Use of chemostat for selection ofStreptomyces hygroscopicus mutants altered in regulation of maltose utilization

Summary Streptomyces hygroscopicus mutants showing altered fermentation kinetics were isolated using a selection procedure in a chemostat. Several mutants were obtained which differed in their capacity to produce the macrolide antibiotic turimycin.     

A simple procedure for quick identification of tryptophanase positive recombinant clones and tryptophanase regulatory mutants of bacteria

Summary A simple and rapid technique for quick identification of tryptophanase regulatory mutants and tryptophanase positive clones in a bacterial population is described. This method was used for the detection of tryptophanase regulatory mutants of Vibrio cholerae and tryptophanase positive recombinant clones of Escherichia coli.     

Oxygen sensitivity of nitrogenase is not always a limiting factor of growth under nitrogen-fixing conditions inAzotobacter vinelandii

Summary The effect of a combined nitrogen source to oxygen sensitive mutants was examined. For some oxygen sensitive mutants, oxygen sensitivity was not restored by the addition of nitrogen compounds to their medium. One of these mutants showed oxygen resistant nitrogenase activity similar to that of a wild strain. Results imply that oxygen sensitivity of nitrogenase is not always a limiting factor of growth under aerobic nitrogen-fixing conditions inAzotobacter vinelandii.     

Use of chemostat for selection ofStreptomyces chrysomallus mutants altered in the induction of D-glucose isomerase

Summary D-glucose isomerase ofStreptomyces chrysomallus PL45 is inducible by D-xylose only. In mutants obtained by means of a selection procedure in a chemostat the isomerase was induced in xylose-free medium containing glucose as carbon source.     

Mutants ofMethylobacterium organophilum unable to synthesize PQQ

The phenotype of mutants unable to synthesize PQQ is analyzed for different categories of methylotrophic bacteria. The advantages offered by strains dissimilating methylamine through methylated amino-acids are discussed. InM.organophilum, 40% of the mutants unable to grow in methanol medium but with normal methylamine utilization, were affected in PQQ metabolism. The genetic properties ofM.organophilum useful to study PQQ mutants are discussed, mainly the use of pSUP106 to create insertion mutations in the bacterial chromosome and to replace wild-type genes by modified genes. An example is given of the possibility to create R plasmids containing large fragments ofM.organophilum DNA. Some physiological properties of a PQQ mutant are described, regarding growth kinetics, PQQ uptake and accumulation.     

Photosynthesis in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> Mutants with Reduced Chloroplast Number

We have used a class of Arabidopsis mutants altered in the accumulation and replication of chloroplasts (arc mutants) to investigate the effect of reduced chloroplast number on the photosynthetic competence of leaves. Each of the arc mutants examined (arc3, arc5, and arc6) accumulate only a few (2–15) large chloroplasts per mesophyll cell [K.A. Pyke and R.M. Leech (1992) Plant Physiology 99: 1005–1008]. The increased plastid size maintains a constant plastid to mesophyll cell volume, which has been suggested to compensate for the lower chloroplast number. In fact, we find that reduced chloroplast number has an effect on both the composition and structure of the photosynthetic apparatus, and that each arc mutant has an altered photosynthetic capacity, and we conclude that photosynthetic competence is dependent on proper chloroplast division and development.     

Characterization of a cytochrome oxidase-deficient yeast mutant which accumulates porphyrins

A cytochrome oxidase-deficient mutant (pop4) of Saccharomycescerevisiae which accumulates porphyrins has been characterized. The pop4 mutation is recessive and affects a single nuclear gene. The bulk of the accumulated porphyrins consists of uroporphyrin and its partial decar?ylation products, suggesting that the mutation causes a block at the level of uroporphyrinogen decar?ylase. However, pop4 is not allelic to hem6 or pop3, putative decar?ylase structural-gene mutants. These results suggest that there may be a uroporphyrinogen decar?ylase isoenzyme specifically involved in heme a production.     

Visual detection of β-fructofuranosidase (inulase) —Regulatory mutants ofKluyveromyces fragilis

Summary Inulase constitutive mutant cells of the yeastKluyveromyces fragilis were enumerated in continuous culture cell populations. After cloning and growth on glycerol agar plates, mutant colonies stained red when exposed to a mixture of sucrose and a chromogenic reagent for glucose.Mutants with improved inulase production on glucose were isolated from opaque agar plates containing undissolved inulin. Mutant colonies were surrounded with clearing zones. Attempts to isolate similar mutants by selection for 2-deoxyglucose resistance proved unsuccessful withK. fragilis.     

Bile acid catabolites accumulated by transposon-induced mutants ofPseudomonas putida: Production of hydroxylated 1,4-androstadiene-3,17-diones

Summary Transposon mutagenesis of a bile acid-utilizingPseudomonas putida strain generated 5 classes of mutants based on their ability to accumulate steroild catabolites. Bile acids (up to 5%) could be fermented using mutant strains, to the appropriate hydroxy-1,4-androstadiene-3,17-dione type product in yields close to theoretical.     

Regulation of mycotoxin production by Fusarium graminearum: Complementation effects between two mutant types

Summary Starting from anileu auxotroph ofFusarium graminearum producing high levels of the mycotoxin zearalenone, selection after UV irradiation gave low-producing mutants of essentially normal morphology,zea,ileu. Heterokaryons betweenzea,ileu strains and an auxotrophic strainlz,inos derived from the lazy morphological mutant ofFusarium graminearum, which has abnormal morphology and also produces little or n zearalenone, produced significant levels (over 50% of the wild-type level) of mycotoxin. The observation confirms views as to the regulatory nature of thelazy mutation.     

A high-affinity iron transport system of Rhizobium meliloti may be required for efficient nitrogen fixation in planta

We have analyzed the ability of single site insertion mutants of Rhizobium meliloti 1021 defective in various components of a high-affinity iron transport system to produce nodules, fix nitogen and promote plant growth. Our results indicate that a high-affinity iron transport system may significantly increase the ability of the differentiated form of the bacterium to fix nitrogen and induce an increase in plant growth.Abbreviations EDDA ethylenediamine-N,N-bis(2-hydroxyphenylacetic acid) - CAS chrome azurol S     

Isolation of spontaneous Streptomyces hygros copicus 111-81 phosphate-deregulated mutants hyperproducing its antibiotic complex

Summary Spontaneous phosphate-deregulated mutants were isolated fromStreptomyces hygroscopicus 111-81, a producer of a nonpolyenic macrolide antibiotic complex. Six of the mutants had stable increased antifungal activity. The activities of the remaining ones were unstable, the same or only slightly higher than that of the initial strain. The most productive mutants had morphological features similar to the parent culture.     

A H<Subscript>2</Subscript>O<Subscript>2</Subscript>-producing glyoxal oxidase is required for filamentous growth and pathogenicity in<Emphasis Type="Italic"> Ustilago maydis</Emphasis>

In the phytopathogenic fungus Ustilago maydis the mating-type loci control the transition from yeast-like to filamentous growth required for pathogenic development. In a large REMI (restriction enzyme mediated integration) screen, non-pathogenic mutants were isolated in a haploid strain that had been engineered to be pathogenic. In one of these mutants, which showed a specific morphological phenotype, the tagged gene, glo1 , was found to encode a product that is highly homologous to a glyoxal oxidase gene from the wood-rot fungus Phanerochaete chrysosporium. Glyoxal oxidase homologues are found in human, plant pathogenic fungi and in plants, but not in other mammals or yeasts. To confirm the function of the glo1 gene, null mutations were generated in compatible haploid U. maydis strains. In crosses null mutants were unable to generate filamentous dikaryons, and were completely non-pathogenic. Using a Glo1-overproducing strain we demonstrated that Glo1 is membrane bound, oxidizes a series of small aldehydes (<C4) and produces H₂O₂. The enzyme needs to be activated, presumably by auto-oxidation, to show full activity. A potential role for Glo1 during filamentous growth and pathogenic development of U. maydis is proposed.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by P. J. PuntThe first two authors contributed equally to this workWe dedicate this work to the memory of Jeff Schell, a charismatic and outstanding person who loved science and respected people     

Construction of multiple herbicide resistant ammonia excreting strains of cyanobacteriumNostoc muscorum

Summary Machete resistant (Mat ^r), basalin resistant (Bas ^r), 3(3,4 dichlorophenyl)-1,1-dimethyl urea resistant (DCMU ^r), atrazine resistant (Atr ^r) and propanil resistant (Prp ^r) phenotypes ofGloeocapsa sp. were cotransformed toNostoc muscorum at high frequency. Spontaneously occurring mutants of the multiple herbicide resistant transformant containing L-methionine-DL-sulfoximine resistant (Msx ^r), ethylene diamine resistant (Eda ^r), or phosphinothricin resistant (Ppt ^r) glutamine synthetase (GS) showed extracellular liberation of ammonia resulting from fixation of N₂ under photosynthetic conditions. Results suggest a definite role of GS activity in regulation of extracellular ammonia.     

Production of mold lactase

A process for production of mold lactase was developed. Tests were carried out in pilot and industrial scale with an Aspergillus niger strain selected after screening a number of molds.A computer coupled autoanalyzer system was used for monitoring enzyme formation in the pilot fermentor. Lactase production was investigated using different pH- and temperature-profiles. A. niger lactase has an acid pH optimum, a high temperature optimum and good stability. It does not require any metal ions. It is suitable for immobilization for hydrolysis of lactose in acid whey.Three-fold enhancement of lactase production was obtained by mutagenizing A. niger using NTG as mutagenic agent.The lactases produced by the mutants have the same pH and temperature optima and stability but the growth properties of the mutants were different from those of the original strain.Sufficient specific activity of the enzyme preparation for immobilization was obtained by purifying the enzyme by selective adsorption on Na-Ca-silicate.     

Non-SMC condensin I complex proteins control chromosome segregation and survival of proliferating cells in the zebrafish neural retina

Background  

The condensation of chromosomes and correct sister chromatid segregation during cell division is an essential feature of all proliferative cells. Structural maintenance of chromosomes (SMC) and non-SMC proteins form the condensin I complex and regulate chromosome condensation and segregation during mitosis. However, due to the lack of appropriate mutants, the function of the condensin I complex during vertebrate development has not been described.     

Flavonoid genetics of the 28-chromosome “Siberian” Iris

Summary A Chromatographic survey of flavonoids in the various flower color mutants of the 28-chromosome Siberian Iris (series Sibiricae subseries Sibiricae) was conducted using mutants of known genotype (Vaughn 1974). Mutants at the C locus contain the malvidin glycoside ensatin, indicating that this gene locus may control methylation of delphinidin. Clear white, a mutation at the W locus, results in the production of flavones in excess.     

Improved sensitivity of genetic complementation of nitrate reductase deficient mutants via protoplast fusion

An improved rapid assay for complementation testing of mutants of Nicotiana tabacum deficient in nitrate reductase is described. The test is based on measurement of in vivo nitrate reductase activity in 7 to 10 day old cultures derived from fusion-treated protoplast mixtures of the respective mutants as a criterion for complementation. It allows to detect complementing hybrids induced by the conventional droplet fusion technique in small numbers of protoplasts per assay (8×10⁴).Abbreviations NR nitrate reductase - 2,4-D dichlorophenoxy-acetic acid - NAA -naphthaleneacetic acid - BAP 6-benzylaminopurine - PEG polyethylene glycol     

Galactoside transport dissociated from proton movement in mutants of Escherichia coli

Two mutants of Escherichia coli have been described in which the transport of β-galactosides is partly uncoupled from the metabolic reactions which drive active transport. It is shown that the effective inflow of H⁺, caused by the addition of β-galactoside, is much less in these mutants than in the parental strains, and it is concluded that β-galactoside transport is partly uncoupled from H⁺ transport.