FAMILY III. CHLOROBACTERIACEAE 



63 



Habitat: Widely distributed in mud and 

 stagnant water. Mass development under 

 conditions of relatively high sulfide con- 

 centrations and low pH in environments 

 exposed to light. 



Illustrations: Nadson, up. cit., 1912, PI. 

 Ill, fig. 3-12; van Niel, Arch. f. Mikrobiol., 

 3, 1931, fig. 8, p. 66. 



2. Chlorobiuin ihiosulfatophilum Lar- 



sen, 1952. (Jour. Bact., 64, 1952, 187.) 



thi.o.sul.fa.to'phi.lum. M.L. noun thio- 

 sulfatum thiosulfate; Gr.adj. phibis loving; 

 M.L. adj. thiosulfatophilus thiosulfate- 

 loving. 



Cells indistinguishable from those of 

 Chlorobium limicola. 



Color: As in Chlorobium limicola. 



Strictly anaerobic, obligatory photosyn- 

 thetic bacteria. Utilize sulfides, sulfur, 

 thiosulfate, tetrathionate and molecular 

 hydrogen as o.xidizable substrates; produce 

 sulfate from inorganic sulfur compounds. 

 Unable to grow in organic media free of oxi- 

 dizable, inorganic sulfur compounds. 



Distinctive characters: Differs from 

 Chlorobium limicola in its ability to oxidize 

 thiosulfate and tetrathionate. 



Source: Isolated from marine and fresh- 

 water mud. 



Habitat: Same as for Chlorobium limicola. 



Genus II. Pelodictyon Lauterborn, 1913. 



(Allgem. botan. Ztschr., 19, 1913, 98; Verhandl. naturhistor.-medizin. Vereins, Heidel- 

 berg, N.F. 13, 1915, 431.) 



Pe.lo.dic'ty.on. Gr. adj. pelos dark-colored; Gr. noun dictyon net; M.L. neut.n. Pelodic- 

 tyon a dark-colored net. 



Sulfur green bacteria, individual cells ovoid to distinctly rod-shaped, producing rather 

 extensive mucoid capsules and generally united into large colonies of characteristic shapes. 

 Non-motile. Contain chlorophyllous pigments different from the common green plant 

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

 hydrogen sulfide, but do not store sulfur globules inside the cells. 



The type species is Pelodictyon clathratiforme (Szafer) Lauterborn. 



Key to the species of genus Pelodictyon. 



I. Cells united in colonies in a net-like fashion. 



1. Pelodictyon clathratiforme. 

 II. Cells arranged in tightly packed colonies without net-like structure. 



A. Colonies composed of irregularly arranged cell-masses, extending in three dimen- 

 sions. 



2. Pelodictyon aggregatum. 



B. Colonies consisting of parallel strands and extending in two dimen.sions. 



3. Pelodictyon parallelum. 



1. Pelodictyon clathratiforme (Szafer, 

 1910) Lauterborn, 1913. (Aphanothece clath- 

 ratiforme Szafer, Bull. Acad. Sci., Cracovie, 

 Ser. B, 3, 1910, 162; Lauterborn, Allgem. 

 botan. Ztschr., 19, 1913, 98; also see Ver- 

 handl. naturhist.-medizin. Vereins, Heidel- 

 berg, N.F. 13, 1915,430.) 



clath.ra.ti.for'me. L. part. adj. clathratus 

 latticed; L. noun forma shape, form; M.L. 

 adj. clathratiformis lattice-like. 



Cells generally rod-shaped, ranging from 

 slightly elongated ovoids to distinct rods, 



often vacuolated, about 0.5 to 1.5 by 2 to 4 

 microns, producing rather wide slime cap- 

 sules. Characteristically united into three- 

 dimensional colonies which present a 

 net-like appearance with mazes of about 10 

 to 50 microns. Non-motile. 



Color: Yellowish green. 



Abnormal cell forms (involution forms) 

 not uncommon, consisting of elongated and 

 curved, forked, or club-shaped and swollen 

 rods, occasionally suggesting rudimentary 

 branching at the extremities. Such cells 



