oxidizing bacteria capable of fixing atmospheric nitrogen were isolated from garden soil, pond mud, oil field soil, and soil exposed to natural gas, indicating a rather wide prevalence in nature. This may explain the high concentration of organic nitrogen commonly found in soils exposed to gas leakage from pipelines or natural-gas seeps. Added molybdenum was a requirement for growth in a nitrogen-free mineral salts medium. All nitrogenfixing, methane-oxidizing bacteria isolated were gram-negative, nonsporeforming, usually motile rods. Colonies were light yellow, yellow, or white. The most common isolate, which formed lightyellow colonies, is referred to as Pseudomonas

SummaryRlicroorganisms have been fomid which concomit8itritsly convert hydrocarbons, selected riaphtherric acids, and atmospheric nitrogen into cellular substance.Bacteria. are incliided in the geriera Psrltdwmmas, Myco:o6ar.terium, and Azotobacter. Carlion sources nt'ilized iiiclude the hydrocarbons metthane, n-butane, n-tetradecme, toliieiie, arid a napht>henic acid, cyclohexane-carboxylate. Uptake of isot,opic. iiitrogeii was employed as a criterion of nitrogen fixatZion. The results indicate a rat.her wide prevalence in natiire of hydrorarbori-oxidizing bact,eria capable of fixing st,mospheric nitrogen. Their ocriirreiice helps explain t.he high conceiitrat,iori of organic nit,rogeri commonly found iii soils exposed to gas leakage from pipelines or natiiral-gas seeps, arid suggests fnrther considerat,ion of t,he possibilit,y of applying selected petroleum residiia to soils iii order to increase t,he agriciiltiiral potenti:tl by riit.rogen-fixiiig processes.

The growth of microorganisms in fermentations where oil had been maintained as the continuous phase was examined to determine whether advantage could be gained from the increased solubility of oxygen in hydrocarbon. Although cell concentrations were highest in the aqueous phase of oil‐continuous systems, due to the large oil fraction, productivities achieved per unit fermenter volume were generally equivalent to those obtained from water‐continuous systems. With the oil‐continuous emulsions, the power requirement for aeration and mixing was less, and phase reversal resulted in a threefold concentration of cells in the aqueous medium, thereby facilitating their recovery.

Experiments using Pichia yeast grown on n-paraffins have been conducted in laboratory 10-L airlift fermenters and in a 640-L module of commercial scale. Results confirmed the design concept of combining oxygen transfer and fermenter cooling with low-pressure air. However, in the absence of mass transport constraints, the build up of toxic factors in the fermenter appeared to be a major variable limiting cell productivity. Foaming in the large fermenter also presented a serious problem, which must be solved before low-pressure airlift fermenters become practical.

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