Phenylobacterium immobile gen. nov., sp. nov., a Gram-Negative Bacterium That Degrades the Herbicide Chloridazon

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Abstract
Bacteria which utilize the xenobiotic compounds chloridazon, antipyrin, and pyramidon as sole carbon sources were isolated from various soil samples. The 22 strains isolated are similar with respect to morphological, physiological, biochemical, serological, and genetic properties. These bacteria are aerobic gram-negative rods or coccal rods (0.7 to 1.0 by 1.0 to 2.0 μm) that occur singly, in pairs, or in short chains and are nonmotile and nonsporeforming. Physiological and biochemical characteristics and susceptibility to antibiotics were determined. The strains need vitamin B12 as a growth factor; they are catalase positive and weakly oxidase positive and show slight H2S production. All of the other tests which we performed were negative. The nutritional spectrum is extraordinarily limited, with optimal growth on chloridazon, antipyrin, pyramidon, and l-phenylalanine. Most sugars, alcohols, amino and carboxylic acids, and ordinary complex media are not utilized. The bacteria are osmotically sensitive. They are a serologically uniform group of organisms, which are harmless to rats and rabbits. Their guanine-plus-cytosine contents range between 65 and 68.5 mol%. The chloridazon-degrading bacteria are characterized as a new genus, Phenylobacterium, with a single species, Phenylobacterium immobile. The type strain Phenylobacterium immobile strain E (= DSM 1986), is not closely related to any other gram-negative bacterium, as shown by a 16S ribosomal ribonucleic acid partial sequence analysis. This organism is a member of group I of the purple nonsulfur bacteria, but is phylogenetically isolated in this group. Phenylobacterium immobile is remotely related to Pseudomonas diminuta, Rhizobium leguminosarum, rhodopseudomonads, and Aquaspirillum itersonii. Like other members of this group, Phenylobacterium immobile contains 2,3-diamino-2,3-dideoxy-d-glucose in its lipopolysaccharide. The murein equals a normal murein from a gram-negative bacterium. All citric acid cycle enzymes are detectable in Phenylobacterium immobile.