Enhanced resistance of anaerobic rumen fungi to the ionophores monensin and lasalocid in the presence of methanogenic bacteria

The presence of Methanobrevibacter smithii altered the susceptibility of the anaerobic fungi Neocallimastix frontalis and Piromonas communis to the carboxylic ionophores monensin and lasalocid. The ionophores depressed growth (measured by chitin accretion), the uptake of glucose and the production of H2, formate and acetate by the fungi growing axenically in semi-solid medium. In the presence of M. smithii , the sensitivity of the fungi to monensin and lasalocid was decreased. For example, the uptake of glucose by N. frontalis strain RE1 in the culture was reduced to 50% of the control value by monensin at 0.5 mUg/ml. In the presence of M. smithii strain PS, approximately three tunes as much monensin was needed to bring about the same effect. In similar tests, the sensitivity of strain RE1 to lasalocid was decreased about nine-fold in the presence of M. smithii. The effect was not observed if the methanogens were killed by autoclaving before inoculation. It is suggested that the enhanced resistance to ionophores in the presence of M. smithii is a consequence of changes in the energy metabolism of the fungi growing in co-culture.     

Localization of GABA-like immunoreactivity in the ectostriatum of domestic chicks: GABA immunocytochemistry combined with Golgi impregnation

Brain Cell Biology - The distribution of GABA-like immunoreactivity (GABA-LI) in the ectostriatal core (Ec) of domestic chicks (one to two days old) was investigated using (1) preembedding GABA...     

Colloquium on scientific authorship: rights and responsibilities

The Colloquium on Scientific Authorship was held at the National Institutes of Health (NIH) at a time of extraordinary scrutiny by the public of the ethics of scientists, as represented by intense interest of the press and the Congress of the United States. Indeed, several regulations dealing with scientific misconduct have been proposed during the last year in the Federal Register, and new legislation has been proposed in the Congress. As a result of these concerns, conferences have been organized by the Institute of Medicine, the American Association for the Advancement of Science/American Bar Association, the Council of Biology Editors, and other groups. The colloquium at NIH, which was held May 31, 1988, and sponsored by the Intramural Scientists, focused on publication practices, especially multiple authorship, as contributing to perceived difficulties. The participants suggested various changes in conventions related to authorship that might help prevent future problems.     

The Development of Infection Structures of Sderotium cepivorum on Onion

Growth of Sderotium cepivorum mycelium on root tissue differed from that on stem tissue. Hyphae grew along the lines of the longitudinal epidermal cell walls often producing side branches which resulted in a distinctive pattern of growth. Penetration occurred mainly between anticlinal wall junctions with occasional direct penetration through the periclinal wall. Growth on the surface of the stem resulted in the formatíon of donne shaped infection cushions, arising from repeated dichotomous branching of hyphal tips. Penetration of the stem tissue occurred solely from these structures. The results of experiments using artificial membranes and surface replicas indicated that the stimulus for attempted penetration was chemical in nature but that the nature of the infection structure produced was determined by the relative strength of the tissue under attack.     

Estimating the rate of plasmid transfer: an end-point method

We describe a method for determining the rate parameter of conjugative plasmid transfer that is based on single estimates of donor, recipient and transconjugant densities and the growth rate in exponential phase of the mating culture. The formula for estimating the plasmid transfer rate, gamma, was derived from a mathematical model describing cell growth and plasmid transfer in batch culture. Computer simulations were used to explore the sensitivity of this method to the realities of bacterial life, such as growth rate differences, plasmid segregation and transitory derepression of pilus synthesis. As predicted by the theory, mating experiments with the plasmid R1 in Escherichia coli K12 demonstrated that the estimate gamma is unaffected by cell density, donor:recipient ratio and mating time. Unlike previous techniques, our method allows us to investigate the effect of environmental factors on plasmid transfer rates when these factors also influence population growth rates. To illustrate this, we examined the effect of temperature on the rate of plasmid transfer.     

Alterations in the longevity and fecundity of adult Trichinella pseudospiralis related to method of isolation of infective larvae

The infectivity of Trichinella pseudospiralis infective larvae was reduced significantly following exposure to low pH or a combination of 1% pepsin at low pH compared to that for larvae isolated in phosphate-buffered saline (PBS) at pH 7.0. Reduction of host gastric pH by administration to mice of sodium bicarbonate solution in PBS was accompanied by an increase in the infectivity of larvae isolated in 1% pepsin/HCl (P/HCl) compared to that for worms inoculated into hosts given PBS alone. Fewer adult worms developing from larvae isolated in P/HCl became established in the host small bowel than was seen with larvae isolated in PBS; moreover, the fecundity in vitro of adult worms developing from P/HCl-isolated larvae was reduced below that for adults developing from larvae isolated from host muscle in PBS. More adult worms were recovered following infection of immune hosts with PBS-isolated larvae than were recovered from immune mice challenged with larvae isolated in P/HCl. Similar findings were observed in mice immunized by infection with Trichinella spiralis and challenged with T. pseudospiralis larvae isolated in either P/HCl or PBS. Immunization of mice with T. pseudospiralis larvae isolated by either method and challenged with larvae of T. spiralis resulted in recovery of similar percentages of the challenge inoculum.     

A rapid method for the detection of potentially viable Mycobacterium leprae in human biopsies: a novel application of PCR

Abstract A simple procedure based on the polymerase chain reaction has been developed to detect Mycobacterium leprae , rapidly and unambiguously, in biological samples. Its application to small numbers of M. leprae cells (∼ 10²) isolated from armadillo liver, mouse footpads or human biopsies is discussed.     

Structure of genes narL and narX of the nar (nitrate reductase) locus in Escherichia coli K-12

narL and narX mediate nitrate induction of nitrate reductase synthesis and nitrate repression of fumarate reductase synthesis. We report here the nucleotide sequences of narL and narX. The deduced protein sequences aid in defining distinct subclasses of regulators and sensors in the family of two-component regulatory proteins.     

The kinesin-like ncd protein of Drosophila is a minus end-directed microtubule motor

The Drosophila ncd gene is required for chromosome segregation during female meiosis. Previous analyses suggested that the ncd gene encoded a protein with sequence similarity to the kinesin motor domain, which suggested that, like kinesin, the ncd protein might be a plus end-directed microtubule motor. Here we describe the expression of ncd protein in E. coli and the initial characterization of the ncd protein's motor properties. The ncd protein is indeed a microtubule motor, but the polarity of movement is minus end directed. The ncd protein also has microtubule bundling activity. These findings limit possible models for the in vivo functions of the ncd protein and suggest that motor proteins with similar sequence can generate movement in opposite directions along a microtubule.