Pseudomonas rhizosphaerae sp. nov., a novel species that actively solubilizes phosphate in vitro

Abstract

A bacterial strain (designated IH5 T ), isolated from rhizospheric soil of grasses growing spontaneously in Spanish soil, actively solubilized phosphates in vitro when bicalcium phosphate was used as a phosphorus source. This strain was Gram-negative, strictly aerobic, rod-shaped and motile. The strain produced catalase, but not oxidase. Cellulose, casein, starch, gelatin, aesculin and urea were not hydrolysed. Growth was observed with many carbohydrates as the carbon source. The main non-polar fatty acids detected were hexadecenoic acid (C 16 : 1 ), hexadecanoic acid (C 16 : 0 ) and octadecenoic acid (C 18 : 1 ). The hydroxy fatty acids detected were 3-hydroxydecanoic acid (C 10 : 0 3-OH), 3-hydroxydodecanoic acid (C 12 : 0 3-OH) and 2-hydroxydodecanoic acid (C 12 : 0 2-OH). Phylogenetic analysis of 16S rRNA indicated that this bacterium belongs to the genus Pseudomonas in the c-subclass of the Proteobacteria and that the closest related species is Pseudomonas graminis. The DNA G+C content was 61 mol%. DNA-DNA hybridization showed 23 % relatedness between strain IH5 T and P. graminis DSM 11363 T . Therefore, strain IH5 T belongs to a novel species from the genus Pseudomonas, for which the name Pseudomonas rhizosphaerae sp. nov. is proposed (type strain, IH5 T =LMG 21640 T =CECT 5726 T ).Phosphorus is an essential plant nutrient that is added to soil as soluble inorganic phosphates, a large proportion of which becomes insoluble and therefore unavailable to plants (Singh & Kapoor, 1994). Many species of bacteria are able to solubilize phosphates in vitro and most of them live in the plant rhizosphere. At present, bacilli, rhizobia and pseudomonads are the most studied phosphate-solubilizers (Rodríguez & Fraga, 1999). Nevertheless, only a small number of species that presently belong to the genus Pseudomonas sensu stricto are known to be phosphatesolubilizers and they all belong to rRNA group I (Palleroni et al., 1973;Palleroni, 1992). Pseudomonas putida (Viveganandan & Jauhri, 2000;Kumar & Singh, 2001;Manna et al., 2001; Villegas & Fortin, 2002), Pseudomonas aeruginosa (Musarrat et al., 2000), Pseudomonas corrugata (Pandey & Palni, 1998), Pseudomonas stutzeri (Vázquez et al., 2000) and Pseudomonas fluorescens (Di Simine et al., 1998;Deubel et al., 2000) are the most studied species. Nevertheless, many rhizospheric, phosphate-solubilizing bacterial species remain unknown and more studies are needed to reveal the high biodiversity of these bacteria. Although the study of rhizospheric bacteria is difficult, due to the high number of bacteria present in soil, characterization and identification of these bacteria are necessary for wide ecological studies of the plant rhizosphere.During a wide study of phosphate-solubilizing, rhizospheric bacteria in soils from northern Spain, we isolated a strain that produced a yellow pigment in media that contained glucose as the carbon source and formed a transparent 'halo' around its colonies in media that contained insoluble bicalcium phosphate as the phosphorus source.A sample...

Pseudomonas argentinensis sp. nov., a novel yellow pigment-producing bacterial species, isolated from rhizospheric soil in Córdoba, Argentina

“…Moreover, several Pseudomonas species producing yellow pigments have been isolated and described, mostly from plant materials. These include Pseudomonas oryzihabitans (Kodama et al, 1985;Anzai et al, 1997), Pseudomonas flavescens (Hildebrand et al, 1994), Pseudomonas straminea (Uchino et al, 2000), Pseudomonas graminis (Behrendt et al, 1999), and the very recently described Pseudomonas rhizosphaerae and Pseudomonas lutea (Peix et al, 2003(Peix et al, , 2004. According to the 16S rRNA gene sequences, all of these species of Pseudomonas are included in rRNA group I (Palleroni et al, 1973;Palleroni, 1992).…”

“…All the methods used gave the same results (data not shown). Together with the closest relative, P. straminea IAM 1598 T , all the type strains of species of the genus Pseudomonas sensu stricto, according to Anzai et al (2000), other species of Pseudomonas with validly published names listed in Peix et al (2003), including the recently described novel species P. rhizosphaerae and P. lutea (Peix et al, 2003(Peix et al, , 2004, and the closely related species previously reclassified from Pseudomonas fulva (Iizuka & Komagata, 1963) by Uchino et al (2001), P. fulva, Pseudomonas parafulva and Pseudomonas cremoricolorata, were included in the analysis. Fig.…”

“…They were compared with sequences retrieved from GenBank by using the BLAST program (Altschul et al, 1990), and aligned by using CLUSTAL_X software (Thompson et al, 1997). The sequences were analysed by using the parameters and methods previously used for P. rhizosphaerae (Peix et al, 2003). Bootstrap analysis was based on 1000 resamplings.…”

Photobacterium halotolerans sp. nov., isolated from Lake Martel in Spain

“…The cells were also stained according to the classic Gram procedure described by Doetsch (1981). For electron microscopy, cells were grown on nutrient agar for 2 days at 22 u C. Cells were gently suspended in sterile water and then stained with 0?2 % uranyl acetate and examined at 80 kV with a Zeiss EM 209 transmission electron microscope (Peix et al, 2003).Extraction and amplification of genomic DNA for 16S rRNA sequence analysis were carried out as described previously and the recA and rpoA genes were amplified and sequenced as described by Thompson et al (2005a, b). The sequences of these genes were compared against the sequences available from GenBank using the BLASTN programme (Altschul et al, 1990) and were aligned using CLUSTAL X software (Thompson et al, 1997).…”

“…The cells were also stained according to the classic Gram procedure described by Doetsch (1981). For electron microscopy, cells were grown on nutrient agar for 2 days at 22 u C. Cells were gently suspended in sterile water and then stained with 0?2 % uranyl acetate and examined at 80 kV with a Zeiss EM 209 transmission electron microscope (Peix et al, 2003).…”