Effect of nutrient sources on growth and acetate production by Clostridium thermoaceticum

Acetate Production from Syngas Produced from Lignocellulosic Biomass Materials along with Gaseous Fermentation of the Syngas: A Review

Biotransformation of lignocellulose-derived synthetic gas (syngas) into acetic acid is a promising way of creating biochemicals from lignocellulosic waste materials. Acetic acid has a growing market with applications within food, plastics and for upgrading into a wide range of biofuels and bio-products. In this paper, we will review the microbial conversion of syngas to acetic acid. This will include the presentation of acetate-producing bacterial strains and their optimal fermentation conditions, such as pH, temperature, media composition, and syngas composition, to enhance acetate production. The influence of syngas impurities generated from lignocellulose gasification will further be covered along with the means to alleviate impurity problems through gas purification. The problem with mass transfer limitation of gaseous fermentation will further be discussed as well as ways to improve gas uptake during the fermentation.

Nipa Sap Can Be Both Carbon and Nutrient Source for Acetic Acid Production by Moorella thermoacetica (f. Clostridium thermoaceticum) and Reduced Minimal Media Supplements

Nipa sap is an excellent microbial nutrient and carbon source since it contains essential minerals and vitamins, in addition to sugars. In this study, nipa sap was successfully fermented to acetic acid by the industrially important Moorella thermoacetica without additional trace metals, without inorganics, or without yeast extract. Although microbial growth kinetics differed from one nutrient condition to another, acetic acid concentrations obtained without trace metals, without inorganics, and without yeast extract supplements were in the same range as that with full nutrient, confirming that nipa sap is a good nutrient source for M. thermoacetica. Fermentations in vials and fermenters showed comparable acetic acid production trends but acetic acid concentrations were higher in fermenters. Upon economic analysis, it was found that the most profitable nutrient condition was without yeast extract. It reduced the cost of culture medium from $1.7 to only $0.3/L, given that yeast extract costs $281/kg, while nipa sap can be available from $0.08/kg. Minimal medium instead of the traditional complex nutrient simplifies the process. This work also opens opportunities for profitable anaerobic co-digestion and co-fermentation of nipa sap with other biomass resources where nipa sap will serve as an inexpensive nutrient source and substrate.

Organic waste streams as feedstock for the production of high volume-low value products

Valorisation of organic wastes to produce industrially relevant commodity products is a sustainable, cost-effective and viable alternative providing a green platform for chemical production while simultaneously leading to waste disposal management. In the present study, organic wastes such as agricultural residue-derived sugars, oilseed meals, poultry waste and molasses were used for substituting expensive organic fermentation medium components. Moorella thermoacetica and Aurantiochytrium limacinum were adapted on these waste-derived hydrolysates to produce high volume-low value products such as bio-acetic acid (80% theoretical yields) and oil-rich fish/animal feed (more than 85% dry cell weight as compared with conventional nutrient sources) respectively. Use of these waste-derived nutrients led to ~ 75% and ~ 90% reduction in media cost for acetic acid and oil-rich biomass production respectively as compared with that of traditionally used high-priced medium components. The strategy will assist in the cost reduction for high volume-low value products while also ensuring waste recovery.

Effects of gas condition on acetic acid fermentation by Clostridium thermocellum and Moorella thermoacetica (C. thermoaceticum)

Fermentation with acetogens can be affected by cultivation gas phase, but to date, there is not enough evidence on that matter for Clostridium thermocellum and Moorella thermoacetica. In this work, the effects of sparged CO₂ as well as sparged and non-sparged N₂ on these microorganisms were studied using glucose and cellobiose as substrates. It was revealed that sparged CO₂ and non-sparged N₂ supported growth and acetic acid production by C. thermocellum and M. thermoacetica, while sparged N₂ inhibited both of the microorganisms. Notably, part of the sparged CO₂ was fermented by the co-culture system and contributed to an overestimation of the products from the actual substrate as well as an erring material balance. The best condition for the co-culture was concluded to be N₂ without sparging. These results demonstrate the importance of cultivation conditions for efficient fermentation by anaerobic clostridia species.

Molecular cloning and sequence analysis of a PVGOX gene encoding glucose oxidase in Penicillium viticola F1 strain and it's expression quantitation

The PVGOX gene (accession number: KT452630) was isolated from genomic DNA of the marine fungi Penicillium viticola F1 by Genome Walking and their expression analysis was done by Fluorescent RT-PCR. An open reading frame of 1806bp encoding a 601 amino acid protein (isoelectric point: 5.01) with a calculated molecular weight of 65,535.4 was characterized. The deduced protein showed 75%, 71%, 69% and 64% identity to those deduced from the glucose oxidase (GOX) genes from different fungal strains including; Talaromyces variabilis, Beauveria bassiana, Aspergillus terreus, and Aspergillus niger, respectively. The promoter of the gene (intronless) had two TATA boxes around the base pair number -88 and -94 and as well as a CAAT box at -100. However, the terminator of the PVGOX gene does not contain any polyadenylation site (AATAAA). The protein deduced from the PVGOX gene had a signal peptide containing 17 amino acids, three cysteine residues and six potential N-linked glycosylation sites, among them, -N-K-T-Y- at 41 amino acid, -N-R-S-L- at 113 amino acid, -N-G-T-I- at 192 amino acid, -N-T-T-A at 215 amino acid, -N-F-T-E at 373 amino acid and -N-V-T-A- at 408 amino acid were the most possible N-glycosylation sites. Furthermore, the relative transcription level of the PVGOX gene was also stimulated in the presence of 4% (w/v) of calcium carbonate and 0.5 % (v/v) of CSL in the production medium compared with that of the PVGOX gene when the fungal strain F1 was grown in the absence of calcium carbonate and CSL in the production medium, suggesting that under the optimal conditions, the expression of the PVGOX gene responsible for gluconic acid biosynthesis was enhanced, leading to increased gluconic acid production. Therefore, the highly glycosylated oxidase enzyme produced by P. viticola F1 strain might be a good producer in the fermentation process for the industrial level production of gluconic acid.

Fermentation of lignocellulosic sugars to acetic acid by Moorella thermoacetica

A systematic study of bioconversion of lignocellulosic sugars to acetic acid by Moorella thermoacetica (strain ATCC 39073) was conducted. Four different water-soluble fractions (hydrolysates) obtained after steam pretreatment of lignocellulosic biomass were selected and fermented to acetic acid in batch fermentations. M. thermoacetica can effectively ferment xylose and glucose in hydrolysates from wheat straw, forest residues, switchgrass, and sugarcane straw to acetic acid. Xylose and glucose were completely utilized, with xylose being consumed first. M. thermoacetica consumed up to 62 % of arabinose, 49 % galactose and 66 % of mannose within 72 h of fermentation in the mixture of lignocellulosic sugars. The highest acetic acid yield was obtained from sugarcane straw hydrolysate, with 71 % of theoretical yield based on total sugars (17 g/L acetic acid from 24 g/L total sugars). The lowest acetic acid yield was observed in forest residues hydrolysate, with 39 % of theoretical yield based on total sugars (18 g/L acetic acid from 49 g/L total sugars). Process derived compounds from steam explosion pretreatment, including 5-hydroxymethylfurfural (0.4 g/L), furfural (0.1 g/L) and total phenolics (3 g/L), did not inhibit microbial growth and acetic acid production yield. This research identified two major factors that adversely affected acetic acid yield in all hydrolysates, especially in forest residues: (i) glucose to xylose ratio and (ii) incomplete consumption of arabinose, galactose and mannose. For efficient bioconversion of lignocellulosic sugars to acetic acid, it is imperative to have an appropriate balance of sugars in a hydrolysate. Hence, the choice of lignocellulosic biomass and steam pretreatment design are fundamental steps for the industrial application of this process.

Ethanol production from syngas by Clostridium strain P11 using corn steep liquor as a nutrient replacement to yeast extract

The feasibility of replacing yeast extract (YE) by corn steep liquor (CSL), a low cost nutrient source, for syngas fermentation to produce ethanol using Clostridium strain P11 was investigated. About 32% more ethanol (1.7 g L(-1)) was produced with 20 g L(-1) CSL media in 250-mL bottle fermentations compared to media with 1 g L(-1) YE after 360 h. Maximum ethanol concentrations after 360 h of fermentation in a 7.5-L fermentor with 10 and 20 g L(-1) CSL media were 8.6 and 9.6 g L(-1), respectively, which represent 57% and 60% of the theoretical ethanol yields from CO. Only about 6.1 g L(-1) of ethanol was obtained in the medium with 1 g L(-1) YE after 360 h, which represents 53% of the theoretical ethanol yield from CO. The use of CSL also enhanced butanol production by sevenfold compared to YE in bottle fermentations. These results demonstrate that CSL can replace YE as the primary medium component and significantly enhance ethanol production by Clostridium strain P11.

Production of desferrioxamine B (Desferal) using corn steep liquor in Streptomyces pilosus

The aim of this study was evaluation of corn steep liquor as an alternative or substitution medium for production of desferrioxamine B in streptomyces pilosus. Desferrioxamine B is the major siderophore of Streptomyces pilosus. The genus Streptomyces are Gram positive and GC (Guanine/Cytosine) rich bacteria that are important for production of many antibiotics and secondary metabolites. These metabolites get more attention in industrial and medical fields. Desferrioxamine B is used clinically to treat disorders related to iron overload and pathological iron deposition in human. Corn Steep Liquor (CSL) is a by-product of corn wet-milling. It is an excellent source of organic nitrogen and important constituent of some culture media. Nowadays CSL was mainly used for feeding of livestock. In this study we substitute the conventional media with CSL and surveyed its effect on production of desferrioxamine B. The CSL is cheaper than other media and its availability is so easy. In this research, for the first time we used a cheap material for production of a valuable product. Our results showed that the use of CSL solely, increased the production of Desferal more than three times in comparison with conventional media such as soybean.

Modeling of sodium acetate recovery from aqueous solutions by electrodialysis

The main engineering parameters (i.e., ion transport numbers in solution and electro-membranes; effective solute and water transport numbers; effective membrane surface area, membrane surface resistances, and limiting current intensity) affecting the recovery of sodium acetate from model solutions by electrodialysis (ED) were determined in accordance with a sequential experimental procedure. Such parameters allowed a satisfactory simulation of a few validation tests carried out under constant or step-wisely variable current intensity. The performance of this ED process was characterized in terms of a current efficiency (omega) of about 93% in the constant-current region, a water transport number (t(W)) of about 15, and a specific energy consumption (epsilon) increasing from 0.14 to 0.31 kWh/kg for a solute recovery yield of 95% as the current density (j) was increased from 112 to 337 A/m2. The specific resistance of the anion- or cation-exchange membranes were found to be three or two times greater than those measured in aqueous NaCl solutions and are to be used to design and/or optimize ED stacks involved in the downstream processing of acetic acid fermentation broths.

Production of glucose oxidase using Aspergillus niger and corn steep liquor

Glucose oxidase production was optimized using an isolated strain of Aspergillus niger and an economical nutrient source, corn steep liquor (CSL). The culture produced 580 +/- 30 units/ml of the enzyme using 70 g/l sucrose as the carbon source. Using CSL as the sole nutrient source enzyme synthesis was increased to 640 +/- 36 units/ml. None of the nitrogen sources (nitrates of calcium, sodium, ammonium, potassium and yeast extract, malt extract, and peptone) was beneficial to the enzyme synthesis. Aeration and agitation enhanced enzyme synthesis to 850 +/- 45 units/ml. Glucose oxidase has numerous applications in food industry and clinical fields.

Potassium acetate by fermentation with Clostridium thermoaceticum

Potassium acetate is currently made by reacting petroleum-based acetic acid with potassium hydroxide. An alternate process, anaerobic fermentation of dextrose with Clostridium thermoaceticum, could be used and could possibly be cheaper. Growth characteristics and productivity of the fermentation were optimized to maximize acetate concentration in the broth. The effects of pH, type, and concentrations of nutrients and reducing agents were also evaluated. Corn steep liquor and stillage from an ethanol plant were effective and much cheaper substitutes for yeast extract. Preconcentrating the cells by ultrafiltration improved productivity, resulting in an acetic acid concentration of 53.6 g/L in 50 h at pH 6.5 using corn steep liquor. Sodium sulfide could be substituted for cysteine as the reducing agent with yields greater than 0.9 g acetic acid/g glucose.