A Bacillus sp. capable of utilizing phosphite and hypophosphite under anaerobic conditions was isolated from Cape Canaveral soil samples. The organism was isolated on a glucose-mineral salts medium with phosphate deleted. Anaerobic cultivation of this isolate resulted in decreases in the hypophosphite or phosphite concentration, increases in turbidity, cell count, and dry-cell weight, and decreases in pH and glucose concentration. The optimum hypophosphite concentration for this isolate was 60 Ag/ml, whereas the optimum phosphate concentration was greater than 1,000 ,.g/ml, suggesting that higher concentrations of hypophosphite may be toxic to this isolate. Hypophosphite or phosphite utilization was accompanied by little or no detectable accumulation of phosphate in the medium, and 32P-labeled hypophosphite was incorporated into the cell as organic phosphate. When phosphate was present in the medium, the isolate failed to metabolize phosphite. In the presence of phosphite and hypophosphite, the isolate first utilized phosphite and then hypophosphite.

Microorganisms capable of growth at 7 C were enumerated and isolated from soil samples from the manufacture and assembly areas of the Viking spacecraft. Populations ranging from 4.2 x 103 to 7.7 x 100/g of soil were isolated from the 15 soil samples examined. Temperature requirements were determined, and those growing at 3 C, but not at 32 C, were designated as obligate psychrophiles in this investigation. Populations of soil bacteria, including aerobic sporeformers, ranging from 1.5 x 102 to 9.8 x 105/g were capable of growth at 3 C, but not at 32 C. Bacterial isolates were identified to major generic groups. No psychrophilic sporeformers were isolated from soil from the manufacture area, but psychrophilic sporeformers ranged from 0 to 6.1 x 103/g from soil from the assembly area.

The dry-heat resistance characteristics of spores of psychrophilic organisms isolated from soil samples from the Viking spacecraft assembly areas at Cape Kennedy Space Flight Center, Cape Canaveral, Fla., were studied. Spore suspensions were produced, and dry-heat D values were deternined for the microorganisms that demonstrated growth or survival under a simulated Martian environment. The dry-heat tests were carried out by using the planchet-boat-hot plate system at 110 and 125°C with an ambient relative humidity of 50% at 22°C. The spores evaluated had a relatively low resistance to dry heat. D(110°C) values ranged from 7.5 to 122 min, whereas the D(125°C) values ranged from <1.0 to 9.8 min.

Microorganisms capable of growth at 7 C were enumerated and isolated from soil samples from the manufacture and assembly areas of the Viking spacecraft. Populations ranging from 4.2 × 10 3 to 7.7 × 10 6 /g of soil were isolated from the 15 soil samples examined. Temperature requirements were determined, and those growing at 3 C, but not at 32 C, were designated as obligate psychrophiles in this investigation. Populations of soil bacteria, including aerobic sporeformers, ranging from 1.5 × 10 2 to 9.8 × 10 5 /g were capable of growth at 3 C, but not at 32 C. Bacterial isolates were identified to major generic groups. No psychrophilic sporeformers were isolated from soil from the manufacture area, but psychrophilic sporeformers ranged from 0 to 6.1 × 10 3 /g from soil from the assembly area.

Soil samples from Cape Canaveral were subjected to a simulated Martian environment and assayed periodically over 45 days to determine the effect of various environmental parameters on bacterial populations. The simulated environment was based on the most recent available data, prior to the Viking spacecraft, describing Martian conditions and consisted of a pressure of 7 millibars, an atmosphere of 99.9% CO2 and 0.1% 02, a freeze-thaw cycle of-65°C for 16 h and 24°C for 8 h, and variable moisture and nutrients. Reduced pressure had a significant effect, reducing growth under these conditions. Slight variations in gaseous composition of the simulated atmosphere had negligible effect on growth. The freeze-thaw cycle did not inhibit growth, but did result in a slower rate of decline after growth had occurred. Dry samples exhibited no change during the 45-day experiment, indicating that the simulated Martian environment was not toxic to bacterial populations. Psychrotrophic organisms responded more favorably to this environment than mesophiles, although both types exhibited increases of approximately 3 logs in 7 to 14 days when moisture and nutrients were available.