Interaction between R-factors and the host cells. I. Lethal interference between R-factor determined streptomycin resistance and streptomycin dependence in Proteus mirabilis

Summary Interaction between R-factor determined streptomycin (Sm) resistance (R-Sm) and chromosomally determined Sm dependence (str-d) has been studied using three different approaches by (i) attempts to transfer by conjugation the R-factor into Sm-dependent recipients, (ii) transduction of str-d alleles into R ⁺ recipients, and (iii) investigation of Sm-dependent revertants of a suppressed Sm-dependent mutant harboring an R-factor. Evidence is presented which strongly suggests a lethal interference between the function of R-Sm genes and str-d allele determined Sm dependence in Proteus mirabilis.Abbreviations used Sm streptomycin sulfate - Cm chloramphenicol - Su sulphathiacol - Tc oxytetracycline - str-s,-r,-d alleles of the str locus, determining Sm sensitivity, resistance, and dependence, respectively. Resistance genes carried by the R-genote are designed as R-Sm, R-Cm, R-Su, R-Tc.     

Genetical studies on the heterocyst and nitrogen fixation of the blue-green alga Nostoc muscorum

Summary The short-trichome-forming, non-heterocystous and non-nitrogen-fixing (het ^– nif^–) mutant of the nitrogen-fixing blue-green alga Nostoc muscorum was isolated by N-methyl-N-nitro-N-nitrosoguanidine (NTG)-mutagenesis after penicillin enrichment technique and characterized. The mutant did not grow and fix nitrogen in combined-nitrogen-free medium while in nitrate-containing medium it grew well (K=0.112/day, G=64.27 h), although its growth was comparatively poor than the parent alga (K=0.128/day; G=56.14 h). The mutant was stable and both the het ^– and nif ^– characters reverted to wild type (het ⁺ nif⁺) with the reversion frequency of 2.62×10^-7.The het ^– nif^– mutant tolerated 0.5 g/ml of streptomycin sulphate on the agar medium and its streptomycin resistant mutant capable of growing in presence of 10g/ml of streptomycin was isolated spontaneously with a frequency of 1.45×10^-8. These streptomycin resistant isolates (het ^– nif^– str^R) resisted 100 g/ml of streptomycin sulphate on the agar medium and 200 g/ml in liquid medium. Spontaneous virus-resistant mutant of het ^– nif^– str^R was isolated with a mutation frequency of 4.02×10^-4.The data of genetic recombination experiments suggested that there is transfer of both het and nif genes to het ^– nif^– strain with the frequency of 2×10^-6 to 2×10^-5 simultaneously. There was increase in recombination frequency with increasing the incubation period. The virus-resistance marker is also transferred to the sensitive recipient.Abbreviations CFU colony forming units - C–N Chu-10 medium without combined nitrogen - C+N Chu-10 medium with 0.232 g/l calcium nitrate - G generation time - het heterocyst differentiating genes - K specific growth rate constant - MOI multiplicity of infection - nif nitrogen-fixing genes - NTG N-methyl-N-nitro-N-nitrosoguanidine - PFU plaque forming units - str ^R streptomycin resistance - str ^R streptomycin sensitive     

Spontane Mutation von einer Monoauxotrophie zu einer anderen in einem Schritt (Auxotrophiesprungmutation)

Summary Serratia strain CV produces spontaneously about 0,5% auxotrophic mutants of different types. By means of a special auxanographic technique, among about 60 monoauxotrophs, 5 were found which frequently and spontaneously mutate to a certain other auxotrophic state loosing the first one (arg 1 ^– nia ^–;arg 2 ^– his ^–,ad, hyx ^–;thr ^– met ^–;prol ^– his ^–;leu ^– ad, hyx ^–). It could be shown that this auxotrophic leap happens in ohne step without a prototrophic intermediate step. By backmutation experiments with the mutationsleu ^– ad ^– it was shown that the second auxotrophy acts as a suppressor mutation to the first auxotrophy. Since the biochemical reaction sequence blocked by the first mutation seems not to be related to the chain blocked by the second mutation, and since the second mutants do not feed the first mutants syntrophically, it is not probable that the suppression of the first auxotrophy is caused by a substance accumulated as an effect of the second mutation, removing the first auxotrophy by intracellular feeding. Rather, the second auxotrophy-gene (in its mutated, suppressing allelic state, e. g.ad ^–) seems to contribute information to the production of the enzyme determined usually by the first auxotrophy-gene, which information was lost by the first mutation (e. g. leu ^–). Thus, the information on the specificity of an enzyme would be stored not only in one single gene but in several genes.     

Intraspecific heterokaryon and fruit body formation in Coprinus macrorhizus by protoplast fusion of auxotrophic mutants

Summary Fusion of protoplasts of Coprinus macrorhizus mutants with different amino acid requirements resulted in the production of prototrophic clones at frequencies of 1–4% of the protoplasts surviving the fusion treatment. The frequencies were at least 200 times higher than those of the appearance of revertants. Few prototrophic colonies appeared also when the mutant protoplasts were individually subjected to fusion treatment, or when they were mixedly cultured without fusion treatment. It was thus concluded that intraspecific heterokaryons were formed by protoplast fusion.The auxotrophic mutants did not form fruit bodies when cultured singly or mixedly with each other. In contrast, the heterokaryons produced by protoplast fusion between the mutants of compatible mating types developed into fruit bodies with intermediate morphology of those of the strains from which the mutants were derived. Heterokaryons were also formed by fusion of mutant protoplasts with identical mating genotype, but they failed to form fruit bodies.Abbreviations PEG polyethyleneglycol - HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

Plasmid mediated silver resistance in Acinetobacter baumannii

Acinetobacter baumannii BL88, an environmental isolate, was resistant to 13 metals and 10 antibiotics. Plumbagin cured resistance to silver, cadmium, antimony, streptomycin and ampicillin at varying frequencies. However, only silver resistance transferred (1 × 10^–6 recepient^–1) to Escherichia coli K12 during conjugation. Correspondingly there was transfer of a 54 kb plasmid (pUPI199) from A. baumannii BL88. The plasmid transformed E. coli DH5 cells at a frequency of 1 × 10^–8 recepient^–1. The growth rate of E. coli DH5; (pUPI199) was slower as compared with E. coli DH5. Plasmid pUPI199 was 76 and 9.6% stable in the host A. baumannii BL88 in the presence and absence of selection pressure, respectively. A. baumannii BL88 was found to accumulate and retain silver whereas E. coli DH5 (pUPI199) effluxed 63% of the accumulated silver ions.     

The Distribution of Bacterio- and Mesozooplankton in the Coastal Waters of the White and Barents Seas

The total population density and the biomass of bacterioplankton, mesozooplankton, and phosphate-accumulating bacteria (PAB) were estimated during the 2000–2001 summer–autumn seasons in the coastal waters of the White and Barents Seas, which are subject to the action of tidal and sea currents, the inflow of riverine waters, and anthropogenic impact. In the shallow estuarine waters with salinities of 6.5–32 near the Chernaya, Pesha, and Pechora River mouths, the population of PAB fluctuated from 0.1 to 9.1 million cells/ml (0–36% of the total bacterial population). In pelagic seawaters, which are low in phosphates (12–50 g/l) and are characterized by an increased iron/phosphorus ratio (2.0–3.6), bacterioplankton amounted to 0.1–1.6 million cells/ml and was mainly represented by small organisms with a volume of 0.08–0.15 m³, commonly lacking intracellular polyphosphates. In the pelagic zone of the Barents Sea, the biomass of mesozooplankton (B _z) was comparable with that of bacterioplankton (B _b = 39–175 mg/m³), the B _b/B _z ratio being 1.4–4.6. Off the Varandeiskii, Pechora, and Kolguyev oil terminals, B _b increased to 155–300 mg/m³ and the B _b/B _z ratio rose to 1.4 to 50.3 (with an average value of 20.9), presumably due to the severe anthropogenic impact on these waters. In this case, the dense population of bacterioplankton (0.9–7.6 million cells/ml) was mainly represented by large cells (0.12–0.76 m³ in volume), most of which (3–43% of the total bacterioplankton population) contained polyphosphates. The chemical composition of these waters was characterized by an elevated content of the total phosphorus (65–128 g/l) and by a low iron/phosphorus ratio (0.9–1.2).     

Model aided design of repeated fed-batch penicillin fermentation

Structured models of antibiotic fermentation that quantify maturation and aging of product forming biomass are fitted to experimental data. Conditions of superiority of repeated fed batch cultivation are characterized on the basis of a performance criterion that includes penicillin productivity and costs of operation. Emphasis is placed on the relevance of such research to the model aided design of optimal cyclic operation.List of Symbols c IU/mg cost factor - D s^–1 dilution rate - J IU · cm^–3 · h^–1 net productivity - k _p IU · mg^–11 · h^–1 specific product formation rate - k _pm IU · mg^–1 · h^–1 maximum specific product formation rate - p IU/cm³ concentration of penicillin - T s final time of fermentation - t s fermentation time - X kg/m³ concentration of biomass dry weight - X ₁kg/m³ concentration of young, immature biomass - X ₂ kg/m³ concentration of mature product forming biomass - X _c kg/m³ biomass concentration of the end of growth phase - X _mkg/m³ maximum biomass concentration Greek Letters s^–1 specific maturation rate - s^–1 specific aging rate - s^–1 specific growth rate - _m s^–1 maximum specific growth rate - _p s^–1 specific growth rate during the product formation phase - s cycle time - % volume fraction of draw-off Abbreviations CC chemostat culture - RFBC repeated fed batch culture - RBC repeated batch culture     

Light and temperature effects on the growth rate of three freshwater [2pt] algae isolated from a eutrophic lake

Effects of light and temperature, on the growth of three freshwater green algae isolated from an eutrophic lake and identified as Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidumwere studied in batch cultures under non-nutrient limited conditions. Experiments were performed to determine the growth rate over a wide range of light intensities (30–456 mol m^–2 s^–1) and temperature (15–35°C), using a 15/9 (light/dark) photoperiod cycle. The maximum growth rates and the optimum light intensities at a temperature of 35°C were 1.73 d^–1 and 420 mol m^–2 s^–1for Selenastrum minutum, 1.64 d^–1 and 400 mol m^–2 s^–1 for Coelastrum microporum and 1.00 d^–1 and 400 mol m^–2 s¹ for Cosmarium subprotumidum. The results were fitted with the mathematical models of Steele (1965), Platt & Jassby (1976) and Peeters & Eilers (1978). Steele's function and equation of Platt & Jassby don't describe correctly the relationship between the growth and light intensity. In the opposite, the equation of Peeters & Eilers provides the best fit for the three species.     

Effects of copper on algal communities at different current velocities

This study examines the influence of current velocity in the toxiceffect of copper in diatom-dominated biofilms grown in artificial channels.Effects on community structure, algal biomass and photosynthesis (carbonincorporation) caused by 15 g L^–1 of copperwere tested at contrasting (1 and 15 cm s^–1)velocities. Moreover, a possible threshold on the effect of copper on algalbiomass and photosynthesis related to current velocity was examined by usingprogressively increasing current velocity (1 to 50 cms^–1) at 15 g L^–1 Cu.Chlorophyll-a decreased ca. 50% as a result of addition of15 g L^–1 Cu. Chlorophyll decrease occurredearlier at 15 cm s^–1 than at 1 cms^–1 when adding 15 g L^–1Cu. Copper also caused a remarkable decrease in carbon incorporation(from 30 to ca. 50%), which was produced earlier at 15 cms^–1 (three days) than at 1 cms^–1 (seven days). Some taxa were affected by thecombination of copper and current velocity. Both Achnanthesminutissima and Stigeoclonium tenue becomedominant at 15 cm s^–1 in the presence of copper.Significant inhibition of algal growth in 15 g L^–1Cu occurred at low (1 cm s^–1) and highvelocities (50 cm s^–1), but not at intermediatevelocity (20 cm s^–1). The experiments indicatethat current velocity triggers the effect that copper has on diatom-dominatedbiofilms, and that the effect is more remarkable at low and high than atintermediate current velocities.