Survival as a criterion for autochthony

A study was conducted to determine characteristics of unicellular microorganisms that are associated with their being indigenous to soil. The approach involved a comparison of the behavior of 12 isolates from soil and 16 from lake water. After addition to soil at approximately 0.15 MPa moisture, the population of microorganisms originally isolated from soil declined somewhat but remained larger than 104 g−1 for 30 days. The populations of most but not all the aquatic bacteria declined to a greater extent under identical conditions, and some were no longer detected. In soil undergoing drying, the abundance of both soil and aquatic microorganisms declined in similar fashions, and a few species could not be detected at 30 days. The resistance of soil and aquatic microorganisms as a group to starvation stress in soil and liquid did not differ. The results indicate that soil microorganisms as a group are more able to endure biological stresses in soil than are non-soil microorganisms. Because some non-soil organisms persist in non-sterile soil, the habitat of a species is an insufficient basis for assessing its ability to survive in soil.