Gram-Negative Bacterial Sensors for Eukaryotic Signal Molecules

Microbes operate their metabolic activities at a unicellular level. However, it has been revealed that a few metabolic activities only prove beneficial to microbes if operated at high cell densities. These cell density-dependent activities termed quorum sensing (QS) operate through specific chemical signals. In Gram-negative bacteria, the most widely reported QS signals are acylhomoserine lactones. In contrast, a novel QS-like system has been elucidated, regulating communication between microbes and plants through strigolactones. These systems regulate bioprocesses, which affect the health of plants, animals, and human beings. This mini-review presents recent developments in the QS and QS-like signal molecules in promoting plant health.

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Bacterial Cellulose Containing Combinations of Antimicrobial Peptides with Various QQ Enzymes as a Prototype of an “Enhanced Antibacterial” Dressing: In Silico and In Vitro Data

Pharmaceutics ◽

10.3390/pharmaceutics12121155 ◽

2020 ◽

Vol 12 (12) ◽

pp. 1155

Author(s):

Aysel Aslanli ◽

Ilya Lyagin ◽

Nikolay Stepanov ◽

Denis Presnov ◽

Elena Efremenko

Keyword(s):

Antimicrobial Peptides ◽

Bacterial Cellulose ◽

In Silico ◽

Antimicrobial Agents ◽

Penicillin Acylase ◽

Signal Molecules ◽

Bacterial Cells ◽

Gram Positive ◽

Gram Negative

To improve the action of already in use antibiotics or new antimicrobial agents against different bacteria, the development of effective combinations of antimicrobial peptides (AMPs) with enzymes that can quench the quorum (QQ) sensing of bacterial cells was undertaken. Enzymes hydrolyzing N-acyl homoserine lactones (AHLs) and peptides that are signal molecules of Gram-negative and Gram-positive bacterial cells, respectively, were estimated as “partners” for antibiotics and antimicrobial peptides in newly designed antimicrobial–enzymatic combinations. The molecular docking of six antimicrobial agents to the surface of 10 different QQ enzyme molecules was simulated in silico. This made it possible to choose the best variants among the target combinations. Further, bacterial cellulose (BC) was applied as a carrier for uploading such combinations to generally compose prototypes of effective dressing materials with morphology, providing good absorbance. The in vitro analysis of antibacterial activity of prepared BC samples confirmed the significantly enhanced efficiency of the action of AMPs (including polymyxin B and colistin, which are antibiotics of last resort) in combination with AHL-hydrolyzing enzymes (penicillin acylase and His6-tagged organophosphorus hydrolase) against both Gram-negative and Gram-positive cells.

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Production ofN-acylhomoserine lactone signal molecules by gram-negative soil-borne and plant-associated bacteria

Folia Microbiologica ◽

10.1007/bf02931516 ◽

2003 ◽

Vol 48 (6) ◽

pp. 794-798 ◽

Cited By ~ 25

Author(s):

M. Vfselova ◽

M. Kholmeckaya ◽

S. Klein ◽

E. Voronina ◽

V. Lipasova ◽

...

Keyword(s):

Signal Molecules ◽

Associated Bacteria ◽

Gram Negative ◽

Acylhomoserine Lactone

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Plants Secrete Substances That Mimic Bacterial N-Acyl Homoserine Lactone Signal Activities and Affect Population Density-Dependent Behaviors in Associated Bacteria

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2000.13.6.637 ◽

2000 ◽

Vol 13 (6) ◽

pp. 637-648 ◽

Cited By ~ 412

Author(s):

Max Teplitski ◽

Jayne B. Robinson ◽

Wolfgang D. Bauer

Keyword(s):

Chemical Nature ◽

Higher Plants ◽

Homoserine Lactone ◽

Signal Molecules ◽

Gram Negative Bacteria ◽

Associated Bacteria ◽

Gram Negative ◽

Density Dependent ◽

Reporter Strains ◽

And Behavior

In gram-negative bacteria, many important changes in gene expression and behavior are regulated in a popula tion density-dependent fashion by N-acyl homoserine lac tone (AHL) signal molecules. Exudates from pea (Pisum sativum) seedlings were found to contain several separable activities that mimicked AHL signals in well-characterized bacterial reporter strains, stimulating AHL-regulated be haviors in some strains while inhibiting such behaviors in others. The chemical nature of the active mimic com pounds is currently unknown, but all extracted differently into organic solvents than common bacterial AHLs. Various species of higher plants in addition to pea were found to secrete AHL mimic activities. The AHL signal-mimic compounds could prove to be important in determining the outcome of interactions between higher plants and a diver sity of pathogenic, symbiotic, and saprophytic bacteria.

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Dominance of Vibrio fischeri in Secreted Mucus outside the Light Organ of Euprymna scolopes: the First Site of Symbiont Specificity

Applied and Environmental Microbiology ◽

10.1128/aem.69.7.3932-3937.2003 ◽

2003 ◽

Vol 69 (7) ◽

pp. 3932-3937 ◽

Cited By ~ 66

Author(s):

Spencer V. Nyholm ◽

Margaret J. McFall-Ngai

Keyword(s):

Fluorescent Protein ◽

Vibrio Fischeri ◽

Signal Molecules ◽

Natural Seawater ◽

Gram Negative Bacteria ◽

Light Organ ◽

Bacterial Cells ◽

Euprymna Scolopes ◽

Gram Negative ◽

Green Fluorescent

ABSTRACT Previous studies of the Euprymna scolopes-Vibrio fischeri symbiosis have demonstrated that, during colonization, the hatchling host secretes mucus in which gram-negative environmental bacteria amass in dense aggregations outside the sites of infection. In this study, experiments with green fluorescent protein-labeled symbiotic and nonsymbiotic species of gram-negative bacteria were used to characterize the behavior of cells in the aggregates. When hatchling animals were exposed to 103 to 106 V. fischeri cells/ml added to natural seawater, which contains a mix of approximately 106 nonspecific bacterial cells/ml, V. fischeri cells were the principal bacterial cells present in the aggregations. Furthermore, when animals were exposed to equal cell numbers of V. fischeri (either a motile or a nonmotile strain) and either Vibrio parahaemolyticus or Photobacterium leiognathi, phylogenetically related gram-negative bacteria that also occur in the host's habitat, the symbiont cells were dominant in the aggregations. The presence of V. fischeri did not compromise the viability of these other species in the aggregations, and no significant growth of V. fischeri cells was detected. These findings suggested that dominance results from the ability of V. fischeri either to accumulate or to be retained more effectively within the mucus. Viability of the V. fischeri cells was required for both the formation of tight aggregates and their dominance in the mucus. Neither of the V. fischeri quorum-sensing compounds accumulated in the aggregations, which suggested that the effects of these small signal molecules are not critical to V. fischeri dominance. Taken together, these data provide evidence that the specificity of the squid-vibrio symbiosis begins early in the interaction, in the mucus where the symbionts aggregate outside of the light organ.

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Peptide signal molecules and bacteriocins in Gram-negative bacteria: a genome-wide in silico screening for peptides containing a double-glycine leader sequence and their cognate transporters

Peptides ◽

10.1016/j.peptides.2003.10.028 ◽

2004 ◽

Vol 25 (9) ◽

pp. 1425-1440 ◽

Cited By ~ 73

Author(s):

G. Dirix ◽

P. Monsieurs ◽

B. Dombrecht ◽

R. Daniels ◽

K. Marchal ◽

...

Keyword(s):

In Silico ◽

Leader Sequence ◽

Signal Molecules ◽

Gram Negative Bacteria ◽

In Silico Screening ◽

Gram Negative ◽

Genome Wide ◽

A Genome

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Quorum sensing N-acyl-homoserine lactone signal molecules of plant beneficial Gram-negative rhizobacteria support plant growth and resistance to pathogens

Rhizosphere ◽

10.1016/j.rhisph.2020.100258 ◽

2020 ◽

Vol 16 ◽

pp. 100258

Author(s):

Anton Hartmann

Keyword(s):

Quorum Sensing ◽

Plant Growth ◽

Homoserine Lactone ◽

Signal Molecules ◽

Acyl Homoserine Lactone ◽

Gram Negative

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l-Canavanine Made by Medicago sativa Interferes with Quorum Sensing in Sinorhizobium meliloti

Journal of Bacteriology ◽

10.1128/jb.187.24.8427-8436.2005 ◽

2005 ◽

Vol 187 (24) ◽

pp. 8427-8436 ◽

Cited By ~ 90

Author(s):

Neela D. Keshavan ◽

Puneet K. Chowdhary ◽

Donovan C. Haines ◽

Juan E. González

Keyword(s):

Quorum Sensing ◽

Medicago Sativa ◽

Sinorhizobium Meliloti ◽

Signal Molecules ◽

Bacterial Strains ◽

Signal Molecule ◽

Gram Negative ◽

Bacterial Quorum Sensing ◽

Bacterial Quorum ◽

Regulated Gene Expression

ABSTRACT Sinorhizobium meliloti is a gram-negative soil bacterium, capable of establishing a nitrogen-fixing symbiosis with its legume host, alfalfa (Medicago sativa). Quorum sensing plays a crucial role in this symbiosis, where it influences the nodulation process and the synthesis of the symbiotically important exopolysaccharide II (EPS II). S. meliloti has three quorum-sensing systems (Sin, Tra, and Mel) that use N-acyl homoserine lactones as their quorum-sensing signal molecule. Increasing evidence indicates that certain eukaryotic hosts involved in symbiotic or pathogenic relationships with gram-negative bacteria produce quorum-sensing-interfering (QSI) compounds that can cross-communicate with the bacterial quorum-sensing system. Our studies of alfalfa seed exudates suggested the presence of multiple signal molecules capable of interfering with quorum-sensing-regulated gene expression in different bacterial strains. In this work, we choose one of these QSI molecules (SWI) for further characterization. SWI inhibited violacein production, a phenotype that is regulated by quorum sensing in Chromobacterium violaceum. In addition, this signal molecule also inhibits the expression of the S. meliloti exp genes, responsible for the production of EPS II, a quorum-sensing-regulated phenotype. We identified this molecule as l-canavanine, an arginine analog, produced in large quantities by alfalfa and other legumes.

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Phage-Encoded LuxR-Type Receptors Responsive to Host-Produced Bacterial Quorum-Sensing Autoinducers

10.1101/577726 ◽

2019 ◽

Cited By ~ 1

Author(s):

Justin E. Silpe ◽

Bonnie L. Bassler

Keyword(s):

Quorum Sensing ◽

Pathogenic Bacteria ◽

Cell Communication ◽

Signal Molecules ◽

Host Bacterium ◽

Gram Negative ◽

Collective Behaviors ◽

Bacterial Quorum Sensing ◽

Genes Encoding ◽

Bacterial Quorum

AbstractQuorum sensing (QS) is a process of cell-to-cell communication that bacteria use to orchestrate collective behaviors. QS relies on the cell-density-dependent production, accumulation, and receptor-mediated detection of extracellular signaling molecules called autoinducers (AIs). Gram-negative bacteria commonly use N-acyl homoserine lactones (AHLs) as their AIs and they are detected by LuxR-type receptors. Often, LuxR-type receptors are insoluble when not bound to a cognate AI. In this report, we show that LuxR-type receptors are encoded on phage genomes and, in the cases we tested, the phage LuxR-type receptors bind to and are solubilized specifically by the AHL AI produced by the host bacterium. We do not yet know the viral activities that are controlled by these phage QS receptors, however, our observations, coupled with recent reports, suggest that their occurrence is more widespread than previously appreciated. Using receptor-mediated detection of QS AIs could enable phages to garner information concerning the population density status of their bacterial hosts. We speculate that such information can be exploited by phages to optimize the timing of execution of particular steps in viral infection.ImportanceBacteria communicate with chemical signal molecules to regulate group behaviors in a process called quorum sensing (QS). In this report, we find that genes encoding receptors for Gram-negative bacterial QS communication molecules are present on genomes of viruses that infect these bacteria. These viruses are called phages. We show that two phage-encoded receptors, like their bacterial counterparts, bind to the communication molecule produced by the host bacterium, suggesting that phages can “listen in” on their bacterial hosts. Interfering with bacterial QS and using phages to kill pathogenic bacteria represent attractive possibilities for development of new antimicrobials to combat pathogens that are resistant to traditional antibiotics. Our findings of interactions between phages and QS bacteria need consideration as new antimicrobial therapies are developed.

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Biofilms on Indwelling Urethral Catheters Produce Quorum-Sensing Signal Molecules In Situ and In Vitro

Applied and Environmental Microbiology ◽

10.1128/aem.64.9.3486-3490.1998 ◽

1998 ◽

Vol 64 (9) ◽

pp. 3486-3490 ◽

Cited By ~ 146

Author(s):

David J. Stickler ◽

Nicola S. Morris ◽

Robert J. C. McLean ◽

Clay Fuqua

Keyword(s):

Quorum Sensing ◽

Signal Molecules ◽

Gram Negative Bacteria ◽

Feeding Assay ◽

Gram Negative ◽

Homoserine Lactones ◽

Acylated Homoserine Lactones

ABSTRACT Acylated homoserine lactones (AHLs) are chemical signals that mediate population density-dependent (quorum-sensing) gene expression in numerous gram-negative bacteria. In this study, gram-negative bacilli isolated from catheters were screened for AHL production by a cross-feeding assay utilizing an AHL-responsive Agrobacterium tumefaciens reporter strain. Positive reactions were obtained from 14 isolates of Pseudomonas aeruginosa; negative or weakly positive reactions were recorded for isolates of five other species. P. aeruginosa biofilms were then produced on catheters in a physical model of the bladder. Sections of colonized all-silicone catheters gave positive reactions for the quorum-sensing signal molecules as did sections that had been cleaned of biofilm and autoclaved. Control sections of unused catheters were negative in the tests. Sections from four of nine catheters that had been freshly removed from patients gave positive reactions for AHLs. Cleaned autoclaved sections of three of these catheters also gave strongly positive reactions for AHLs. These results demonstrate that AHLs are produced by biofilms as they develop on the catheters both in vitro in the model and in vivo in the patient’s bladder. They represent the first demonstration of AHL production by biofilms in a clinical setting.

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