Pseudoalteromonas rhizosphaerae sp. nov. , a novel plant growth-promoting bacterium with potential use in phytoremediation

Abstract

Strain RA15^T was isolated from the rhizosphere of the halophyte plant Arthrocnemum macrostachyum growing in the Odiel marshes (Huelva, Spain). RA15^T cells were Gram stain-negative, non-spore-forming, aerobic rods and formed cream-coloured, opaque, mucoid, viscous, convex, irregular colonies with an undulate margin. Optimal growth conditions were observed on tryptic soy agar (TSA) plates supplemented with 2.5 % NaCl (w/v) at pH 7.0 and 28 °C, although it was able to grow at 4-32 °C and at pH values of 5.0-9.0. The NaCl tolerance range was from 0 to 15 %. The major respiratory quinone was Q8 but Q9 was also present. The most abundant fatty acids were summed feature 3 (C_{16 : 1} ω7c and/or C_{16 : 1} ω6c), C_{17 : 1} ω8c and C_{16 : 0}. The polar lipids profile comprised phosphatidylglycerol and phosphatidylethanolamine as the most abundant representatives. Phylogenetic analyses confirmed the well-supported affiliation of strain RA15^T within the genus Pseudoalteromonas, close to the type strains of Pseudoalteromonas neustonica, Pseudoalteromonas prydzensis and Pseudoalteromonas mariniglutinosa. Results of comparative phylogenetic and phenotypic studies between strain RA15^T and its closest related species suggest that RA15^T could be a new representative of the genus Pseudoalteromonas, for which the name Pseudoalteromonas rhizosphaerae sp. nov. is proposed. The type strain is RA15^T (=CECT 9079^T=LMG 29860^T). The whole genome has 5.3 Mb and the G+C content is 40.4 mol%.

Keywords: Arthrocnemum macrostachyum; heavy metals; nitrogen fixation; odiel marshes; rhizosphere.

Fig. 1.

Total lipid profiles (labelled by the Rf values) of strain RA15^T after separation by two-dimensional TLC using the solvents chloroform/methanol/water (65 : 25 : 4, by vol.) in the first dimension and chloroform/methanol/acetic acid/water (80 : 12 : 15 : 4, by vol.) in the second dimension. Plates were sprayed with molybdatophosphoric acid (3.5 %; Merck) for detection of total polar lipids. PE, phosphatidylethanolamine; PG, phosphatidylglycerol; AL1–2, unidentified aminolipids.

Fig. 2.

Maximum-likelihood phylogenetic tree inferred from 16S rRNA gene sequences, showing the phylogenetic position of strain RA15^T relative to type strains of species within the genus Pseudoalteromonas . The branches are scaled in terms of the expected number of substitutions per site. Support values obtained from 1000 replicates from maximum-likelihood (left) and maximum-parsimony (right) bootstrapping are shown above the branches if ≥60 %. Sequence accession numbers are given in parentheses.