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1.
Kuit W Minton NP López-Contreras AM Eggink G 《Applied microbiology and biotechnology》2012,94(3):729-741
In microorganisms, the enzyme acetate kinase (AK) catalyses the formation of ATP from ADP by de-phosphorylation of acetyl phosphate into acetic acid. A mutant strain of Clostridium acetobutylicum lacking acetate kinase activity is expected to have reduced acetate and acetone production compared to the wild type. In this work, a C. acetobutylicum mutant strain with a selectively disrupted ack gene, encoding AK, was constructed and genetically and physiologically characterized. The ack (-) strain showed a reduction in acetate kinase activity of more than 97% compared to the wild type. The fermentation profiles of the ack (-) and wild-type strain were compared using two different fermentation media, CGM and CM1. The latter contains acetate and has a higher iron and magnesium content than CGM. In general, fermentations by the mutant strain showed a clear shift in the timing of peak acetate production relative to butyrate and had increased acid uptake after the onset of solvent formation. Specifically, in acetate containing CM1 medium, acetate production was reduced by more than 80% compared to the wild type under the same conditions, but both strains produced similar final amounts of solvents. Fermentations in CGM showed similar peak acetate and butyrate levels, but increased acetoin (60%), ethanol (63%) and butanol (16%) production and reduced lactate (-50%) formation by the mutant compared to the wild type. These findings are in agreement with the proposed regulatory function of butyryl phosphate as opposed to acetyl phosphate in the metabolic switch of solventogenic clostridia. 相似文献
2.
Isolation and Characterization of Clostridium butyricum DSM 5431 Mutants with Increased Resistance to 1,3-Propanediol and Altered Production of Acids 总被引:6,自引:0,他引:6 下载免费PDF全文
S. Abbad-Andaloussi C. Manginot-Durr J. Amine E. Petitdemange H. Petitdemange 《Applied microbiology》1995,61(12):4413-4417
Clostridium butyricum mutants were isolated from the parent strain DSM 5431 after mutagenesis with N-methyl-N(prm1)-nitro-N-nitrosoguanidine and two selection procedures: osmotic pressure and the proton suicide method. Isolated mutants were more resistant to glycerol and to 1,3-propanediol (1,3-PD) than was the wild type, and they produced more biomass. In batch culture on 62 g of glycerol per liter, the wild type produced more acetic acid than butyrate, with an acetate/butyrate ratio of 5.0, whereas the mutants produced almost the same quantities of both acids or more butyrate than acetate with acetate/butyrate ratios from 0.6 to 1.1. The total acid formation was higher in the wild-type strain. Results of analysis of key metabolic enzymatic activities were in accordance with the pattern of fermentation product formation: either the butyrate kinase activity increased or the acetate kinase activity decreased in cell extracts of the mutants. A decreased level of the hydrogenase and NADH-ferredoxin activities concomitant with an increase in ferredoxin-NAD(sup+) reductase activities supports the conclusion that the maximum percentage of NADH available and used for the formation of 1,3-PD was higher for the mutants (97 to 100%) than for the wild type (70%). In fed-batch culture, at the end of the fermentation (72 h for the wild-type strain and 80 to 85 h for the mutants), 44% more glycerol was consumed and 50% more 1,3-PD was produced by the mutants than by the wild-type strain. 相似文献
3.
W. Stephenie B. M. Kabeir M. Shuhaimi M. Rosfarizan A. M. Yazid 《Biotechnology and Bioprocess Engineering》2007,12(2):106-113
Bifidobacterium pseudocatenulatum G4, a wild strain isolated from infant stools that has previously exhibited probiotic characteristics, was used in this study.
The aim of this research was to improve the growth potential of this strain in milk-based medium. An initial screening study
using a 23 full factorial design was carried out to identify the impact on biomass production of the various components of the medium
which were skim milk, yeast extract, and glucose. Statistical analysis suggested that yeast extract had a significant positive
effect on viable cell count whereas glucose had a negative effect. Response surface methodology (RSM) was then applied to
optimize the use of skim milk and yeast extract. A quadratic model was derived using a 32 face-centered central composite design to represent cell mass as a function of the two variables. The optimized medium composition
was found to be 2.8% skim milk and 2.2% yeast extract, w/v. The optimized medium allowed a maximum biomass of 9.129 log10 cfu/mL, 3.329 log units higher than that achieved with 10% skim milk, which is the amount commonly used. The application
of RSM resulted in an improvement in the biomass production of this strain in a more cost-effective milk medium, in which
skim milk use was reduced by 71.8%. 相似文献
4.
The primary alcohol/aldehyde dehydrogenase (coded by the aad gene) is responsible for butanol formation in Clostridium acetobutylicum. We complemented the non-sporulating, non-solvent-producing C. acetobutylicum M5 strain (which has lost the pSOL1 megaplasmid containing aad and the acetone-formation genes) with aad expressed from the phosphotransbutyrylase promoter and restored butanol production to wild type levels. Because no acetone was produced, no acids (acetate or butyrate) were re-assimilated leading to high butyrate but especially acetate levels. To counter acetate production, we examined thiolase overexpression in order reduce the acetyl-CoA pool and enhance the butyryl-CoA pool. We combined thiolase overexpression with aad overexpression aiming to also enhance butanol formation. While limiting the formation of acetate and ethanol, the butanol titers were not improved. We also generated acetate kinase (AK) and butyrate kinase (BK) knockout (KO) mutants of M5 using a modified protocol to increase the antibiotic-resistance gene expression. These strains exhibited greater than 60% reduction in acetate or butyrate formation, respectively. We complemented the AKKO M5 strain with aad overexpression, but could not successfully transform the BKKO M5 strain. The AKKO M5 strain overexpressing aad produced less acetate, but also less butanol compared to the M5 aad overexpression strain. These data suggest that loss of the pSOL1 megaplasmid renders cells resistant to changes in the two acid-formation pathways, and especially so for butyrate formation. We argue that the difficulty in generating high butanol producers without acetone and acid production is hindered by the inability to control the electron flow, which appears to be affected by unknown pSOL1 genes. 相似文献
5.
6.
Summary To improve the conversion of hexoses and pentoses to ethanol, a pyruvate-negative (PN) mutant of Clostridium saccharolyticum, having lower acetate kinase activity, was obtained. The PN mutant used more substrate (glucose or xylose) and produced more biomass and ethanol, but less acetic acid. This shift in catabolism raised the ethanol/acetate ratio from 6.7 to 13. The PN mutant converted both glucose and xylose to ethanol at an efficiency of 80% of the theoretical yield as compared to 64% for C. saccharolyticum wild type. This improved production of ethanol was also accompanied by an increased tolerance to ethanol. The PN mutant showed 50% growth inhibition at an ethanol concentration of 6.5% (v/v) as compared to 3.5% for the parent strain.National Research Council of Canada No. 21316 相似文献
7.
The antimutagenicity and fermentation pattern of three Bifidobacterium longum strains (B. longum, B. longum PS+, and B. longum PS-) in skim milk were studied. The increase in fermentation time significantly increased antimutagenicity with all strains tested against the mutagenicity of both 3-amino-1,4-dimethyl-5H-pyrido-[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) in an Ames-like test using streptomycin-dependent strain SD510 of Salmonella typhimurium TA98. Bifidobacterium longum PS+, a polysaccharide-producing strain, had a longer lag phase but showed the highest inhibition percentage against both mutagens tested. The viability of B. longum PS+ cells was not affected by the low pH of 4.1, probably owing to the protection offered by the polysaccharide produced. The antimutagenicity of the fermented milk against Trp-P-1 was dose dependent. The strains were also able to bind with different amino acid pyrolysates, and B. longum showed the highest binding. Acetone extracts of fermented skim milk dissolved in water showed less antimutagenicity than extracts dissolved in dimethylsulfoxide. The isolated crude polysaccharide from B. longum PS+ showed a dose-dependent inhibition of the mutagenicity of Trp-P-1. Thus, we conclude that the polysaccharide of B. longum PS+ can be used as an antimutagen. 相似文献
8.
Langa S Maldonado-Barragán A Delgado S Martín R Martín V Jiménez E Ruíz-Barba JL Mayo B Connor RI Suárez JE Rodríguez JM 《Applied microbiology and biotechnology》2012,94(5):1279-1287
Lactobacillus salivarius CECT 5713, isolated from human milk, has immunomodulatory, anti-inflammatory and antiinfectious properties, as revealed by several in vitro and in vivo assays, which suggests a strong potential as a probiotic strain. In this work, the relationships between several genetic features of L. salivarius CECT 5713 and the corresponding phenotypes were evaluated. Although it contains a plasmid-encoded bacteriocin cluster, no bacteriocin biosynthesis was observed, possibly due to a 4-bp deletion at the beginning of the histidine kinase determinant abpK. The genome of L. salivarius CECT 5713 harbours two apparently complete prophages of 39.6 and 48?kbp. Upon induction, the 48-kbp prophage became liberated from the bacterial genome, but no DNA replication took place, which resulted in lysis of the cultures but not in phage progeny generation. The strain was sensitive to most antibiotics tested and no transmissible genes potentially involved in antibiotic resistance were detected. Finally, the genome of L. salivarius CECT 5713 contained four ORFs potentially involved in human molecular mimetism. Among them, protein 1230 was considered of particular relevance because of its similarity with dendritic cell-related proteins. Subsequently, in vitro assays revealed the ability of L. salivarius CECT 5713 to stimulate the maturation of immature dendritic cells and to inhibit the in vitro infectivity of HIV-1. 相似文献
9.
A. Banina M. Vukasinovic S. Brankovic D. Fira M. Kojic & L. Topisirovic 《Journal of applied microbiology》1998,84(4):593-599
Lactobacillus acidophilus BGRA43 was selected from a set of human origin isolates of Lact. acidophilus strains for the highest growth rates and antagonistic effect against both Gram-positive and Gram-negative bacteria. The strain BGRA43 also exhibited an inhibitory effect on the growth of Clostridium sporogenes. Inhibition of this strain seems to be due to lactic acid production rather than hydrogen peroxide or bacteriocin. Growth of Lact. acidophilus BGRA43 in non-fat skim milk for 6 h at 37 °C resulted in a lowering of the pH value to 4·53. Besides the fast acidification, this strain generated a high viscosity of skim milk. These characteristics make the strain BGRA43 attractive for acidophilus milk production. Lactobacillus acidophilu s BGRA43 produces an extracellular proteinase. Whole cells efficiently degraded casein for 3 h at 37 °C especially α- and β-casein fractions. Total DNA isolated from the strain BGRA43 did not show any hybridization with lactococcal proteinase probes indicating that this strain produces a distinctive proteinase. 相似文献
10.
Fatty acids and monoglycerides were evaluated in brain heart infusion broth and in milk for antimicrobial activity against the Scott A strain of Listeria monocytogenes. C12:0, C18:3, and glyceryl monolaurate (monolaurin) had the strongest activity in brain heart infusion broth and were bactericidal at 10 to 20 micrograms/ml, whereas potassium (K)-conjugated linoleic acids and C18:2 were bactericidal at 50 to 200 micrograms/ml. C14:0, C16:0, C18:0, C18:1, glyceryl monomyristate, and glyceryl monopalmitate were not inhibitory at 200 micrograms/ml. The bactericidal activity in brain heart infusion broth was higher at pH 5 than at pH 6. In whole milk and skim milk, K-conjugated linoleic acid was bacteriostatic and prolonged the lag phase especially at 4 degrees C. Monolaurin inactivated L. monocytogenes in skim milk at 4 degrees C, but was less inhibitory at 23 degrees C. Monolaurin did not inhibit L. monocytogenes in whole milk because of the higher fat content. Other fatty acids tested were not effective in whole or skim milk. Our results suggest that K-conjugated linoleic acids or monolaurin could be used as an inhibitory agent against L. monocytogenes in dairy foods. 相似文献
11.
Mugocha P.T. Taylor J.R.N. Bester B.H. 《World journal of microbiology & biotechnology》2000,16(4):341-344
Fermented composite beverages of finger millet and milk are popular, nutritious, traditional foods in many parts of Zimbabwe. With the aim of commercial production, we determined what type of microbial cultures can be used to ferment a composite finger millet and skimmed milk powder gruel and the optimum conditions for its production. Composites containing between 0 and 100% finger millet gruel by volume were inoculated and incubated at various temperatures. The desired pH of 4.5 or less was obtained with incubation at 30 to 45 °C (but not at lower temperatures) with lower pH values being obtained as the temperature increased. YC380 (a yoghurt type bacterial starter culture) produced a pH of 4.5 or less only when skim milk was also present; V2 (another yoghurt type bacterial starter culture) did so at all levels of finger millet gruel and JC (a mixed strain culture developed to ferment cereals) only when finger millet gruel was present. A clear relationship between incubation temperature and syneresis could not be established but syneresis decreased significantly (p < 0.05) with increasing proportions of finger millet gruel. A thick product with a set consistency was obtained with YC380 at an incubation temperature of 45 °C and a storage temperature of 7 °C regardless of proportion of finger millet gruel. V2 produced a thick product with a set consistency at an incubation temperature of 45 °C, and storage temperature of 7 °C and when the proportions of finger millet gruel were between 0 and 50%. It appears that yoghurt type bacterial cultures can be successfully used to produce a composite fermented beverage from finger millet and skim milk, but cultures developed for fermentation of cereals are not suitable. 相似文献
12.
Fatty acids and monoglycerides were evaluated in brain heart infusion broth and in milk for antimicrobial activity against the Scott A strain of Listeria monocytogenes. C12:0, C18:3, and glyceryl monolaurate (monolaurin) had the strongest activity in brain heart infusion broth and were bactericidal at 10 to 20 micrograms/ml, whereas potassium (K)-conjugated linoleic acids and C18:2 were bactericidal at 50 to 200 micrograms/ml. C14:0, C16:0, C18:0, C18:1, glyceryl monomyristate, and glyceryl monopalmitate were not inhibitory at 200 micrograms/ml. The bactericidal activity in brain heart infusion broth was higher at pH 5 than at pH 6. In whole milk and skim milk, K-conjugated linoleic acid was bacteriostatic and prolonged the lag phase especially at 4 degrees C. Monolaurin inactivated L. monocytogenes in skim milk at 4 degrees C, but was less inhibitory at 23 degrees C. Monolaurin did not inhibit L. monocytogenes in whole milk because of the higher fat content. Other fatty acids tested were not effective in whole or skim milk. Our results suggest that K-conjugated linoleic acids or monolaurin could be used as an inhibitory agent against L. monocytogenes in dairy foods. 相似文献
13.
14.
Spores of the Phycomyces blakesleeanus strain S440 germinated only for some 4 to 7% when activated with a heat treatment or with ammonium acetate. Contrary to wild type spores, they showed no increase in trehalase activity during or after the activating treatment. This was not due to a variant trehalase or a defective protein kinase but rather to the absence of an increase in cellular cyclic AMP which normally occurs in the wild type. Phosphodiesterase activity in the mutant was comparable to wild type activity and in both strains phosphodiesterase was inactivated by a heat treatment. The phosphodiesterase inhibitor 1-isobutyl, 3-methyl xanthine caused germination and trehalase activation in the wild type but not in the mutant. The results corroborate the importance of cyclic AMP in the breaking of dormancy and the activation of trehalase in this fungus. 相似文献
15.
Dr. A. El Kanouni A. -M. Junelles R. Janati-Idrissi H. Petitdemange R. Gay 《Current microbiology》1989,18(3):139-144
Pyruvate halogen analogs, 3-fluoropyruvate and 3-bromopyruvate, are toxic towardClostridium acetobutylicum. After mutagenesis with nitrosoguanidine, mutants resistant to these compounds were selected. In a normal batch culture regulated at pH 4.8, mutants quickly initiated the acid-solvent transition, accumulating more acetoin and lactate than the wild type strain. The maximum rate of specific glucose uptake was higher in the mutants than in the wild type: 1.76 h–1 and 0.9 h–1 respectively. When the pH was uncontrolled, mutants converted glucose into solvents, essentially butanol, while the wild-type strain ceased its fermentation at the acidogenic stage. Enzymatic investigations revealed that acetate kinase, butyrate kinase, and acetoacetate decarboxylase activities decreased sooner in the mutants than in the parent strain. 相似文献
16.
Kikuchi-Hayakawa H Shibahara-Sone H Osada K Onodera-Masuoka N Ishikawa F Watanuki M 《Bioscience, biotechnology, and biochemistry》2000,64(3):466-475
The effect of fermented skim milk (FSM) by Lactobacillus casei strain Shirota on plasma lipids in hamsters was examined. Hamsters fed on cholesterol-free and -enriched diets containing 30% FSM had lower levels of plasma triglyceride than those fed on the control diet. In the experiment with the cholesterol-enriched diet-fed hamsters, the plasma triglyceride level was suppressed by FSM at concentrations of 10% to 30%. Unfermented milk tended to lower the level of triglyceride, but not significantly. The plasma cholesterol concentration was not affected by an FSM and unfermented skim milk supplement to the diet. L. casei strain Shirota grew well in the presence of mixed lipid micelles containing bile acid, but did not have the ability to remove cholesterol from the culture broth. These results indicate that FSM lowered the plasma triglyceride level in hamsters. 相似文献
17.
An isolate of L. monocytogenes Scott A that is tolerant to high hydrostatic pressure (HHP), named AK01, was isolated upon a single pressurization treatment of 400 MPa for 20 min and was further characterized. The survival of exponential- and stationary-phase cells of AK01 in ACES [N-(2-acetamido)-2-aminoethanesulfonic acid] buffer was at least 2 log units higher than that of the wild type over a broad range of pressures (150 to 500 MPa), while both strains showed higher HHP tolerance (piezotolerance) in the stationary than in the exponential phase of growth. In semiskim milk, exponential-phase cells of both strains showed lower reductions upon pressurization than in buffer, but again, AK01 was more piezotolerant than the wild type. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella, were elongated, and showed slightly lower maximum specific growth rates than the wild type at 8, 22, and 30 degrees C. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H(2)O(2) compared with the wild type. The difference in HHP tolerance between the piezotolerant strain and the wild-type strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wild type had identical in situ lipid melting curves as determined by Fourier transform infrared spectroscopy. The demonstrated occurrence of a piezotolerant isolate of L. monocytogenes underscores the need to further investigate the mechanisms underlying HHP resistance of food-borne microorganisms, which in turn will contribute to the appropriate design of safe, accurate, and feasible HHP treatments. 相似文献
18.
Avşaroğlu MD Buzrul S Sanlibaba P Alpas H Akçelik M 《Journal of industrial microbiology & biotechnology》2007,34(11):729-737
Absract The plasmid stability of three wild type Lactococcus lactis strains and their mutants was investigated at different incubation time and temperatures in two different media [M17 broth
and reconstituted skim milk (RSM)]. The results showed that both incubation times and temperature are effective on plasmid
loss. The plasmid profiles of wild type strains exhibited 8 to 9 distinct plasmid species with molecular weights from 2.1
to 24.0 kb. Lactose fermentation ability was found to be encoded by 22.2 (strain U70), 23.6 (strain U29) and 24.0 (strain
U52) kb plasmids in the wild type strains, respectively. The stabilities of the plasmids were explained by applying a second-order
polynomial modeling system. Reasonable fittings were obtained for the model and the adjusted regression coefficients (R
2
adj) were between 0.76 and 0.99 for the overall data. Overall, it was found that incubation time had the most profound effect
on plasmid stability, with plasmid loss occurring after 72 h, while temperatures in the range of 15–40°C also induced plasmid
instability. 相似文献
19.
Involvement of PorK,a component of the type IX secretion system,in Prevotella melaninogenica pathogenicity 下载免费PDF全文
Yoshio Kondo Keiko Sato Keiji Nagano Miyuki Nishiguchi Tomonori Hoshino Taku Fujiwara Koji Nakayama 《Microbiology and immunology》2018,62(9):554-566
20.
Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor 总被引:5,自引:0,他引:5
Fed-batch fermentations of glucose by P. acidipropionici ATCC 4875 in free-cell suspension culture and immobilized in a fibrous-bed bioreactor (FBB) were studied. The latter produced a much higher propionic acid concentration (71.8 +/- 0.8 g/L vs. 52.2 +/- 1.1 g/L), indicating enhanced tolerance to propionic acid inhibition by cells adapted in the FBB. Compared to the free-cell fermentation, the FBB culture produced 20-59% more propionate (0.40-0.65 +/- 0.02 g/g vs. 0.41 +/- 0.02 g/g), 17% less acetate (0.10 +/- 0.01 g/g vs. 0.12 +/- 0.02 g/g), and 50% less succinate (0.09 +/- 0.02 g/g vs. 0.18 +/- 0.03 g/g) from glucose. The higher propionate production in the FBB was attributed to mutations in two key enzymes, oxaloacetate transcarboxylase and propionyl CoA: succinyl CoA transferase, leading to the production of propionic acid from pyruvate. Both showed higher specific activity and lower sensitivity to propionic acid inhibition in the mutant than in the wild type. In contrast, the activity of PEP carboxylase, which converts PEP directly to oxaloacetate and leads to the production of succinate from glucose, was generally lower in the mutant than in the wild type. For phosphotransacetylase and acetate kinase in the acetate formation pathway, however, there was no significant difference between the mutant and the wild type. In addition, the mutant had a striking change in its morphology. With a threefold increase in its length and approximately 24% decrease in its diameter, the mutant cell had an approximately 10% higher specific surface area that should have made the mutant more efficient in transporting substrates and metabolites across the cell membrane. A slightly lower membrane-bound ATPase activity found in the mutant also indicated that the mutant might have a more efficient proton pump to allow it to better tolerate propionic acid. In addition, the mutant had more longer-chain saturated fatty acids (C17:0) and less unsaturated fatty acids (C18:1), both of which could decrease membrane fluidity and might have contributed to the increased propionate tolerance. The enhanced propionic acid production from glucose by P. acidipropionici was thus attributed to both a high viable cell density maintained in the reactor and favorable mutations resulted from adaptation by cell immobilization in the FBB. 相似文献