Intra- and Interprotein Phosphorylation between Two-hybrid Histidine Kinases Controls Myxococcus xanthus Developmental Progression

Starved Myxococcus xanthus cells glide to aggregation centers and form fruiting bodies in which rod-shaped cells differentiate into ovoid spores. Commitment to development was investigated by adding nutrients at specific times after starvation and determining whether development halted or proceeded. At 24 h poststarvation, some rod-shaped cells were committed to subsequent shape change and to becoming sonication-resistant spores, but nutrients caused partial disaggregation of fruiting bodies. By 30 h poststarvation, 10-fold more cells were committed to becoming sonication-resistant spores, and compact fruiting bodies persisted after nutrient addition. During the critical period of commitment around 24 to 30 h poststarvation, the transcription factors MrpC and FruA cooperatively regulate genes important for sporulation. FruA responds to short-range C-signaling, which increases as cells form fruiting bodies. MrpC was found to be highly sensitive to nutrient-regulated proteolysis both before and during the critical period of commitment to sporulation. The rapid turnover of MrpC upon nutrient addition to developing cells halted expression of the dev operon, which is important for sporulation. Regulated proteolysis of MrpC appeared to involve ATP-independent metalloprotease activity and may provide a mechanism for monitoring whether starvation persists and halting commitment to sporulation if nutrients reappear.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Nutrient-Regulated Proteolysis of MrpC Halts Expression of Genes Important for Commitment to Sporulation during Myxococcus xanthus Development

Rajagopalan

Kroos

2014

“…Protein half-lives were calculated assuming a first-order kinetic degradation reaction, as described previously (48). Signal intensities, after subtracting background, were normalized to the relevant intensity at t ϭ 0, and the natural log of the resulting values was plotted versus minutes after chloramphenicol (200 g/ml) treatment, as described previously (5).…”

Section: Methodsmentioning

confidence: 99%

The dev Operon Regulates the Timing of Sporulation during Myxococcus xanthus Development

Rajagopalan

Kroos

2017

Myxococcus xanthus undergoes multicellular development when starved. Thousands of rod-shaped cells coordinate their movements and aggregate into mounds in which cells differentiate into spores. Mutations in the dev operon impair development. The dev operon encompasses a clustered regularly interspaced short palindromic repeat-associated (CRISPR-Cas) system. Null mutations in devI, a small gene at the beginning of the dev operon, suppress the developmental defects caused by null mutations in the downstream devR and devS genes but failed to suppress defects caused by a small in-frame deletion in devT. We provide evidence that the original mutant has a second-site mutation. We show that devT null mutants exhibit developmental defects indistinguishable from devR and devS null mutants, and a null mutation in devI suppresses the defects of a devT null mutation. The similarity of DevTRS proteins to components of the CRISPR-associated complex for antiviral defense (Cascade), together with our molecular characterization of dev mutants, support a model in which DevTRS form a Cascade-like subcomplex that negatively autoregulates dev transcript accumulation and prevents DevI overproduction that would strongly inhibit sporulation. Our results also suggest that DevI transiently inhibits sporulation when regulated normally. The mechanism of transient inhibition may involve MrpC, a key transcription factor, whose translation appears to be weakly inhibited by DevI. Finally, our characterization of a devI devS mutant indicates that very little exo transcript is required for sporulation, which is surprising since Exo proteins help form the polysaccharide spore coat.IMPORTANCE CRISPR-Cas systems typically function as adaptive immune systems in bacteria. The dev CRISPR-Cas system of M. xanthus has been proposed to prevent bacteriophage infection during development, but how dev controls sporulation has been elusive. Recent evidence supported a model in which DevR and DevS prevent overproduction of DevI, a predicted 40-residue inhibitor of sporulation. We provide genetic evidence that DevT functions together with DevR and DevS to prevent DevI overproduction. We also show that spores form about 6 h earlier in mutants lacking devI than in the wild type. Only a minority of natural isolates appear to have a functional dev promoter and devI, suggesting that a functional dev CRISPR-Cas system evolved recently in niches where delayed sporulation and/or protection from bacteriophage infection proved advantageous.KEYWORDS CRISPR-Cas, Myxococcus xanthus, bacterial development, dev operon, gene regulation, signaling, sporulation M yxococcus xanthus is a Gram-negative soil bacterium that exhibits social behaviors (1). In nature, cells of M. xanthus move in groups, feeding on prey bacteria and organic detritus. When starved, thousands of cells aggregate to form mounds that mature into fruiting bodies as rod-shaped cells differentiate into dormant ovoid spores.

Section: Regulators Of the Timing Of Sporulationmentioning

confidence: 99%

“…Recent in vitro studies showed that the transmitter domain of EspA transfers a phosphoryl group to its own receiver domain (94). Furthermore, the transmitter domain of EspA, but not the transmitter domain of EspC, is capable of transferring a phosphoryl group to the receiver domain of EspC (94). This result and the similarity of the early sporulation phenotypes of the espA and espC mutants (92,93) suggest that EspA and EspC form a signaling unit that inhibits sporulation until the proper time in fruiting body development.…”

Section: Regulators Of the Timing Of Sporulationmentioning

confidence: 99%

Two-Component Signal Transduction Systems That Regulate the Temporal and Spatial Expression of Myxococcus xanthus Sporulation Genes

Sarwar

Garza

2016

bWhen starved for nutrients, Myxococcus xanthus produces a biofilm that contains a mat of rod-shaped cells, known as peripheral rods, and aerial structures called fruiting bodies, which house thousands of dormant and stress-resistant spherical spores. Because rod-shaped cells differentiate into spherical, stress-resistant spores and spore differentiation occurs only in nascent fruiting bodies, many genes and multiple levels of regulation are required. Over the past 2 decades, many regulators of the temporal and spatial expression of M. xanthus sporulation genes have been uncovered. Of these sporulation gene regulators, twocomponent signal transduction circuits, which typically contain a histidine kinase sensor protein and a transcriptional regulator known as response regulator, are among the best characterized. In this review, we discuss prototypical two-component systems (Nla6S/Nla6 and Nla28S/Nla28) that regulate an early, preaggregation phase of sporulation gene expression during fruiting body development. We also discuss orphan response regulators (ActB and FruA) that regulate a later phase of sporulation gene expression, which begins during the aggregation stage of fruiting body development. In addition, we summarize the research on a complex two-component system (Esp) that is important for the spatial regulation of sporulation.