Relationship between pH and medium dissolved solids in terms of growth and metabolism of lactobacilli and Saccharomyces cerevisiae during ethanol production

The specific growth rates of four species of lactobacilli decreased linearly with increases in the concentration of dissolved solids (sugars) in liquid growth medium. This was most likely due to the osmotic stress exerted by the sugars on the bacteria. The reduction in growth rates corresponded to decreased lactic acid production. Medium pH was another factor studied. As the medium pH decreased from 5.5 to 4.0, there was a reduction in the specific growth rate of lactobacilli and a corresponding decrease in the lactic acid produced. In contrast, medium pH did not have any significant effect on the specific growth rate of yeast at any particular concentration of dissolved solids in the medium. However, medium pH had a significant (P < 0.001) effect on ethanol production. A medium pH of 5.5 resulted in maximal ethanol production in all media with different concentrations of dissolved solids. When the data were analyzed as a 4 (pH levels) by 4 (concentrations of dissolved solids) factorial experiment, there was no synergistic effect (P > 0.2923) observed between pH of the medium and concentration of dissolved solids of the medium in reducing bacterial growth and metabolism. The data suggest that reduction of initial medium pH to 4.0 for the control of lactobacilli during ethanol production is not a good practice as there is a reduction (P < 0.001) in the ethanol produced by the yeast at pH 4.0. Setting the mash (medium) with > or =30% (wt/vol) dissolved solids at a pH of 5.0 to 5.5 will minimize the effects of bacterial contamination and maximize ethanol production by yeast.     

Relationship between pH and Medium Dissolved Solids in Terms of Growth and Metabolism of Lactobacilli and Saccharomyces cerevisiae during Ethanol Production

The specific growth rates of four species of lactobacilli decreased linearly with increases in the concentration of dissolved solids (sugars) in liquid growth medium. This was most likely due to the osmotic stress exerted by the sugars on the bacteria. The reduction in growth rates corresponded to decreased lactic acid production. Medium pH was another factor studied. As the medium pH decreased from 5.5 to 4.0, there was a reduction in the specific growth rate of lactobacilli and a corresponding decrease in the lactic acid produced. In contrast, medium pH did not have any significant effect on the specific growth rate of yeast at any particular concentration of dissolved solids in the medium. However, medium pH had a significant (P < 0.001) effect on ethanol production. A medium pH of 5.5 resulted in maximal ethanol production in all media with different concentrations of dissolved solids. When the data were analyzed as a 4 (pH levels) by 4 (concentrations of dissolved solids) factorial experiment, there was no synergistic effect (P > 0.2923) observed between pH of the medium and concentration of dissolved solids of the medium in reducing bacterial growth and metabolism. The data suggest that reduction of initial medium pH to 4.0 for the control of lactobacilli during ethanol production is not a good practice as there is a reduction (P < 0.001) in the ethanol produced by the yeast at pH 4.0. Setting the mash (medium) with ≥30% (wt/vol) dissolved solids at a pH of 5.0 to 5.5 will minimize the effects of bacterial contamination and maximize ethanol production by yeast.     

Ammonium uptake in carrot cell structures is influenced by pH-dependent cell aggregation

Semicontinuously grown wild carrot ( Daucus carota L.) cells were used in an investigation of the effect of culture medium pH on ammonium uptake in suspension cultures as a first step in exploring the relationship between pH and anthocyanin biosynthesis. In contrast to published data showing decreasing uptake rates with decreasing culture medium pH, ammonium-limited, semicontinuous carrot cell cultures showed a 25% greater ammonium uptake rate at pH 4.5 than at pH 5.5. When cells that had been grown semicontinuously in medium with a pH of 4.5 or 5.5 were grown in batch cultures at pH 4.5, 5.5 or 6.5 the ammonium uptake rates were those of the semicontinuous cultures, indicating that the pH of the batch culture medium had no effect on ammonium uptake rates over 7 days. The cell culture was composed of very small aggregates when it was grown semicontinuously in medium at pH 4.5, but was composed of large aggregates when it was grown semicontinuously in medium at pH 5.5. The aggregation/disaggregation of the cells was pH dependent, as changing the pH of the semicontinuous culture medium altered the extent of the aggregation. We conclude that the change in culture medium pH caused the cells to aggregate or disaggregate which in turn decreased or increased the rate of ammonium uptake from the medium.     

Dependence of erythromycin biosynthesis on the active acidity of the medium]

Dependence of erythromycin biosynthesis on the medium active acidity was studied by the following methods: by changing pH of the initial medium, by changing the concentration of the medium components determining the active acidity of the culture, by using buffer mixtures by automatic control of pH. It was found that pH of the initial medium within 5.7-8.1 had no effect on the culture growth. Biosynthesis of erythromycin markedly decreased at pH 6.3 or lower. The values of pH within 6.6-7.5 (optimal values 6.7-6.9) were favourable for the antibiotic biosynthesis. At pH 6.2-6.3 the antibiotic accumulation was equal to 5-10 per cent of the control.     

The effect of beta-galactosides on the protonmotive force and growth of Escherichia coli

The effect of three beta-galactosides on the components membrane potential (delta psi) and pH gradient (delta pH) of protonmotive force and growth of Escherichia coli has been examined. A good correlation between the reduction of the protonmotive force and growth inhibition was observed. Thus some galactosides had little effect on either the protonmotive force or growth while lactose diminished the protonmotive force and caused growth inhibition. This effect of lactose was dependent on the ionic composition of the growth media. In Medium A (77 mM-Na+, 85 mM-K+) lactose diminished delta psi but had no effect on delta pH. Growth inhibition was transient at an external pH 6.0 but complete at pH 7.5. In medium KA (approximately 1 mM-Na+, 162 mM-K+) delta pH was diminished and delta psi was not affected and consequently growth inhibition was complete at pH 6.0. In medium NA (163 mM-Na+, 20 mM-K+) lactose had little effect on delta psi, delta pH or growth. These data support Skulachev's hypothesis of buffering of the protonmotive force by K+ and Na+ gradients.     

Conditions Influencing the Synthesis of Acid Protease by Mucor pusillus Lindt

Protease synthesis by Mucor pusillus Lindt, in a wheat bran medium under submerged conditions, was influenced by substrate concentration, initial pH of the medium, and temperature of incubation. A 4% wheat bran (dry weight) concentration was satisfactory for enzyme production. The initial pH of the medium had a substantial effect on enzyme synthesis; adjustment of the enzyme production medium to pH 5.0 prior to sterilization was desirable. Incubation at 35 C resulted in the best enzyme yields. Under optimal conditions of enzyme production, maximal activity was detected after 5 days of incubation. The enrichment of the medium with glucose increased the yield of mycelia but lowered the amount of enzyme produced.     

Role of pH in fibroblast proliferation

Secondary cultures of human diploid fibroblasts were used to study the effect of pH on cellular proliferation. In nonconfluent cultures, the growth rate at pH 7.1 was similar to that at pH 7.7 regardless of serum concentration. However, the saturation density achieved at pH 7.7 at any serum concentration was always 2–4 times that achieved at pH 7.1, although the greatest differences in saturation density were observed at the higher serum levels. The results suggest that the effect of pH on saturation density is due to two factors. One, cells at pH 7.1 seem to have a greater ability to undergo contact-inhibition than at pH 7.7, independent of any serum functions; and, two, confluent cells in medium at pH 7.1 are somewhat less sensitive to growth stimulation by increasing serum concentration than are confluent cells raised in medium at pH 7.7.     

Osmotic stress leads to decreased intracellular pH of Listeria monocytogenes as determined by fluorescence ratio-imaging microscopy

Intracellular pH (pH(i)) of Listeria monocytogenes was determined after exposure to NaCl or sorbitol in liquid and solid media (agar). Both compounds decreased pH(i), and recovery on solid medium was impaired compared to that in liquid medium. N,N'-dicyclohexylcarbodiimide abolished pH(i) recovery, and lowering a(w) with glycerol showed no effect on pH(i).     

Effect of thiosulphinates contained in garlic extract on growth, proton fluxes and membrane potential in maize (Zea mays L.) coleoptile segments

The effect of thiosulphinates contained in garlic extract (GE) on endogenous growth, growth in the presence of either indoleacetic acid (IAA) or fusicoccin (FC), and proton extrusion in maize coleoptile segments were studied. In addition, membrane potential changes at some GE dilutions and the protective effect of dithiothreitol (DTT) against GE toxicity were also determined. It was found that GE at almost all dilutions studied, when added to the incubation medium inhibited endogenous growth as well as growth in the presence of either IAA or FC. Simultaneous measurements of growth and external pH indicated that the administration of GE resulted in a complex change in the pH of the external medium; after an initial transient acidification, pH increased and reached the maximal value followed by a gradual decrease of medium pH. When IAA or FC was added after preincubation of the segments in the presence of GE the changes in medium pH were not significantly different from these obtained with GE only. If the coleoptile segments were first preincubated with GE and subsequently GE was removed, the addition of IAA induced strong growth and medium acidification. Dithiothreitol added together with GE neutralized the toxic effect of GE on growth of coleoptile segments incubated in the presence of IAA. The addition of GE to the control medium caused a depolarization of the membrane potential, the value of witch depended on GE dilution. These results indicate that the toxic effect of GE on growth of plant cells might be caused by disruption of the catalytic function of the plasma membrane H⁺-ATPase on formation of the disulfide bonds.     

Influence of ammonium and extracellular pH on the amino and organic acid contents of suspension culture cells of Acer pseudoplatanus

The effects of supplied ammonium and nitrate on the amino and organic acid contents and enzyme activities of cell suspension cultures of Acer pseudoplatanus L. were examined. Regardless of nitrogen source the pH of the culture medium strongly affected the malate and citrate contents of the cells; these organic acid pools declined at pH 5, but increased at pH 7 and 8. Over a period of two days, ammonium had little effect on the responses of the organic acid pool sizes to the pH of the medium. In contrast, ammonium had a strong influence on amino acid pool sizes, and this effect was dependent on the pH of the medium. At pH 5 there was no increase in cell ammonium or amino acid contents, but at higher pH values cellular ammonium content rose, accompanied by accumulation of glutamine, glutamate and asparagine. Over several days, supplied ammonium led to an increase in activity of glutamate dehydrogenase irrespective of any changes in internal ammonium and amino acid contents. If the pH of the medium was allowed to fall below pH 4 in the presence of ammonium, phosphoenolpyruvate (PEP) carboxylase activity declined to a very low value over several days; at higher pH, the activity of this enzyme, and that of NAD malic enzyme and NAD malate dehydrogenase, remained substantial irrespective of whether the nitrogen source was NH⁺₄ or NO-₃.     

The effect of citric acid on growth of proteolytic strains of Clostridium botulinum

In strictly anaerobic conditions in a culture medium adjusted to pH 5.2 with HCl and incubated at 30 degrees C, inocula containing less than 10 vegetative bacteria of Clostridium botulinum ZK3 (type A) multiplied to give greater than 10(8) bacteria per ml in 3 d. Growth from an inoculum of between 10 and 100 spores occurred after a delay of 10-20 weeks. Citric acid concentrations of 10-50 mmol/l at pH 5.2 inhibited growth from both vegetative bacteria and spore inocula, a concentration of 50 mmol/l increasing the number of vegetative bacteria or of spores required to produce growth by a factor of approximately 10(6). The citric acid also reduced the concentration of free Ca2+ in the medium. The inhibitory effect of citric acid on vegetative bacteria at pH 5.2 could be prevented by the addition of Ca2+ or Mg2+ and greatly reduced by Fe2+ and Mn2+. The addition of Ca2+, but not of the remaining divalent metal ions, restored the concentration of free Ca2+ in the medium to that in the citrate-free medium. The inhibitory effect of citric acid on growth from a spore inoculum was only partially prevented by Ca2+. Citric acid (50 mmol/l) did not inhibit growth of strain ZK3 at pH 6 despite the greater chelating activity of citrate at pH 6 than at pH 5.2. The effect of citric acid and Ca2+ at pH 5.2 on vegetative bacteria of strains VL1 (type A) and 2346 and B6 (proteolytic type B) was similar to that on strain ZK3.     

微藻培养基平衡pH的研究

平衡pH是培养基中二氧化碳分压与空气中二氧化碳分压平衡时的pH,是微藻培养基的一个重要特征参数。选用常用的三种微藻培养基:BG11培养基、BBM培养基和Zarrouk培养基,使用鼓泡通入空气的方法,研究碳源、氮源、磷源浓度和盐度对培养基平衡pH的影响。结果如下:在NaHCO3浓度016.8 g/L范围内,三种培养基的平衡pH都随碳源浓度的增加而升高;NaNO3浓度在02.5 g/L范围内,对培养基平衡pH没有影响;0.1 g/L KH2PO4使BG11培养基的平衡pH稍有升高,与之相反,BBM培养基的平衡pH稍有下降,进一步提高磷（P）浓度（最高0.4 g/L）,BG11培养基和BBM培养基的平衡pH不再变化;P浓度变化对Zarrouk培养基的平衡pH没有影响;三种培养基的平衡pH都随盐度的升高而降低。碳源浓度是影响培养基平衡pH的最主要因素,平衡pH与碳源浓度的关系可以用回归方程y=0.3504ln（x）+8.9647（R2=0.9708）表示,氮源浓度对平衡pH没有显著影响,磷源浓度和盐度对培养基平衡pH有影响,但影响不大。控制藻液pH不低于平衡pH,可以提高微藻培养中CO2的利用效率,有利于实现微藻CO2生物固定的环境效益。       

pH值对沼液培养的普通小球藻生长及油含量积累的影响

以50％的沼液为普通小球藻的全营养培养基,考察培养基的起始pH值对小球藻生长及油脂含量的影响,普通小球藻对不同初始pH的沼液中氮、磷的去除情况。设定了2组实验,一组只调节初始接种培养液的pH,分别为6.0、6.5、7.0、7.5、8.0、8.5;另一组将培养液pH分别固定在6.0、6.5、7.0、7.5、8.0、8.5,pH用稀HCl和NaOH进行调节。研究发现在pH 6.5和pH 7.0的偏酸环境有利于小球藻生长,而pH在7.0~8.5的偏碱性条件下有利于小球藻油脂的积累,因此综合小球藻生长和油脂积累2个因素,得到最适合小球藻生长和油脂积累的pH为7.0。培养结束后沼液中氮磷的去除率分别达到了95％和97％,沼液中的总氮由原来的134.91 mg/L降至4.86 mg/L,总磷由10.19 mg/L降到0.32 mg/L。     

Effect of intracellular Na+ on platelet aggregation and Ca2+ mobilization

The effects of ionophores, which can carry alkali metal cations, on platelet aggregation were examined. At an alkaline extracellular pH, alkali metal cation/H+ exchanger nigericin accelerated aggregation in K+-enriched medium, whereas it rather inhibited aggregation in Na+-enriched medium, even though the intracellular pH was only slightly alkaline. The inhibitory effect of Na+ on platelet aggregation was more clearly shown with the alkali metal cation exchanger gramicidin D. The ionophore had no effect or a slightly accelerative effect on aggregation in K+-enriched medium, whereas it significantly inhibited aggregation induced by thrombin, ADP and platelet activating factor in Na+-enriched medium. Fluorescence studies on fura-2-labeled platelets revealed that in Na+-enriched medium gramicidin D inhibited agonist-induced Ca2+ mobilization both in the presence and absence of extracellular Ca2+. These results suggest that the intracellular Na+ inhibits platelet aggregation by inhibiting Ca2+ mobilization.     

The effect of pH on the propagation of the diploid cell WI-38 in galactose medium

The pH range for optimal growth of WI-38 in Eagle's minimum essential medium varies with the carbohydrate utilized. Growth with glucose occurred only in the pH range 6.8–7.4. Glucose-free galactose supported growth only if the pH of the medium was adjusted to 6.4–6.8. Supplementing the galactose medium with pyruvate extended the pH range for growth to 7.4. The addition of 0.01% glucose to the galactose medium increased growth at pH 7.0–7.4, reduced growth at pH 6.8, and completely inhibited growth at pH 6.6. This toxic effect of glucose under conditions impairing glycolysis was considered to be a contributing factor to the post-confluent growth rate decline associated with “contact inhibition.”     

Chemical mutagenesis and the use of indirect enzymatic criteria for the selection of virulent clones of Bacillus thuringiensis

The effect of the mutagene nitrosoguanidine (N-methyl-N'-nitro-N-nitrosoguanidine) on the growth of Bacillus thuringiensis subsp. galleriae st. 69/6 was being studied. It depends on the physiological state of the cells, dose of the mutagene, pH of the culture medium and exposition. Nitrosoguanidine was found to have the maximum mutagenic effect on the vegetative cells at pH 6.2 and on the spores at pH 5.6.     

Effect of the initial pH value of the medium on the growth of Streptococcus lactis and the biosynthesis of nisin]

The effect of the initial pH value of the medium within 4.0 to 6.6 on the growth of Str. lactis and biosynthesis of nicin was studied. It was found that at the initial pH 4.0--4.5 of the medium the growth of the culture was poor, i.e. 11--14% of the control (initiral pH 6.6). With an increase in the value of the initial pH at least to 5.0 the growth of Str. lactis also increased. At the initial pH 4.0 no biosynthesis of nicin was observed. Under the experimental conditions the antibiotic synthesis by tr. lactic started at the initial pH being equal to 4.5 and reached its maximum at pH 6.6.     

Cell Expansion and Tracheary Element Differentiation Are Regulated by Extracellular pH in Mesophyll Cultures of Zinnia elegans L

The effects of medium pH on cell expansion and tracheary element (TE) differentiation were investigated in differentiating mesophyll suspension cultures of Zinnia elegans L. In unbuffered cultures initially adjusted to pH 5.5, the medium pH fluctuated reproducibly, decreasing about 1 unit prior to the onset of TE differentiation and then increasing when the initiation of new Tes was complete. Elimination of large pH fluctuations by buffering the culture medium with 20 mM 2-(N-morpholino)ethanesulfonic acid altered both cell expansion and TE differentiation, whereas altering the starting pH of unbuffered culture medium had no effect on either process. Cell expansion in buffered cultures was pH dependent with an optimum of 5.5 to 6.0. The direction of cell expansion was also pH dependent in buffered cultures. Cells elongated at pH 5.5 to 6.0, whereas isodiametric cell expansion was predominant at pH 6.5 to 7.0. The onset of TE differentiation was delayed when the pH was buffered higher or lower than 5.0. However, TEs eventually appeared in cultures buffered at pH 6.5 to 7.0, indicating that a decrease in pH to 5.0 is not necessary for differentiation. Very large TEs with secondary cell wall thickenings resembling metaxylem differentiated in cultures buffered at pH 5.5 to 6.0, which also showed the greatest cell expansion. The correlation between cell expansion and delayed differentiation of large, metaxylem-like TEs may indicate a link between the regulatory mechanisms controlling cell expansion and TE differentiation.     

控制pH环境对出芽短梗霉胞外多糖合成的影响

采用添加 Ca CO₃ 和 HCl的方法研究了 p H对出芽短梗霉多糖发酵的影响规律。在 P2培养基中发酵2 4 h,该菌有一个强烈的产酸期 ,导致 p H迅速下降到 3.6左右。在此 p H环境下继续发酵 12 0 h,多糖产量仅为 5.9g/ L。如果用 MP2培养基 (P²⁺ 0 .5% Ca CO₃ )发酵 ,由于 Ca CO₃ 缓冲了发酵 p H的下降 ,在整个发酵过程中 p H值可以维持在 5.0以上 ,多     

Studies on aspergilli XVII. Effect of nitrogen sources on growth and fruiting

Summary The effect of ammonium, nitrate, and organic nitrogen on growth and sporulation of 18 Aspergilli was examined in a chemically defined medium in surface culture under controlled conditions. All three forms of nitrogen were metabolized by all the Aspergilli tested. Ammonium nitrogen was not good both for growth and fruiting. This was due to the sharp fall in the pH level which resulted due to the rapid utilization of anions of the ammonium nitrogen than cations. The effect of adding succinic acid in the medium containing ammonium nitrogen has been discussed.Good growth of Aspergilli in media containing nitrate nitrogen with the accompanying rise in the pH of the medium showed that these species are capable of reducing nitrate nitrogen to the level of ammonia. The role of succinic acid in the utilization of nitrate nitrogen was investigated. All fungi accomplished good growth on a medium containing asparagine.