Ensifer adhaerens gen. nov., sp. nov.: A Bacterial Predator of Bacteria in Soil †

A bacterial predator of bacteria in soil is described. This gram-negative predator was previously designated strain A. It is not an obligate predator, for it grows in the absence of host cells on a variety of media, including a medium composed of Noble agar in distilled water. It does not hydrolyze agar. The presence of host cells causes an overall increase in the growth of strain A on Noble agar but, except for tracking, does not do so on nutritionally richer media. During growth on most media in the presence of host cells, such as cells of Micrococcus luteus, strain A attaches in a picket fence arrangement to the host cells. Lysis of the host cells ensues if the pH of the environment remains approximately in the range from 6.0 to 6.5. At higher pH values, tracking and attachment occur, but without lysis of the host cells. A factor that diffuses through agar and causes lysis was detected emanating from strain A during growth on a nutritionally dilute medium. Strain A was shown to multiply by budding at one pole of the cell, followed by asymmetric polar growth and binary fission. Additional morphological and biochemical characteristics of strain A are presented. A new genus, Ensifer, is proposed for this bacterium. The type species is Ensifer adhaerens sp. nov., and strain A (= ATCC 33212) is the type strain of this species.