ABSTRACT
I. INTRODUCTION A General Description of the Myxobacteria The myxobacteria are Gram-negative gliding bacteria that live on solid surfaces in dense populations called swarms. Upon nutrient deprivation, the individual bacteria aggregate and construct spore-filled fruiting bodies. The life cycle of Stigmatella is drawn in Figure 1. For this organism, light plays a critical role in that it stimulates fruiting body formation when cell densities are below the threshold required for fruiting in the dark. A broad-band action spectrum revealed that low irradiances of blue light between 400 and 555 nm were most effective (1). At higher irradiances, other wavelengths, including those in the far red region of the spectrum, also stimulate fruiting. The light increases the sensitivity of the cells to a fruiting pheromone that is produced at the time that aggregates appear (2). Underlying the morphogenetic movements and cellular differentiation are intercellular signals that are poorly understood but are being analyzed using modern molecular and genetic approaches. It is also becoming clear that the matrix in which the myxobacteria move also plays an important role in morphogenesis. The mechanism of motility, called gliding motility, is not understood and has been the subject of much speculation (3,4). It is clear that calcium ion plays a necessary role (5). The myxobacteria diverged from their nearest relatives approximately 1 billion years ago and thus may represent the
~1I101kli 1 Life cycle of Stigmatella aurantiaca. When cells are plated on nonnutrient
agar in the light, aggregates appear in 8-10 h and fully mature fruits in approximately 20 h. In the absence of light the cells tend to aggregate into ridges and fruiting is depressed, although myxospores form. When the cell density is sufficiently low, there is a requirement for light or the addition of exogeneous pheromone for aggregation to occur.
