The proteobacterial genus Pseudomonas consists of species with versatile metabolism and physiology, which are colonizing various aquatic, terrestrial and biotic environments. Since its discovery by Migula (1894), many new species have been added to this genus, now comprising more than 300 validly published species at the time of writing this manuscript (List of Prokaryotic Names with Standing in Nomenclature; https://lpsn.dsmz.de/genus/pseudomonas, accessed on 8 July 2022).

Representatives of the Pseudomonas genus display different lifestyles – some species are opportunistic human, insect or plant pathogens, some can be used in bioremediation, while others can act as Plant Growth-Promoting Rhizobacteria (PGPR) by providing phytostimulation and/or phytoprotection functions (Silby et al., 2011). MultiLocus Sequence Analysis (MLSA) of four housekeeping genes (the 16S rRNA gene rrs, gyrB, rpoB and rpoD) and Average Nucleotide Identity (ANI) comparisons revealed three distinct lineages within the Pseudomonas genus – referred to as the P. aeruginosa, P. fluorescens and P. pertucinogena lineages (Peix et al., 2018). However, this classification contained inconsistencies, as the genus Pseudomonas was not monophyletic and included genera such as Azotobacter and Azomonas (Nikolaidis et al., 2020, Rudra and Gupta, 2021, Saati-Santamaría et al., 2021). In 2021, two articles published one month apart developed a phylogenomic analysis of the genus Pseudomonas, proposing the reclassification of the monophyletic lineage of P. pertucinogena, which forms a clade distinct from the main Pseudomonas clade and consists of halotolerant species, into the genus ‘Neopseudomonas’ (Saati-Santamaría et al., 2021) or Halopseudomonas (Rudra and Gupta, 2021). They also repositioned the deep branching species Pseudomonas hussainii into a new genus termed ‘Parapseudomonas’ (Saati-Santamaría et al., 2021) or Aptomonas (Rudra and Gupta, 2021). Another phylogenomic study reclassified the P. stutzeri nitrogen-fixing clade and defined the new genus Stuzerimonas (Laculat et al., 2022). Together with the P. aeruginosa lineage, the P. fluorescens lineage remains in the Pseudomonas genus. The P. fluorescens lineage (the most complex and diverse) is often subdivided into six phylogenetic groups, branching further into nine subgroups, represented by the species P. fluorescens, P. gessardi, P. fragi, P. mandelii, P. jesseni, P. koreensis, P. corrugata, P. chlororaphis and P. asplenii (Mulet et al., 2010, Gomila et al., 2015, Peix et al., 2018). It is known that the P. fluorescens group contains a few phytopathogens (such as strains P. corrugata or P. mediterranea; Trantas et al., 2015) and various plant-beneficial species with properties such as siderophore production (Garrido-Sanz et al., 2016), phosphate solubilization (Meyer et al., 2010) and production of phytohormones (Vacheron et al., 2016, Keshavarz-Tohid et al., 2017), thus modulating plant growth. Besides, production of extracellular lytic enzymes such as chitinases, cellulases and proteases (Ali et al., 2019), as well as hydrogen cyanide (Frapolli et al., 2012) and various other antifungal secondary metabolites (Dutta et al., 2020) make some strains of the P. fluorescens group good candidates for biocontrol.

In the present study, four Pseudomonas strains were isolated from the rhizosphere of wheat grown in soils collected from different fields (some of them suppressive to Fusarium graminearum disease), located near Mionica, Serbia, and their genomes were fully sequenced in order to assign them at the species level. Genome sequence similarities of strains presented in this study and type strains from the closest, currently described Pseudomonas species were below the ANI and dDDH threshold levels established for differentiating bacterial species. These strains, belonging to the P. fluorescens group, were further described phenotypically and phylogenetically, and we propose the names Pseudomonas serbica (with IT-P366T as type strain) and Pseudomonas serboccidentalis (with IT-P374T as type strain) for these novel species.