Lichens are of interest because of their ability to survive and thrive under extreme environmental conditions on Earth. Biological activity of slow-growing lichens was detected by metabolic gas exchange, CO2 detection being especially convenient. Siegel points out that this method is sensitive and nondestructive, to be preferred to staining techniques, which at present are limited because they are only semiquant.i.tative, subjective, and destructive of the lichen.
A Russian study of simulated planetary environments has been performed with good simulation but for periods of only 2 to 6 hours. Comments on simulation experiments made by Zhukova and Kondratyev ([ref.69]) are presented as follows:
On the basis of modern conceptions on Martian conditions it is difficult to imagine that higher forms of animals or plants exist on the planet. A Martian change of seasons similar to that of our planet empowers us to think that there is a circulation of an organic substance on Mars, which cannot exist without partic.i.p.ation of microbic forms of life. Microorganisms are the most probable inhabitants of Mars although the possibility is not excluded that their physiological features will be very specific. That is why the solution of the problem concerning the character of life on Mars is of exceptional interest. But still the answer to this question can be verified only by simulating Martian conditions, taking into account the information obtained from astrophysicists.
Experiments aimed at creating artificial Martian climatic conditions have been started quite recently; their number is not large since they cannot be combined with the results of numerous experiments investigating the effect of extreme factors on microorganisms. The result of the effect of such physicochemical parameters of the medium as pressure, sharp temperature changes, the absence of oxygen and insolation, depends on their combination and simultaneity. These examples convincingly show that while simulating Martian conditions one should strive to the most comprehensive complex of simultaneously acting factors.
The creation of individual climatic parameters acting successively leads to absolutely different, often opposite results. It should be mentioned also that refusal to imitate insolation and the performance of experiments with specimens of soil which itself has protective effect on cells of microorganisms, but not with pure culture of bacteria, are usual shortcomings in the bulk of studies on this problem.
It appears that organisms from Earth might survive in large numbers when introduced to Martian environment. Whether these organisms will be capable of growth and explosive contamination of the planet in a biological sense or not is highly questionable. The likelihood of an organism from Earth finding ideal conditions for growth on Mars seems extremely low. However, the likelihood of an organism from Earth serving as a contaminant for any life-detection device flown to Mars for the purpose of searching out carbon-based life is considerably higher. The chance that life has originated and evolved on Mars is a completely separate question and much more difficult to answer.
It would be interesting to attempt to determine possible evolutionary trends which might occur on a planet by means of selection of organisms in a simulated planetary environment. Rapid genetic selection combined with radiation and chemicals to speed up mutation rate under these conditions should reveal possible evolutionary trends under the planetary environmental conditions. This could be attempted after the planetary environments are more accurately defined.
EXTREME AND LIMITING ENVIRONMENTAL PARAMETERS OF LIFE
The question of the existence of extraterrestrial life is one of the most important and interesting biological questions facing mankind and has been the subject of much controversial discussion and conjecture.
Many of the quant.i.tative, and even qualitative, environmental const.i.tuents of the planets also are still subjects of controversy and speculation. Best guesses about a relatively unknown planetary environment, combined with lack of information about the capabilities of Earth life to grow in extreme environments, do not provide the basis for making informed scientific estimates.
Life on Earth is usually considered to be relatively limited in its ability to grow, reproduce, or survive in extreme environmental conditions. While many common plants and animals (including man) are quite sensitive to, or incapable of, surviving severe chemical and physical changes or extremes of environment, a large number of micro-organisms are highly adapted and flourish in environments usually considered lethal. Certain chemoautotrophic bacteria require high concentrations of ammonia, methane, or other chemicals to grow.
Anaerobic bacteria grow only in the absence of oxygen.
Besides adapting to the extremes of environments on Earth, life is also capable of growing and reproducing under extreme environmental conditions not normally encountered: e.g., from a few rad of radiation in normal habitats to 106 or more rad from artificial sources, from 0.5 gauss of Earth magnetism to 167 000 gauss in manmade magnetic fields, and from 1-g force of gravity to 110 000 g. The extreme ranges of physical and chemical environmental factors for growth, reproduction, and survival for Earth micro-organisms are phenomenally large.
Life is ubiquitous on Earth and is found in almost every possible environment, including the most severe habitats, from the bottom of the ocean to the highest mountain tops and from cold Arctic habitats to hot springs, as well as in volcanic craters, deep wells, salt flats, and mountain snowfields. Earth life has become adapted to, and has invaded, nearly every habitat, no matter how severe. The physiological and morphological adaptations of life are exceedingly diverse and complex.
Surprisingly, the extreme parameters or ranges of the physical and chemical environmental factors permitting growth, reproduction, and other physiological processes of Earth organisms have not been critically compiled. A partial compilation of certain selected environmental factors has been made by Vallentyne ([ref.76]). A compilation of available published data on certain environmental extremes, particularly from recent NASA-supported research (compiled by Dale W. Jenkins, in press), is presented in tables III to VI. These data can serve as a starting point for a more intensive literature review by specialists, critical evaluation, standardization of end points, and especially to point out areas where critical experimentation is urgently needed.
This critical compilation involves a review of a very broad and complex range of subjects involved in many different disciplines with widely scattered literature. Since the effects of many of the specific environmental factors are harmful, it is difficult to select a point on a scale from no effect to death and use some criteria to say that normal or even minimal growth and reproduction are occurring. The effects of environmental factors are dependent on (1) the specific factor, times, (2) the concentration or energy, times, (3) the time of exposure or application of the factor. Many reports, especially older ones, do not give all of the necessary data to permit proper evaluation. A complicating factor is that the effect of each factor depends on the other factors before, during, and after its application. The condition of the organism itself is a great variable. Proper evaluation requires the critical review by a variety of biological specialists, physicists, and chemists.
To determine the potential of Earth organisms to survive or grow under other planetary environmental conditions, a number of experiments have been carried out attempting to simulate planetary environments, especially of Mars, as reviewed previously. While the results are of real interest, they do not provide much basic information. Further, as the Martian environment is more accurately defined, the experimental conditions are changed. In addition, some experimenters have altered certain factors, such as water content, to allow for potential microhabitats or for areas which might contain more water at certain times.
Table III.-_Extreme Physical Environmental Factors_
----------------------------------------------------------------- Physical Minimum Organism factors ----------------------------------------------------------------- Temperature -30 C Algae (photosynthesis), pink yeast (growth) ----------------------------------------------------------------- Magnetism 0-50 gamma (=10?5 Human gauss)
----------------------------------------------------------------- Gravity 0 g Human, plants, animals
----------------------------------------------------------------- Pressure 10?? mm Hg (5 days) _Mycobacterium_ _s.m.e.g.m.atis_ ----------------------------------------------------------------- Microwave 0 W/cm
----------------------------------------------------------------- Visible 0 ft-c Animals, fungi, bacteria
----------------------------------------------------------------- Ultraviolet 0 erg/cm
----------------------------------------------------------------- X-ray 0 rad ----------------------------------------------------------------- Gamma ray 0 rad
----------------------------------------------------------------- Acoustic 0 dyne/cm
Table III.-_Extreme Physical Environmental Factors_
---------------------------------------------------------------------- Physical Maximum Organism Activity factors ---------------------------------------------------------------------- Temperature 104 C (1000 _Desulfovibrio Grows and reduces atm) desulfuricans_ sulfate ---------------------------------------------------------------------- Magnetism 167 000 _Neurospora_ 1 hr-no effect, gauss _Arbacia_ _Arbacia_ _Drosophila_ development delayed ---------------------------------------------------------------------- Gravity 400 000 g _Ascaris_ eggs 1 hr-eggs hatch, 40 110 000 g _Escherichia coli_ days" growth ---------------------------------------------------------------------- Pressure 1400 atm Marine organisms Growth
---------------------------------------------------------------------- Microwave 2450 Mc/sec _Drosophila_ 68 hr, growth not 0.3 to 1 affected W/cm ---------------------------------------------------------------------- Visible 50 000 ft-c _Chlorella_, Seconds, 17 000 ft-c higher plants recurrently continuous ---------------------------------------------------------------------- Ultraviolet 108 erg/cm, Bean embryos Suppressed growth 2537 ---------------------------------------------------------------------- X-ray 2106 rad Bacteria Growth ---------------------------------------------------------------------- Gamma ray 2.45106 rad _Microcoleus_ Continued growth _Phormidium_ _Synechococcus_ ---------------------------------------------------------------------- Acoustic 140 db or Man Threshold of pain 6500 dyne/cm at 0.02 to 4.8 kcs/sec ----------------------------------------------------------------------
Table IV.-_Extreme Low and High Temperature Effects Permitting Life Processes_
----------------------------------------------------------------- Minimum Organism Activity or condition temperature, C ----------------------------------------------------------------- -11 Bacteria Growth (on fish) ----------------------------------------------------------------- -12 Bacteria Growth ----------------------------------------------------------------- -12 Molds Growth ----------------------------------------------------------------- -15 _Pyramidomonas_ Swimming ----------------------------------------------------------------- -15 _Dunaliella salina_ Swimming ----------------------------------------------------------------- -18 Mold Growth ----------------------------------------------------------------- -18 Yeast Growth ----------------------------------------------------------------- -18 _Aspergillus Growth (in glycerol) glaucus_ ----------------------------------------------------------------- -18 to -20 Mold Growth (in fruit juice) ----------------------------------------------------------------- -18 to -20 _Pseudomonads_ Growth (in fruit juice) ----------------------------------------------------------------- -20 Bacteria Growth ----------------------------------------------------------------- -20 Bacteria Growth ----------------------------------------------------------------- -20 Bacteria Luminescence development accelerated ----------------------------------------------------------------- -20 to -24 Insect eggs (diapause) ----------------------------------------------------------------- -30 Algae Photosynthesis ----------------------------------------------------------------- -30 Pink yeast Growth (on oysters) ----------------------------------------------------------------- -30 Lichens Photosynthesis ----------------------------------------------------------------- -20 to -40 Lichens and conifers Photosynthesis ----------------------------------------------------------------- -44 Mold spores Sporulation and germination -----------------------------------------------------------------
Table IV.-_Extreme Low and High Temperature Effects Permitting Life Processes_
------------------------------------------------------------------ Maximum Organism Activity or condition temperature, C ------------------------------------------------------------------ 73 Thermophilic organisms Growth (P metabolism) ------------------------------------------------------------------ 73 _Phormidium_ (alga) Acclimatized ------------------------------------------------------------------ 70 to 73 _Bacillus calidus_ Growth and spore germination ------------------------------------------------------------------ 70 to 74 _Bacillus cylindricus_ Growth and spore germination ------------------------------------------------------------------ 70 to 75 _Bacillus tostatus_ Growth and spore germination ------------------------------------------------------------------ 80 _Bacillus Cultured in laboratory stearothermophilus_ ------------------------------------------------------------------ 83 Sulfate-reducing Found in a well bacteria ------------------------------------------------------------------ 89 Sulfate-reducing Found in oil waters bacteria ------------------------------------------------------------------ 65 to 85 Sulfate-reducing Cultured in laboratory bacteria ------------------------------------------------------------------ 89 Micro-organisms Found in hot springs ------------------------------------------------------------------ 95 _Bacillus coagulans_ In 80 min. sporulation activation ------------------------------------------------------------------ 110 _Bacillus coagulans_ In 6 min, sporulation activation ------------------------------------------------------------------ 104 _Desulfovibrio Grow and reduce sulfate desulfuricans_ at 1000 atm ------------------------------------------------------------------
Table V.-_Extreme Temperature Limits of Survival_
-------------------------------------------------- Minimum Organism temperature C -------------------------------------------------- -190 Yeast bacteria, 10 species -------------------------------------------------- -197 _Trebouxia erici_ from lichens -------------------------------------------------- -197 Protozoa, _Anguillula_ -------------------------------------------------- -252 Yeasts, molds, bacteria, 10 species -------------------------------------------------- -253 Black currant, birch -------------------------------------------------- -273 Bacteria, many species -------------------------------------------------- -273 Bacteria, many species -------------------------------------------------- -272 Desiccated rotifers -------------------------------------------------- -269 Human spermatozoa --------------------------------------------------
Table V.-_Extreme Temperature Limits of Survival_
------------------------------------------------------------------ Maximum Organism Time of exposure temperature C ------------------------------------------------------------------ 140 Bacterial spores 5-hr immersion ------------------------------------------------------------------ 170-200 Desiccated rotifers 5 min ------------------------------------------------------------------ 151 Desiccated rotifers 35 min ------------------------------------------------------------------ 150 _Clostridium tetani_ 180 min ------------------------------------------------------------------ 170 Aerobic bacteria, molds. 5 days at actinomycetes 610??mm Hg ------------------------------------------------------------------ 127 (dry) Bacteria (in activated charcoal) 60 min ------------------------------------------------------------------ 110 (wet) _Bacillus subtilis_ var. _niger_ 400 min ------------------------------------------------------------------ 120 _Bacillus subtilis_ var. _niger_ 400 min ------------------------------------------------------------------ 141 _Bacillus subtilis_ var. _niger_ 70 min ------------------------------------------------------------------ 160 _Bacillus subtilis_ var. _niger_ 15 min ------------------------------------------------------------------ 180 _Bacillus subtilis_ var. _niger_ 2 min ------------------------------------------------------------------ 188 _Bacillus subtilis_ var. _niger_ 1 min ------------------------------------------------------------------ 120 (wet) _Bacillus stearothermophilus_ 25 min ------------------------------------------------------------------ 120 (dry) _Bacillus stearothermophilus_ 100 min ------------------------------------------------------------------ 141 _Bacillus stearothermophilus_ 12 min ------------------------------------------------------------------ 160 _Bacillus stearothermophilus_ 2 min ------------------------------------------------------------------ 166 _Bacillus stearothermophilus_ 1 min ------------------------------------------------------------------
Table VI.-_Extremes of Chemical Environmental Factors Permitting Growth or Activity_
-------------------------------------------------------- Chemical Minimum Organism factor -------------------------------------------------------- O2 0% HeLa cells, _Cephalobus_, anaerobic bacteria -------------------------------------------------------- O3 (ozone) 0%
-------------------------------------------------------- H2 0%
-------------------------------------------------------- H2O Aw 0.48 _Pleurococcus vulgaris_ ------------------------------------------ Aw 0.5 _Xenopsylla cheopis_ (prepupae) -------------------------------------------------------- H2O2 0%
-------------------------------------------------------- He 0%
-------------------------------------------------------- CO 0%
-------------------------------------------------------- CO2 0%