The Family Phyllobacteriaceae comprises a group of 19 genera of Alphaproteobacteria, commonly associated with Plants, with many species associated with nitrogen-fixation, nutrient cycling and bioremediation (converting toxic substances into non-toxic substances), although other species are found free-living in soil or water. Strains belonging to the family Phyllobacteriaceae are usually Gram-stain-negative, rod-shaped, aerobic, non-spore forming and non-motile or motile utilising polar, subpolar or lateral flagella. Many members of the genera Mesorhizobium and Phyllobacterium have Plant-growth-promoting properties, with Mesorhizobium in particular commonly associated with the rhizosphere (root-system and associated biological community) of Legumes, where some species have been shown both to fix nitrogen, which is then utilised by the Plants, and receive carbon compounds from the Plants in return. Members of the genus Aminobacter have also been shown to be capable of fixing nitrogen and in some cases to be associated with the root-nodules of Legumes, although this genus is typically free-living in soil or water, with some species surviving entirely chemolithotropicly, utilising carbon monoxide in the process.
In a paper published in the International Journal of Systematic and Evolutionary Microbiology on 3 November 2025, Sinchan Banerjee of the School of Life Sciences at the University of Warwick, András Táncsics of the Department of Molecular Ecology at the Hungarian University of Agriculture and Life Sciences, Zeqin Wu, Tudor Stafioiu, and Jiacheng Gao, also of the School of Life Sciences at the University of Warwick, Erika Tóth of the Department of Microbiology at Eötvös Loránd University, Erzsébet Baka, also of the Department of Molecular Ecology at the Hungarian University of Agriculture and Life Sciences, and Gary Bending and Hendrik Schäfer, again of the School of Life Sciences at the University of Warwick, describe a new species of Phyllobacterium, derived from the leaves of a Holly tree, with the ability to oxidise carbon monoxide.
Carbon monoxide is a common pollutant, produced by a range of industrial and other Human activities, and deadly to both Human and most Animal life. Notably, it is a significant product of biomass burning, which many countries are looking to as a potential energy source as they try to move away from a dependence on fossil fuels. Carbon monoxide is also produced by a range of natural occurrences, from forest fires to rock weathering, but does not build up in the environment, as it is also removed by a range of biological and non-biological processes. This means that carbon monoxide does not present a global atmosphere-changing threat, in the way that carbon dioxide or methane emissions do, but that it does represent a significant hazard at the local level, and that means of reducing that hazard are of interest to a range of researchers.
The phyllosphere, that part of Plants which is above the ground, presents a novel and often challenging environment for micro-organisms, with fluctuating exposure to heat and ultraviolet radiation, nutrient supplies strictly controlled by the host-Plant, and, frequently, exposure to a range of environmental pollutants.
Banerjee et al. collected Common Holly, Ilex aquifolium, leaves from Tocil Wood Nature Reserve in Coventry, UK. Leaf-wash preparations were made from these, and stored in vials with the headspace filled with carbon monoxide. Samples where the carbon monoxide level was found to drop were placed on agar plates, and incubated at 25°C for five days, to promote Bacterial growth.
The resultant colonies were subject to 16S rRNA gene sequence analysis, which established that Banerjee et al. had found a novel Barcterial strain, which they identified as SB112ᵀ. This strain was then subjected to a full genome phylogenomic analysis, establishing that it was a novel species of Phyllobacterium, related to the genus Mesorhizobium.
Since SB112ᵀ does not appear to fir into any currently designated genus, Banerjee et al. assign it to a new genus, which they name Foliimonas, which is derived from 'folium' meaning 'leaf' and 'monas' meaning 'unit' (a common suffix for Bacterial names), and give it the specific name ilicis, meaning 'of the Holly Tree'.
Foliimonas ilicis is a Gram- reaction- negative, aerobic, rod-shaped Bacterium, which is motile with a polar flagellum. Cells have an average length of 1.18 μm. The species has an optimum growth range of 20-37°C, with growth stopping completely below 4°C. Foliimonas ilicis can oxidise carbon monoxide, but is unable to reduce nitrous oxides of ferric citrate. It produces esterase (C4), esterase lipase (C8), leucine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase, valine arylamidase, cystine arylamidase and trypsin, but not urase. It could assimilate d-glucose, l-arabinose, d-mannitol, d-mannose, potassium gluconate and malic acid, and metabolise l-arabinose, d-xylose and xylitol.
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