Defined medium for Moraxella bovis

A defined medium (medium MB) for Moraxella bovis was formulated. Nineteen strains grew well on medium MB. One strain was auxotrophic for asparagine, and another was auxotrophic for methionine. Strains of M. equi and M. lacunata also grew on medium MB. All strains had an absolute requirement for thiamine and were stimulated by or actually required the other growth factors in the medium.     

Standard YPD, even supplemented with extra nutrients, does not always compensate growth defects of Saccharomyces cerevisiae auxotrophic strains

Conventional complex media are routinely used to grow auxotrophic strains under the assumption that they can compensate the latter's nutritional deficiencies. We here demonstrate that this is not always true. This study compares the growth parameters of Saccharomyces cerevisiae (S288C) and its derived auxotrophic strains FY1679-14C and BY4741 in synthetic minimal medium (SD), standard YPD medium from two of the most commonly used suppliers, or modified YPD medium. Maximum specific growth rates of auxotrophic strains were slightly lower than the prototrophic case in all growth conditions tested. Also, the biomass production of auxotrophic strains in synthetic medium was slightly less than the prototrophic case. However in both of the two standard YPD media used, the biomass production of both auxotrophic strains was markedly lower than that of the prototrophic one. The extent of the differences depended on the medium used. Indeed in one of the two YPD media, the lower biomass production of auxotrophic strains was evident even at the diauxic shift. Uracil seems to be the main limiting growth factor for both auxotrophic strains growing in the two standard YPD medium tested. No YPD media or specific supplement was able to compensate for the effect of the auxotrophic mutations in the multiple auxotrophic marker strain BY4741. The fact that auxotrophic strains grew poorly on YPD when compared to their prototrophic counterpart indicates that standard YPD medium is not sufficient to overcome the effect of auxotrophic mutations.     

米曲霉原生质体的营养互补融合及二倍体的诱发分离*

采用1％溶壁酶加1％蜗牛酶的混合液获得的原生质体,以30％聚乙二醇(MW=6,000)、0.01M CaCl_2、0.05M Gly做为融合剂,对米曲霉进行了原生质体的营养互补融合,融合频率为0.27—0.47％。自4个菌株的4对杂交组合中获得了异核体,并分离到97株绿色融合株。二倍体的孢子经PFA和UV诱发分离后,获得了二株生长速度快、蛋白酶活性高和产孢能力强的单倍体菌株。     

Development of gene transfer systems in Methylobacillus flagellatum KT: Isolation of auxotrophic mutants

A collection of polyauxotrophic mutants of the obligate methylotroph Methylobacillus flagellatum KT was obtained. On the first step two stable auxotrophic mutants with a high requirement for amino acids supplements were isolated by treatment with nitrosoguanidine and selection on complete medium. Spontaneous variants of these mutants with a low requirement for nutrient supplements were the base for obtaining polyauxotrophic strains. It was shown, that the growth of mutants of M. flagellatum KT is inhibited by complete medium. Some amino acids and nucleotides are the inhibitor components of complete media. An approach for selection of auxotrophic mutants of individual genes was worked out on minimal medium. The optimal conditions for nitrosoguanidine mutagenesis of M. flagellatum KT were developed. The possible mechanisms of action of some of the nutrient supplements on the growth of M. flagellatum KT are discussed.     

Characterization of Leucine Auxotrophs of the White Rot Basidiomycete Phanerochaete chrysosporium

Six leucine auxotrophic strains of the white rot basidiomycete Phanerochaete chrysosporium were characterized genetically and biochemically. Complementation studies involving the use of heterokaryons identified three leucine complementation groups. Since all of the leucine auxotrophs grew on minimal medium supplemented with α-ketoisocaproate as well as with leucine, the transaminase catalyzing the last step in the leucine pathway was apparently normal in all strains. Therefore, the wild-type, auxotrophic, and several heterokaryotic strains were assayed for the activities of the other enzymes specific to leucine biosynthesis. Leu2 and Leu4 strains (complementation group I) lacked only α-isopropylmalate synthase activity; Leu3 and Leu6 strains (group III) lacked isopropylmalate isomerase activity; and Leu1 and Leu5 strains (group II) lacked β-isopropylmalate dehydrogenase. Heterokaryons formed from leucine auxotrophs of different complementation groups had levels of activity for all three enzymes similar to those found in the wild-type strain.     

灵芝尿嘧啶营养缺陷型菌株的筛选和分子鉴定

【背景】营养缺陷型是一种应用广泛的分子标记,但是目前在灵芝中还未有研究和应用报道。【目的】为灵芝遗传转化研究、杂交育种和菌种鉴别提供亲本材料和技术支持。【方法】采用紫外光诱变、单单杂交、孢子单核化的方法从灵芝单核体菌株出发得到尿嘧啶营养缺陷型双核体菌株。【结果】获得8株稳定的尿嘧啶营养缺陷型单核体突变菌株和7株尿嘧啶营养缺陷型双核体菌株。【结论】灵芝尿嘧啶营养缺陷型菌株在添加外源营养物的基础上可恢复正常生长,可以为灵芝遗传转化体系的构建和灵芝育种提供材料。     

Folate production by bifidobacteria as a potential probiotic property

The ability of 76 Bifidobacterium strains to produce folate was investigated. In order to evaluate folic acid productivity, bifidobacteria were cultivated in the folate-free semisynthetic medium SM7. Most of the tested strains needed folate for growth. The production and the extent of vitamin accumulation were not a function of species but were distinctive features of individual strains. Six strains among the 17 that grew without folate produced significantly higher concentrations of vitamin (between 41 and 82 ng ml(-1)). The effects of exogenous folate and p-aminobenzoic acid (PABA) concentrations on folate production were evaluated. In contrast to most of the other strains, the folate yield of B. adolescentis MB 239 was not negatively affected by either PABA or exogenous folic acid. Folate production by B. adolescentis MB 239 was studied in the pH range of the colonic environment, and a comparison of folate production on raffinose, lactose, and fructo-oligosaccharides, which belong to three important groups of fermentable intestinal carbon sources, was established. Differences in folate biosynthesis by B. adolescentis MB 239 were not observed as a function either of the pH or of the carbon source. Fecal culture experiments demonstrated that the addition of B. adolescentis MB 239 may increase the folate concentration in the colonic environment.     

Induced parasexual processes in Claviceps sp. strain SD58.

A homokaryotic, clavine alkaloid-producing strain of ergot, Claviceps sp. strain SD 58, was used in an attempt to demonstrate parasexuality. Genetically marked auxotrophic strains were produced by mutation with N-methyl-N'-nitro-N-nitrosoguanidine. Protoplast fusion of pairs of unlike doubly auxotrophic strains and isolation of stable prototrophic fusion products were carried out. By growth of the fusion products on complete medium, selective pressure for prototrophy was removed and auxotrophic segregants were allowed to form. Analysis of these and recovery of segregants with nonleaky, non-parent-type combinations of auxotrophic characteristics has provided strong evidence that a parasexual cycle can function in Claviceps sp. strain SD 58. Preliminary work suggests that the genetics of ergot might be studied by mitotic analysis and that protoplast fusion and selection procedures might be useful for the enhancement of favorable characteristics in Claviceps strains.     

Induced parasexual processes in Claviceps sp. strain SD58

A homokaryotic, clavine alkaloid-producing strain of ergot, Claviceps sp. strain SD 58, was used in an attempt to demonstrate parasexuality. Genetically marked auxotrophic strains were produced by mutation with N-methyl-N'-nitro-N-nitrosoguanidine. Protoplast fusion of pairs of unlike doubly auxotrophic strains and isolation of stable prototrophic fusion products were carried out. By growth of the fusion products on complete medium, selective pressure for prototrophy was removed and auxotrophic segregants were allowed to form. Analysis of these and recovery of segregants with nonleaky, non-parent-type combinations of auxotrophic characteristics has provided strong evidence that a parasexual cycle can function in Claviceps sp. strain SD 58. Preliminary work suggests that the genetics of ergot might be studied by mitotic analysis and that protoplast fusion and selection procedures might be useful for the enhancement of favorable characteristics in Claviceps strains.     

Rational development of a simple synthetic medium for the sustained growth of Lactococcus lactis

The growth of two strains of Lactococcus lactis subsp. lactis from vegetable (NCDO 2118) and dairy origin (IL 1403) were compared on various culture media. Both strains grew more rapidly on a complex organic medium than on a defined synthetic medium. The best growth was obtained under nitrogen gas phase. The single omission technique was applied to each component of a non-optimized synthetic medium in order to determine the true nutritional requirements. Requirements for macro-elements, oligo-elements, bases and vitamins were identical for the two strains. As expected, the dairy strain (IL 1403) was seen to be auxotrophic for some amino acids, whereas the vegetable strain (NCDO 2118) was seen to be prototrophic for all amino acids when using the single omission technique. Growth was then characterized on progressively simplified media and the composition of the absolute minimal media for the growth of both strains was defined. Sustained growth of the vegetable strain was only possible in minimal media supplemented with six amino acids (Glu, Met, Ile, Leu, Val, Ser), indicating that the definition of prototrophy/auxotrophy is partly dependent upon the medium composition. The dairy strain showed a requirement for Arg, His and Thr in addition to the six amino acids necessary for growth of the vegetable strain. The removal of ammonium salt from the medium did not affect the growth, illustrating that the amino acids may satisfy the totality of the nitrogen requirement for biomass synthesis.     

Physiological and Serological Comparisons Among Strains of Mycoplasma granularum and Mycoplasma laidlawii

Mycoplasma granularum strains grew on a medium devoid of animal serum or of serum fractions containing sterols; all strains possessed properties, including carotenoid biosynthesis, similar to those described for M. laidlawii. Some common antigenic components were noted among M. granularum and M. laidlawii strains by indirect fluorescent-antibody tests. The growth of M. granularum strains was slightly inhibited by antiserum to M. laidlawii PG-8, and the electrophoretic patterns of cell proteins of the M. granularum strains showed a close resemblance to that of M. laidlawii. However, direct fluorescent-antibody procedures performed on colonies grown on a serum-free medium clearly distinguished M. granularum from M. laidlawii. The occurrence of nonsterol-requiring mycoplasmas, in addition to M. laidlawii, raises questions as to the taxonomy of M. granularum and of the saprophytic mycoplasmas in general.     

Parasexual genetic analysis of Candida albicans by spheroplast fusion.

Doubly auxotrophic strains of Candida albicans were selected from mutagenized cultures. Spheroplasts prepared from the auxotrophic strains were fused with polyethylene glycol. Prototrophic derivatives formed by this fusion protocol from auxotrophic strains were selected by complementation on minimal medium. These prototrophs had a cell volume twice that of the original strain and were shown to be heterozygous at four loci. Prototrophs obtained by this procedure infrequently gave rise to auxotrophic recombinants whose cell volume remained twice that of the original strain. It is suggested that these auxotrophic recombinants arise from mitotic crossing-over. This paper is the first report of a parasexual cycle in C. albicans.     

sn-Glycerol-3-phosphate auxotrophy of plsB strains of Escherichia coli: evidence that a second mutation, plsX, is required.

sn-Glycerol-3-phosphate auxotrophs defective in phospholipid synthesis contain a Km-defective sn-glycerol-3-phosphate acyltransferase. Detailed genetic analysis revealed that two mutations were required for the auxotrophic phenotype. One mutation, in the previously described plsB locus (sn-glycerol-3-phosphate acyltransferase structural gene), mapped near min 92 on the Escherichia coli linkage map. Isolation of Tn10 insertions cotransducible with the auxotrophy in phage P1 crosses revealed that a second mutation was required with plsB26 to confer the sn-glycerol-3-phosphate auxotrophic phenotype. This second locus, plsX, mapped between pyrC and purB near min 24 on the E. coli linkage map. Tn10 insertions near plsX allowed detailed mapping of the genetic loci in this region. A clockwise gene order putA pyrC flbA flaL flaT plsX fabD ptsG thiK purB was inferred from results of two- and three-factor crosses. Strains harboring the four possible configurations of the mutant and wild-type plsB and plsX loci were constructed. Isogenic plsB+ plsX+, plsB+ plsX50, and plsB26 plsX+ strains grew equally well on glucose minimal medium without sn-glycerol-3-phosphate. In addition, plsX or plsX+ had no apparent effect on sn-glycerol-3-phosphate acyltransferase activity measured in membrane preparations. The molecular basis for the plsX requirement for conferral of sn-glycerol-3-phosphate auxotrophy in these strains remains to be established.     

Relation of Salmonella typhi and Salmonella gallinarum auxotrophicity to the ability to grow on Simmons' medium

A total of 9 S. typhi strains and 1 S. gallinarum strain isolated from clinical material are auxotrophic with respect to tryptophan. The growth of S. typhi is accelerated in a glucose- and tryptophan-containing minimal medium with cysteine and methionine added. S. typhi strains are incapable of using sodium citrate as the only source of carbon. S. typhi cannot grow on Simmons citrate agar as these organisms are auxotrophic with respect to tryptophan and incapable of using sodium citrate as the only source of carbon, and S. gallinarum cannot grow on this medium as they are auxotrophic with respect to tryptophan.     

Isolation of auxotrophic mutants from acetobacter methanolicus MB 58

The lysine content of the biomass of the acidophilic facultatively methylotrophic bacterium Acetobacter methanolicus MB 58 was increased by genetic manipulations. A homoserine auxotroph, MB 58.196, and a threonine auxotroph, MB 58.195, were obtained from Acetobacter methanolicus MB 58 by N-methyl-N′-nitro-N-nitrosoguanidine treatment. Investigations of enzyme activities revealed that the homoserine auxotroph lacks homoserine dehydrogenase activity, and the threonine auxotroph lacks homoserine kinase activity. Concerning the lysine-producing ability, only the homoserine auxotrophic mutant accumulates lysine in the intracellular pool. The intracellular lysine content of this mutant was increased 40-fold. An excretion of amino acids into the medium was not detected. A homoserine resistant mutant, MB 58.196.10, isolated from MB 58.196 by UV-irradiation, was able to excrete lysine. About 95% of free lysine were found in the culture medium. Altogether, the free lysine concentration was increased 800-fold in comparison to the wild-type strain. By these genetic manipulations the total lysine concentration of MB 58.196 was increased to 2.7% and of MB 58.196.10 to 56% in comparison to the wild-type strain.     

Folate Production by Bifidobacteria as a Potential Probiotic Property

The ability of 76 Bifidobacterium strains to produce folate was investigated. In order to evaluate folic acid productivity, bifidobacteria were cultivated in the folate-free semisynthetic medium SM7. Most of the tested strains needed folate for growth. The production and the extent of vitamin accumulation were not a function of species but were distinctive features of individual strains. Six strains among the 17 that grew without folate produced significantly higher concentrations of vitamin (between 41 and 82 ng ml⁻¹). The effects of exogenous folate and p-aminobenzoic acid (PABA) concentrations on folate production were evaluated. In contrast to most of the other strains, the folate yield of B. adolescentis MB 239 was not negatively affected by either PABA or exogenous folic acid. Folate production by B. adolescentis MB 239 was studied in the pH range of the colonic environment, and a comparison of folate production on raffinose, lactose, and fructo-oligosaccharides, which belong to three important groups of fermentable intestinal carbon sources, was established. Differences in folate biosynthesis by B. adolescentis MB 239 were not observed as a function either of the pH or of the carbon source. Fecal culture experiments demonstrated that the addition of B. adolescentis MB 239 may increase the folate concentration in the colonic environment.     

High-frequency fusion of Streptomyces parvulus or Streptomyces antibioticus protoplasts induced by polyethylene glycol.

Conditions were established for the regeneration of protoplasts of Streptomyces parvulus and Streptomyces antibioticus to the mycelial form. Regeneration was accomplished with a hypertonic medium that contained sucrose, CaCl2, MgCl2, and low levels of phosphate. High-frequency fusion of protoplasts derived from auxotrophic strains of S. parvulus or S. antibioticus was induced by polyethylene glycol 4,000 (42%, wt/vol). The frequency of genetic transfer by the fusogenic procedure varied with the auxotrophic strains examined. Fusion with auxotrophic strains of S. parvulus resulted in the formation of true prototrophic recombinants. Similar studies with S. antibioticus revealed that both stable prototrophic recombinants and heterokaryons were formed.     

Differences in Arginine Requirement for Growth Among Arginine-Utilizing Mycoplasma Species

The essentiality of arginine for initiation of growth of arginine-utilizing, nonglycolytic Mycoplasma species from small populations was studied by growing the organisms in a semisynthetic medium proven to be free from arginine by chemical and biological assays. Initiation of growth of two strains of M. arginini did not require arginine, whereas another strain of M. arginini required 4 mM arginine, as did M. gallinarum. M. hominis grew in 0.4 mM arginine. A species which utilizes both arginine and glucose, N. fermentans, did not require arginine but did require glucose for growth. When mycoplasmata were grown in human heteroploid cell cultures employing medium free from arginine but supplemented with citrulline, similar results were obtained: two M. arginini strains grew in the absence of arginine, whereas growth of M. gallinarum and M. hominis and a third M. arginini strain was dependent on arginine even though mammalian cells were present. The arginine deiminases were heterogeneous serologically: antisera to M. hominis and M. arginini showed reciprocal inhibition of their enzymes but did not inhibit arginine deiminase from M. gallinarum. Antiserum to M. gallinarum inhibited only M. gallinarum enzyme.     

Effect of titanium (III) citrate as reducing agent on growth of rumen bacteria.

We compared the growth of 10 strains of rumen bacteria in an anaerobic medium reduced with cysteine hydrochloride, dithiothreitol, or titanium (III) citrate. The redox potential of medium reduced with cysteine hydrochloride was -167.8 mV; with dithiothreitol it was -175.8 mV; and with titanium(III) citrate it was -302.4 mV at a concentration of 5 X 10(-4) M titanium and -403.9 mV at 2 X 10(-3) M titanium. Maximum growth of the strains was generally lower with dithiothreitol or titanium(III) citrate than with cysteine hydrochloride, although growth was greater than in medium lacking an added reducing agent. Strains for which cysteine was required or markedly stimulatory grew only poorly with titanium(III) citrate. No strain grew in medium with sodium citrate as the energy source. Titanium(III) citrate could be used to reduce anaerobic media for some rumen bacteria if the exclusion of a sulfur-containing reducing agent is required.     

Direct mating between diploid sake strains of Saccharomyces cerevisiae

Various auxotrophic mutants of diploid heterothallic Japanese sake strains of Saccharomyces cerevisiae were utilized for selecting mating-competent diploid isolates. The auxotrophic mutants were exposed to ultraviolet (UV) irradiation and crossed with laboratory haploid tester strains carrying complementary auxotrophic markers. Zygotes were then selected on minimal medium. Sake strains exhibiting a MATa or MATα mating type were easily obtained at high frequency without prior sporulation, suggesting that the UV irradiation induced homozygosity at the MAT locus. Flow cytometric analysis of a hybrid showed a twofold higher DNA content than the sake diploid parent, consistent with tetraploidy. By crossing strains of opposite mating type in all possible combinations, a number of hybrids were constructed. Hybrids formed in crosses between traditional sake strains and between a natural nonhaploid isolate and traditional sake strains displayed equivalent fermentation ability without any apparent defects and produced comparable or improved sake. Isolation of mating-competent auxotrophic mutants directly from industrial yeast strains allows crossbreeding to construct polyploids suitable for industrial use without dependence on sporulation.