Genetic Determinants of Swarming in Rhizobium etli

Braeken, Kristien; Daniels, Ruth; Vos, Karen; Fauvart, Maarten; Bachaspatimayum, Debkumari; Vanderleyden, Jos; Michiels, Jan

doi:10.1007/s00248-007-9250-1

Cited by 31 publications

(22 citation statements)

References 59 publications

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“…To study swimming activity, TY plates containing 0.2% agar were spot inoculated with cultures in exponential phase and incubated at 30°C in a closed container as described previously [91]. Each strain was tested five-fold in two independent experiments.…”

Section: Methodsmentioning

confidence: 99%

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli

et al. 2011

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BackgroundThe alarmone (p)ppGpp mediates a global reprogramming of gene expression upon nutrient limitation and other stresses to cope with these unfavorable conditions. Synthesis of (p)ppGpp is, in most bacteria, controlled by RelA/SpoT (Rsh) proteins. The role of (p)ppGpp has been characterized primarily in Escherichia coli and several Gram-positive bacteria. Here, we report the first in-depth analysis of the (p)ppGpp-regulon in an α-proteobacterium using a high-resolution tiling array to better understand the pleiotropic stress phenotype of a relA/rsh mutant.ResultsWe compared gene expression of the Rhizobium etli wild type and rsh (previously rel) mutant during exponential and stationary phase, identifying numerous (p)ppGpp targets, including small non-coding RNAs. The majority of the 834 (p)ppGpp-dependent genes were detected during stationary phase. Unexpectedly, 223 genes were expressed (p)ppGpp-dependently during early exponential phase, indicating the hitherto unrecognized importance of (p)ppGpp during active growth. Furthermore, we identified two (p)ppGpp-dependent key regulators for survival during heat and oxidative stress and one regulator putatively involved in metabolic adaptation, namely extracytoplasmic function sigma factor EcfG2/PF00052, transcription factor CH00371, and serine protein kinase PrkA.ConclusionsThe regulatory role of (p)ppGpp in R. etli stress adaptation is far-reaching in redirecting gene expression during all growth phases. Genome-wide transcriptome analysis of a strain deficient in a global regulator, and exhibiting a pleiotropic phenotype, enables the identification of more specific regulators that control genes associated with a subset of stress phenotypes. This work is an important step toward a full understanding of the regulatory network underlying stress responses in α-proteobacteria.

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Section: Methodsmentioning

confidence: 99%

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli

et al. 2011

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“…Sequence analysis of various Rhizobium etli mutants defective in swarming showed effects on quorum sensing, polysaccharide composition or export, motility, and metabolism of amino acids and polyamines. Several such mutants showed reduced symbiotic nitrogen‐fixing activity (Braeken et al , 2008). Quorum‐sensing signal molecules are involved in the control of the swarming behavior of R. etli , and quorum sensing helps regulate dispersion of existing biofilms and interactions between bacteria and higher organisms, for example, in the Rhizobium– bean symbiosis (Daniels et al , 2004).…”

Section: Introductionmentioning

confidence: 99%

An integrated view of biofilm formation in rhizobia

Rinaudi

Giordano

2010

FEMS Microbiology Letters

181

124

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Biofilms are bacterial communities enclosed within an extracellular matrix of polysaccharides produced by the bacteria, which adhere to a living or an inert macrosurface. In nature, biofilms constitute a protected growth modality allowing bacteria to survive in hostile environments. Studies of environmental isolates have revealed a highly ordered, three-dimensional organization of the extracellular matrix, which has important implications for biofilm physiology. The zone of soil immediately surrounding a plant root where complex biological and ecological processes occur, termed rhizosphere, forms an environment that fulfills the requirements for biofilm formation, including sufficient moisture and supply of nutrients, which are provided by the plant. Biofilm formation on plants appears to be associated with symbiotic and pathogenic responses, but it is unclear how plants regulate the association. Biofilms function as structures resistant against stress factors such as desiccation, UV radiation, predation, and antibiosis, which help create protective niches for rhizobia. However, the role of biofilms in rhizobial-legume symbiosis remains to be clarified. Here, the mechanisms involved in bacterial biofilm formation and attachment on plant roots, and the relation of these mechanisms to rhizobial function and survival are reviewed.

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“…The cinR and cinI genes are required for normal symbiotic nitrogen fixation and swarming in R. etli (5,9,11) and for normal levels of expression of raiI, which encodes another AHL synthase. The expression of raiI in R. etli is regulated by RaiR (39).…”

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confidence: 99%

ThecinandraiQuorum-Sensing Regulatory Systems inRhizobium leguminosarumAre Coordinated by ExpR and CinS, a Small Regulatory Protein Coexpressed with CinI

et al. 2009

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To understand how the Rhizobium leguminosarum raiI-raiR quorum-sensing system is regulated, we identified mutants with decreased levels of RaiI-made N-acyl homoserine lactones (AHLs). A LuxR-type regulator, ExpR, is required for raiR expression, and RaiR is required to induce raiI. Since raiR (and raiI) expression is also reduced in cinI and cinR quorum-sensing mutants, we thought CinI-made AHLs may activate ExpR to induce raiR. However, added CinI-made AHLs did not induce raiR expression in a cinI mutant. The reduced raiR expression in cinI and cinR mutants was due to lack of expression of cinS immediately downstream of cinI. cinS encodes a 67-residue protein, translationally coupled to CinI, and cinS acts downstream of expR for raiR induction. Cloned cinS in R. leguminosarum caused an unusual collapse of colony structure, and this was delayed by mutation of expR. The phenotype looked like a loss of exopolysaccharide (EPS) integrity; mutations in cinI, cinR, cinS, and expR all reduced expression of plyB, encoding an EPS glycanase, and mutation of plyB abolished the effect of cloned cinS on colony morphology. We conclude that CinS and ExpR act to increase PlyB levels, thereby influencing the bacterial surface. CinS is conserved in other rhizobia, including Rhizobium etli; the previously observed effect of cinI and cinR mutations decreasing swarming in that strain is primarily due to a lack of CinS rather than a lack of CinI-made AHL. We conclude that CinS mediates quorum-sensing regulation because it is coregulated with an AHL synthase and demonstrate that its regulatory effects can occur in the absence of AHLs.

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Genetic Determinants of Swarming in Rhizobium etli

Cited by 31 publications

References 59 publications

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli

An integrated view of biofilm formation in rhizobia

ThecinandraiQuorum-Sensing Regulatory Systems inRhizobium leguminosarumAre Coordinated by ExpR and CinS, a Small Regulatory Protein Coexpressed with CinI

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