The genus Halomonas belongs to the family Halomonadaceae of the order Oceanospirillales, within the phylum Pseudomonadota, and was established in 1980 (Vreeland et al., 1980). At present, genus Halomonas contained more than 120 species with valid published name listed in LPSN (https://lpsn.dsmz.de/genus/halomonas) (Parte et al., 2020). Halomonas strains are usually Gram-stain-negative, aerobic or facultatively anaerobic, halophilic or halotolerant, and non-spore forming bacteria (Vreeland et al., 1980) and take Q-9 as the major respiratory quinone, and C16 : 0, Summed Feature 8, C17 : 0 cyclo, Summed Feature 3, and C19 : 0 cyclo ω8c as the major fatty acids (Arahal et al., 2007, Li et al., 2023; Lin et al., 2023; Ventosa et al., 2013). Halomonas is widely distributed within hypersaline environments, for example, salt and soda lakes, saline soils, seafood, marine invertebrates, and seawater (Shang et al., 2022). Halomonas strains play an important role in carbon and nitrogen recycling within ecosystems. For example, numerous Halomonas strains were able to degrade toxic organic compounds, such as reactive red-195 (Saha et al., 2022), polycyclic aromatic hydrocarbons (Cheffi et al., 2020; Govarthanan et al., 2021), crude oil (Neifar et al., 2019), benzoate, salicylate, and phenol (Alva and Peyton, 2003, Oie et al., 2007). Many of the strains can remove nitrogen from wastewater via denitrification (Huang et al., 2023, Wang et al., 2019, Wang et al., 2017).Fig 1.Fig 2.

Vanillic acid (VA), a common allelochemical, is released as an intermediate from the lignin-degradation process that occurs in soil. High VA concentration not only affect soil microbial communities, but also inhibit plant growth and development (Shao et al., 2021). Although some bacteria, such as Sphingobacterium sp. HY-H (Wang et al., 2018), are known to degrade soil VA, very few reports exist concerning the VA degradation by Halomonas strains.

Kalidium cuspidatum is a euhalophyte and plays a key role in carbon and energy fixation, as well as maintaining ecological stability in saline-alkaline soils. During an ongoing project on the diversity of phenolic acids-degrading bacteria in the rhizosphere of Kalidium cuspidatum, four halophilic VA-degrading bacterial strains were isolated from the rhizosphere soils or bulk saline soil. This study presents accurate taxonomic classification of all these strains using a polyphasic taxonomic method, and elucidates the VA degradation mechanism of these four strains using genome annotation.