The Genus Zoogloea
Bacteria of the genus Zoogloea have historically been differentiated from other obligately aerobic, Gram-negative, nonsporeforming, rod-shaped bacteria that grow in aquatic habitats on the basis of the presence of a characteristic gelatinous matrix, often
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The Genus Zoogloea PATRICK R. DUGAN
Bacteria of the genus Zoogloea have historically been differentiated from other obligately aerobic, Gram-negative, nonsporeforming, rod-shaped bacteria that grow in aquatic habitats on the basis of the presence of a characteristic gelatinous matrix, often called a "zoogloeal matrix", that surrounds clumps of cells when they are found in their aquatic habitat or in unshaken liquid culture in the laboratory (Butterfield, 1935; Butterfield, Ruchhoft, and McNamee, 1937; Wattie, 1943). The name Zoogloea is derived from Greek and means animal glue. This has been the primary trait used to distinguish Zoogloea from other bacteria which can be confused with Zoogloea on the basis of similar metabolic and biochemical capabilities, e.g., lack of sugar fermentation, metabolic by-product formation. The genus Zoogloea has two species: Z. ramigera and Z. jilipendula. Both have been isolated from sewage (Butterfield, Ruchhoft, and McNamee, 1937; Butterfield and Wattie, 1941; McKinney and Horwood, 1952; McKinney and Weichlein, 1953) or from sewage-treatment systems that employ oxidative methods, i.e., activated sludge systems, trickling filters, or oxidation ponds. Both species produce branched, finger-like projections or outgrowths from the floc under quiescent culture conditions. The two species have been differentiated on the basis of cell size, biochemical reactions, and appearance of the zoogloeal matrix. The zoogloeal matrix is a capsular envelopment that surrounds several cells and commonly results in a flocculent growth habit in liquid media. That is, cell flocs settle from suspension, leaving a relatively clear supernatant. Although there continues to be confusion relative to the distinction between zoogloea formation and flocculent growth, there is a consensus that microbial floc-formation results from the presence of adherant extracellular fibrils (Bush and Stumm, 1968; Deinema and Zevenhuizen, 1971; Finstein, 1969; Friedman and Dugan, 1968b; Friedman et al. 1968, 1969; Tago and Aida, 1977). All floc-forming bacteria appear to possess extracellular fibrillar strands, but not all Gram-negative floc-formers produce the characteristic zoogloeal matrix such as that seen in Figs. 1 and 2 for Zoogloea ramigera 115. There continues to be a M. P. Starr et al. (eds.), The Prokaryotes © Springer-Verlag Berlin Heidelberg 1981
tendency to equate flocculent growth habit with the genus Zoogloea, and greater consideration is needed of the relation of extracellular fibril formation, flocculation, and zoogloeal matrix formation.
Fig. 1. Photomicrograph of Zoogloea ramigera 115 floc negatively stained by the Maneval method and photographed through the light microscope. The cells are shown embedded within the zoogleal matrix and with the characteristic finger-like projections. Bar = 10 /Lm.
Fig. 2. Photomicrograph of Zoogloea ramigera 115 floc stained with 1% aqueous crystal violet. The gelatinous zoogloeal matrix in which cells are embedded is shown. The variable staining appearance is due to polybet
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