- Volume 66, Issue 1, 1971

SUMMARY: The ultrastructural features of developing croziers are similar to those described in other ascomycete hyphal elements. The variations in vacuolation during development suggest that vacuoles control the movement of cytoplasm. Conjugate nuclear division occurs in the crozier before segmentation. During this division the continuous spindle fibres of the two nuclei are essentially parallel and extend from polar centriolar plaques. All the observations made with the electron microscope indicate that the nuclear envelope remains intact during division. After conjugate nuclear division the terminal cell is delimited. Subsequently, a septum is formed between the penultimate cell and the stalk cell. Both septa are formed by an inward deposition of wall material and possess a single central pore. The walls between a portion of the stalk and terminal cells dissolve and protoplasmic continuity is established between the two hyphal elements.

SUMMARY: Conidia of Botrytis fabae germinate in the presence of sublethal concentrations of benomyl to produce swollen and distorted germ tubes which branch more frequently than those of normal conidia. Multiple germ-tube emergence also occurs to a greater extent in treated conidia.

The orientation of organelles towards the hyphal tip is disorganized in benomyl-treated germ tubes. Endoplasmic reticulum which occurs as multiple strands surrounding the nuclei in normal germinating spores is broken up into a fragmented network. Part of the endoplasmic reticulum occurs as strands and vesicles close to the plasmalemma, a configuration which corresponds closely to the situation in resting conidia. The findings inchemically fixed sections are confirmed by the appearance of freeze-etched replicas. Benomyl treatment seems to stimulate lomasome formation, and freeze-etched treated nuclei appear deeply lobed and convoluted.

SUMMARY: Electron microscopy of ultra-thin sections of the phloem of strawberry plants with green petal disease revealed mycoplasma-like organisms. Similar sections of the phloem of apple trees with chat fruit disease contained similar organisms that differed in size from those in apple with rubbery wood disease. No organisms were found in normal trees of the same varieties.

SUMMARY: Mycobacterium smegmatis is mutated by exposure to nitrosoguanidine at 0.1 and 1.0 mg./ml. for 15 and 60 min. After incubation for 24 h. in a complete medium, to allow for phenotypic expression, isoniazid (at 0.1 mg./ml. for 24 h.) is used to reduce the numbers of unwanted mutants and surviving wild-type bacteria in a procedure analagous to penicillin selection with other bacteria.

SUMMARY: A two-stage continuous culture apparatus was used to study the growth and feeding kinetics of the ciliated protozoon Tetrahymena pyriformis GL. The food organism, the bacterium Klebsiella aerogenes, was grown in the first stage using sucrose as the limiting nutrient to establish steady-state populations. By pumping some of this culture to a second fermentor which contained T. pyriformis a continuous supply of K. aerogenes was made available for predation. In the early stages after inoculation the ciliates were few in numbers but large in size, but over a period of a week or two the ciliate cells became smaller and more numerous.

The feeding rate of Tetrahymena was found to be dependent upon size and growth rate. The kinetics of feeding and growth were related to the mean volume of the ciliate which increased with dilution rate.

It was possible to grow Tetrahymena pyriformis in continuous culture at a rate of 0.38 h.−1 and the maximum specific growth rate was estimated to be 0.43 h.−1, which is almost twice that obtained from batch culture studies. The yield constant of Tetrahymena was 0.54.

SUMMARY: The rates at which two strains each of four species of cellulolytic rumen bacteria could grow on and solubilize ball-milled filter paper were compared in vitro. Strains of Ruminococcus albus solubilized it most rapidly, followed by R. flavefaciens. Butyrivibrio fibrisolvens showed consistently low rates of solubilization while strains of Cillobacterium cellulosolvens maintained on cellobiose-containing medium gradually lost their ability to solubilize cellulose. Cellulolysis could not be restored by successive transfers to media each containing one of different cellulose oligosaccharides. Strains of R. albus and R. flavefaciens grew almost as rapidly in cellulose- as in cellobiose-containing media, while B. fibrisolvens strains grew better in medium with cellobiose. On this basis the ruminococci were termed true cellulolytic bacteria.

A mushroom-shaped budding bacterium, isolated from fresh pond water, is unlike any previously described aquatic budding bacteria (Whittenbury & McLee, 1967; Hirsch & Rheinheimer, 1968; Staley, 1968). Its morphological ‘life-cycle’ and other properties are described.