Bacterial Communication System Research Articles

Disrupting quorum sensing as a strategy to inhibit bacterial virulence in human, animal, and plant pathogens.

The development of sustainable alternatives to conventional antimicrobials is needed to address bacterial virulence while avoiding selecting resistant strains in a variety of fields, including human, animal, and plant health. Quorum sensing (QS), a bacterial communication system involved in noxious bacterial phenotypes such as virulence, motility, and biofilm formation, is of utmost interest. In this study, we harnessed the potential of the lactonase SsoPox to disrupt QS of human, fish, and plant pathogens. Lactonase treatment significantly alters phenotypes including biofilm formation, motility, and infection capacity. In plant pathogens, SsoPox decreased the production of plant cell wall degrading enzymes in Pectobacterium carotovorum and reduced the maceration of onions infected by Burkholderia glumae. In human pathogens, lactonase treatment significantly reduced biofilm formation in Acinetobacter baumannii, Burkholderia cepacia, and Pseudomonas aeruginosa, with the cytotoxicity of the latter being reduced by SsoPox treatment. In fish pathogens, lactonase treatment inhibited biofilm formation and bioluminescence in Vibrio harveyi and affected QS regulation in Aeromonas salmonicida. QS inhibition can thus be used to largely impact the virulence of bacterial pathogens and would constitute a global and sustainable approach for public, crop, and livestock health in line with the expectations of the One Health initiative.

Molecular Assessments of Antimicrobial Protein Enterocins and Quorum Sensing Genes and Their Role in Virulence of the Genus Enterococcus.

Enterococcus has emerged as an opportunistic pathogen because of its antibiotic resistance and virulence profile, which makes it a causative agent of several diseases like endocarditis, surgical site, and urinary tract infections. Currently, species of this genus are the 2nd most frequently isolated microorganisms from hospital-acquired infections. Significant association with hospitals and unhygienic conditions of the environments has made them resistant to a wide range of antibiotics. On the brighter side, enterococci have the ability to produce antimicrobial proteins (i.e., enterocins) that exhibit wide antagonistic activity, thus making them useful microbes in the food and pharmaceutical industries. Enterocins are also involved in niche control in gut microbiota which is regulated by the quorum sensing (QS) system. A bacterial communication system that is controlled by the fsr operon in enterococci consists of FsrABDC, ef1097, and GelE/SprE genes. Hence, the present study was conducted for molecular assessment of enterocins and quorum sensing genes, inter-environmental correlation, and species prevalence of enterococci isolated from different environmental niches of Karachi, Pakistan. Obtained results revealed the highest prevalence of E. faecium and E. faecalis in all environments. Bacterial antagonism and enterocin genes were observed significantly high in poultry environments. The inter-environmental correlation indicated a strong positive correlation of freshwater with sewage and soil environments. Similarly, the fsr regulatory system was mostly identified in poultry-related environments, and a significant correlation between QS system and biofilm formation was established. In conclusion, this study confirmed the high prevalence of E. faecium in all tested sources, high enterocin production in non-clinical environments, and more fsr regulatory genes in poultry-related environments.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination.

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

Multidimensional Criteria for Virtual Screening of PqsR Inhibitors Based on Pharmacophore, Docking, and Molecular Dynamics.

Pseudomonas aeruginosa is a clinically challenging pathogen due to its high resistance to antibiotics. Quorum sensing inhibitors (QSIs) have been proposed as a promising strategy to overcome this resistance by interfering with the bacterial communication system. Among the potential targets of QSIs, PqsR is a key regulator of quorum sensing in Pseudomonas aeruginosa. However, the current research on PqsR inhibitors is limited by the lack of diversity in the chemical structures and the screening methods. Therefore, this study aims to develop a multidimensional screening model for PqsR inhibitors based on both ligand- and receptor-based approaches. First, a pharmacophore model was constructed from a training set of PqsR inhibitors to identify the essential features and spatial arrangement for the activity. Then, molecular docking and dynamics simulations were performed to explore the core interactions between PqsR inhibitors and their receptor. The results indicate that an effective PqsR inhibitor should possess two aromatic rings, one hydrogen bond acceptor, and two hydrophobic groups and should form strong interactions with the following four amino acid residues: TYR_258, ILE_236, LEU_208, and GLN_194. Moreover, the docking score and the binding free energy should be lower than -8 kcal/mol and -40 kcal/mol, respectively. Finally, the validity of the multidimensional screening model was confirmed by a test set of PqsR inhibitors, which showed a higher accuracy than the existing screening methods based on single characteristics. This multidimensional screening model would be a useful tool for the discovery and optimization of PqsR inhibitors in the future.

УНИВЕРСАЛЬНЫЕ ПРИНЦИПЫ БАКТЕРИАЛЬНОЙ КОММУНИКАЦИИ

This article presents up-to-date information on the phenomenon of intercellular communication in bacteria, its role in the expression of virulence genes and, in particular, in the spread of antibiotic resistance. The basic principles of quorum functioning inherent in all currently known bacterial communication systems are highlighted. The main signaling molecules (autoinducers) of intraspecies, interspecies, epinephrine and peptide communication have been analyzed. The role of blocking information communication (signaling molecules) between bacteria as an alternative to the discovery of new antibiotics against bacteria with extreme and complete antibiotic resistance have been evaluated. Key words: quorum sensing, signaling molecules, receptors, gene expression, quorum suppression.

DegQ is an important policing link between quorum sensing and regulated adaptative traits in Bacillus subtilis.

Quorum sensing (QS) is a widespread bacterial communication system that controls important adaptive traits in a cell density-dependent manner. However, mechanisms by which QS-regulated traits are linked within the cell and mechanisms by which these links affect adaptation are not well understood. In this study, Bacillus subtilis was used as a model bacterium to investigate the link between the ComQXPA QS system, DegQ, surfactin and protease production in planktonic and biofilm cultures. The work tests two alternative hypotheses predicting that hypersensitivity of the QS signal-deficient mutant (comQ::kan) to exogenously added ComX, resulting in increased surfactin production, is linked to an additional genetic locus, or alternatively, to overexpression of the ComX receptor ComP. Results are in agreement with the first hypothesis and show that the P srfAA hypersensitivity of the comQ::kan mutant is linked to a 168 strain-specific mutation in the P degQ region. Hence, the markerless ΔcomQ mutant lacking this mutation is not overresponsive to ComX. Such hyper-responsiveness is specific for the P srfAA and not detected in another ComX-regulated promoter, the P aprE , which is under the positive control by DegQ. Our results suggest that DegQ by exerting differential effect on P srfAA and P aprE acts as a policing mechanism and the intracellular link, which guards the cell from an overinvestment into surfactin production. IMPORTANCE DegQ levels are known to regulate surfactin synthesis and extracellular protease production, and DegQ is under the control of the ComX-dependent QS. DegQ also serves as an important policing link between these QS-regulated processes, preventing overinvestment in these costly processes. This work highlights the importance of DegQ, which acts as the intracellular link between ComX production and the response by regulating extracellular degradative enzyme synthesis and surfactin production.

Targeting Pseudomonas aeruginosa quorum sensing with sodium salicylate modulates immune responses in vitro and in vivo.

Chronic infections are a major clinical challenge in hard-to-heal wounds and implanted devices. Pseudomonas aeruginosa is a common causative pathogen that produces numerous virulence factors. Due to the increasing problem of antibiotic resistance, new alternative treatment strategies are needed. Quorum sensing (QS) is a bacterial communication system that regulates virulence and dampens inflammation, promoting bacterial survival. QS inhibition is a potent strategy to reduce bacterial virulence and alleviate the negative impact on host immune response. This study investigates how secreted factors from P. aeruginosa PAO1, cultured in the presence or absence of the QS inhibitor sodium salicylate (NaSa), influence host immune response. In vitro, THP-1 macrophages and neutrophil-like HL-60 cells were used. In vivo, discs of titanium were implanted in a subcutaneous rat model with local administration of P. aeruginosa culture supernatants. The host immune response to virulence factors contained in culture supernatants (+/-NaSa) was characterized through cell viability, migration, phagocytosis, gene expression, cytokine secretion, and histology. In vitro, P. aeruginosa supernatants from NaSa-containing cultures significantly increased THP-1 phagocytosis and HL-60 cell migration compared with untreated supernatants (-NaSa). Stimulation with NaSa-treated supernatants in vivo resulted in: (i) significantly increased immune cell infiltration and cell attachment to titanium discs; (ii) increased gene expression of IL-8, IL-10, ARG1, and iNOS, and (iii) increased GRO-α protein secretion and decreased IL-1β, IL-6, and IL-1α secretion, as compared with untreated supernatants. In conclusion, treating P. aeruginosa with NaSa reduces the production of virulence factors and modulates major immune events, such as promoting phagocytosis and cell migration, and decreasing the secretion of several pro-inflammatory cytokines.

Molecular modeling study of micro and nanocurcumin with in vitro and in vivo antibacterial validation

Repurposing natural compounds as inhibitory targets to combat bacterial virulence is an important potential strategy to overcome resistance to traditional antibiotics, in the present study, the antibacterial activity of micro-curcumin and nano-sized curcumin was investigated against four predominant bacterial pathogens, namely, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis. Curcumin bactericidal susceptibility could be summarized as the order, P. aeruginosa > B. subtilis > S. aureus > E. coli. Molecular docking analysis was conducted to confirm the impact of curcumin on the most vital and positively identified quorum-sensing pathway signaling proteins SecA-SecY, LsrR, PqsR (MvfR), AgrA which act as key players in the bacterial communication systems. The in silico physicochemical properties revealed that curcumin as a nutraceutical can be classified as a drug-like compound. An in vivo infected wound model was employed in four groups of albino rats. Topical application of nano-curcumin lotion showed a marked reduction in wound area (98.8%) as well as nearly 100% reduction in total bacterial viable count compared to the control group, on the fifteenth day post-treatment post-injury. The obtained data suggested that curcumin nanoparticles exhibited superior antibacterial activity and may possess clinical utility as a novel topical antimicrobial and wound healing agent.

Investigation of some basil genotypes in terms of their effect on bacterial communication system, and antimicrobial activity

The exponential growth of multiresistant bacterial strains creates the need to explore new or combined strategies to combat bacterial resistance. Medicinal plant-derived compounds against pathogenic bacteria may provide new, simple approaches to developing more environmentally friendly antimicrobial agents. Many researchers focus on exploring novel or combined strategies for combating bacterial resistance. Aromatic plants containing essential oils, such as basil, are often used as therapeutic agents in the pharmaceutical industry. Recent research has shown that basil is effective against certain harmful food phytopathogenic bacteria and has antimicrobial and anti-quorum sensing properties, which were investigated in this study. Our results have shown that the essential oil and ethanol extract of basil exhibits both antibacterial activity and anti-quorum sensing activity against some Gram-negative and Gram-positive bacterial species. It has also been found to have antifungal effects on C. albicans. Among the tested microorganisms, the genotypes of PI 531396, PI 296390, PI 414199, PI 253157, PI 296391, PI 652071, midnight, and Dino cultivars have been found to be more effective than other genotypes. The highest effect on quorum sensing system was found in Moonlight and Dino cultivars, PI 296391, PI 414199, PI 652070, PI 172997 and PI 190100 genotypes. Dendrogram analysis has shown that there is a relationship between different genotypes depending on microorganisms and anti-quorum sensing activity. Ames 29184, PI 207498, and PI 379412 genotypes were in the same group. Biplot analyses were performed to determine the relationship between the studied properties, and the results showed that more than 47% of the total variation was in all forms.

Innovative microbial disease biocontrol strategies mediated by quorum quenching and their multifaceted applications: A review.

With the increasing resistance exhibited by undesirable bacteria to traditional antibiotics, the need to discover alternative (or, at least, supplementary) treatments to combat chemically resistant bacteria is becoming urgent. Quorum sensing (QS) refers to a novel bacterial communication system for monitoring cell density and regulation of a network of gene expression that is mediated by a group of signaling molecules called autoinducers (AIs). QS-regulated multicellular behaviors include biofilm formation, horizontal gene transfer, and antibiotic synthesis, which are demonstrating increasing pathogenicity to plants and aquacultural animals as well as contamination of wastewater treatment devices. To inhibit QS-regulated microbial behaviors, the strategy of quorum quenching (QQ) has been developed. Different quorum quenchers interfere with QS through different mechanisms, such as competitively inhibiting AI perception (e.g., by QS inhibitors) and AI degradation (e.g., by QQ enzymes). In this review, we first introduce different signaling molecules, including diffusible signal factor (DSF) and acyl homoserine lactones (AHLs) for Gram-negative bacteria, AIPs for Gram-positive bacteria, and AI-2 for interspecies communication, thus demonstrating the mode of action of the QS system. We next exemplify the QQ mechanisms of various quorum quenchers, such as chemical QS inhibitors, and the physical/enzymatic degradation of QS signals. We devote special attention to AHL-degrading enzymes, which are categorized in detail according to their diverse catalytic mechanisms and enzymatic properties. In the final part, the applications and advantages of quorum quenchers (especially QQ enzymes and bacteria) are summarized in the context of agricultural/aquacultural pathogen biocontrol, membrane bioreactors for wastewater treatment, and the attenuation of human pathogenic bacteria. Taken together, we present the state-of-the-art in research considering QS and QQ, providing theoretical evidence and support for wider application of this promising environmentally friendly biocontrol strategy.

Targeting Peptide-Based Quorum Sensing Systems for the Treatment of Gram-Positive Bacterial Infections.

Bacteria utilize a cell density-dependent communication system called quorum sensing (QS) to coordinate group behaviors. In Gram-positive bacteria, QS involves the production of and response to auto-inducing peptide (AIP) signaling molecules to modulate group phenotypes, including pathogenicity. As such, this bacterial communication system has been identified as a potential therapeutic target against bacterial infections. More specifically, developing synthetic modulators derived from the native peptide signal paves a new way to selectively block the pathogenic behaviors associated with this signaling system. Moreover, rational design and development of potent synthetic peptide modulators allows in depth understanding of the molecular mechanisms that drive QS circuits in diverse bacterial species. Overall, studies aimed at understanding the role of QS in microbial social behavior could result in the accumulation of significant knowledge of microbial interactions, and consequently lead to the development of alternative therapeutic agents to treat bacterial infectivity. In this review, we discuss recent advances in the development of peptide-based modulators to target QS systems in Gram-positive pathogens, with a focus on evaluating the therapeutic potential associated with these bacterial signaling pathways.

Comparative genomic and functional analysis of Arthrobacter sp. UMCV2 reveals the presence of luxR-related genes inducible by the biocompound N, N-dimethylhexadecilamine.

Quorum sensing (QS) is a bacterial cell-cell communication system with genetically regulated mechanisms dependent on cell density. Canonical QS systems in gram-negative bacteria possess an autoinducer synthase (LuxI family) and a transcriptional regulator (LuxR family) that respond to an autoinducer molecule. In Gram-positive bacteria, the LuxR transcriptional regulators "solo" (not associated with a LuxI homolog) may play key roles in intracellular communication. Arthrobacter sp. UMCV2 is an actinobacterium that promotes plant growth by emitting the volatile organic compound N, N-dimethylhexadecylamine (DMHDA). This compound induces iron deficiency, defense responses in plants, and swarming motility in Arthrobacter sp. UMCV2. In this study, the draft genome of this bacterium was assembled and compared with the genomes of type strains of the Arthrobacter genus, finding that it does not belong to any previously described species. Genome explorations also revealed the presence of 16 luxR-related genes, but no luxI homologs were discovered. Eleven of these sequences possess the LuxR characteristic DNA-binding domain with a helix-turn-helix motif and were designated as auto-inducer-related regulators (AirR). Four sequences possessed LuxR analogous domains and were designated as auto-inducer analogous regulators (AiaR). When swarming motility was induced with DMHDA, eight airR genes and two aiaR genes were upregulated. These results indicate that the expression of multiple luxR-related genes is induced in actinobacteria, such as Arthrobacter sp. UMCV2, by the action of the bacterial biocompound DMHDA when QS behavior is produced.

Targeting quorum sensing and biofilm formation in the control of Vibrio harveyi infections in Penaeus vannamei

Vibriosis, a disease caused by Vibrio spp., including V. harveyi, contributes to enormous economic loss to the shrimp aquaculture industry. With the worsening incidences of antimicrobial resistance in aquaculture, novel strategies for combating this bacterial infection are urgently needed. One of these is by targeting the bacterial communication system, called quorum sensing (QS), which is responsible for the expression of genes necessary for bacterial pathogenesis. Recently, bioactive compounds capable of inhibiting QS were identified. This review focuses on the discovery of bioactive substances from animal, plant, and microbial origins with the capability of inhibiting QS and biofilm formation, a mechanism important in the pathogenesis of vibriosis. Furthermore, recent developments in the use of these QS inhibitors (QSIs) as feed supplement for Penaeus vannamei shrimp were also discussed. These findings will provide the necessary information for the discovery, development, and eventual commercialization of these QSIs as tools in mitigating vibriosis in the shrimp industry.

Study of the Bacterial "Conversations" and Pattern Formation in the Quorum Sensing System using Numerical Simulation

Cell-to-cell communication processes in the bacterial world can be considered as a collective bacterial behavior, which is coordinated by chemical signaling molecules (autoinducers, quorum sensing molecules, or pheromones). This complex biological process is termed the quorum sensing mechanism, which is considered a density-dependent bacterial communication system. As the bacterial culture grows, signal molecules are released into the extracellular milieu and accumulate, changing water fluidity. Under such threshold conditions, swimming bacterial suspensions impose a coordinated water movement on a length scale of the order of 10 to 100 micrometers compared with a bacterial size of the order of 3 micrometers. Here, we propose a non-local hydrodynamics of the quorum state and wave-like pattern formation using the forced Burgers equation with Kwak transformation. Such an approach resulted in the conversion of the Burgers equation paradigm into a reaction-diffusion system. The examination of the dynamics of the quorum sensing system, both analytically as well as numerically, results in similar long-time dynamical behaviour. Moreover, we find out the range kinematics viscosity of the living fluid, which is one of the significant parameters for pattern formation in the system.AMS Subject Classification: 92B05, 65N06, 65Z05. Doi: 10.28991/HEF-SP2022-01-03 Full Text: PDF

A computational approach to explore the binding mechanism of secondary metabolites of Hamigera ingelheimensis with AgrA quorum sensing proteins

AbstractBacterial resistance to existing antibacterials can be handled by focusing on the bacterial communication system, specifically bacterial quorum sensing system. Inhibiting AgrA‐DNA binding is an effective strategy for reducing the expression of diverse genes involved with the secretion of virulence factors by the Agr quorum sensing system. Hamigera ingelheimensis, a common soil fungus, produces several bioactive secondary metabolites including avellanin C which is a well‐recognised and deeply studied quorum sensing inhibitor. Among the several metabolites, we selected ten metabolites and other metabolites have been rejected either some of them were exhaustively studied or during primary docking screening, they did not show promising docking scores. These ten metabolites were docked with template protein (PDB ID: 4G4K) and with five homologies modelled AgrA proteins using AutoDock tool. Avellanin A, avellanin B and PF1171B showed a promising binding score with all the proteins with binding free energy less than ‐8.00 kcal.mol‐1. Molecular dynamics simulations suggest that their docked complexes are stable. These three metabolites have drug‐likeness features and thus have the tremendous prospect to be used as the AgrA inhibitors.

Analysis and application of bacterial cell-cell communication system

Analysis and application of bacterial cell-cell communication system

Quorum Sensing Inhibitors to Quench P. aeruginosa Pathogenicity.

The emergence and the dissemination of multidrug-resistant bacteria constitute a major public health issue. Among incriminated Gram-negative bacteria, Pseudomonas aeruginosa has been designated by the WHO as a critical priority threat. During the infection process, this pathogen secretes various virulence factors in order to adhere and colonize host tissues. Furthermore, P. aeruginosa has the capacity to establish biofilms that reinforce its virulence and intrinsic drug resistance. The regulation of biofilm and virulence factor production of this micro-organism is controlled by a specific bacterial communication system named Quorum Sensing (QS). The development of anti-virulence agents targeting QS that could attenuate P. aeruginosa pathogenicity without affecting its growth seems to be a promising new therapeutic strategy. This could prevent the selective pressure put on bacteria by the conventional antibiotics that cause their death and promote resistant strain survival. This review describes the QS-controlled pathogenicity of P. aeruginosa and its different specific QS molecular pathways, as well as the recent advances in the development of innovative QS-quenching anti-virulence agents to fight anti-bioresistance.

Quorum sensing disruption regulates hydrolytic enzyme and biofilm production in estuarine bacteria.

Biofilms of heterotrophic bacteria cover organic matter aggregates and constitute hotspots of mineralization, primarily acting through extracellular hydrolytic enzyme production. Nevertheless, regulation of both biofilm and hydrolytic enzyme synthesis remains poorly investigated, especially in estuarine ecosystems. In this study, various bioassays, mass spectrometry and genomics approaches were combined to test the possible involvement of quorum sensing (QS) in these mechanisms. QS is a bacterial cell-cell communication system that relies notably on the emission of N-acylhomoserine lactones (AHLs). In our estuarine bacterial collection, we found that 28 strains (9%), mainly Vibrio, Pseudomonas and Acinetobacter isolates, produced at least 14 different types of AHLs encoded by various luxI genes. We then inhibited the AHL QS circuits of those 28 strains using a broad-spectrum lactonase preparation and tested whether biofilm production as well as β-glucosidase and leucine-aminopeptidase activities were impacted. Interestingly, we recorded contrasted responses, as biofilm production, dissolved and cell-bound β-glucosidase and leucine-aminopeptidase activities significantly increased in 4%-68% of strains but decreased in 0%-21% of strains. These findings highlight the key role of AHL-based QS in estuarine bacterial physiology and ultimately on biogeochemical cycles. They also point out the complexity of QS regulations within natural microbial assemblages.

Inhibitory Effects of Artificial Sweeteners on Bacterial Quorum Sensing.

Despite having been tagged as safe and beneficial, recent evidence remains inconclusive regarding the status of artificial sweeteners and their putative effects on gut microbiota. Gut microorganisms are essential for the normal metabolic functions of their host. These microorganisms communicate within their community and regulate group behaviors via a molecular system termed quorum sensing (QS). In the present study, we aimed to study the effects of artificial sweeteners on this bacterial communication system. Using biosensor assays, biophysical protein characterization methods, microscale thermophoresis, swarming motility assays, growth assays, as well as molecular docking, we show that aspartame, sucralose, and saccharin have significant inhibitory actions on the Gram-negative bacteria N-acyl homoserine lactone-based (AHL) communication system. Our studies indicate that these three artificial sweeteners are not bactericidal. Protein-ligand docking and interaction profiling, using LasR as a representative participating receptor for AHL, suggest that the artificial sweeteners bind to the ligand-binding pocket of the protein, possibly interfering with the proper housing of the native ligand and thus impeding protein folding. Our findings suggest that these artificial sweeteners may affect the balance of the gut microbial community via QS-inhibition. We, therefore, infer an effect of these artificial sweeteners on numerous molecular events that are at the core of intestinal microbial function, and by extension on the host metabolism.

Features of the Opportunistic Behaviour of the Marine Bacterium Marinobacter algicola in the Microalga Ostreococcus tauri Phycosphere.

Although interactions between microalgae and bacteria are observed in both natural environment and the laboratory, the modalities of coexistence of bacteria inside microalgae phycospheres in laboratory cultures are mostly unknown. Here, we focused on well-controlled cultures of the model green picoalga Ostreococcus tauri and the most abundant member of its phycosphere, Marinobacter algicola. The prevalence of M. algicola in O. tauri cultures raises questions about how this bacterium maintains itself under laboratory conditions in the microalga culture. The results showed that M. algicola did not promote O. tauri growth in the absence of vitamin B12 while M. algicola depended on O. tauri to grow in synthetic medium, most likely to obtain organic carbon sources provided by the microalgae. M. algicola grew on a range of lipids, including triacylglycerols that are known to be produced by O. tauri in culture during abiotic stress. Genomic screening revealed the absence of genes of two particular modes of quorum-sensing in Marinobacter genomes which refutes the idea that these bacterial communication systems operate in this genus. To date, the ‘opportunistic’ behaviour of M. algicola in the laboratory is limited to several phytoplanktonic species including Chlorophyta such as O. tauri. This would indicate a preferential occurrence of M. algicola in association with these specific microalgae under optimum laboratory conditions.