Multi-host lifestyle in plant-beneficial bacteria: an evolutionary advantage for survival and dispersal?

Plants harbour a wide diversity of microorganisms that efficiently colonize different internal and external plant organs and compartments, including the phyllosphere (above-ground plant surface), spermosphere (seeds and area surrounding seeds), endosphere (internal tissues) and rhizosphere (roots and soil in the vicinity of plant roots), establishing complex and dynamic interactions with the host plants (Trivedi et al., 2020). The plant microbiome plays major roles in the nutrition, growth and resistance against biotic and abiotic threats (Trivedi et al., 2020; Bakker and Berendsen, 2022; Yuan et al., 2022) and there is complex communication between microorganisms and their plant hosts (Berlanga- Clavero et al., 2020; Rico-Jiménez et al., 2022). Indeed, the secretion of a great variety of plant compounds directs the assembly of plant-associated microbial communities and it has been proposed that plants produce a range of chemical signals to selectively recruit specific microorganisms in order to assemble protective microbiomes that enable them to cope with the imposed biotic and abiotic stresses (Rizaludin et al., 2021; Rolli et al., 2021; Trivedi et al., 2022). As a consequence of this selective pressure exerted by the plants, the microbial composition of the rhizosphere and the non-rooted bulk soil differ – with the rhizosphere having a larger microbial abundance but lower diversity (Berlanga- Clavero et al., 2020; Sokol et al., 2022).Spanish Ministry for Science and Innovation/Agencia Estatal de Investigacion PID2019-103972GA-I00 RYC2019-026481-

The emerging role of auxins as bacterial signal molecules: Potential biotechnological applications

This study was supported through grants from the Spanish Ministry for Science and Innovation/Agencia Estatal de Investigación 10.13039/501100011033 (PID2019-103972GA-I00 to M.A.M., PID2020- 112612GB-I00 to T.K. and PID2020-116261GB-I00 to J.A.G.) and the Junta de Andalucía (grant P18- FR-1621 to T.K.). A.R. was supported by the Ramon y Cajal R&D&i Programme (RYC2019- 026481-I) from the Spanish Ministry for Science and Innovation/Agencia Estatal de Investigación 10.13039/501100011033 y FSE ‘El FSE invierte en tu futuro’.Microorganisms are exposed in their natural niches to a wide diversity of sig- nal molecules. Specific detection of these signals results in alterations in mi- crobial metabolism and physiology. Auxins like indole-3-acetic acid are key phytohormones that regulate plant growth and development. Nonetheless, auxin biosynthesis is not restricted to plants but is ubiquitous in all kingdoms of life. This wide phylogenetic distribution of auxins production, together with the diversity of regulated cellular processes, have made auxins key intra- and inter-kingdom signal molecules in life modulating, for example microbial physiology, metabolism and virulence. Despite their increasing importance as global signal molecules, the mechanisms by which auxins perform their regu- latory functions in microorganisms are largely unknown. In this article, we outline recent research that has advanced our knowledge of the mechanisms of bacterial auxin perception. We also highlight the potential applications of this research in aspects such as antibiotic production, biosensor design, plant microbiome engineering and antivirulence therapies.Spanish Ministry for Science and Innovation/Agencia Estatal de Investigacion PID2020-112612GB-I00, PID2020-116261GB-I00, RYC2019- 026481-IJunta de Andalucia P18-FR-1621, PID2019-103972GA-I0

Potential of the quorum-quenching and plant-growth promoting halotolerant Bacillus toyonensis AA1EC1 as biocontrol agent

The use of fertilizers and pesticides to control plant diseases is widespread in intensive farming causing adverse effects together with the development of antimicrobial resistance pathogens. As the virulence of many Gram-negative phytopathogens is controlled by N-acyl- homoserine lactones (AHLs), the enzymatic disruption of this type of quorum-sensing (QS) signal molecules, mechanism known as quorum quenching (QQ), has been proposed as a promising alternative antivirulence therapy. In this study, a novel strain of Bacillus toyonensis isolated from the halophyte plant Arthrocaulon sp. exhibited numerous traits associated with plant growth promotion (PGP) and degraded a broad range of AHLs. Three lactonases and an acylase enzymes were identified in the bacterial genome and verified in vitro. The AHL-degrading activity of strain AA1EC1 significantly attenuated the virulence of relevant phytopathogens causing reduction of soft rot symptoms on potato and carrots. In vivo assays showed that strain AA1EC1 significantly increased plant length, stem width, root and aerial dry weights and total weight of tomato and protected plants against Pseudomonas syringae pv. tomato. To our knowledge, this is the first report to demonstrate PGP and QQ activities in the species B. toyonensis that make this strain as a promising phytostimulant and biocontrol agent.Spanish Ministry for Science and Innovation/Agencia Estatal de Investigación 10.13039/501100011033ESF Investing in your future (Grant: RYC2019- 026481-I)Spanish Ministry for Science and Innovation/Agencia Estatal de Investigación 10.13039/501100011033 (Grant: PID2019-106704RB-100)Consejería de Universidad, Investigación e Innovación de la Junta de AndalucíaERDF A way of making Europe (Grant: B-AGR-222-UGR20

Estudio del metabolismo del formaldehído en Pseudomonas putida KT2440

Tesis Univ. Granada. Departamento de Fisiología Vegetal. Leída el 10 de noviembre de 200

Histamine: A Bacterial Signal Molecule

This work was supported by FEDER funds and the Fondo Social Europeo through grants from the CSIC to M.A.M. (PIE-202040I003), the Spanish Ministry for Science, Innovation and Universities to M.A.M. (PID2019-103972GA-I00), the Junta de Andalucia to T.K. (P18-FR-1621) and Spanish Ministry of Economy and Competitiveness (BIO2016-76779-P to T.K. and BIO2016-74875-P to J.A.G.). A.R. was supported by the Spanish Ministry of Science and Innovation, Promotion of Talent and its Employability-Ramon y Cajal R&D&i Programme (RYC2019-026481-I).Bacteria have evolved sophisticated signaling mechanisms to coordinate interactions with organisms of other domains, such as plants, animals and human hosts. Several important signal molecules have been identified that are synthesized by members of different domains and that play important roles in inter-domain communication. In this article, we review recent data supporting that histamine is a signal molecule that may play an important role in inter-domain and inter-species communication. Histamine is a key signal molecule in humans, with multiple functions, such as being a neurotransmitter or modulator of immune responses. More recent studies have shown that bacteria have evolved different mechanisms to sense histamine or histamine metabolites. Histamine sensing in the human pathogen Pseudomonas aeruginosa was found to trigger chemoattraction to histamine and to regulate the expression of many virulence-related genes. Further studies have shown that many bacteria are able to synthesize and secrete histamine. The release of histamine by bacteria in the human gut was found to modulate the host immune responses and, at higher doses, to result in host pathologies. The elucidation of the role of histamine as an inter-domain signaling molecule is an emerging field of research and future investigation is required to assess its potential general nature.European CommissionFondo Social Europeo through CSIC PIE-202040I003Spanish Ministry for Science, Innovation and Universities PID2019-103972GA-I00Junta de Andalucia P18-FR-1621Spanish Ministry of Economy and Competitiveness BIO2016-76779-P BIO2016-74875-PSpanish Ministry of Science and Innovation, Promotion of Talent and its Employability-Ramon y Cajal RDi Programme RYC2019-026481-