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Modern crop production relies on the application of chemical pesticides and fertilizers causing environmental and economic challenges. In response, less environmentally impactful alternatives have emerged such as the use of beneficial microorganisms. These microorganisms, particularly plant growth-promoting bacteria (PGPB), have demonstrated their ability to enhance plant growth, protect against various stresses, and reduce the need for chemical inputs. Among the PGPB, Bacillus species have garnered attention due to their adaptability and commercial potential. Recent reports have highlighted Bacillus strains as biocontrol agents against phytopathogenic bacteria while concurrently promoting plant growth. We also examined Bacillus plant growth-promoting abilities in Arabidopsis thaliana seedlings. In this study, we assessed the potential of various Bacillus strains to control diverse phytopathogenic bacteria and inhibit quorum sensing using Chromobacterium violaceum as a model system. In conclusion, our results suggest that bacteria of the genus Bacillus hold significant potential for biotechnological applications. This includes developments aimed at reducing agrochemical use, promoting sustainable agriculture, and enhancing crop yield and protection.

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Resistance mechanisms occur in almost all clinical bacterial isolates and represent one of the most worrisome health problems worldwide. Bacteria can form biofilms and communicate through quorum sensing (QS), which allow them to develop resistance against conventional antibiotics. Thus, new therapeutic candidates are sought. We focus on alkylglycerols (AKGs) because of their recently discovered quorum sensing inhibition (QSI) ability and antibiofilm potential. Fifteen natural enantiopure AKGs were tested to determine their effect on the biofilm formation of other clinical bacterial isolates, two reference strains and their QSI was determined using Chromobacterium violaceum ATCC 12472. The highest biofilm inhibition rates (%) and minimum QS inhibitory concentration were determined by a microtiter plate assay and ciprofloxacin was used as the standard antibiotic. At subinhibitory concentrations, each AKG reduced biofilm formation in a concentration-dependent manner against seven bacterial isolates, with values up to 97.2%. Each AKG displayed QSI at different levels of ability without affecting the growth of C. violaceum. AKG (2S)-3-O-(cis-13'-docosenyl)-1,2-propanediol was the best QS inhibitor (20 µM), while (2S)-3-O-(cis-9'-hexadecenyl)-1,2-propanediol was the least effective (795 µM). The results showed for the first time the QSI activity of this natural AKG series and suggest that AKGs could be promising candidates for further studies on preventing antimicrobial resistance.

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Faced with the global health threat of increasing resistance to antibiotics, researchers are exploring interventions that target bacterial virulence factors. Quorum sensing is a particularly attractive target because several bacterial virulence factors are controlled by this mechanism. Furthermore, attacking the quorum-sensing signaling network is less likely to select for resistant strains than using conventional antibiotics. Strategies that focus on the inhibition of quorum-sensing signal production are especially attractive because the enzymes involved are expressed in bacterial cells but are not present in their mammalian counterparts. We review here various approaches that are being taken to interfere with quorum-sensing signal production via the inhibition of autoinducer-2 synthesis, PQS synthesis, peptide autoinducer synthesis, and N-acyl-homoserine lactone synthesis. We expect these approaches will lead to the discovery of new quorum-sensing inhibitors that can help to stem the tide of antibiotic resistance.

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Background: the emergence of bacterial resistance has led to a search for new natural products as alternatives starting points to prevent and control diseases caused by microorganisms. Among the potential candidates were bioactive compounds from octocorals of the genus Eunicea due to their chemical structures and their wide range of biological activities. Objective: the purpose of this study was to evaluate the quorum sensing inhibition (QSI) and antibacterial activity of compounds previously isolated from two Eunicea species and synthesized alkylglycerols (AKG). Methods: the QSI of three nonpolar compounds and a mixture of AKGs from Eunicea were evaluated by a microtiter plate assay using Chromobacterium violaceum (ATCC 31532). Four naturally occurring, saturated, and enantiomerically pure AKGs, all of which were derived from the chiral precursor (R)-solketal, were synthesized from alkyl chains of 12, 14, 16 and 18 carbons, and their structures were spectroscopically verified by NMR, ESI-MS and optical rotation data. Their QSI by the disc diffusion assay and minimum inhibitory concentrations (MIC) against 14 clinical bacterial isolates in microtiter plates were determined. Results: cembradiene 1, the AKG mixture and AKG (2S)-3-O-dodecyl-1,2-propanediol 4 inhibit QS at the same concentration as kojic acid (10 µg/well or 20 µg/disc, respectively). In this study, the bioactive compounds 1, stearyl oleate 2, acylglycerol 3 and AKGs 4 and (2S)-3-O-tetradecyl-1,2-propanediol 5 showed in vitro IQS activity for the first time. Additionally, 4 and 5 displayed in vitro antibacterial activity against Listeria innocua and Staphylococcus aureus (MIC = 32 µg/mL for both 4 and 5), Enterococcus faecalis (128 µg/mL and 64 µg/mL respectively), Micrococcus luteus (128 µg/mL for both) and Brevibacillus brevis (Bacillus brevis) (512 µg/mL and 64 µg/mL respectively). Conclusion: results suggest that natural compounds 1, 2, 3, 4 and 5 showed QSI, also 4 and 5 have antibacterial activity and they are an interesting alternative to continue researching their effect against pathogenic microorganisms.

Antecedentes: la aparición de resistencia bacteriana ha llevado a la búsqueda de nuevos productos naturales como puntos de partida alternativos para prevenir y controlar las enfermedades causadas por microorganismos. Entre los posibles candidatos se encontraban los compuestos bioactivos de octocorales del género Eunicea debido a sus estructuras químicas y su gama amplia de actividades biológicas. Objetivos: el propósito de este estudio fue evaluar la inhibición del quorum sensing (IQS) y la actividad antibacteriana de compuestos aislados previamente de dos especies de Eunicea y de alquilgliceroles (AQG) sintetizados. Métodos: la IQS de tres compuestos no polares y de una mezcla de AQGs de Eunicea se evaluaron mediante un ensayo de placa de microtitulación usando Chromobacterium violaceum (ATCC 31532). Cuatro AQG naturales, saturados y enantioméricamente puros, todos los cuales se derivaron del precursor quiral (R)-solketal, se sintetizaron a partir de cadenas alquílicas de 12, 14, 16 y 18 carbonos, y sus estructuras se verificaron espectroscópicamente mediante RMN, ESI-MS y datos de rotación óptica. Se determinó su IQS mediante el ensayo de difusión de disco y las concentraciones inhibitorias mínimas (CIM) en placas de microtitulación frente a 14 aislamientos bacterianos clínicos. Resultados: cembradieno 1, la mezcla de AQGs y AQG (2S)-3-O-dodecil-1,2-propanodiol 4 inhiben el QS a la misma concentración que el ácido kójico (10 µg/pocillo o 20 µg/disco, respectivamente). En este estudio, los compuestos bioactivos 1, estearil oleato 2, acilglicerol 3 y AQGs 4 y (2S)-3-O-tetradecil-1,2-propanodiol 5 mostraron actividad de IQS in vitro por primera vez. Además, 4 y 5 presentaron actividad antibacteriana in vitro contra Listeria innocua y Staphylococcus aureus (CIM = 32 µg/mL para 4 y 5), Enterococcus faecalis (128 µg/mL y 64 µg/mL respectivamente), Micrococcus luteus (128 µg/mL para ambos) y Brevibacillus brevis (Bacillus brevis) (512 µg/ mL y 64 µg/mL respectivamente). Conclusiones: los resultados sugieren que los compuestos naturales 1, 2, 3, 4 y 5 mostraron IQS, también 4 y 5 tenían actividad antibacteriana y son una alternativa interesante para continuar investigando su efecto contra microorganismos patógenos.

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