Page:Bergey's manual of determinative bacteriology.djvu/84

 :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.


 * 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 I. Chlorobium Nadson, 1912.

Chlo.ro′bi.um. Gr. adj. chlorus greenish yellow, green; Gr. noun bios 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 chlorophyllous pigment different from the common green plant chlorophylls and from bacteriochlorophyll. Capable of photosynthesis in the presence of hydrogen sulfide, during which they produce elemental sulfur which is excreted outside the cells. Do not form spores.

The type species is Chlorobium limicola Nadson.

I. Does not utilize thiosulfates as oxidizable substrate.

II. Utilizes thiosulfates as oxidizable substrate.

1. Chlorobium limicola Nadson, 1912. (Bull. Jard. Impér. Botan., St. Pétersb., 12, 1912, 64 (Russian), 83 (German).)

li.mi′co.la. L. noun limus mud; L. v. colo to dwell; M.L. fem. n. limicola the mud dweller.

Cells occur in various sizes and shapes which are markedly dependent upon environmental conditions. In young and healthy cultures, predominantly small, ovoid to short rods, 0.7 by 0.9 to 1.5 microns, frequently united in chains resembling streptococci. Greatly elongated and irregularly bent and curved rods also occur as involution forms; these rods may likewise remain united in chains. Club-shaped and spirally wound to tightly coiled involution forms have been described, but the conditions for their formation are not understood, and in recent pure-culture studies these have never been encountered (Larsen, Jour. Bact., 64, 1952, 187). Regularly produce mucus; in media of inadequate composition this may lead to the formation of cell conglomerates of different sizes and shapes and a stringy appearance of the cultures. In healthy cultures the bacteria remain evenly dispersed and settle very slowly. Non-motile.

Color: Intensely green in healthy cultures; poor pigmentation and then yellowish green in media deficient in iron. Strictly anaerobic, obligatory photosynthetic bacteria whose occurrence in nature is dependent upon the presence of hydrogen sulfide. They utilize this substance, as well as elemental sulfur and molecular hydrogen, as oxidizable substrates; produce sulfur from sulfides but do not store sulfur globules inside the cells. Oxidation of sulfide may yield sulfur as an end product, but under optimal conditions the sulfur is further oxidized to sulfate. Unable to use thiosulfate and tetrathionate as oxidizable substrates. Development in organic media free of sulfide has not been obtained. Source: Isolated from mud and stagnant water, containing hydrogen sulfide, from the St. Petersburg Botanical Garden. Also found by Bicknell (Lloydia, 12, 1949, 183) in Sodon Lake, Bloomfield Hills, Michigan.