PubMed · 5971972
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C M Feldherr. 1966. Nucleocytoplasmic exchanges during cell division.. https://doi.org/10.1083/jcb.31.1.199
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W. Fontana & L.W. Buss (Proc. Natn. Acad. Sci. U.S.A. 91, 757 (1994) and Bull. math. Biol. 56, 1 (1994) have put forward a scheme for a theory of biological organization based on the lambda-calculus. Their key innovation was to represent, with the aid of this calculus, a certain minimal chemistry. Although this idea is very promising, their concrete formulation could be improved if suggestions for the following items were incorporated: (i) a better coding of chemical reactions; (ii) a reinterpretation of the evolutionary behaviour of autocatalytic chemical networks; (iii) a better appreciation of morphological and genetic factors; (iv) a more complete embedding of the theory into the background of relevant earlier contributions. Confusion can be stopped by the application of a proper classification of replicators (important categories being: processive and modular, limited and unlimited hereditary replicators). Suggestions to facilitate improvement are made explicit in this paper. The most challenging task would be to model the transition from processive, limited hereditary replicators to modular replicators with limited and unlimited heredity.
To assess the possible risk of microbial keratitis associated with swimming or bathing in public pools, the microbiological quality as well as the presence of free living amoebae in 16 halogenated swimming pools and whirlpools, located in Helsinki, Finland, was determined. Five additional whirlpools situated in the ferries cruising from Finland to Sweden were included in the study. Other parameters investigated were the total bacterial count, identification of Pseudomonas aeruginosa and Staphylococcus aureus, measurement of free residual and combined chlorine, potassium permanganate index, urine, pH, and turbidity. Amoebae were detected in 41% of the pool water samples studied. Seven of 11 whirlpools and four of 10 swimming pools were shown to contain amoebae. An Acanthamoeba species was isolated from only one outdoor swimming pool; the other amoebae belonged to the genera Vexillifera, Flabellula, Hartmannella, and Rugipes. Although not a single verified case of Acanthamoeba keratitis has been found in Finland, the findings show that there is a theoretical risk of amoebic and bacterial keratitis associated with swimming or bathing in properly cleaned public pools. Consequently, we do not recommend swimming or bathing with contact lenses.
Small free-living amoebae (FLA) are the main predators controlling bacterial populations in soils. They are distributed in the rhizospheric zone and the surrounding bulk soil; however, they may spread deeper, reaching the vadose zone of groundwater systems, especially where bacterial populations get to high densities. Soil texture is the physical factor controlling the distribution of FLA because it determines the mean bore pore of soil aggregates and other important physical factors. FLA help maintain the high bacterial mineralization rate of organic matter through predation. As attachment onto a surface is necessary for feeding, the quantity of available surfaces is very important for developing this activity. However, the role of protozoa on plant growth promotion is still unclear because they may increase this effect by feeding on both fungi and bacteria. Small FLA are found in soils or sediments, as well as attached to suspended particulate matter in water columns, in the first 30 microns of water surface, or on the bodies of submerged animals and plants. These microorganisms do not distinguish between terrestrial or aquatic environments because they live in the interfaces between them. However, their importance in aquatic systems has been considered as negligible because they are outcompeted by free swimmers. The water conditions affecting amoebae survival are pH, temperature, concentration of sulfhydric acid and salinity. These factors have a strong influence on the structure of amoebae communities in aquatic environments. FLA are considered cosmopolitan as a group, and they live inside vertebrates, in soils, freshwater, marine waters, and on the aerial parts of plants and animals. These microbes, are spread by wind and water currents. Once in the air, cysts and trophozoites behave like any other suspended particulate matter. Therefore, suspension transportation, and removal depend on atmospheric dynamics rather than on their own mechanisms. Ultraviolet light and drought are the main causes of losing viability, but much needs to be learned about the effects of air contaminants on amoebal survival. Naked amoebae also live in the phyllosphere as part of phylloplane community, but their importance and participation in this environment remain unknown. Some species belonging to the genera Acanthamoebae, Naegleria, and Balamuthia cause fatal diseases in humans and are carriers of other pathogens such as Legionella pneumophilia. However, FLA communities can be of some utility in sewage treatment works based in soil filters. FLA's predatory activity in the root zone method may be of greater importance than previously thought, because this is their natural or more favorable environment.(ABSTRACT TRUNCATED AT 400 WORDS)