Summary auto-generated
Researchers isolated three Gram-negative, facultatively alkaliphilic bacterial strains from Japanese seawater that grow optimally at neutral to alkaline pH and at cool temperatures (4-30°C). These rod-shaped, polar-flagellated bacteria were characterized using phenotypic tests, chemotaxonomic analysis, and molecular methods. They possessed ubiquinone-9 as their major quinone and distinctive fatty acid profiles that changed based on growth pH. Sequence analysis of the 16S rRNA gene showed the strains clustered within the Pseudomonas genus, specifically related to P. mendocina subgroup members. However, DNA-DNA hybridization values (23-60% similarity) with closely related Pseudomonas species were significantly below the threshold for species classification, indicating these isolates represented a new species. The strains required sodium chloride for growth at pH 10 but not at neutral pH, suggesting different transport mechanisms operate at different pH values. Notably, the relative abundance of trans-unsaturated fatty acids increased when cells grew at neutral pH compared to alkaline pH, marking the first observation of cis-trans fatty acid isomerization in response to ambient pH. Based on all evidence, researchers formally proposed Pseudomonas alcaliphila sp. nov. as the name for this novel alkaliphilic bacterium.
Key findings
- Three novel Gram-negative bacterial strains isolated from seawater are identified as a new species, Pseudomonas alcaliphila, based on 16S rRNA sequencing and DNA-DNA hybridization data showing <61% similarity to related species
- P. alcaliphila is a facultatively psychrophilic alkaliphile that grows at 4-30°C and requires NaCl only at pH 10, suggesting pH-dependent ion-transport systems
- The bacteria exhibit pH-dependent changes in fatty acid composition, with increased trans-unsaturated fatty acids at neutral pH compared to alkaline pH—the first report of cis-trans isomerization responding to pH
- Chemotaxonomic analysis confirms classification in Pseudomonas group I based on 3-hydroxy fatty acid composition, ubiquinone-9 presence, and DNA G-C content of 62.3-63.2 mol%
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Abstract
Facultatively psychrophilic alkaliphilic strains were isolated from seawater obtained off the coast of Rumoi, Hokkaido, Japan. They were Gram-negative, aerobic straight rods with polar flagella. The isolates were catalase- and oxidase-positive and able to grow at 4 degrees C, but not at 40 degrees C. They produced acid from D-glucose under aerobic conditions. The isolates reduced nitrate to nitrite and hydrolysed casein and gelatin, but not starch or DNA. NaCl was required for growth at pH 10 but was not required at neutral pH. The major isoprenoid quinone was ubiquinone-9 (Q-9) and the DNA G+C content was 62.3--63.2 mol%. The whole-cell fatty acids mainly consisted of C(16:0), C(16:1(9c)) and C(18:1(9c)), with 3-OH C(10:0) and 3-OH C(12:0) as the hydroxyl fatty acids. A larger amount of trans-unsaturated fatty acid, C(16:1(9t)) was observed when the cells were grown at pH 7 compared to when cells were grown at pH 10. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that the bacteria are members of the genus Pseudomonas. Analysis of DNA--DNA relatedness data with several close phylogenetic neighbours revealed a low level of hybridization (less than 61%). On the basis of phenotypic characteristics, phylogenetic analysis and DNA--DNA relatedness data, it is concluded that these isolates represent a separate new species. Accordingly, the name Pseudomonas alcaliphila is proposed. The type strain is AL15-21(T) (=JCM 10630(T)=IAM 14884(T)).