A Small Molecule Coordinates Symbiotic Behaviors in a Host Organ

ABSTRACT The lifelong relationship between the Hawaiian bobtail squid Euprymna scolopes and its microbial symbiont Vibrio fischeri represents a simplified model system for studying microbiome establishment and maintenance. The bacteria colonize a dedicated symbiotic light organ in the squid, from which bacterial luminescence camouflages the host in a process termed counterillumination. The squid host hatches without its symbionts, which must be acquired from the ocean amidst a diversity of nonbeneficial bacteria, such that precise molecular communication is required for initiation of the specific relationship. Therefore it is likely there are specialized metabolites used in the light organ microenvironment to modulate these processes. To identify small molecules that may influence the establishment of this symbiosis, we used imaging mass spectrometry to analyze metabolite production in V. fischeri with altered biofilm production, which correlates directly to colonization capability in its host. “Biofilm-up” and “biofilm-down” mutants were compared to a wild-type strain, and ions that were more abundantly produced by the biofilm-up mutant were detected. Using a combination of structural elucidation and synthetic chemistry, one such signal was determined to be a diketopiperazine, cyclo(d-histidyl-l-proline). This diketopiperazine modulated luminescence in V. fischeri and, using imaging mass spectrometry, was directly detected in the light organ of the colonized host. This work highlights the continued need for untargeted discovery efforts in host-microbe interactions and showcases the benefits of the squid-Vibrio system for identification and characterization of small molecules that modulate microbiome behaviors. IMPORTANCE The complexity of animal microbiomes presents challenges to defining signaling molecules within the microbial consortium and between the microbes and the host. By focusing on the binary symbiosis between Vibrio fischeri and Euprymna scolopes, we have combined genetic analysis with direct imaging to define and study small molecules in the intact symbiosis. We have detected and characterized a diketopiperazine produced by strong biofilm-forming V. fischeri strains that was detectable in the host symbiotic organ, and which influences bacterial luminescence. Biofilm formation and luminescence are critical for initiation and maintenance of the association, respectively, suggesting that the compound may link early and later development stages, providing further evidence that multiple small molecules are important in establishing these beneficial relationships.

Discovery of a microbially produced small molecule in a host-specific organ

The lifelong relationship between the Hawaiian bobtail squid, Euprymna scolopes, and its microbial symbiont, Vibrio fischeri, represents a simplified model system for studying microbiome establishment and maintenance. The bacteria colonize a dedicated symbiotic light organ in the squid, from which bacterial luminescence camouflages the hosts in a process termed counterillumination. The squid hosts hatch without their symbionts, which must be acquired from the ocean amid a diversity of non-beneficial bacteria, so precise molecular communication is required for initiation of the specific relationship. It is therefore likely that there may be specialized metabolites used in the light organ microenvironment to modulate these processes. To identify small molecules that may influence the establishment of this symbiosis, we used imaging mass spectrometry to analyze metabolite production in V. fischeri with altered biofilm production, which correlates directly to colonization capability in its host. ‘Biofilm-Up’ and ‘Biofilm-Down’ mutants were compared to a wild-type strain, and masses that were more abundantly produced by the biofilm-up mutant were detected. Using a combination of structure elucidation and synthetic chemistry, one such signal was determined to be a diketopiperazine, cyclo(d-histidyl-l-proline). This diketopiperazine modulated luminescence in V. fischeri and, using label-free imaging mass spectrometry, was directly detected in the light organ of the colonized host. This work highlights the continued need for untargeted discovery efforts in host-microbe interactions and showcases the benefits of the squid-Vibrio system for identification and characterization of small molecules that modulate microbiome behaviors.Significance StatementThe complexity of animal microbiomes presents challenges to defining signaling molecules within the microbial consortium and between the microbes and the host. By focusing on the binary symbiosis between Vibrio fischeri and Euprymna scolopes, we have combined genetic analysis with direct imaging to define and study small molecules in the intact symbiosis. We have detected and characterized a diketopiperazine produced by strong biofilm-forming V. fischeri strains that was detectable in the host symbiotic organ, and which influences bacterial luminescence. Biofilm formation and luminescence are critical for initiation and maintenance of the association, respectively, suggesting that the compound may link early and later development stages, providing further evidence that multiple small molecules are important in establishing these beneficial relationships.

Ecotoxicological assessment of the urban environment on the example of Moscow

Using lichinoindication and biotesting on the basis of bacterial luminescence the ecological state of the air environment and soils of 14 streets 8 of the administrative districts of the city of Moscow was assessed. Lichens of 28 species are distinguished, mainly in relation to air pollution of the I and II classes of toxicophobia. The influence of specificity of chemical contamination by pollutants of the air environment on the growth of certain lichen species is discussed. A large number of identified nitrophilous lichen species indicates a specific ecology of the urban environment. Express method (30 min) of biotesting on the basis of bacterial luminescence identified the toxicity index of soil samples from the lichen collection sites. Many soil samples were toxic or very toxic. In some soil samples soil mosaic was revealed, in which samples of one soil sample had different toxicity indices. The joint use of lichinoindication and biotesting on the basis of bacterial luminescence can be useful for eliminating local pollutants and an essential link in the improvement of habitats. This indicates the expediency of practical use of these biomonitoring methods.

Efecto del pH y la salinidad en el crecimiento y luminiscencia de una bacteria marina como biosensor ambiental

Effect of pH and salinity on the growth and luminescence of a marine bacterium as an environmental biosensor Resumen El trabajo se desarrolló en el Centro de Estudios de Proteínas de la Facultad de Biología de la Universidad de La Habana en septiembre de 2012 con el objetivo de evaluar el crecimiento y la luminiscencia de la cepa bacteriana CBM-784 en el medio LM a diferentes intervalos de pH y salinidad y determinar los rangos óptimos para sus crecimiento y luminiscencia. Los resultados demuestran que la bacteria luminiscente CBM-784 mostró su mejor crecimiento y luminiscencia a pH= 8,3 y concentraciones de NaCl entre 2,95 y 3,5%. Palabras clave: bacterias; ecología marina; luciferase; luminiscencia bacteriana; medio de cultivo. Abstract The work was developed at the Center for Protein Studies of the Faculty of Biology of the University of Havana in September 2012 with the objective of evaluating the growth and luminescence of the bacterial strain CBM-784 in the LM medium at different intervals of pH and salinity and to determine the optimal ranges for its growth and luminescence. The results demonstrate that the luminescent bacterium CBM-784 showed its best growth and luminescence at pH = 8.3 and NaCl concentrations between 2.95 and 3.5%. Keywords: bacteria; marine ecology; luciferase; bacterial luminescence; culture medium.

A sensitive and high throughput bacterial luminescence assay for assessing aquatic toxicity – the BLT-Screen

The development of a cost effective, sensitive and high throughput aquatic toxicity assay with a wide range of research and monitoring applications.