Lysis of the Rhizobiaceae

The following members of the Rhizobiaceae were tested for their lytic response to various treatments: Agrobacterium tumefaciens, Chromobacterium violaceum, Rhizobium phaseoli, Rhizobium trifolii, Rhizobium lupini, and Rhizobium japonicum. Lysis was observed in spent growth media and as a function of saline concentration, pH, buffer composition, disodium (ethylenedinitrilo) tetraacetate (EDTA) concentration, and lysozyme. Cells were harvested by centrifugation, washed, and resuspended in various treatment solutions. The lytic response was followed spectrophotometrically. The different responses of the six cultures was applied to a summation of reclassification proposals evolved through modern taxonomic techniques such as DNA homology and percent guanine and cytosine nitrogen base composition. Average percent lysis of the tested bacteria formed three groups. These were Agrobacterium tumefaciens, Rhizobium phaseoli, and Rhizobium trifolii; Rhizobium lupini and Rhizobium japonicum; and Chromobacterium violaceum. These groupings lend further support to the need to reclassify these organisms according to the suggested proposals. The presence of a “typical” mucopeptide in Agrobacterium tumefaciens, Chromobacterium violaceum, Rhizobium phaseoli, and Rhizobium trifolii was demonstrated by their lytic response to EDTA-lysozyme treatment. Furthermore, the results depended upon the addition of EDTA. This suggests the presence of a “typical” gram-negative cell wall membrane (lipoprotein). Rhizobium lupini and Rhizobium japonicum exhibited little or no lysis in all tests. This suggests the lack of a mucopeptide, a lysozyme resistant mucopeptide, different bonding of the cell wall membrane, and/or an additional accessory layer such as the capsule. The author suspects the last possibility