FAMILY I. NITROBACTERACEAE 67 



f. Hydrobiol., Suppl. 5, 1925, 279) that the grate, whereupon the green constituents 



complex Chlorochromatium aggregalum may, appear as small Pelodictyon aggregatum 



especially in the presence of oxygen, disinte- {Schmidlea luteola) colonies. 



Suborder II. Pseiidomonadineae Breed, Murray and Smith, Sub-Ordo Nov. 



Pseu.do.mo.na.di'ne.ae. M.L. fem.n. Pseudomonas, -adds a genus of bacteria; -ineae end- 

 ing to denote a suborder; ALL. fern. pi. n. Pseiidovionadineae the Pseudomonas suborder. 



Cells normally about 1 micron in diameter, but among the colorless sulfur bacteria they 

 may be as much as 14 microns in diameter. The cells do not contain photosynthetic pig- 

 ments, but diffusible, water-soluble pigments of a type not found elsewhere among bacteria 

 occur in many species. Also, non-water-soluble yellow or red pigments occur in some gen- 

 era. The motile species are invariably polar flagellate. Some groups are strictly autotrophic, 

 oxidizing simple inorganic compounds; others are also oxidative but are facultatively 

 heterotrophic or heterotrophic in their physiology. A few genera include species that fer- 

 ment simple sugars, even producing H2 and CO2 as do the common acid- and gas-producing 

 coliform bacteria. The organisms in one genus {Zijmomonas) even carry out an alcoholic 

 fermentation similar to that of j^easts. The majority of the species grow well and fairly 

 rapidly on the surfaces of ordinary culture media. Some species that attack agar or cellulose 

 or that show other unusual types of physiology are more fastidious in their requirements. 

 Only a few species are strictly anaerobic as in Vibrio and Desulfovibrio . The species in this 

 suborder are largely found in salt- or fresh-water or in soil. Some are parasitic and a few 

 are pathogenic to vertebrates including man. 



Key to (he families of siihordcr Pseiidomonadineae. 



I. Coccoid to rod-shaped cells. Occasionally individual rods may be curved although the 

 majority of the cells are straight. 



A. Cells not attached to a substrate. 



1. Cells have the power to oxidize simple compounds such as ammonia, nitrites, 

 methane, hydrogen, carbon monoxide, sulfur or sulfur compounds. Chemo-auto- 

 trophic or facultatively chemo-autotrophic. 



a. Do not secure their energy from the oxidation of sulfur compounds, 

 b. Oxidize ammonia to nitrites or nitrites to nitrates. Autotrophic. 

 Family I. Nitrobacteraceae, p. 68. 

 bb. Oxidize methane, hydrogen or carbon monoxide. Autotrophic. 

 Family II. Methanomonadaceae , p. 74. 

 aa. Oxidize sulfur compounds, frequently with a deposit of free sulfur granules 

 or crystals within or without the cells. 



Family III. Thiobacteriaceae, p. 78. 



2. Cells frequently oxidative, although they are sometimes fermentative in their 

 physiology. Usually heterotrophic. Rarely facultatively autotrophic 



Family IV. Pseudomonadaceae, p. 88. 



B. Cells in free-floating films or attached to a substrate. 



a. Cells attached to the substrate by means of a stalk, usually with a holdfast. 

 Family V. Caulobacteraceae , p. 212. 

 aa. Cells in free-floating films or attached to the substrate by means of capsular 

 material. 



Family VI. Siderocapsaceae, p. 217. 

 II. Curved, vibrio-like to spiral-shaped cells. 



Family VII. Spirillaceae, p. 228. 



