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12 páginas, 4 figuras y 2 tablas., The pine engraver beetle, Ips acuminatus Gyll, is a bark beetle that causes important damages in Scots pine (Pinus sylvestris) forests and plantations. As almost all higher organisms, Ips acuminatus harbours a microbiome, although the role of most members of its microbiome is not well understood. As part of a work in which we analysed the bacterial diversity associated to Ips acuminatus, we isolated the strain Arthrobacter sp. IA7. In order to study its potential role within the bark beetle holobiont, we sequenced and explored its genome and performed a pan-genome analysis of the genus Arthrobacter, showing specific genes of strain IA7 that might be related with its particular role in its niche. Based on these investigations, we suggest several potential roles of the bacterium within the beetle. Analysis of genes related to secondary metabolism indicated potential antifungal capability, confirmed by the inhibition of several entomopathogenic fungal strains (Metarhizium anisopliae CCF0966, Lecanicillium muscarium CCF6041, L. muscarium CCF3297, Isaria fumosorosea CCF4401, I. farinosa CCF4808, Beauveria bassiana CCF4422 and B. brongniartii CCF1547). Phylogenetic analyses of the 16S rRNA gene, six concatenated housekeeping genes (tuf-secY-rpoB-recA-fusA-atpD) and genome sequences indicated that strain IA7 is closely related to A. globiformis NBRC 12137T but forms a new species within the genus Arthrobacter; this was confirmed by digital DNA-DNA hybridization (37.10%) and average nucleotide identity (ANIb) (88.9%). Based on phenotypic and genotypic features, we propose strain IA7T as the novel species Arthrobacter ipsi sp. nov. (type strain IA7T = CECT 30100T = LMG 31782T) and suggest its protective role for its host., The project was funded by Czech Science Foundation project GACR 19-09072S. ZSS received a grant from the Junta de Castilla y León, Spanish Regional Government, and LIGD received a grant supported by Junta de Castilla y León (Escalera de Excelencia CLU-2018-04), co-funded by the P.O. FEDER of Castilla y León 2014-2020.

Because of their plant-growth-promoting (PGP) properties, microbes play crucial roles in plant development, making them potential candidates for substituting chemical fertilizers, especially when the soil conditions are not the most appropriate to obtain maximum crop yields. This is the case of strain Pseudomonas brassicacearum CDVBN10, a bacterial endophyte isolated from rapeseed (Brassica napus) roots. Previous in vitro, in planta and in silico experiments have demonstrated that strain CDVBN10 has interesting PGP potential. This endophyte synthetizes cellulose, produces siderophores, solubilizes P, promotes plant height and root length in rapeseed seedlings, and carries genes implicated in several PGP pathways. Based on these data, we conducted greenhouse experiments using this strain as a biofertilizer under normal and salinity stress conditions, finding significant improvements in those inoculated plants, compared to the negative control. To prove its biofertilizer potential under field conditions, we carried out a field trial in which plants inoculated with CDVBN10 showed a 216%, 174.3%, and 197.8% increase in number of pods, seed weight, and aerial part weight, respectively. Along-read (SMRT; PacBio) 16S rRNA gene amplicon sequencing was performed in root samples from this field trials to study possible shifts on the rapeseed root microbiome due to the inoculation with CDVBN10. Interestingly, despite the great plant improvements, there were no significant differences in root bacterial communities of inoculated plants; thus, other potential beneficial members of the plant microbiome had not been displaced. According to the results, the strain P. brassicacearum CDVBN10 is suggested as a promising bacterial biofertilizer with great performance on B. napus crops.