Host-parasite relationships in mycoparasite /

A mycoparasite, Piptocephalis virginiana ^ shows a resemblance to fungal parasites of higher plants in the fine structure of hyphae and haustoria. The morphology and fine structure of host and parasitic fungi have been described. The mode of penetration of the host cell, Choanephora cucurbitarum , probably involves mechanical forces. Although the presence of cell wall degrading enzyme was not detected by conventional techniques, its role in penetration can't be ruled out. A collar around the haustorial neck is formed as an extension of the host cell wall. No papilla was detected although appressorixim was seen during penetration. The young haustorium is enclosed in highly invaginating plasmalemma of the host cell and n\imerous cisternae of endoplasmic reticulum. Appearance of an electron—dense sheath around the mature haustorium seems to coincide with the disappearance of cisternae of endoplasmic reticulum from the host cystoplasm in the vicinity of the haustorium. The role of host cytoplasm particularly of endoplasmic reticulum in the development of the sheath is discussed. Extensive accumulation of spherosomes-like bodies, containing lipids, is found in haustorium, parasite and host hypha. Electron microscope revealed the parasiticculture spore has more lipid content than the axenic culture spore of P. virginiana . The biochemical and cytochemical tests also support these results. The mature spore of C. cucurbitarum possesses a thick three-layered cell wall, different from the hyphal wall. Its germination is accompanied by the formation of an elastic thin inner layer which surrounds the emerging germ tube and the growing hypha. High resolution autoradiography showed that H N-acetyl-glucosamine , a precursor of chitin, was incorporated preferentially in the thin inner layer of the spore wall and also in the cell wall of the growing hypha. When the label was fed to the infected cells, at different intervals after inoculation, grains were observed on the sheath which developed around the haustorium of P. virginiana , 30 hours after inoculation. The significance of these results in relation to the origin and composition of the sheath is discussed.

Syntrophic relationships between algae and bacteria in a fresh-water stream and in culture /

Interactions between freshwater algae and bacteria were examined in a natural stream habitat and a laboratory model. Field observations provided circumstantial evidence, in statistical correlation for syntrophy between the microbial populations. This relation is probably subject to control by the temperature and pH of the aquatic environment. Several species of a pond community were isolated in axenic culture and tests were performed to determine the nature of mixed species interactions. Isolation procedures and field studies indicated that selected strains of Chlorella and Azotobacter were closely associated in their natural habitat. With the suspected controlling parameters, pH and temperature, held constant, mixed cultures of algae and bacteria were compared to axenic cultures of the same organisms, and a mutual stimulation of growth was observed. A mixed pure culture apparatus was designed in this laboratory to study the algal-bacterial interaction and to test the hypothesis that such an interaction may take place through a diffusable substance or through certain medium-borne conditions, Azotobacter was found to take up a Chlorella-produced exudate, to stimulate protein synthesis, to enhance chlorophyll production and to cause a numerical increase in the interacting Chlorella population. It is not clear whether control is at the environmental, cellular or genetic level in these mixed population interactions. Experimental observations in the model system, taken with field correlations allow one to state that there may be a direct relationship governing the population fluctuations of these two organisms in their natural stream surroundings.