Physiological and nutritional factors affecting synthesis of extracellular metalloproteases by Clostridium bifermentans NCTC 2914.

Extracellular protease production by Clostridium bifermentans NCTC 2914 occurred throughout the growth phase in batch culture. In both glucose-excess and -limited chemostats, protease formation was inversely related to the dilution rate, over the range D = 0.03 to 0.70 h-1. At high dilution rates (D greater than 0.25 h-1), protease activities were greatest under excess glucose conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of chemostat culture effluents showed the presence of up to 18 bands of protease activity at low dilution rates, with apparent molecular masses ranging from about 36 to 125 kDa. High-performance liquid chromatography gel filtration of culture supernatants gave four peaks of activity at 34, 42, 60, and 102 kDa. Glucose, peptone, and phosphate stimulated protease formation, but ammonia concentrations up to 10 g liter-1 had little effect on the process. Culture pH in glucose-excess chemostats strongly influenced protease synthesis, which was maximal during growth at pH 6.4. The optimal pH of protease activity was 7.0. Although a wide variety of proteins were hydrolyzed by C. bifermentans proteases, none of the enzymes were collagenolytic. Of 21 different p-nitroanilide, beta-naphthylamide, and N-carbobenzoyl substrates tested, none were hydrolyzed. With the exception of Ca2+, divalent metal ions inhibited proteolysis. Experiments with protease inhibitors demonstrated that 1 mM EDTA inhibited protease activities in culture supernatants by over 90%, indicating that the enzymes were principally of the metalloprotease type.     

Regulation of protease production in Clostridium sporogenes.

The physiological and nutritional factors that regulate protease synthesis in Clostridium sporogenes C25 were studied in batch and continuous cultures. Formation of extracellular proteases occurred at the end of active growth and during the stationary phase in batch cultures. Protease production was inversely related to growth rate in glucose-excess and glucose-limited chemostats over the range D = 0.05 to 0.70 h-1. In pulse experiments, glucose, ammonia, phosphate, and some amino acids (tryptophan, proline, tyrosine, and isoleucine) strongly repressed protease synthesis. This repression was not relieved by addition of 4 mM cyclic AMP, cyclic GMP, or dibutyryl cyclic AMP. Protease formation was markedly inhibited by 4 mM ATP and ADP, but GTP and GDP had little effect on the process. It is concluded that protease production by C. sporogenes is strongly influenced by the amount of energy available to the cells, with the highest levels of protease synthesis occurring under energy-limiting conditions.     

Regulation of protease production in Clostridium sporogenes

The physiological and nutritional factors that regulate protease synthesis in Clostridium sporogenes C25 were studied in batch and continuous cultures. Formation of extracellular proteases occurred at the end of active growth and during the stationary phase in batch cultures. Protease production was inversely related to growth rate in glucose-excess and glucose-limited chemostats over the range D = 0.05 to 0.70 h-1. In pulse experiments, glucose, ammonia, phosphate, and some amino acids (tryptophan, proline, tyrosine, and isoleucine) strongly repressed protease synthesis. This repression was not relieved by addition of 4 mM cyclic AMP, cyclic GMP, or dibutyryl cyclic AMP. Protease formation was markedly inhibited by 4 mM ATP and ADP, but GTP and GDP had little effect on the process. It is concluded that protease production by C. sporogenes is strongly influenced by the amount of energy available to the cells, with the highest levels of protease synthesis occurring under energy-limiting conditions.     

Production of Serine Proteases by the Oyster Pathogen Perkinsus marinus (Apicomplexa) In Vitro

ABSTRACT. Analysis of the cell-free supernatants of Perkinsus marinus cultures by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining revealed the presence of as many as 17 bands ranging in molecular weight from 239 to 32 kDa. These bands were not present in un-inoculated medium. Moreover, P. marinus produces extracellular proteins that possess proteolytic activities; the cell-free supernatants of P. marinus cultures could digest a variety of proteins including gelatin, casein, fibronectin and laminin. Oyster plasma was also digested by cell-free culture supernatants. The proteolytic activity in cell-free culture supernatants was detected 24 h post-inoculation, while no proteolytic activity could be detected in cell lysates. The proteolytic activities were characterized using substrate-impregnated sodium dodecylsulfate-polyacrylamide gels and had approximate molecular weights ranging from 55 to 35 kDa. The proteolytic activity of cell-free culture supernatants was inhibited by the serine protease inhibitors phenylmethylsulphonyl fluoride, 3,4-dichloroisocoumarin and soybean trypsin inhibitor. In contrast, inhibitors (i.e. trans-epoxysuccinyll-leucylamido(4-guanidino)-butane, 1, 10-phenanthroline, captopril, ethylenediaminetetracetic acid, pepstatin A or diazoacetyl-DL-norleucine methyl ester) from the other three classes of proteases had no effect. It was concluded that the P. marinus proteases in cell-free culture supernatants are serine proteases.     

Involvement of an extracellular protease in algicidal activity of the marine bacterium Pseudoalteromonas sp. strain A28

The marine bacterium Pseudoalteromonas sp. strain A28 was able to kill the diatom Skeletonema costatum strain NIES-324. The culture supernatant of strain A28 showed potent algicidal activity when it was applied to a paper disk placed on a lawn of S. costatum NIES-324. The condensed supernatant, which was prepared by subjecting the A28 culture supernatant to ultrafiltration with a 10,000-M(w)-cutoff membrane, showed algicidal activity, suggesting that strain A28 produced extracellular substances capable of killing S. costatum cells. The condensed supernatant was then found to have protease and DNase activities. Two Pseudoalteromonas mutants lacking algicidal activity, designated NH1 and NH2, were selected after N-methyl-N'-nitrosoguanidine mutagenesis. The culture supernatants of NH1 and NH2 showed less than 15% of the protease activity detected with the parental strain, A28. The protease was purified to homogeneity from A28 culture supernatants by using ion-exchange chromatography followed by preparative gel electrophoresis. Paper-disk assays revealed that the purified protease had potent algicidal activity. The purified protease had a molecular mass for 50 kDa, and the N-terminal amino acid sequence was determined to be Ala-Thr-Pro-Asn-Asp-Pro. The optimum pH and temperature of the protease were found to be 8.8 and 30 degrees C, respectively, by using succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate. The protease activity was strongly inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, antipain, chymostatin, and leupeptin. No significant inhibition was detected with EDTA, EGTA, phenanthroline or tetraethylenepentamine. These results suggest that Pseudoalteromonas sp. strain A28 produced an extracellular serine protease which was responsible for the algicidal activity of this marine bacterium.     

Co-utilization of polymerized carbon sources by Bacteroides ovatus grown in a two-stage continuous culture system.

Bacteroides ovatus NCTC 11153 was grown in a two-stage continuous culture system at various growth rates (vessel 1, D = 0.06 to 0.19 h-1; vessel 2, D = 0.03 to 0.09 h-1) on media containing mixtures of starch and arabinogalactan as carbon sources. The cell-associated enzyme activities needed to hydrolyze both substrates (amylase, arabinogalactanase, alpha-glucosidase, beta-galactosidase, and alpha-arabinofuranosidase) were variously influenced by growth rate and polysaccharide availability but were detected under all growth conditions tested. Measurements of residual carbohydrate in spent culture media showed that both polysaccharides were co-utilized during growth under putative C-limited conditions. The arabinogalactan was partly depolymerized in N-limited chemostats, and significant amounts of arabinose- and galactose-containing oligosaccharides accumulated in the cultures, indicating that starch was being preferentially utilized. Acetate, propionate, and succinate were the major fermentation products formed by C-limited bacteria, but under N limitation, lactate was also produced. Molar ratios of succinate increased concomitantly with the dilution rate in C-limited chemostats, whereas molar ratios of propionate decreased. During N-limited growth, however, decarboxylation of succinate to propionate was relatively independent of growth rate. Cell viability was higher in C-limited cultures compared with those grown under N limitation and was greatest at high dilution rates, irrespective of nutrient limitation.     

Co-utilization of polymerized carbon sources by Bacteroides ovatus grown in a two-stage continuous culture system

Bacteroides ovatus NCTC 11153 was grown in a two-stage continuous culture system at various growth rates (vessel 1, D = 0.06 to 0.19 h-1; vessel 2, D = 0.03 to 0.09 h-1) on media containing mixtures of starch and arabinogalactan as carbon sources. The cell-associated enzyme activities needed to hydrolyze both substrates (amylase, arabinogalactanase, alpha-glucosidase, beta-galactosidase, and alpha-arabinofuranosidase) were variously influenced by growth rate and polysaccharide availability but were detected under all growth conditions tested. Measurements of residual carbohydrate in spent culture media showed that both polysaccharides were co-utilized during growth under putative C-limited conditions. The arabinogalactan was partly depolymerized in N-limited chemostats, and significant amounts of arabinose- and galactose-containing oligosaccharides accumulated in the cultures, indicating that starch was being preferentially utilized. Acetate, propionate, and succinate were the major fermentation products formed by C-limited bacteria, but under N limitation, lactate was also produced. Molar ratios of succinate increased concomitantly with the dilution rate in C-limited chemostats, whereas molar ratios of propionate decreased. During N-limited growth, however, decarboxylation of succinate to propionate was relatively independent of growth rate. Cell viability was higher in C-limited cultures compared with those grown under N limitation and was greatest at high dilution rates, irrespective of nutrient limitation.     

The effects of temperature, pH and growth rate on secondary metabolism in Streptomyces thermoviolaceus grown in a chemostat.

Streptomyces thermoviolaceus was grown in a chemostat under conditions of glutamate limitation. The effects of growth rate on production of the antibiotic granaticin, extracellular protein and protease activity as components of secondary metabolism were studied at 37, 45 and 50 degrees C. The amount of each secondary metabolite synthesized was highly dependent on growth rate and temperature. Granaticin yields were highest at growth rates of 0.1 to 0.15 h-1 at 37 degrees C, 0.175 h-1 at 45 degrees C and 0.045 h-1 at 50 degrees C. Protease activity of culture supernatants responded to low nutrient concentration and/or low growth rate. Measurements of extracellular protein revealed complex changes in amount which were dependent on growth rate and temperature. At 45 degrees C and a growth rate of 0.15 h-1, biomass yield was highest between pH 5.5 to 6.5 whereas granaticin synthesis was low at pH 5.5 and rose to highest values at between pH 6.5 and 7.5.     

Supernatant proteolytic activities of High-Five insect cells grown in serum-free culture

The proteolytic activity of High-Five insect cell culture supernatants was analysed using substrate gel electrophoresis (zymography). During growth in serum-free media, High-Five cells constitutively expressed and secreted proteases that were active on casein gel but not on gelatin or bovine serum albumin gels. Two main protease bands were visible at about 41–42 kDa and 32–33 kDa. By addition of various protease inhibitors in the incubation buffer, the proteases were identified as metalloproteases as complete and specific inhibition of the proteolytic activities was only obtained by 1,10-phenanthroline.     

Characterization of excretory/secretory endopeptidase and metallo-aminopeptidases from Taenia crassiceps metacestodes

Cysticercosis is caused by Taenia spp. metacestodes, which must survive in the host tissues to complete their life cycle. Their survival depends on their control of host immune responses. Because many parasites use proteases to modulate host responses, we examined culture media from Taenia crassiceps metacestodes for protease activity using peptide substrates. We identified prominent aminopeptidase activity at neutral pH, which was inhibited by chelating agents and partially inhibited by the aminopeptidase inhibitor, bestatin. Endopeptidase substrates were optimally cleaved at slightly acidic pH and endopeptidase activity was inhibited by cysteine protease inhibitors. Gel filtration FPLC and subsequent visualization by silver staining revealed a metallo-aminopeptidase of molecular weight 21 kDa and cysteine proteases of Mr 70 and 64 kDA. Recombinant IL-2 was digested when incubated with parasite culture supernatants, but not with control media. IL-2 degradation was completely inhibited by 1,10 phenanthroline and partially inhibited by bestatin, suggesting that a metallo-aminopeptidase was responsible. Incubation of human IgG with culture supernatants resulted in complete degradation of IgG, which was blocked by cysteine protease inhibitors. These observations demonstrate that Taenia spp. metacestodes secrete a number of proteolytic enzymes, which may target molecules from the host immune system and assist in evasion of the host immune response.     

Involvement of an Extracellular Protease in Algicidal Activity of the Marine Bacterium Pseudoalteromonas sp. Strain A28

The marine bacterium Pseudoalteromonas sp. strain A28 was able to kill the diatom Skeletonema costatum strain NIES-324. The culture supernatant of strain A28 showed potent algicidal activity when it was applied to a paper disk placed on a lawn of S. costatum NIES-324. The condensed supernatant, which was prepared by subjecting the A28 culture supernatant to ultrafiltration with a 10,000-M_w-cutoff membrane, showed algicidal activity, suggesting that strain A28 produced extracellular substances capable of killing S. costatum cells. The condensed supernatant was then found to have protease and DNase activities. Two Pseudoalteromonas mutants lacking algicidal activity, designated NH1 and NH2, were selected after N-methyl-N′-nitrosoguanidine mutagenesis. The culture supernatants of NH1 and NH2 showed less than 15% of the protease activity detected with the parental strain, A28. The protease was purified to homogeneity from A28 culture supernatants by using ion-exchange chromatography followed by preparative gel electrophoresis. Paper-disk assays revealed that the purified protease had potent algicidal activity. The purified protease had a molecular mass for 50 kDa, and the N-terminal amino acid sequence was determined to be Ala-Thr-Pro-Asn-Asp-Pro. The optimum pH and temperature of the protease were found to be 8.8 and 30°C, respectively, by using succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate. The protease activity was strongly inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, antipain, chymostatin, and leupeptin. No significant inhibition was detected with EDTA, EGTA, phenanthroline or tetraethylenepentamine. These results suggest that Pseudoalteromonas sp. strain A28 produced an extracellular serine protease which was responsible for the algicidal activity of this marine bacterium.     

Purification and characterization of a fibrinolytic protease from a culture supernatant of Flammulina velutipes mycelia

In this study we purified a fibrinolytic enzyme from the culture supernatant of Flammulina velutipes mycelia by ion exchange and gel filtration chromatographies, it was designated as F. velutipes protease (FVP-I). This purification protocol resulted in 18.52-fold purification of the enzyme at a final yield of 0.69%. The molecular mass of the purified enzyme was estimated to be 37 kDa by SDS-PAGE, fibrin-zymography and size exclusion by FPLC. This protease effectively hydrolyzed fibrin, preferentially digesting alpha-chain over beta-and gamma-gamma chain. Optimal protease activity was found to occur at a pH of 6.0 and a temperature of 20 to 30 degrees C. The protease activity was inhibited by Cu2+, Fe2+ and Fe3+ ions, but was found to be enhanced by Mn2+ and Mg2+ ions. Furthermore, FVP-I activity was potently inhibited by EDTA and EGTA, and it was found to exhibit a higher specificity for chromogenic substrate S-2586 for chymotrypsin, indicating that the enzyme is a chymotrypsin-like metalloprotease. The first 20 amino acid residues of the N-terminal sequence of FVP-I were LTYRVIPITKQAVTEGTELL. They had a high degree of homology with hypothetical protein CC1G_11771, GeneBank Accession no. EAU86463.     

Fibrinolytic and antithrombotic protease from Spirodela polyrhiza

A fibrinolytic protease was purified from a Chinese herb (Spirodela polyrhiza). The protease has a molecular mass of 145 kDa and 70 kDa in gel filtration and SDS-polyacrlamide gel electrophoresis (PAGE), respectively, implying it is a dimer. Its optimum pH was 4.5-5.0. The enzyme was stable below 42 degrees C and after lyophilization. The enzyme activity was inhibited significantly by leupeptin and aprotinin. The protease hydrolyzed not only fibrin but also fibrinogen, cleaving Aalpha and Bbeta without affecting the gamma chain of fibrinogen. It preferentially cleaved the peptide bond of Arg or Lys of synthetic substrates (P1 position). The enzyme had an anticoagulating activity measured with activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT) tests. It delayed APTT, TT, and PT two times at the concentration of 36, 39, and 128 nM, respectively and this was drastically reduced after heat treatment.     

Utilization of starch and synthesis of a combined amylase/αα-glucosidase by the human colonic anaerobe Bacteroides ovatus

Bacteroides ovatus preferentially utilized starch and pectin when grown on a mixture of polysaccharides in batch culture, indicating that these carbohydrates are important substrates for the bacterium in the human large intestine. Further studies on starch breakdown showed that continuous cultures grew on the polysaccharide when it provided the sole carbohydrate source, to yield a single hydrolytic product at low dilution rates ( D = 0·04 h⁻¹), with an estimated molecular mass of 13 kDa. In contrast, two major types of oligomeric products were formed at higher dilution rates ( D = 0·44 h⁻¹), with approximate molecular weights of 11 and 140 kDa. Analysis of cell-associated starch-degrading enzymes produced by Bact. ovatus using ion exchange chromatography and HPLC gel-filtration showed that amylase and α-glucosidase activities eluted in the same fractions. The single peak containing amylase and α-glucosidase activities obtained by HPLC gel-filtration chromatography corresponded to a molecular mass of approximately 140 kDa, and activity staining of gels for α-glucosidase activity after polyacrylamide gel electrophoresis, in the presence of sodium dodecyl sulphate, gave an estimated molecular mass of 70 kDa, indicating this enzyme to be a dimer. After renaturation, the 70 kDa band was cut from the gels and solubilized. The extract hydrolysed gelatinized starch and p -nitrophenyl-α- D -glucopyranoside.     

Evaluation of 16s rRNA and cellular fatty acid profiles as markers of human intestinal bacterial growth in the chemostat

Chemostats were used to study the effects of carbon and nitrogen limitation and specific growth rate on 16S rRNA synthesis and cellular fatty acid (CFA) profiles in four human intestinal bacteria (Bacteroides thetaiotaomicron, Bifidobacterium adolescentis, Clostridium bifermentans and Cl. difficile). Cellular fatty acid synthesis varied with dilution rate and nutrient availability in different species, but these cellular constituents were relatively stable phenotypic characteristics in Bact. thetaiotaomicron, where branched chain and hydroxy CFA were good taxonomic markers. Conversely, CFA in the Gram-positive bacteria varied markedly with changes in growth environment. For example, in chemostats, cyclopropane CFA were only synthesized in Cl. bifermentans and Cl. difficile under N-limited conditions. Similarly, Dimethyl acetal (DMA) fatty acids in Bif. adolescentis were primarily produced during N-limited growth, and this was inversely related to dilution rate. At low growth rates, 16S rRNA concentrations (microg rRNA per ml culture) correlated with viable bacterial counts, but were more closely related to specific growth rate when expressed as a function of cell mass (microg rRNA per mg dry weight bacteria). However, this did not reveal differences in bacterial population size and rRNA concentration in C-limited cultures. Thus, at low dilution rates, C limitation strongly reduced rRNA synthesis in Cl. bifermentans, despite viable cell counts being similar to those in N-limited cultures. These results indicate that, while 16S rRNA is a useful indicator of microbial activity, cell growth rate does not necessarily relate to rRNA concentration under all nutritional conditions. Consequently, bowel habit and diet will affect both CFA and rRNA content in bacteria isolated from intestinal samples, and this should be taken into consideration when interpreting such data measurements.     

Studies on the proteolytic activity of Bacteroides fragilis

The proteolytic activity of the intestinal bacterium Bacteroides fragilis NCDO 2217 was cell-bound during exponential growth, but was progressively released from the cells in stationary phase. Proteins hydrolysed included casein, trypsin, chymotrypsin, azocasein and the proteins in azosoya bean flour. Collagen, azocoll, elastin, gelatin, ovalbumin and bovine serum albumin were either weakly degraded or completely refractory to proteolysis. Arylamidase activity was exhibited against leucine p-nitroanilide (LPNA), leucine beta-naphthylamide, glycyl-proline p-nitroanilide and valyl-alanine p-nitroanilide. The bacterium grew with ammonia, peptone or casein as sole nitrogen source. Azocasein- and LPNA-hydrolysing activities were consistently higher when grown on casein. Cell-bound protease activity increased concomitantly with growth rate in both carbon- and nitrogen-limited continuous culture. Leucine arylamidase activity was also growth-rate-dependent, being 3-fold greater at D = 0.18 h-1 compared to D = 0.03 h-1. Extracellular proteolytic activity was only detected at low growth rates, accounting for about 25% of total protease activity.     

Purification and properties of a thiol protease from lung fluke adult Paragonimus ohirai

The thiol protease was purified from adult Paragonimus ohirai by alpha 1-antitrypsin-Sepharose, Sephadex G-75 and CM-cellulose, measuring its activities to hydrolyze hemoglobin and tosyl-L-lysine alpha-naphthyl-ester. The purified protease showed a single band on polyacrylamide disc gel isoelectrophoresis as zymogram with Tos-Lys-NE and also by protein staining, and its pI was found to be 6.4. The molecular weight was calculated to be 29,000 by gel filtration and 27,000 by SDS-polyacrylamide gel electrophoresis as a single polypeptide. The protease hydrolyzed hemoglobin and Tos-Lys-NE optimally at pH 4.0 and 5.0, respectively. The both hydrolyzing activities were inhibited by alpha 1-AT and soybean trypsin inhibitor as well as thiol protease inhibitors such as antipain, E-64 and p-hydroxymercuriphenylsulfonate. These results indicate that this enzyme is a new type thiol protease.     

Co-culture of Bifidobacterium adolescentis and Bacteroides thetaiotaomicron in arabinogalactan-limited chemostats: effects of dilution rate and pH

The effects of dilution rate (D = 0.04-0.38/h) and pH (5.0-6.5) on co-cultures of Bifidobacterium adolescentis and Bacteroides thetaiotaomicron were studied in arabinogalactan-limited chemostats. B. thetaiotaomicron outcompeted B. adolescentis at all dilution rates at culture pH values between 5.0 and 6.0, although the bifidobacterium was always detected in the fermenters. At pH 6.5, however, B. adolescentis predominated in co-cultures at dilution rates above 0.24/h. Arabinogalactan degrading enzymes (beta-galactosidase, alpha-arabinofuranosidase) were strongly catabolite repressed in bacteroides at high dilution rates, but were constitutive and growth rate-associated in B. adolescentis. The increased competitiveness of B. adolescentis at high specific growth rates was not related to its ability to synthesise increased levels of depolymerising enzymes. Measurements of residual carbohydrate in pure and mixed culture chemostats showed that the bacteroides extensively digested the galactose backbone of the polymer, and to a lesser degree, the arabinose sidechains. Nevertheless, arabinose monomers and oligosaccharides (d.p. < 10) accumulated in these cultures under all growth conditions. In contrast, the bifidobacterium utilized considerably less arabinogalactan than the bacteroides, and this was reflected in the mixed culture studies. These experiments demonstrate that B. thetaiotaomicron was able to compete most successfully for this plant cell wall polysaccharide under nutritional, physiological and environmental conditions broadly similar to those encountered in the human colon, and indicate the existence of synergistic interactions between the two organisms that were growth rate dependent.     

Alterations in lipopolysaccharide produced by chemostat-grown Escherichia coli O157:H7 as a function of growth rate and growth-limiting nutrient

Escherichia coli O157:H7 was grown in chemostats as continuous cultures at different controlled growth rates and under different nutrient limitations to determine the effects on lipopolysaccharide (LPS) structure. LPS from whole cells and extracted using the hot aqueous phenol method was examined by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE) and by gel filtration after hydrolysis with acetic acid. At low growth rates under glucose limitation (D = 0.1 h-1, doubling time (td), approx. 416 min; or D = 0.4 h-1, td, approx. 104 min), E. coli O157 produced high molecular weight LPS identical to that previously characterized from cells grown in batch culture. At a high growth rate (D = 0.8 h-1, td, approx. 52 min), the ratio of high molecular weight LPS to low molecular weight LPS produced greatly decreased. A small amount of high molecular weight LPS, containing O-polysaccharide which lacked amino sugars, and which thus was chemically different from that previously characterized, was produced by the cells at high growth rates. The predominant form of LPS from these cells was of slightly higher molecular weight than rough LPS, probably S-R LPS, and it consistently formed aggregates on SDS-PAGE. This form of LPS was also predominant when E. coli O157 was grown under Mg2+ limitation at an intermediate growth rate (D = 0.4 h-1, td, approx. 104 min).