Fig. 2.

The wolfpack-like attack of M. xanthus DK1622 on S. meliloti requires a functional rhizobial expR gene. Diagrams of the spontaneous mutations of expR in the S. meliloti laboratory strains Rm1021 and Rm2011 (insertion of ISRm1), GR4b (frameshift deletion) and RMO17b (S₂₀₂L), and their associated non-mucoid phenotypes on plates are shown in the left panels. M. xanthus preys on these strains by a frontal attack as shown in Fig. 1. The expR⁺ engineered derivatives (Rm8530, 1021R, 2011R) or natural variants (GR4 and RMO17) of these strains exhibit a mucoid phenotype and a wolfpack-like pattern in co-culture with M. xanthus (Mx) as shown in the images to the right.