Role of autocide AMI in development of Myxococcus xanthus

Abstract

A new developmental mutant of Myxococcus xanthus has been isolated by screening TnV insertion mutants for AMI-dependent development in submerged culture. This mutant (ER304) aggregated and sporulated on agar surfaces but required at least 3.8 ,ug of autocide AMI per ml for development in submerged cultures. Spore rescue of ER304 was obtained with the saturated, monounsaturated, and diunsaturated fatty acid fractions of AMI, with specific activities of 68, 115, and 700 U/mg, respectively. In addition, several model fatty acids were capable of rescuing sporulation of ER304; however, there was no correlation between specific lytic activity observed in vegetative cultures and specific rescue activity. Rescue of ER304 was effected during the first ca. 12 h after the initiation of starvation conditions; after this time, addition of AMI or model fatty acids killed the cells. Supernatant fluids of ER304 rescued development in dsg mutants (e.g., DK3260) in submerged cultures, but dsg mutant supernatant fluids were incapable of rescuing ER304 development. The data presented in this article support the idea that the primary mechanism of rescue by AMI is not via lysis, although developmental lysis may be an indirect result of the rescue event. A membrane permeability model is presented to explain the role of autocides in early developmental events in wild-type strains and in the aggregation and sporulation rescue of developmental mutants ER304 and DK3260.Myxococcus xanthus, the most extensively studied member of the Myxobacterales, is a gram-negative, gliding bacterium, characterized by a complex, multicellular development program (33). Development of M. xanthus, which culminates in the building of spore-filled fruiting bodies, is contingent upon the fulfillment of several conditions: (i) a minimal cell density, (ii) a solid substratum to support the aggregating cells, and (iii) nutritional downshift of exponentially growing cells (25). Successful completion of the developmental process depends upon the proper functioning of many genes. Some of these genes are directly involved in the intercellular signaling necessary for coordinating specific multicellular activities (16); others affect development by controlling the motility (11, 12) or cohesiveness (27) of the cells.Autocides are substances produced by vegetative M. xanthus cells which are capable of inducing lysis in the producing and related strains (29). The two major autocides, referred to as AMI and AMV, have been isolated and chemically characterized (6, 30). Autocide AMV is phosphatidylethanolamine (PE), the major component of the inner and outer cell membranes of M. xanthus. Autocide AMI, a mixture of saturated, monounsaturated, and polyunsaturated fatty acids, appears to be an enzymatic breakdown product of AMV and its active lytic moiety. In addition to its autolytic activity, autocide AMI has recently been shown to be capable of accelerating aggregation and sporulation in the wild-type strain and of rescuing aggregation and sporulation in dsg development mutan...

Novel Iso-branched Ether Lipids as Specific Markers of Developmental Sporulation in the Myxobacterium Myxococcus xanthus

“…Supply of additional nutrients during the fruiting body formation might partially complement the defect in aggregation but might not restore sporulation. Similar results were obtained for different fatty acids and lipid classes isolated from M. xanthus, which could speed up and increase aggregation and sporulation of some developmental-deficient mutants (69,70). Here, the authors postulated that this effect is due to an increased autolysis in the treated cultures.…”

Programmed Death in Bacteria

“…xanthus development. Fruiting body formation and sporulation in Myxococcus bacteria is another example of controlled death aiding development (25,65,81). "Autocides," which include fatty acids as well as glucosamine, induce autolysis in dense cultures of Myxococcus xanthus and are required for normal fruiting body development and sporulation.…”

Cell Death in Pseudomonas aeruginosa Biofilm Development

“…Increasing evidence suggests that programmed cell death also occurs in bacterial development (19,35,56). For example, development of multicellular fruiting bodies in Myxococcus xanthus requires autolysis of a subpopulation of M. xanthus cells (50,67). Autolysis, which appears to be undesirable for a single-cell organism, may be advantageous for a bacterial population at the multicellular level.…”