Heat shock proteins of vegetative and fruiting Myxococcus xanthus cells

Abstract

The heat shock response of Myxococcus xanthus was investigated and characterized. When shifted from 28 to 40°C, log-phase cells rapidly ceased growth, exhibited a 50% reduction in CFU, and initiated the synthesis of heat shock proteins (HTPs). Heat-shocked log-phase M. xanthus cells labeled with [35S]methionine were found to produce 18 major HTPs. The HTPs, analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, were characterized with regard to molecular mass, subcellular location (periplasm, membrane, or cytoplasm), and temperature required for expression. Most HTPs were expressed at 36°C, the optimum growth temperature of M. xanthus. Cells preincubated at 36°C for 1 h before being shifted to 40°C demonstrated increased thermotolerance compared with cells shifted directly from 28 to 40°C. The HTPs produced by heat-shocked starvation-induced fruiting cells and glycerol-induced sporulating cells were also analyzed and characterized. Thirteen HTPs were detected in fruiting cells shifted from 28 to 40°C. Six of these HTPs were not seen in vegetative M. xanthus cells. Log-phase cells induced to sporulate by the addition of glycerol produced 17 HTPs after being shifted to 40°C. These HTPs were found to be a mixture of HTPs detected in heat-shocked log-phase cells and heat-shocked fruiting cells.Myxococcus xanthus is a gram-negative, gliding, rodshaped bacterium that is commonly found in soil where it grows by preying upon other microorganisms and by degrading complex organic matter (14,29). When subjected to starvation on a solid surface, vegetative swarms of M. xanthus reverse their outward growth and migrate inwards to localized centers of aggregation, forming raised mounds of cells. Within these mounds, individual cells convert to ovoid or round, environmentally resistant myxospores. These mounds of myxospores are termed fruiting bodies (19). Rapid, synchronous myxospore formation may also be induced in vegetative M. xanthus cells by the addition of glycerol (to 0.5 M), dimethyl sulfoxide, or a variety of alcohols (6,15,30). In contrast to fruiting body formation which occurs over 48 to 72 h and requires a solid surface, glycerol-induced myxospores form within 3 h, do not aggregate, and do not require a solid surface (6). Glycerol-induced myxospores also lack some of the proteins characteristic of starvation-induced fruiting cells (15).The intent of this investigation was to examine the response of M. xanthus to heat shock. It has been shown that organisms from all three urkingdoms respond to elevated temperatures by altering their patterns of growth and protein synthesis. Upon experiencing elevated temperatures, cells rapidly cease growth, repress the synthesis of most proteins, and begin to preferentially synthesize a small number of new proteins (21). This has been termed the heat shock response. Studies have shown that some of the genes coding for heat shock proteins (HTPs) are highly conserved across all three urkingdoms (1, 21). In this paper, we demonstrate that M. xanthus e...

Multiple chaperonins in bacteria—novel functions and non-canonical behaviors

“…Interestingly, major duplication occurs with the genes encoding molecular chaperones, although some of the duplicated paralogs are not heat induced (Otani et al 2001). As observed in the pulse-chase experiments with 35 S-labeled cells during vegetative growth and spore formation stages, heat-shock genes follow social phase-specific expression patterns (Nelson and Killeen 1986;Killeen and Nelson 1988) and probably support the sociality of these organisms (Weimer et al 1998;Yang et al 1998).…”

Ectopic production of guanosine penta- and tetraphosphate can initiate early developmental gene expression in Myxococcus xanthus.

“…M. xanthus also elevates cAMP, presumably as a consequence of carbon starvation (Yajko and Zusman 1978). Neither of these responses is exceptional, and other stress responses may be mounted as well under such conditions (Nelson and Killeen 1986). Rather, the issue is how starvation initiates the program of fruiting body development.…”

The starvation-stress response of Vibrio (Listoneila) anguillarum

“…One-dimensional SDS-PAGE was performed as described by Laemmli (1970) using 5 % stacking gels and 10% separating gels. Autoradiography was performed as previously described (Nelson & Killeen, 1986). Equal volumes of labelled cell suspensions were loaded onto each lane.…”