Improvement of acetate production from lactose by growing Clostridium thermolacticum in mixed batch culture

AIMS: The objective of this study was to increase the acetate production by Clostridium thermolacticum growing on lactose, available as a renewable resource in the milk and whey permeate from the cheese industry. METHODS AND RESULTS: Experiments for increased acetate productivity by thermophilic anaerobes grown on lactose were carried out in batch cultures. Lactose at concentration of 30 mmol l(-1) (10 g l(-1)) was completely degraded by Cl. thermolacticum and growth rate was maximal. High concentrations of by-products, ethanol, lactate, hydrogen and carbon dioxide were generated. By using an efficient hydrogenotroph, Methanothermobacter thermoautotrophicus, in a defined thermophilic anaerobic consortium (58 degrees C) with Cl. thermolacticum and the acetogenic Moorella thermoautotrophica, the hydrogen partial pressure was dramatically lowered. As a consequence, by-products concentrations were significantly reduced and acetate production was increased. CONCLUSION: Through efficient in situ hydrogen scavenging in the consortium, the metabolic pattern was modified in favour of acetate production, at the expense of reduced by-products like ethanol. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of this thermophilic anaerobic consortium opens new opportunities for the efficient valorization of lactose, the main waste from the cheese industry, and production of calcium-magnesium acetate, an environmentally friendly road de-icer.     

Anaerobic thermophilic fermentation for acetic acid production from milk permeate

Fermentation of milk permeate to produce acetic acid under anaerobic thermophilic conditions (approximately 60 degrees C) was studied. Although none of the known thermophilic acetogenic bacteria can ferment lactose, it has been found that one strain can use galactose and two strains can use lactate. Moorella thermoautotrophica DSM 7417 and M. thermoacetica DSM 2955 were able to convert lactate to acetate at thermophilic temperatures with a yield of approximately 0.93 g g(-1). Among the strains screened for their abilities to produce acetate and lactate from lactose, Clostridium thermolacticum DSM 2910 was found precisely to produce large amounts of lactate and acetate. However, it also produced significant amounts of ethanol, CO2 and H2. The lactate yield was affected by cell growth. During the exponential phase, acetate, ethanol, CO2 and H2 were the main products of fermentation with an equimolar acetate/ethanol ratio, whereas during the stationary phase, only lactic acid was produced with a yield of 4 mol per mol lactose, thus reaching the maximal theoretical value. When this bacterium was co-cultured with M. thermoautotrophica, lactose was first converted mainly to lactic acid, then to acetic acid, with a zero residual lactic acid concentration and an overall yield of acetate around 80%. Under such conditions, only 13% of the fermented lactose was converted to ethanol by C. thermolacticum.     

Acetic acid production from lactose by an anaerobic thermophilic coculture immobilized in a fibrous-bed bioreactor

An anaerobic thermophilic coculture consisting of a heterofermentative bacterium (Clostridium thermolacticum) and a homoacetogen (Moorella thermoautotrophica) was developed for acetic acid production from lactose and milk permeate. The fermentation kinetics with free cells in conventional fermentors and immobilized cells in a recycle batch fibrous-bed bioreactor were studied. The optimal conditions for the cocultured fermentation were found to be 58 degrees C and pH 6.4. In the free-cell fermentation, C. thermolacticum converted lactose to acetate, ethanol, lactate, H(2) and CO(2), and the homoacetogen then converted lactate, H(2), and CO(2) to acetate. The overall acetate yield from lactose ranged from 0.46 to 0.65 g/g lactose fermented, depending on the fermentation conditions. In contrast, no ethanol was produced in the immobilized-cell fermentation, and the overall acetate yield from lactose increased to 0.8-0.96 g/g lactose fermented. The fibrous-bed bioreactor also gave a higher final acetate concentration (up to 25. 5 g/L) and reactor productivity (0.18-0.54 g/L/h) as compared to those from the free-cell fermentation (final acetate concentration, 15 g/L; productivity, 0.06-0.08 g/L/h). The superior performance of the fibrous-bed bioreactor was attributed to the high cell density (20 g/L) immobilized in the fibrous-bed and adaptation of C. thermolacticum cells to tolerate a higher acetate concentration. The effects of yeast extract and trypticase as nutrient supplements on the fermentation were also studied. For the free-cell fermentation, nutrient supplementation was necessary for the bacteria to grow in milk permeate. For the immobilized-cell fermentation, plain milk permeate gave a high acetate yield (0.96 g/g), although the reactor productivity was lower than those with nutrient supplementation. Balanced growth and fermentation activities between the two bacteria in the coculture are important to the quantitative conversion of lactose to acetic acid. Lactate and hydrogen produced by C. thermolacticum must be timely converted to acetic acid by the homoacetogen to avoid inhibition by these metabolites.     

Metabolism of lactose by Clostridium thermolacticum growing in continuous culture

The objective of the present study was to characterize the metabolism of Clostridium thermolacticum, a thermophilic anaerobic bacterium, growing continuously on lactose (10 g l⁻¹) and to determine the enzymes involved in the pathways leading to the formation of the fermentation products. Biomass and metabolites concentration were measured at steady-state for different dilution rates, from 0.013 to 0.19 h⁻¹. Acetate, ethanol, hydrogen and carbon dioxide were produced at all dilution rates, whereas lactate was detected only for dilution rates below 0.06 h⁻¹. The presence of several key enzymes involved in lactose metabolism, including beta-galactosidase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate:ferredoxin oxidoreductase, acetate kinase, ethanol dehydrogenase and lactate dehydrogenase, was demonstrated. Finally, the intracellular level of NADH, NAD⁺, ATP and ADP was also measured for different dilution rates. The production of ethanol and lactate appeared to be linked with the re-oxidation of NADH produced during glycolysis, whereas hydrogen produced should come from reduced ferredoxin generated during pyruvate decarboxylation. To produce more hydrogen or more acetate from lactose, it thus appears that an efficient H₂ removal system should be used, based on a physical (membrane) or a biological approach, respectively, by cultivating C. thermolacticum with efficient H₂ scavenging and acetate producing microorganisms.     

Influence of dilution rate on the acidogenic phase products distribution during two-phase lactose anaerobiosis

Acidogenic fermentation of lactose was carried out in a continuous stirred reactor with a mixed anaerobic culture. From the variation of the reactor products with pH and dilution rate two possible carbon flow schemes were proposed for the reaction. In both schemes the carbon flow from pyruvate to butyrate and lactate was assumed to occur in parallel. A change in gas composition and in product concentrations at dilution rates between 0.1 and 0.15 h(-1) for pH levels between 4.5 and 6.0 was ascribed to a shift in microbial population. To clarify the mechanism radiotracer tests were made using [U-(14)C]-butyrate, [2-(14)C]-propionate and [U-(14)C]-lactate to determine the path of carbon flow during acidogenesis of lactose using a mixed culture. At a dilution rate between 0.1 and 0.15 h(-1) and pH from 4.5 to 6.0 a rise in the lactate concentration in the product was shown to be due to a microbial population shift which disabled the conversion of lactate to other intermediary metabolites. It was also found that the flow of carbon from pyruvate to butyrate and lactate occurred by parallel pathways. Also, in the presence of hydrogen reducing methanogens, lactate was almost completely converted to acetate and not propionate. Butyrate was found to be converted to acetate at a slow rate as long as hydrogen reducing methanogens were present. The role played by propionibacteria in this lactose acidogenic eocosystem was minor. From the carbon flow model it can be concluded that lactate is the most suitable marker for optimizing an acidogenic reactor in a two-phase biomethanation process.     

Microbial Ecophysiology of Whey Biomethanation: Intermediary Metabolism of Lactose Degradation in Continuous Culture

The intermediary carbon and electron flow routes for lactose degradation during whey biomethanation were studied in continuous culture. The chemostat was operated under lactose-limited conditions with a 100-h retention time. The carbon balance observed for lactose degradation was 4.65 mmol of CH₄, 4.36 mmol of CO₂ and 1.15 mmol of cellular carbon per mmol of lactose consumed, with other intermediary metabolites (i.e., acetate, lactate, etc.) accounting for less than 2% of the lactose consumed. The carbon and electron recoveries for this biomethanation were 87 and 90%, respectively. ¹⁴C tracer studies demonstrated that lactose biomethanation occurred in three distinct but simultaneous phases. Lactose was metabolized primarily into lactate, ethanol, acetate, formate, and carbon dioxide. During this hydrolytic phase, 82% of the lactose was transformed into lactate. These metabolites were transformed into acetate and H₂-CO₂ in a second, acetogenic, phase. Finally, the direct methane precursors were transformed during the methanogenic phase, with acetate accounting for 81% of the methane formed. A general scheme is proposed for the exact carbon and electron flow route during lactose biomethanation, which predicts the prevalent microbial populations in this ecosystem.     

Methanobacterium thermoautotrophicus sp. n., an Anaerobic, Autotrophic, Extreme Thermophile

The isolation of a new methanogenic bacterium, Methanobacterium thermoautotrophicus sp. n., is described. Successful isolation required a medium containing inorganic salts, an atmosphere consisting of an 80:20 mixture of hydrogen-carbon dioxide, and incubation temperatures of 65 to 70 C. Isolates of M. thermoautotrophicus were gram-positive, nonmotile, irregularly curved rods which frequently formed long filaments. The organism was found to be an autotroph and a strict anaerobe, and to have a pH optimum of 7.2 to 7.6. The optimal temperature for growth was 65 to 70 C, the maximum being 75 C and the minimum about 40 C. The generation time at the optimum was about 5 hr. The deoxyribonucleic acid of M. thermoautotrophicus had a guanine plus cytosine (GC) content of 52 moles per cent, whereas Methanobacterium sp. strain M.O.H. had a GC content of 38%. When heated, intact ribosomes of Methanobacterium sp. strain M.O.H. were stable up to 55 C and had a T(m) of 73 C. In contrast, ribosomes of M. thermoautotrophicus were stable up to 75 C and had a T(m) of 82 C. Upon complete thermal denaturation, ribosomes of strain M.O.H. underwent a 59% hyperchromic shift, whereas those of the thermophile showed only a 20% increase in hyperchromicity. Methane formation in cell-free extracts of M. thermoautotrophicus was temperature-dependent and required hydrogen and carbon dioxide; methyl cobalamin served as a methyl donor, and addition of coenzyme M stimulated methanogenesis.     

Phylogenetic diversity and activity of anaerobic microorganisms of high-temperature horizons of the Dagang Oilfield (China)

The number of microorganisms of major metabolic groups and the rates of sulfate-reducing and methanogenic processes in the formation waters of the high-temperature horizons of Dagang oilfield have been determined. Using cultural methods, it was shown that the microbial community contained aerobic bacteria oxidizing crude oil, anaerobic fermentative bacteria, sulfate-reducing bacteria, and methanogenic bacteria. Using cultural methods, the possibility of methane production from a mixture of hydrogen and carbon dioxide (H2 + CO2) and from acetate was established, and this result was confirmed by radioassays involving NaH14CO3 and 14CH3COONa. Analysis of 16S rDNA of enrichment cultures of methanogens demonstrated that these microorganisms belong to Methanothermobacter sp. (M. thermoautotrophicus), which consumes hydrogen and carbon dioxide as basic substrates. The genes of acetate-utilizing bacteria were not identified. Phylotypes of the representatives of Thermococcus spp. were found among 16S rDNAs of archaea. 16S rRNA genes of bacterial clones belong to the orders Thermoanaerobacteriales (Thermoanaerobacter, Thermovenabulum, Thermacetogenium, and Coprothermobacter spp.), Thermotogales, Nitrospirales (Thermodesulfovibrio sp.) and Planctomycetales. 16S rDNA of a bacterium capable of oxidizing acetate in the course of syntrophic growth with H2-utilizing methanogens was found at high-temperature petroleum reservoirs for the first time. These results provide further insight into the composition of microbial communities of high-temperature petroleum reservoirs, indicating that syntrophic processes play an important part in acetate degradation accompanied by methane production.     

Microbial acetate conversion to methane: kinetics,yields and pathways in a two-step digestion process

Summary Organic waste is converted in a two-stage process to methane and carbon dioxide by mixed cultures of microorganisms. Acetate, a product of acidogenic and acetogenic bacteria and the main substrate for methanogenic bacteria, is an important intermediate of the anaerobic degradation process, which results in the generation of methane. It was shown by labelling experiments using (U-¹⁴C) acetate that as much as 65%–96% of the total methane produced came from the acetate. The first order utilization rate for acetate in the methanogenic stages of a two-stage digestion process was between 0.17 h^-1 and 0.5 h^-1. The kinetics as well as the mass flow and yields of acetate and the methyl group of acetate were determined by pulse-labelling experiments with (U-¹⁴C) acetate and (2-¹⁴C) acetate without a significant rise of the total concentrations. Up to 58% of the acetate carbon was transformed to methane, and about 30% to carbon dioxide; only 4%–15% was incorporated into the biomass. There are at least two parallel degradation mechanisms in the metabolic transformation of acetate to methane: acetate is cleaved either to form methane and carbon dioxide or to form hydrogen and carbon dioxide, which can be transformed by an additional reaction to methane. Labelling experiments with (2-¹⁴C) acetate show that both mechanisms took place at similar order.     

Reaction engineering analysis of hydrogenotrophic production of acetic acid by Acetobacterium woodii

Great interest has emerged in biological CO₂‐fixing processes in the context of current climate change discussions. One example for such a process is the hydrogenotrophic production of acetic acid by anaerobic microorganisms. Acetogenic microorganisms make use of carbon dioxide in the presence of hydrogen to produce acetic acid and biomass. In order to establish a process for the hydrogenotrophic production of acetic acid, the formation of acetate by Acetobacterium woodii was studied in a batch‐operated stirred‐tank bioreactor at different hydrogen partial pressures (pH₂) in the gas phase. The volumetric productivity of the batch processes increased with increasing hydrogen partial pressure. A maximum of the volumetric productivity of 7.4 g_acetate L⁻¹ day⁻¹ was measured at a pH₂ of 1,700 mbar. At this pH₂ a final acetate concentration of 44 g L⁻¹ was measured after a process time of 11 days, if the pH was controlled at pH 7.0 (average cell density of 1.1 g L⁻¹ cell dry weight). The maximum cell specific actetate productivity was 6.9 g_acetate g day⁻¹ under hydrogenotrophic conditions. Biotechnol. Bioeng. 2011;108: 470–474. © 2010 Wiley Periodicals, Inc.     

沼泽红假单胞菌乙酸光合放氢研究

依据光合细菌生长代谢特性和有机废水降解主要产物类型,11种有机物被用于沼泽红假单胞菌（Rhodopseudomonas palustris）Z菌株的光合产氢研究,其中,乙酸反应体系产氢活性最高。在此基础上,研究了该菌株的生长与产氢动力学行为,探求了影响该菌株光合放氢的主要限制性影响因素。结果表明,该菌株产氢与生长部分相关。种子培养基和菌龄对产氢活性有明显影响。细胞最适产氢和生长所需要的光照强度和温度基本一致。当种子来源于硫酸铵高菌龄预培养物或谷氨酸钠对数期预培养物时,该菌株产氢活性显著增加,产氢延滞期明显缩短。氧浓度和接种量对产氢活性也有显著影响。供氢体和氮源浓度直接决定细胞的生长与光放氢活性。在低于70 mmol/L乙酸钠和15 mmol/L谷氨酸钠时,产氢活性随底物浓度的增加而增强。谷氨酸钠浓度高于15mmol/L时,由于游离NH₄⁺的出现,产氢活性受到抑制,但却明显刺激细胞的生长。在标准状况下,该菌株的最大产氢速率可达19.4 mL·L^-1·h^-1。     

Citrate Metabolism by Enterococcus faecalis FAIR-E 229

Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in various growth media containing citrate either in the presence of glucose or lactose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citrate), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate, while citrate was converted into acetate, formate, and ethanol. When de Man-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected. Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MRS broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism, although citrate itself was not catabolized. Glucose was converted stoichiometrically into lactate, while small amounts of ethanol were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in MRS broth without glucose, the main end products were acetate and formate. Small amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabolic potential to metabolize citrate and therefore to actively contribute to the flavor development of fermented dairy products.     

Intrinsic fermentation kinetics of lactose in acidogenic biofilms

The intrinsic fermentation kinetics of lactose in acidogenic biofilms were investigated in situ in a continuous flow fermentor at 35 degrees C and pH 4.6. The external and internal mass transfer resistances to lactose molecules from bulk solution to inside the biofilms were experimentally minimized or eliminated in a thin biofilm and recycled medium. In a chemically defined culture medium, the immobilized acidogens converted lactose mainly to acetate and butyrate; the minor products included ethanol. propionate, lactate, and hydrogen. The utilization rate of lactose, as a function of lactose concentration in the fermentor, can be described by a Michaelis-Menten equation, as can the formation rates of acetate, butyrate, and ethanol. The production rates of propionate and lactate had a liner relationship with lactose concentration under the experimental conditions. The low pH (4.6) of culture medium could depress the formation of propionate, and intermediate which is most difficulty digested by acetogenic bacteria located in the second fermentor in a two-phase process. Production rate of acetate quickly reached a constant, and additional utilization of lactose produced more butyrate and other minor products. (c) 1993 John Wiley & Sons, Inc.     

Competitive exclusion of Salmonella enterica serovar Enteritidis by Lactobacillus crispatus and Clostridium lactatifermentans in a sequencing fed-batch culture

Competitive exclusion of Salmonella enterica serovar Enteritidis by a mixed culture of Lactobacillus crispatus and Clostridium lactatifermentans was studied in a sequencing fed-batch reactor mimicking the cecal ecophysiology of broiler chickens. Growth of serovar Enteritidis was inhibited by a mixed culture of L. crispatus and C. lactatifermentans at pH 5.8 but not by a monoculture of L. crispatus at the same pH. Moreover, experiments performed at pH 7.0 did not show growth inhibition of serovar Enteritidis. L. crispatus fermented lactose to lactate, and C. lactatifermentans fermented the lactate to acetate and propionate in a mixed culture of L. crispatus and C. lactatifermentans growing on lactose. In contrast, only lactate was produced from lactose by a monoculture of L. crispatus. At pH 5.8 considerable concentrations of acetate and propionate were present as undissociated acids, whereas only trace levels of undissociated lactate were present at pH 5.8 due to the low pK(a) of lactate. At pH 7.0 all three acids were present in their dissociated forms. We conclude that a mixed culture of L. crispatus and C. lactatifermentans inhibits growth of serovar Enteritidis under cecal growth conditions. The undissociated forms of acetate and propionate produced in the mixed culture inhibited the growth of serovar Enteritidis.     

Desulfobulbus mediterraneus sp. nov., a sulfate-reducing bacterium growing on mono- and disaccharides

A new sulfate-reducing bacterium, strain 86FS1, was isolated from a deep-sea sediment in the western Mediterranean Sea with sodium lactate as electron and carbon source. Cells were ovoid, gram-negative and motile. Strain 86FS1 contained b- and c-type cytochromes. The organism was able to utilize propionate, pyruvate, lactate, succinate, fumarate, malate, alanine, primary alcohols (C(2)-C(5)), and mono- and disaccharides (glucose, fructose, galactose, ribose, sucrose, cellobiose, lactose) as electron donors for the reduction of sulfate, sulfite or thiosulfate. The major products of carbon metabolism were acetate and CO(2), with exception of n-butanol and n-pentanol, which were oxidized only to the corresponding fatty acids. The growth yield with sulfate and glucose or lactate was 8.3 and 15 g dry mass, respectively, per mol sulfate. The temperature limits for growth were 10 degrees C and 30 degrees C with an optimum at 25 degrees C. Growth was observed at salinities ranging from 10 to 70 g NaCl l(-1). Sulfide concentrations above 4 mmol l(-1) inhibited growth. The fatty acid pattern of strain 86FS1 resembled that of Desulfobulbus propionicus with n-14:0, n-16:1omega7, n-16:1 omega5, n-17:1 omega6 and n-18:1 omega7 as dominant fatty acids. On the basis of its phylogenetic position and its phenotypic properties, strain 86FS1 affiliates with the genus Desulfobulbus and is described as a new species, Desulfobulbus mediterraneus sp. nov.     

Optimisation of media and cultivation conditions for L(+)(S)-lactic acid production by Lactobacillus casei NRRL B-441

Process variables and concentration of carbon in media were optimised for lactic acid production by Lactobacillus casei NRRL B-441. Lactic acid yield was inversely proportional to initial glucose concentration within the experimental area (80-160 g l(-1)). The highest lactic acid concentration in batch fermentation, 118.6 g l(-1), was obtained with 160 g 1(-1) glucose. The maximum volumetric productivity, 4.4 g 1(-1) h(-1) at 15 h, was achieved at an initial glucose concentration of 100 g l(-1). Similar lactic acid concentrations were reached with a fedbatch approach using growing cells, in which case the fermentation time was much shorter. Statistical experimental design and response surface methodology were used for optimising the process variables. The temperature and pH optima for lactic acid production were 35 degrees C, pH 6.3. Malt sprout extract supplemented with yeast extract (4 g l(-1)) appeared to be an economical alternative to yeast extract alone (22 g l(-1)) although the fermentation time was a little longer. The results demonstrated both the separation of the growth and lactic acid production phases and lactic acid production by non-growing cells without any nutrient supplements. Resting L. casei cells converted 120 g l(-1) glucose to lactic acid with 100% yield and a maximum volumetric productivity of 3.5 g l(-1) h(-1).     

Energetics of Growth of a Defined Mixed Culture of Desulfovibrio vulgaris and Methanosarcina barkeri: Interspecies Hydrogen Transfer in Batch and Continuous Cultures

Interspecies hydrogen transfer was studied in Desulfovibrio vulgaris-Methanosarcina barkeri mixed cultures. Experiments were performed under batch and continuous growth culture conditions. Lactate or pyruvate was used as an energy source. In batch culture and after 30 days of simultaneous incubation, these organisms were found to yield 1.5 mol of methane and 1.5 mol of carbon dioxide per mol of lactate fermented. When M. barkeri served as the hydrogen acceptor, growth yields of D. vulgaris were higher compared with those obtained on pyruvate without any electron acceptor other than protons. In continuous culture, all of the carbon derived from the oxidation of lactate was recovered as methane and carbon dioxide, provided the dilution rate was minimal. Increasing the dilution rate induced a gradual accumulation of acetate, causing acetate metabolism to cease at above μ = 0.05 h⁻¹. Under these conditions all of the methane produced originated from carbon dioxide. The growth yields of D. vulgaris were measured when sulfate or M. barkeri was the electron acceptor. Two key observations resulted from the present study. First, although sulfate was substituted by M. barkeri, metabolism of D. vulgaris was only slightly modified. The coculture-fermented lactate produced equimolar quantities of carbon dioxide and methane. Second, acetogenesis and methane formation from acetate were completely separable.     

Acetic acid production from whey lactose by the co-culture ofStreptococcus lactis andClostridium formicoaceticum

Summary Acetic acid was produced from anaerobic fermentation of lactose by the co-culture ofStreptococcus lactis andClostridium formicoaceticum at 35° C and pHs between 7.0 and 7.6. Lactose was converted to lactic acid, and then to acetic acid in this mixed culture fermentation. The overall acetic acid yield from lactose was about 95% at pH 7.6 and 90% at pH 7.0. The fermentation rate was also higher at pH 7.6 than at pH 7.0. In batch fermentation of whey permeate containing about 5% lactose at pH 7.6, the concentration of acetic acid reached 20 g/l within 20 h. The production rate then became very slow due to end-product inhibition and high Na⁺ concentration. About 30 g/l acetate and 20 g/l lactate were obtained at a fermentation time of 80 h. However, when diluted whey permeate containing 2.5% lactose was used, all the whey lactose was converted to acetic acid within 30 h by this mixed culture.     

Isolation of saccharolytic dissimilatory sulfate-reducing bacteria

Abstract Four unidentified saccharolytic dissimilatory sulfate-reducing strains were isolated from an anaerobic digester. Cells were Gram-negative, motile, nonsporulating rods which differ markedly from known sulfate reducers especially with respect to carbon source utilisation and sulfur sources which can be reduced. The strains were capable of metabolising at least 26 out of 50 carbohydrates tested. Carbohydrates were, in the absence of exogenous sulfate, fermented to acetate, ethanol, lactate, carbon dioxide and hydrogen. In the presence of excess sulfate carbohydrates were fermented to acetate, ethanol, carbon dioxide, hydrogen and hydrogen sulfide, but lactate was not detected. An oxidized organic or inorganic sulfur source, including elemental sulfur, was not required as a prerequisite for growth on carbohydrates, Lactate was, in the presence of sulfate, converted to acetate, ethanol, carbon dioxide, hydrogen and hydrogen sulfide. In the absence of sulfate no lactate was utilised and no growth was observed.     

Low-cost propionate salt as road deicer: evaluation of cheese whey and other media constituents

Propionate and acetate salts are environmentally friendly, effective road deicer substitutes for widely used sodium chloride. A low-cost medium, using raw cheese whey and hydrolyzed whey permeate/whey permeate powder as substrates, and corn-steep liquor as a nutrient supplement, was studied for lactic acid production, replacing synthetic lactose and other high-cost nutrients. A non-sterile stage-I fermentation process for improved lactate productivity using an inexpensive commercial medium was performed at a 20-L fermenter level. A lactate yield of 0.98 g/g lactose and a productivity of 1.1 g/L/h was obtained with complete lactose utilization. When synthetic lactate and glucose were used as substrates in propionate and acetate fermentation, a total acid yield of 0.55 g/g glucose and lactate consumed and a batch productivity of 0.22 g/L/h was obtained. A stage-II fermentation process to produce propionate and acetate salts from cheese whey-derived lactate (stage-I fermentation broth) resulted in 1.6%( w/v) propionate after a total of 161 h (stages I and II).