FAMILY III. LEUCOTRICHACEAE 



851 



1. Leucothrix niucor Oersted, 1844. 

 (Oersted, De regionibus marinis, elementa 

 topographiae historiconaturalis freti Oere- 

 sund. J. C. Scharling, Copenhagen, 1844, 

 44; Chlamydothrix longissima Molisch, Cent, 

 f. Bakt., II Abt., 33, 1912, 60; Pontothrix 

 longissima Nadson and Krassilnikov, Compt. 

 rend. Acad. Sci. de U.R.S.S., A. No. 1, 1932, 

 243; also see Harold and Stanier, Bact. Rev., 

 19, 1955, 49.) 



mu'cor. L. noun mucor mold; M.L. noun 

 Mucor a genus of molds. 



Cells short, 1 to 5 microns long, cylindri- 

 cal. Sulfur granules are found only on the 

 exterior, never in the interior, of the cells, 

 and they occur only when the trichomes lie 

 near the surface of the water where there is 

 an abundance of oxj'gen. Trichomes are 

 colorless, unbranched, non-motile, occa- 

 sionally surrounded by a gelatinous sheath 

 2 to 6 microns wide, and very long, fre- 

 quently reaching a length of 0.5 cm or more; 

 they are either entwined about each other 

 or occur in loosely arranged bundles of sev- 

 eral hundred or more where they lie parallel 

 to each other or twist like the individual 

 strands of a rope. The trichomes remain in 



contact with the surface film or with solid 

 particles by means of an inconspicuous 

 holdfast; in young colonics the trichomes 

 radiate from the solid particles in a manner 

 similar to that of Thiothrix sp. Reproduc- 

 tion occurs by the fragmentation of the 

 trichomes into gonidia. 



A large variety of carbohydrates and 

 other simple organic compounds may serve 

 as sources of carbon and energy. 



No growth factors are required. 



Strictly aerobic. 



Temperature relations: Optimum, 25° C. 

 Maximum, 30° C. 



Grows best at a salt concentration (syn- 

 thetic sea water) of 16 grams per liter; a 

 salt concentration of 3 grams per liter sup- 

 ports growth, but with abnormal morphol- 

 ogy. 



Source: Isolated from decaying algal 

 infusions. Found in the harbor at Trieste. 

 Nadson and Krassilnikov (op. cit., 1932, 

 243) report this organism on Zostera marina 

 in the Bay at Sebastopol on the Black Sea. 



Habitat: Found in fresh- and salt-water 

 containing decomposing algal material. 



FAMILY IV. ACHROMATIACEAE MASSART, 1902.* 

 (Rec. Inst. Bot., Univ. Bruxells, 5, 1902, 251.) 



A.chro.ma.ti.a'ce.ae. M.L. neut.n. Achromatium type genus of the family; -aceae ending 

 to denote a family; M.L. fem.pl.n. Achromatiaceae the Achromatium family. 



Large, unicellular organisms which are spherical to ovoid or shortly cylindrical with 

 hemispherical extremities. Movements, if any, are of a slow, rolling, jerky type and are 

 dependent upon the presence of a substrate; no special organs of locomotion are known. 

 Division of cells is by a constriction in the middle. Do not possess photosynthetic pigments. 

 In their natural habitat, the cells contain sulfur droplets and sometimes additional in- 

 clusions, such as large spherules of calcium carbonate. Found in fresh-water and marine 

 environments. 



The organisms in the family Achromatiaceae have so far been studied exclusively as found 

 in their natural habitats. Pure-culture studies are greatly needed; they may show that the 

 peculiar calcium carbonate inclusions (not calcium oxalate as thought by Schewiakoff nor 

 calcium thiosulfate as believed by Hannevart) occur only under special environmental 

 conditions. 



There is a single genus, Achromatium Schewiakoff. 



* Revised by Prof. C. B. van Niel, Hopkins Marine Station, Pacific Grove, California, 

 January, 1944; further revision, October, 1955. 



