62 ORDER I. PSEUDOMONADALES 



B. Aggregates composed of two different types of bacteria. 



1. Aggregates small, barrel -shaped, actively motile and consisting of a central, polar 

 flagellate, rod-shaped bacterium with a covering of sulfur green bacteria. 



Genus V. Chlorochromatium, p. 65. 



2. Aggregates large, cylindrical, non-motile and composed of a central filamentous 

 bacterium with a more or less extensive covering of sulfur green bacteria. 



Genus VI. Cylindrogloea, p. 66. 



Genus I. Chlorobium Nadson, 1912. 



(Bull. Jard. Imper. Botan., St. P^tersb., 12, 1912, 64 (Russian), 83 (German).) 

 Chlo.ro 'bi.um. Gr. adj. chlorus greenish yellow, green; Gr. noun hios life; M.L. neut.n. 

 Chlorobium green life. 



Sulfur green bacteria, occurring singly or in chains, individual cells of various sizes and 

 shapes, from spherical to relatively long rod -shaped, the latter sometimes coiled into tight 

 spirals; often united in chains and generally embedded in a slime capsule. Non-motile. 

 Gram-negative. Contain a chlorophjdlous pigment different from the common green plant 

 chlorophylls and from bacteriochlorophyll. Capable of photosynthesis in the presence of 

 hydrogen sulfide, during which thej^ produce elemental sulfur which is excreted outside the 

 cells. Do not form spores. 

 The tj^pe species is Chlorobium limicola Nadson. 



Key to the species of genus Chlorobium. 



I. Does not utilize thiosulfates as oxidizable substrate. 



1. Chlorobium limicola. 

 II. Utilizes thiosulfates as oxidizable substrate. 



2. Chlorobium thiosulfatophihan. 



1. Chlorobium limicola Nadson, 1912. appearance of the cultures. In healthy cul- 



(Bull. Jard. Imper. Botan., St. Petersb., 12, tures the bacteria rem.ain evenly dispersed 



1912, 64 (Russian), 83 (German).) and settle very slowly. Non-motile. 



li.mi'co.la. L. noun limus mud; L. v. colo Color: Intensely green in healthy cul- 

 to dwell; M.L. fem.n. limicola the mud tures; poor pigmentation and then yellow- 

 dweller, ish green in media deficient in iron. 



Cells occur in various sizes and shapes Strictly anaerobic, obligatory photosyn- 

 which are markedly dependent upon en- thetic bacteria whose occurrence in nature 

 vironmental conditions. In young and is dependent upon the presence of hydrogen 

 healthy cultures, predominantly small, sulfide. They utilize this substance, as well 

 ovoid to short rods, 0.7 by 0.9 to 1.5 microns, as elemental sulfur and molecular hydrogen, 

 frequently united in chains resemblingstrep- as oxidizable substrates; produce sulfur 

 tococci. Greatly elongated and irregularly from sulfides but do not store sulfur glob- 

 bent and curved rods also occur as involu- ules inside the cells. Oxidation of sulfide 

 tion forms; these rods may likewise remain may yield sulfur as an end product, but 

 united in chains. Club-shaped and spirally under optimal conditions the sulfur is 

 wound to tightly coiled involution forms further oxidized to sulfate. Unable to use 

 have been described, but the conditions for thiosulfate and tetrathionate as oxidizable 

 their formation are not understood, and in substrates. Development in organic media 

 recent pure-culture studies these have never free of sulfide has not been obtained, 

 been encountered (Larsen, Jour. Bact., 64, Source: Isolated from mud and stagnant 

 1952, 187). Regularly produce mucus; in water, containing hydrogen sulfide, from 

 media of inadequate composition this may the St. Petersburg Botanical Garden. Also 

 lead to the formation of cell conglomerates found by Bicknell (Lloydia, 12, 1949, 183) in 

 of different sizes and shapes and a stringy Sodon Lake, Bloomfield Hills, Michigan. 



