FAMILY II. METHANOMONADACEAE 75 



CH4 and 321 ml O2 to the following: In addition, 21 ml CO2 were dissolved in 



CH4 ml the liquid. 



CO2 78 ml Habitat : Presumably widely distributed 



O2 172 ml in soil. 



Genus II. Hydrogenomonas Orla-Jensen, 1909. 

 (Cent. f. Bakt., II Abt., 22, 1909, 311.) 



Hj-.dro.ge.no.mo'nas. Gr. hydro water; Gr. genus race, offspring; whence, M.L. hy- 

 drogenum hydrogen, that which produces water; Gr. monas a unit, monad; M.L. fem. noun 

 Hydrogenomonas hydrogen monad. 



Short rods that are polar flagellate when motile. Cells capable of deriving energy from the 

 oxidation of hydrogen. They may grow well on organic media without hydrogen although 

 this has not been shown to be true in all cases. Gram-negative. Found in soil and water. 



This group of bacteria is characterized by the ability to grow in substrates containing no 

 organic matter and to use elemental hydrogen as the source of energj^ for growth. Under 

 these conditions CO2 is used as the source of carbon. Bacteria with similar phj'siological 

 characteristics but differing in morpholog}' are placed in the genera Bacillus and Clos- 

 tridium. Although other bacteria and even certain algae have enzyme systems which can 

 activate hydrogen and reduce CO2 in the process, there is no evidence that these organisms 

 are able to grow in inorganic media with hydrogen as the exclusive source of energj^ (see 

 Stephenson and Strickland, Biochem. Jour., 25, 1931, 205-215; Woods, Biochem. Jour., 30, 

 1936, 515; Lee and Umbreit, Zent. f. Bakt., II Abt., 101, 1940, 354; Gaffron, Amer. Jour. 

 Bot., 27, 1940, 273). 



The tj'pe species is Hydrogenomonas pantotropha (Kaserer) Orla-Jensen. 



Key to the species of genus Hydrogenomonas. 



I. Not sensitive to high concentrations of O2 . 



A. When growing autotrophically, no pellicle on liquid media. 



1. Hydrogenomonas pantotropha. 



B. When growing autotrophically, pellicle formed on liquid media. 



2. Hydrogenomonas facilis. 

 II. Sensitive to high concentrations of O2 . 



A. When growing autotrophically, no pellicle on liquid media. 



3. Hydrogenomonas flava . 



B. When growing autotrophically, pellicle formed on liquid media. 



4. Hydrogenomonas vitrea. 



1. Hydrogenomonas pantotropha (Ka- Inorganic solution: When cultivated 



serer, 1906) Orla-Jensen, 1909. (Bacillvs under an atmosphere of O2 , CO2 and Ho , 



paniotrophus Kaserer, Cent. f. Bakt., II the liquid becomes turbid without pellicle 



Abt., 16, 1906, 688; Orla-Jensen, Cent. f. formation. 



Bakt., II Abt., .?^, 1909, 311.) Inorganic solid media: When cultivated 



pan.to'troph.a. Gr. prefix panto all; Gr. ""^er an atmosphere of O2 , CO2 and H2 , 



, 7 r 1 TiTT J- I i I the colonies are yellow and slimy, and the 



trophus feeder; M.L. adj. pantotrophus om- , , ^ , , ,- , 



agar plates have an odor resembling hot, 



mvorous. x 



soapy water. 



Rods, 0.4 to 0.5 by 1.2 to 1.5 microns, with G^\^t\,, colonies: Yellow, smooth, rarely 



rounded ends. Occur singly, in pairs and in concentrically ringed or greenish, 



chains. Encapsulated. Actively motile by Gelatin stab: Growth only at surface. As 



means of a single, long, polar flagellum. a rule no liquefaction. 



Gram stain not recorded. Bipolar staining Agar colonies: Same as on gelatin, green- 

 in old cultures. ish, often slimy. 



