Assessing the Effects of Recombinant AK Genes on the Growth and Development of Myxococcus xanthus

In many eukaryotic cell systems, phosphagen kinases help modulate ATP levels during periods of rapid energy consumption. In the past decade, more than two dozen bacterial species have been identified which express Arginine Kinases (AKs); it has been suggested that some of these organisms acquired these genes via horizontal gene transfer due to the discrepancies between trees of protein homology and species phylogeny. Myxococcus xanthus is a model of single-celled socially cooperative organisms that develop fruiting bodies to sustain themselves during starvation. Due to several research tools that have been developed for this organism, M. xanthus has become a convenient system for in-depth analysis of eukaryotic genetics and multicellular physiology. Bragg et al (2012) have determined that the gene MX2252 seems to buffer arginine and ATP levels, and that the absence of the protein Ark following the deletion of this gene elicits a nonfatal physiological change such that the strain ΔAK is impaired at fruiting body formation and sporulation. This suggests a key role for the Ark protein or for the arginine phosphate within the pathways of cellular developmental signaling. This work addresses the hypothesis that the fruiting-deficient phenotype of ΔAK can be rescued by heterologous genes; this is intended to reveal whether the Ark protein performs strictly a biochemical function that can be satisfied by a comparable kinase or whether its true function is novel to its structure. Homologous recombination has been utilized and confirmed to insert the wildtype Ark gene (MX2252, or mxAK) and a heterologous AK from the invertebrate Limulus polyphemus (horseshoe crab; hcAK) back into the ΔAK strain. The main efforts of this work are focused on observing the phenotypes of these strains when subject to developmental and non-developmental stresses, such that we may draw conclusions between the AK genes involved and the restoration of social competence. These transformed strains have regained their abilities to undergo developmental changes during periods of starvation and to recover from environmental stressors like high ionicity. However, these conclusions are called into question by the unexpected finding that the ΔAK strain which was used for plasmid recombination also able to form fruiting bodies. This finding suggests another pre-existing mechanism for carrying out developmental protocols despite the Ark protein’s absence