Figure 2. D. discoideum mutants with growth defects on Gram(+) or Gram(−) bacteria.

a, Each spot represents a co-culture of about 500 D. discoideum cells and a thick bacterial culture spotted on buffered agar, imaged after 4 days of incubation. The image (top view) was assembled from 12 images of 12 experiments conducted under similar conditions. All D. discoideum strains were tested on the same day with the same culture of a given bacterium. Rows represent different Gram(−) or Gram(+) bacterial species as indicated on the left, and columns represent different wild-type or mutant amoebae as indicated on the top. The left-most column contains no amoebae. Wild-type amoebae (second column) grew on all the bacterial species (the dark speckles within each spot are D. discoideum fruiting bodies that formed after all the bacteria had been consumed). The nagB1⁻, gpi⁻, swp1⁻, and gp130⁻ mutants exhibit severe growth defects on Gram(+) bacteria compared to the wild type (blue frame). The clkB⁻, spc3⁻, alyL⁻, and Ω1334 (insertion site within the mutant AK1334) mutants exhibit severe growth defect on Gram(−) bacteria (red frame). b, D. discoideum growth on heat-killed S. aureus. Rows represent wild type or nagB1⁻ mutant amoeba as indicated on left, and columns represent different bacterial species or a mixture of bacterial species (live or heat-killed) in different mass ratios as indicated (HK, heat-killed; S.a., S. aureus; K.p., K. pneumoniae). Each spot is a co-culture of about 500 D. discoideum cells and a thick bacterial culture spotted on buffered agar and imaged after 4 days of incubation. The bacteria appear as tan areas within the spots. Intermediate levels of feeding are indicated by partial clearing of the tan bacterial lawn. Similar results were obtained for the other Gram(+)-growth-defective mutants gpi⁻ and swp1⁻ (unpublished observations).