyricum ATCC25755. Tween 80, a non-ionic surfactant, was chosen to sequester inhibitors by forming micelles, consequently preventing direct contact of inhibitors with cell membranes. When Tween 80 was added during fermentation, butyric acid production was significantly enhanced in the presence of hydrophobic phenolics such as p -coumaric acid (0 vs. 3.1 g/L butyric acid) and ferulic acid (2.2 vs. 4.6 g/L butyric acid) even at 0.016 g/L of Tween 80 (corresponding to the critical micelle concentration). Lignin, a polyphenol compound in lignocellulose, was also detoxified by Tween 80. When Tween 80 was added to acid-pretreated rice straw hydrolysate, butyric acid production significantly increased (0.1 vs. 8.7 g/L butyric acid), thus verifying detoxification effect of Tween 80 on lignocellulosic hydrolysate. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the hydraulic retention time (HRT=8, 10, 12 or 16.7h) and glucose concentration (30, 40 or 50g/L) on the production of hydrogen and butyrate by an immobilized Clostridium tyrobutyricum culture, grown under continuous culturing conditions, were evaluated. With 30g/L glucose, the higher HRTs tested led to greater butyrate concentrations in the culture, i.e., 9.3g/L versus 12.9g/L with HRTs of 8h and 16.7h, respectively. In contrast, higher biogas and hydrogen production rates were generally seen when the HRT was lower. Experiments with different glucose concentrations saw a significant amount of glucose washed out when 50g/L was used, the highest being 22.7g/L when the HRT was 16.7h. This study found the best conditions for the continuous production of hydrogen and butyric acid by C. tyrobutyricum to be with an HRT of 12h and a glucose concentration of 50g/L, respectively. [Copyright &y& Elsevier]