Fig. 4
Experimental analysis of guanine crystal formation and melanin production in selected bacterial species. Comparative information related to the presence of genes encoding guanine deaminase (guaD) and xanthine dehydrogenase (xdh) is included. The symbol * indicates that the genome for the corresponding strain is not available, but the gene(s) is (are) present or absent in the type strain of the species (genome information in Additional file 4: Table S3). Presence of melanin and/or guanine crystals is indicated by colored circles or diamonds