In the fruiting body-forming myxobacterium Stigmatella aurantiaca a 21,000-Mr protein, SP21, is synthesized during fruiting, heat shock, and stress induced by oxygen limitation. The corresponding gene was isolated from a gene expression library in Agtll with an antiserum to the purified protein. The DNA sequence of the gene reveals that SP21 is a member of the a-crystallin family of low-molecular-weight heat shock proteins.

StigmateUa aurantiaca is a gram-negative bacterium with a complex life cycle, including cellular aggregation resulting in the formation of a characteristic three-dimensional structure, the so-called fruiting body. During fruiting and upon chemical induction of sporulation, a major development-specific protein, SP21, is synthesized. SP21 was purified to homogeneity from the membranous fraction of chemically induced spores.Expression of SP21 was studied with an antiserum raised against the purified protein.Stigmatella aurantiaca is a gram-negative, rod-shaped myxobacterium that grows on decaying organic matter in soil. The myxobacteria possess a biphasic cell cycle, during which they form a fruiting body. During vegetative growth the cells glide in swarms upon insoluble organic substrates which they degrade by secreted lytic enzymes. When nutrients are depleted, the cells migrate into aggregation centers from which the fruiting bodies arise (for a review, see reference 8). The fruiting body of S. aurantiaca consists of a branched stalk supporting the sporangioles, which in turn contain several thousand myxospores.Spore formation in S. aurantiaca is not strictly coupled to fruiting and can be directly induced in liquid culture by a number of chemicals, of which the most potent are indole and some of its derivatives (2). Chemically induced sporulation is much more rapid than fruiting-body formation (3).Features observed during eukaryotic multicellular morphogenesis, such as the processing of positional information and cell communication by close contact or diffusible molecules, are predicted to play an important role in fruiting of the myxobacteria (7). As morphogenic processes depend on the highly coordinated synthesis of development-specific proteins, the genes involved in fruiting have to be tightly regulated depending on the progress of development and on the location of the individual cell within the evolving fruiting body. To study this process, markers for the progress of development are needed. Proteins specifically expressed during development may serve as such markers.We report here the detection of SP21, a marker protein for development, and its purification from chemically induced spores. Further, we demonstrate the pattern of SP21 expression in the course of sporulation and fruiting-body formation.Comparison of vegetative cells and chemically induced spores. S. aurantiaca DW4 (7) was grown in 1% (wt/vol) Casitone (Difco)-0.15% (wt/vol) MgSO4-0.1-mg/ml streptomycin sulfate in a 10-liter fermentor at 32°C with maximal aeration and a constant pH of 7.2. For analytical purposes, DW4 was cultured in shake flasks in 1% Tryptone-0.1%

The localization and distribution of the stress protein SP21 in indole-induced vegetative cells, fruiting bodies, and heat shocked cells of Stigmatella aurantiaca were determined by immunoelectron microscopy. SP21 was found at the cell periphery in heat-shocked cells and either at the cell periphery or within the cytoplasm in indole-induced cells, often concentrated in clusters. In fruiting-body-derived spores, SP21 was located mainly at the cell wall, preferentially at the outer periphery. Furthermore, SP21 antigen was associated with cellular remnants within the stalk and within the peripheral horizon next to the fruiting body.Stigmatella aurantiaca is a gram-negative, rod-shaped myxobacterium that grows on decaying organic matter in soil. The myxobacteria possess a biphasic cell cycle, in the course of which they form a fruiting body.During vegetative growth, the cells glide in swarms upon insoluble organic substrates which they partially degrade by means of secreted lytic enzymes. Cells that live in a dense swarm accumulate a high local concentration of enzymes which provide the cells with a higher concentration of soluble metabolites and efficiently prevent these metabolites from escaping (2). When nutrients are depleted, the cells migrate into aggregation centers, from which the fruiting bodies arise. The fruiting body of S. aurantiaca consists of a branched stalk supporting the sporangioles, which in turn contain several thousands of myxospores. During fruiting-body formation, large amounts of slimes are produced and there is a concomitant massive cell lysis (22). Within the sporangiole, cells convert into myxospores as resting cells with increased resistance to environmental stresses, such as heat, UV light, and desiccation.Features observed during eukaryotic multicellular morphogenesis, such as the processing of positional information and cell communication by close contact or diffusible molecules, are predicted to play an important role in fruiting of the myxobacteria (17).Spore formation of S. aurantiaca is not strictly coupled to fruiting-body formation and can be directly induced in liquid culture by a number of chemicals, of which the most potent are indole and some of its derivatives (3).During development, a protein with an M r of 21,000 (SP21) which was found in fruiting bodies and in indole-induced spores but was not detected in vegetative cells growing under standard conditions is synthesized (5). Stress conditions such as heat shock or limitation of oxygen also induce the synthesis of SP21. Sequence homology of the polypeptide sequence deduced from the corresponding gene (hspA) identifies SP21 as a member of the family of low-molecular-weight heat shock proteins (LMW-HSP). The predicted polypeptide is more similar to some plant LMW-HSP (53% identity) than it is to any of the known bacterial LMW-HSP (4).As SP21 was sedimented in the membrane fraction of cell lysates, we wanted to know if the protein is associated with the membranes or if it is part of a high-molecular-weight complex. Immunoele...

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