Myxococcus xanthus Viability Depends on GroEL Supplied by Either of Two Genes, but the Paralogs Have Different Functions during Heat Shock, Predation, and Development

Myxococcus xanthus DK1622 contains two paralogous groEL gene loci that possess both different sequences and different organizations within the genome. Deletion of either one of these two genes alone does not affect cell viability. However, deletion of both groEL genes results in cell death unless a complemented groEL1 or groEL2 gene is present. The groEL1 gene was determined to be essential for cell survival under heat shock conditions; a strain with mutant groEL2 caused cells to be more sensitive than the wild-type strain to higher temperatures. Mutants with a single deletion of either groEL1 (MXAN_4895) or groEL2 (MXAN_4467) had a growth curve similar to that of the wild-type strain DK1622 in medium containing hydrolyzed proteins as the substrate. However, when cells were cultured on medium containing either Escherichia coli cells or casein as the substrate, deletion of groEL2, but not groEL1, led to a deficiency in cell predation and macromolecular feeding. Furthermore, groEL1 was found to play an indispensable role in the development and sporulation of cells, but deletion of groEL2 had no visible effects. Our results suggest that, although alternatively required for cell viability, the products of the two groEL genes have divergent functions in the multicellular social life cycle of M. xanthus DK1622.