Norman H. Horowitz

Cellular and extracellular siderophores of Aspergillus nidulans and Penicillium chrysogenum.

Aspergillus nidulans and Penicillium chrysogenum produce specific cellular siderophores in addition to the well-known siderophores of the culture medium. Since this was found previously in Neurospora crassa, it is probably generally true for filamentous ascomycetes. The cellular siderophore of A. nidulans is ferricrocin; that of P. chrysogenum is ferrichrome. A. nidulans also contains triacetylfusigen, a siderophore without apparent biological activity. Conidia of both species lose siderophores at high salt concentrations and become siderophore dependent. This has also been found in N. crassa, where lowering of the water activity has been shown to be the causal factor. We used an assay procedure based on this dependency to reexamine the extracellular siderophores of these species. During rapid mycelial growth, both A. nidulans and P. chrysogenum produced two highly active, unidentified siderophores which were later replaced by a less active or inactive product--coprogen in the case of P. chrysogenum and triacetylfusigen in the case of A. nidulans. N. crassa secreted coprogen only. Fungal siderophore metabolism is varied and complex.

The Viking Carbon Assimilation Experiments: Interim Report

A synthesis of organic matter from atmospheric carbon monoxide or carbon dioxide, or both, appears to take place in the surface material of Mars at a low rate. The synthesis appears to be thermolabile and to be inhibited by moisture.

The carbon-assimilation experiment: The Viking Mars Lander

Abstract The carbon-assimilation experiment detects life in soils by measuring the incorporation of carbon from 14CO and 14CO2 into organic matter. It is based on the premise that Martian life, if it exists, is carbonaceous and exchanges carbon with the atmosphere, as do all terrestrial organisms. It is especially sensitive for photosynthesizing cells, but it detects heterotrophs also. The experiment has the particular advantage that it can be carried out under essentially Martian conditions of temperature, pressure, atmospheric composition, and water abundance.

Television experiment for Mariner Mars 1971

Abstract The Television Experiment objectives are to provide imaging data which will complement previously gathered data and extend our knowledge of Mars. The two types of investigations will be fixed-feature (for mapping) and variable-feature (for surface and atmospheric changes). Two cameras with a factor-of-ten difference in resolution will be used on each spacecraft for medium- and high-resolution imagery. Mapping of 70% of the planets surface will be provided by medium-resolution imagery. Spot coverage of about 5% of the surface will be possible with the high-resolution imagery. The experiments 5 Principal Investigators and 21 Co-Investigators are organized into a team. Scientific disciplines and technical task groups have been formed to provide the formulation of experiment requirements for mission planning and instrument development. It is expected that the team concept will continue through the operational and reporting phases of the Mariner Mars 1971 Project.

Sterile Soil from Antarctica: Organic Analysis

Soils from the dry-valley region of Antarctica can be sterile by the usual microbiological criteria and yet contain significant amounts of organic carbon. Examination of one such soil shows that the organic material is finely divided anthracite coal. These findings have significant implications for the biological exploration of Mars.

ON THE ENERGETICS OF DIFFERENTIATIONp VIIc COMPARISON OF THE RESPIRATORY RATES OF PARTHENOGENETIC AND FERTILIZED URECHIS EGGS

It has been long been known that the rate of respiration rises during development. This increase in rate is evidently not directly proportional to the increase in the number of cells (cf. Needham, 1931). It might, nevertheless, depend upon changes in the egg brought about by cell division, so that when cleavage fails to occur the rise in respiration would be inhibited. We have considered in previous work the dependence of the form-changes on the respiration, the rate of oxygen consumption being taken as a measure of the energy available for the various developmental processes. We consider now the possibility that the developmental changes determine in turn the rate of respiration. If, for example, early cleavage is inhibited in a manner that does not affect the absolute rate of respiration at the particular stage, then we may expect, on this basis, failure of the subsequent rise. In the early work of Warburg (1910) it has been shown that cleavage could be suppressed in sea urchin eggs by means of phenylurethane without immediately affecting the respiratory rate. However, the question of whether or not the rate would rise later was not investigated. Also it has been shown that after parthenogenetic activation of sea urchin eggs the same increase in rate occurs that is obtained normally upon fertilization (Warburg, 1910; Loeb and Wasteneys, 1913). But here again it would be desirable to know what happens later, especially since the parthenogenetically activated eggs develop much more slowly in general and often stop in early cleavage or even fail to divide.

THE ACTIVITIES OF VARIOUS SUBSTITUTED PHENOLS IN STIMULATING THE RESPIRATION OF SEA URCHIN EGGS

1. Data on the concentrations required for optimum respiratory stimulation and reversible cleavage block in fertilized sea urchin eggs are presented for fifteen different nitro- and halophenols.2. The experiments show that it is necessary to define the optimum as the highest respiratory increase that does not diminish with time.3. Cleavage block occurs with concentrations just beyond the optimum defined in this manner.4. Comparison of the calculated concentrations of undissociated molecules and of anions inside the cell for the different substituted phenols supports the previously expressed view that the anion is the active agent. Penetration is accomplished in the undissociated form, as previously shown.5. The results of experiments in which the internal pH is raised also support this view.6. Titration curves of egg brei indicate a high buffer capacity for the egg and support the assumption that the internal pH does not change in the presence of the substituted phenols.

A centennial: George W. Beadle, 1903-1989.

GEORGE BEADLE was a quadruple-threat man—scientist, teacher, administrator, and public citizen. He excelled in each. Furthermore, he did what very few geneticists did in his time: he studied three different organisms and made outstanding discoveries in every case. He followed his interests and

Commentary life on Mars — A reply

In his thoughful review of my book, To Utopia and Back: The Search for Life in the Solar System, Richard S. Young (1987) raises two objections to my conclusion that life does not exist on Mars. Both, I believe, are based on misconceptions. I appreciate the opportunity to comment on them here. The first rests on the discovery (Friedmann, 1982) that in the dry Antarctic desert, where microbial life in the soil is sparse or even absent, dense growths of lichens and bacteria can be found in a narrow zone a few millimeters beneath the north-facing surfaces of translucent, porous rocks. This phenomenon, Friedmann showed, is explained by the fact that the rocks are warmed sufficiently by the sun to melt snow, which is then absorbed by the rock; a sheltered, moist environment is thus created for microbial life. In his review, Young argues that such endolithic habitats may exist also on Mars. It is not easy, however, to transfer the Antarctic scenario to Mars. The difficulty is the same one that stands in the way of all efforts to find a biological habitat on that planet: snow cannot melt, and liquid water cannot exist, on the surface of Mars, owing to the low pressure, high CO2, and low water content of its atmosphere. In this respect, and in many others, there is no resemblance between Mars and the Antarctic desert. The latter is incomparably more favorable as a habitat. It is within but a few miles of the ocean, to name another major difference. At its worst, the Antarctic desert is just marginally unfit for life. Even in the driest areas, only 10 to 15°70 of soil samples are actually sterile. In such a place, a small climatic variation like the one that gives rise to the endolithic habitats can make the difference between a livable environment and a non-livable one. This would not be the case on Mars. Although the Antarctic desert is not truly Marstike, we learned an important lesson in planetary biology there; namely, that the range of biological adaptability is very limited where the need for water is concerned. The discovery of sterile and nearly sterile soils in this desert, which has been exposed for tens of thousands of years to a constant airborne influx of contaminants and genetic variants from a vast pool of microbial life outside the area, was a revelation. It demonstrated in the clearest possible way the importance of water for life, and it caused some of us to begin to wonder whether it was reasonable to expect to find life on a planet as dry as Mars. It is perhaps worth pointing out here that the question of endolithic habitats on Mars is one that can be approached experimentally. Enough is now known about the Martian environment to perform meaningful laboratory tests of this question. For any who are not satisfied by theoretical arguments, the experimental way is open. Youngs second objection to my conclusion that Mars is lifeless rests on the fact that there have been only two landings on Mars. He considers this an inadequate base for such large conclusions.