scholarly journals The FtcR-Like Protein ActR in Azorhizobium caulinodans ORS571 Is Involved in Bacterial Motility and Symbiosis With the Host Plant

2021 ◽  
Vol 12 ◽  
Author(s):  
Li Sun ◽  
Dandan Wang ◽  
Zhiqiu Yin ◽  
Chengsheng Zhang ◽  
Amber Bible ◽  
...  
Keyword(s):  
Host Plant ◽  
Brucella Melitensis ◽  
Transcriptional Regulator ◽  
Adaptive Responses ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
Bacterial Flagellum ◽  
Flagellar Biosynthesis ◽  
Living State ◽  
Two Component Systems

Bacterial signal transduction pathways are important for a variety of adaptive responses to environment, such as two-component systems (TCSs). In this paper, we reported the characterization of a transcriptional regulator in Azorhizobium caulinodans ORS571, ActR, with an N-terminal receiver domain and one C-terminal OmpR/PhoB-type DNA binding domain. Sequence analysis showed that ActR shared a high similarity with FtcR regulator of Brucella melitensis 16M known to be involved in flagellar regulation. The structural gene of this regulator was largely distributed in Alphaproteobacteria, in particular in Rhizobiales and Rhodobacterales, and was located within clusters of genes related to motility functions. Furthermore, we studied the biological function of ActR in A. caulinodans grown at the free-living state or in association with Sesbania rostrata by constructing actR gene deletion mutant. In the free-living state, the bacterial flagellum and motility ability were entirely deleted, the expression of flagellar genes was downregulated; and the exopolysaccharide production, biofilm formation, and cell flocculation decreased significantly compared with those of the wild-type strain. In the symbiotic state, ΔactR mutant strain showed weakly competitive colonization and nodulation on the host plant. These results illustrated that FtcR-like regulator in A. caulinodans is involved in flagellar biosynthesis and provide bacteria with an effective competitive nodulation for symbiosis. These findings improved our knowledge of FtcR-like transcriptional regulator in A. caulinodans.

scholarly journals FixJ family regulator AcfR of Azorhizobium caulinodans is involved in symbiosis with the host plant

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Wei Liu ◽  
Xue Bai ◽  
Yan Li ◽  
Haikun Zhang ◽  
Xiaoke Hu
Keyword(s):  
Signal Transduction ◽  
Host Plant ◽  
Type Strain ◽  
Wild Type Strain ◽  
Response Regulator ◽  
Azorhizobium Caulinodans ◽  
Wild Type ◽  
Response Regulators ◽  
Free Living ◽  
Two Component

Abstract Background A wide variety of bacterial adaptative responses to environmental conditions are mediated by signal transduction pathways. Two-component signal transduction systems are one of the predominant means used by bacteria to sense the signals of the host plant and adjust their interaction behaviour. A total of seven open reading frames have been identified as putative two-component response regulators in the gram-negative nitrogen-fixing bacteria Azorhizobium caulinodans ORS571. However, the biological functions of these response regulators in the symbiotic interactions between A. caulinodans ORS571 and the host plant Sesbania rostrata have not been elucidated to date. Results In this study, we identified and investigated a two-component response regulator, AcfR, with a phosphorylatable N-terminal REC (receiver) domain and a C-terminal HTH (helix-turn-helix) LuxR DNA-binding domain in A. caulinodans ORS571. Phylogenetic analysis showed that AcfR possessed close evolutionary relationships with NarL/FixJ family regulators. In addition, six histidine kinases containing HATPase_c and HisKA domains were predicted to interact with AcfR. Furthermore, the biological function of AcfR in free-living and symbiotic conditions was elucidated by comparing the wild-type strain and the ΔacfR mutant strain. In the free-living state, the cell motility behaviour and exopolysaccharide production of the ΔacfR mutant were significantly reduced compared to those of the wild-type strain. In the symbiotic state, the ΔacfR mutant showed a competitive nodule defect on the stems and roots of the host plant, suggesting that AcfR can provide A. caulinodans with an effective competitive ability for symbiotic nodulation. Conclusions Our results showed that AcfR, as a response regulator, regulates numerous phenotypes of A. caulinodans under the free-living conditions and in symbiosis with the host plant. The results of this study help to elucidate the involvement of a REC + HTH_LuxR two-component response regulator in the Rhizobium-host plant interaction.

scholarly journals Poly-β-Hydroxybutyrate Turnover inAzorhizobium caulinodans Is Required for Growth and AffectsnifA Expression

1998 ◽  
Vol 180 (19) ◽  
pp. 5070-5076 ◽  
Author(s):  
Karine Mandon ◽  
Nathalie Michel-Reydellet ◽  
Sergio Encarnación ◽  
P. Alexandre Kaminski ◽  
Alfonso Leija ◽  
...  
Keyword(s):  
Nitrogenase Activity ◽  
Constitutive Expression ◽  
Reducing Power ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
Nucleotide Pools ◽  
Living State ◽  
Mutant Strains ◽  
Growth Properties ◽  
Phb Synthase

ABSTRACT Azorhizobium caulinodans is able to fix nitrogen in the free-living state and in symbiosis with the tropical legumeSesbania rostrata. The bacteria accumulate poly-β-hydroxybutyrate (PHB) under both conditions. The structural gene for PHB synthase, phbC, was inactivated by insertion of an interposon. The mutant strains obtained were devoid of PHB, impaired in their growth properties, totally devoid of nitrogenase activity ex planta (Nif−), and affected in nucleotide pools and induced Fix− nodules devoid of bacteria. The Nif− phenotype was the consequence of the lack ofnifA transcription. Nitrogenase activity was partially restored to a phbC mutant by constitutive expression of thenifA gene. However, this constitutive nifAexpression had no effect on the nucleotide content or on growth of thephbC mutant. It is suggested that PHB is required for maintaining the reducing power of the cell and therefore the bacterial growth. These observations also suggest a new control ofnifA expression to adapt nitrogen fixation to the availability of carbon and reducing equivalents.

scholarly journals LuxR-Type Regulator AclR1 of Azorhizobium caulinodans Regulates Cyclic di-GMP and Numerous Phenotypes in Free-Living and Symbiotic States

2020 ◽  
Vol 33 (3) ◽  
pp. 528-538
Author(s):  
Wei Liu ◽  
Yan Li ◽  
Xue Bai ◽  
Haiguang Wu ◽  
Lanxing Bian ◽  
...  
Keyword(s):  
Biofilm Formation ◽  
Host Plants ◽  
Biological Processes ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
A Genome ◽  
Living State ◽  
And Control ◽  
Functional Mechanisms ◽  
Azorhizobium Caulinodans Ors571

LuxR-type regulators play important roles in transcriptional regulation in bacteria and control various biological processes. A genome sequence analysis showed the existence of seven LuxR-type regulators in Azorhizobium caulinodans ORS571, an important nitrogen-fixing bacterium in both its free-living state and in symbiosis with its host, Sesbania rostrata. However, the functional mechanisms of these regulators remain unclear. In this study, we identified a LuxR-type regulator that contains a cheY-homologous receiver (REC) domain in its N terminus and designated it AclR1. Interestingly, phylogenetic analysis revealed that AclR1 exhibited relatively close evolutionary relationships with MalT/GerE/FixJ/NarL family proteins. Functional analysis of an aclR1 deletion mutant (ΔaclR1) in the free-living state showed that AclR1 positively regulated cell motility and flocculation but negatively regulated exopolysaccharide production, biofilm formation, and second messenger cyclic diguanylate (c-di-GMP)-related gene expression. In the symbiotic state, the ΔaclR1 mutant was defective in competitive colonization and nodulation on host plants. These results suggested that AclR1 could provide bacteria with the ability to compete effectively for symbiotic nodulation. Overall, our results show that the REC-LuxR-type regulator AclR1 regulates numerous phenotypes both in the free-living state and during host plant symbiosis.

scholarly journals Azorhizobium caulinodans PIIand GlnK Proteins Control Nitrogen Fixation and Ammonia Assimilation

1999 ◽  
Vol 181 (8) ◽  
pp. 2655-2658 ◽  
Author(s):  
Nathalie Michel-Reydellet ◽  
P. Alexandre Kaminski
Keyword(s):  
Gene Expression ◽  
Nitrogen Fixation ◽  
Nitrogenase Activity ◽  
Ammonia Assimilation ◽  
Ammonium Excretion ◽  
Azorhizobium Caulinodans ◽  
Wild Type ◽  
Free Living ◽  
Living State ◽  
High Level

ABSTRACT We herein report that Azorhizobium caulinodansPII and GlnK are not necessary for glutamine synthetase (GS) adenylylation whereas both proteins are required for complete GS deadenylylation. The disruption of both glnB andglnK resulted in a high level of GS adenylylation under the condition of nitrogen fixation, leading to ammonium excretion in the free-living state. PII and GlnK also controllednif gene expression because NifA activated nifHtranscription and nitrogenase activity was derepressed in glnB glnK double mutants, but not in wild-type bacteria, grown in the presence of ammonia.

scholarly journals A Novel Regulatory Pathway for K+ Uptake in the Legume Symbiont Azorhizobium caulinodans in Which TrkJ Represses the kdpFABC Operon at High Extracellular K+ Concentrations

2017 ◽  
Vol 83 (19) ◽  
Author(s):  
Lowela Siarot ◽  
Hiroki Toyazaki ◽  
Makoto Hidaka ◽  
Keigo Kurumisawa ◽  
Tomoki Hirakawa ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Uptake System ◽  
Azorhizobium Caulinodans ◽  
Free Living ◽  
Content Type ◽  
High K ◽  
Living State ◽  
In The Wild ◽  
Low K ◽  
Distinct Locus

ABSTRACT Bacteria have multiple K+ uptake systems. Escherichia coli, for example, has three types of K+ uptake systems, which include the low-K+-inducible KdpFABC system and two constitutive systems, Trk (TrkAG and TrkAH) and Kup. Azorhizobium caulinodans ORS571, a rhizobium that forms nitrogen-fixing nodules on the stems and roots of Sesbania rostrata, also has three types of K+ uptake systems. Through phylogenetic analysis, we found that A. caulinodans has two genes homologous to trkG and trkH, designated trkI and trkJ. We also found that trkI is adjacent to trkA in the genome and these two genes are transcribed as an operon; however, trkJ is present at a distinct locus. Our results demonstrated that trkAI, trkJ, and kup were expressed in the wild-type stem nodules, whereas kdpFABC was not. Interestingly, Δkup and Δkup ΔkdpA mutants formed Fix– nodules, while the Δkup ΔtrkA ΔtrkI ΔtrkJ mutant formed Fix+ nodules, suggesting that with the additional deletion of Trk system genes in the Δkup mutant, Fix+ nodule phenotypes were recovered. kdpFABC of the Δkup ΔtrkJ mutant was expressed in stem nodules, but not in the free-living state, under high-K+ conditions. However, kdpFABC of the Δkup ΔtrkA ΔtrkI ΔtrkJ mutant was highly expressed even under high-K+ conditions. The cytoplasmic K+ levels in the Δkup ΔtrkA ΔtrkI mutant, which did not express kdpFABC under high-K+ conditions, were markedly lower than those in the Δkup ΔtrkA ΔtrkI ΔtrkJ mutant. Taking all these results into consideration, we propose that TrkJ is involved in the repression of kdpFABC in response to high external K+ concentrations and that the TrkAI system is unable to function in stem nodules. IMPORTANCE K+ is a major cytoplasmic cation in prokaryotic and eukaryotic cells. Bacteria have multiple K+ uptake systems to control the cytoplasmic K+ levels. In many bacteria, the K+ uptake system KdpFABC is expressed under low-K+ conditions. For years, many researchers have argued over how bacteria sense K+ concentrations. Although KdpD of Escherichia coli is known to sense both cytoplasmic and extracellular K+ concentrations, the detailed mechanism of K+ sensing is still unclear. In this study, we propose that the transmembrane TrkJ protein of Azorhizobium caulinodans acts as a sensor for the extracellular K+ concentration and that high extracellular K+ concentrations repress the expression of KdpFABC via TrkJ.

Adaptive responses of free‐living and symbiotic microalgae to simulated future ocean conditions

2021 ◽  
Vol 27 (9) ◽  
pp. 1737-1754
Author(s):  
Wing Yan Chan ◽  
John G. Oakeshott ◽  
Patrick Buerger ◽  
Owain R. Edwards ◽  
Madeleine J. H. Oppen
Keyword(s):  
Adaptive Responses ◽  
Free Living ◽  
Ocean Conditions ◽  
Symbiotic Microalgae

scholarly journals Paraburkholderia phymatum STM815 σ54 Controls Utilization of Dicarboxylates, Motility, and T6SS-b Expression

Nitrogen ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 81-98
Author(s):  
Martina Lardi ◽  
Yilei Liu ◽  
Sebastian Hug ◽  
Samanta Bolzan de Campos ◽  
Leo Eberl ◽  
...  
Keyword(s):  
Wild Type Strain ◽  
Nitrogenase Activity ◽  
Secretion Systems ◽  
Free Living ◽  
Major Life ◽  
Life Styles ◽  
Type Vi Secretion ◽  
Flagellar Biosynthesis ◽  
Free Living Conditions

Rhizobia have two major life styles, one as free-living bacteria in the soil, and the other as bacteroids within the root/stem nodules of host legumes where they convert atmospheric nitrogen into ammonia. In the soil, rhizobia have to cope with changing and sometimes stressful environmental conditions, such as nitrogen limitation. In the beta-rhizobial strain Paraburkholderia phymatum STM815, the alternative sigma factor σ54 (or RpoN) has recently been shown to control nitrogenase activity during symbiosis with Phaseolus vulgaris. In this study, we determined P. phymatum’s σ54 regulon under nitrogen-limited free-living conditions. Among the genes significantly downregulated in the absence of σ54, we found a C4-dicarboxylate carrier protein (Bphy_0225), a flagellar biosynthesis cluster (Bphy_2926-64), and one of the two type VI secretion systems (T6SS-b) present in the P. phymatum STM815 genome (Bphy_5978-97). A defined σ54 mutant was unable to grow on C4 dicarboxylates as sole carbon source and was less motile compared to the wild-type strain. Both defects could be complemented by introducing rpoNin trans. Using promoter reporter gene fusions, we also confirmed that the expression of the T6SS-b cluster is regulated by σ54. Accordingly, we show that σ54 affects in vitro competitiveness of P. phymatum STM815 against Paraburkholderia diazotrophica.

scholarly journals Bioactive Peptides Produced by Cyanobacteria of the Genus Nostoc: A Review

Marine Drugs ◽  
2019 ◽  
Vol 17 (10) ◽  
pp. 561 ◽  
Author(s):  
Anna Fidor ◽  
Robert Konkel ◽  
Hanna Mazur-Marzec
Keyword(s):  
Potential Application ◽  
Bioactive Peptides ◽  
Sole Source ◽  
Therapeutic Agents ◽  
Bioactive Metabolites ◽  
Pharmaceutical Companies ◽  
Free Living ◽  
Lead Compounds ◽  
Living State

Cyanobacteria of the genus Nostoc are widespread in all kinds of habitats. They occur in a free-living state or in association with other organisms. Members of this genus belong to prolific producers of bioactive metabolites, some of which have been recognized as potential therapeutic agents. Of these, peptides and peptide-like structures show the most promising properties and are of a particular interest for both research laboratories and pharmaceutical companies. Nostoc is a sole source of some lead compounds such as cytotoxic cryptophycins, antiviral cyanovirin-N, or the antitoxic nostocyclopeptides. Nostoc also produces the same bioactive peptides as other cyanobacterial genera, but they frequently have some unique modifications in the structure. This includes hepatotoxic microcystins and potent proteases inhibitors such as cyanopeptolins, anabaenopeptins, and microginins. In this review, we described the most studied peptides produced by Nostoc, focusing especially on the structure, the activity, and a potential application of the compounds.

scholarly journals Metatranscriptomics by In Situ RNA Stabilization Directly and Comprehensively Revealed Episymbiotic Microbial Communities of Deep-Sea Squat Lobsters

mSystems ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Kaori Motoki ◽  
Tomo-o Watsuji ◽  
Yoshihiro Takaki ◽  
Ken Takai ◽  
Wataru Iwasaki
Keyword(s):  
Deep Sea ◽  
Expression Profiles ◽  
Rna Degradation ◽  
Rna Expression ◽  
Free Living ◽  
Content Type ◽  
Living State ◽  
Rna Stabilization ◽  
Squat Lobsters

ABSTRACT Shinkaia crosnieri is an invertebrate that inhabits an area around deep-sea hydrothermal vents in the Okinawa Trough in Japan by harboring episymbiotic microbes as the primary nutrition. To reveal physiology and phylogenetic composition of the active episymbiotic populations, metatranscriptomics is expected to be a powerful approach. However, this has been hindered by substantial perturbation (e.g., RNA degradation) during time-consuming retrieval from the deep sea. Here, we conducted direct metatranscriptomic analysis of S. crosnieri episymbionts by applying in situ RNA stabilization equipment. As expected, we obtained RNA expression profiles that were substantially different from those obtained by conventional metatranscriptomics (i.e., stabilization after retrieval). The episymbiotic community members were dominated by three orders, namely, Thiotrichales, Methylococcales, and Campylobacterales, and the Campylobacterales members were mostly dominated by the Sulfurovum genus. At a finer phylogenetic scale, the episymbiotic communities on different host individuals shared many species, indicating that the episymbionts on each host individual are not descendants of a few founder cells but are horizontally exchanged. Furthermore, our analysis revealed the key metabolisms of the community: two carbon fixation pathways, a formaldehyde assimilation pathway, and utilization of five electron donors (sulfide, thiosulfate, sulfur, methane, and ammonia) and two electron accepters (oxygen and nitrate/nitrite). Importantly, it was suggested that Thiotrichales episymbionts can utilize intercellular sulfur globules even when sulfur compounds are not usable, possibly also in a detached and free-living state. IMPORTANCE Deep-sea hydrothermal vent ecosystems remain mysterious. To depict in detail the enigmatic life of chemosynthetic microbes, which are key primary producers in these ecosystems, metatranscriptomic analysis is expected to be a promising approach. However, this has been hindered by substantial perturbation (e.g., RNA degradation) during time-consuming retrieval from the deep sea. In this study, we conducted direct metatranscriptome analysis of microbial episymbionts of deep-sea squat lobsters (Shinkaia crosnieri) by applying in situ RNA stabilization equipment. Compared to conventional metatranscriptomics (i.e., RNA stabilization after retrieval), our method provided substantially different RNA expression profiles. Moreover, we discovered that S. crosnieri and its episymbiotic microbes constitute complex and resilient ecosystems, where closely related but various episymbionts are stably maintained by horizontal exchange and partly by their sulfur storage ability for survival even when sulfur compounds are not usable, likely also in a detached and free-living state.

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