Abstract
Species of genus Shewanella are among the most frequently identified psychrotrophic bacteria. Here, we have studied the cellular properties, growth dynamics, and stress conditions of cold-active Shewanella strain #4, which was previously isolated from Baltic Sea ice. The cells are rod-shaped of ~2μm in length and 0.5μm in diameter, and they grow between 0 and 25°C, with an optimum at 15°C. The bacterium grows at a wide range of conditions, including 0.5–5.5% w/v NaCl (optimum 0.5–2% w/v NaCl), pH 5.5–10 (optimum pH 7.0), and up to 1mM hydrogen peroxide. In keeping with its adaptation to cold habitats, some polyunsaturated fatty acids, such as stearidonic acid (18:4n-3), eicosatetraenoic acid (20:4n-3), and eicosapentaenoic acid (20:5n-3), are produced at a higher level at low temperature. The genome is 4,456kb in size and has a GC content of 41.12%. Uniquely, strain #4 possesses genes for sialic acid metabolism and utilizes N-acetyl neuraminic acid as a carbon source. Interestingly, it also encodes for cytochrome c3 genes, which are known to facilitate environmental adaptation, including elevated temperatures and exposure to UV radiation. Phylogenetic analysis based on a consensus sequence of the seven 16S rRNA genes indicated that strain #4 belongs to genus Shewanella, closely associated with Shewanella aestuarii with a ~97% similarity, but with a low DNA–DNA hybridization (DDH) level of ~21%. However, average nucleotide identity (ANI) analysis defines strain #4 as a separate Shewanella species (ANI score=76). Further phylogenetic analysis based on the 92 most conserved genes places Shewanella strain #4 into a distinct phylogenetic clade with other cold-active marine Shewanella species. Considering the phylogenetic, phenotypic, and molecular characterization, we conclude that Shewanella strain #4 is a novel species and name it Shewanella glacialimarina sp. nov. TZS-4T, where glacialimarina means sea ice. Consequently, S. glacialimarina TZS-4T constitutes a promising model for studying transcriptional and translational regulation of cold-active metabolism.
Highlights
MATERIALS AND METHODSThe genus Shewanella belongs to the order Alteromonadales of class Gammaproteobacteria
Bacterial strain S. glacialimarina TZS-4T was originally isolated from the Baltic Sea ice outside of Tvärminne Zoological station, Hanko, Finland, and cultivated on Zobell media containing undefined Baltic Sea water (Luhtanen et al, 2014)
To standardize the growth media and remove any influence of seasonal fluctuation in seawater composition, we investigated if marine broth (MB) could be used to cultivate S. glacialimarina TZS-4T
Summary
The genus Shewanella belongs to the order Alteromonadales of class Gammaproteobacteria. Certain Shewanella species, such as S. putrefaciens and S. baltica, have been associated with spoilage of fishery food products due to their psychrotrophic nature, which permits growth at low temperatures (Jørgensen and Huss, 1989; Vogel et al, 2005) These bacteria reduce trimethylamine-N-oxide (TMAO) to trimethylamine (TMA), which generates a pungent odor that alongside hydrogen sulfide (H2S) gas, produced by degradation of amino acids, further exacerbates the spoilage process (Gram et al, 1987). Temperature, pH, and Salinity Conditions The cells were prepared in rMB media as described in section Growth Conditions, except for the starter culture to assess growth at 0°C, which was grown at 4°C for 48 h (necessary for growth at 0°C). The cells were grown, as described in section Growth Conditions, in 10 ml of M-9 minimal media using starter cultures grown in rMB. GenBank accession numbers of Shewanella whole genome sequences used for fastANI and UBCG analysis were as follows: NZ_CP050313.1, NZ_CP047422.1, NZ_CP018456.1, NZ_ CP033575.1, NZ_CP046378.1, NC_008700.1, NC_017571.1, NC_017579.1, NC_009052.1, NC_009665.1, NC_009997.1, NC_011663.1, NC_016901.1, NZ_CP028730.1, NZ_CP028355.1, NZ_LS483452.1, NZ_CP022358.1, NZ_CP045857.1, NC_007954.1, NZ_CP041783.1, NC_008345.1, NC_010334.1, NZ_CP020472.1, NZ_CP020373.1, NZ_CP034015.1, NC_009092.1, NZ_CP041153.1, NZ_CP022272.1, NZ_CP036200.1, NC_004347.2, NC_009901.1, NC_011566.1, NZ_CP041036.1, NZ_CP014782.1, NC_017566.1, NC_009438.1, NZ_CP046329.1, NZ_LR134321.1, NZ_LR134303.1, NZ_CP028435.1, NC_009831.1, NC_008577.1, NZ_CP048031.1, NZ_CP022089.2, NZ_CP039928.1, NC_008321.1, NC_008322.1, NZ_CP015194.1, NZ_CP041329.1, NZ_CP041151.1, NC_008750.1, NZ_CP023019.1, NZ_CP041614.1, NC_014012.1, and NC_010506.1
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