Shewanella marina sp. nov., isolated from seawater

Novel Insights on Extracellular Electron Transfer Networks in the Desulfovibrionaceae Family: Unveiling the Potential Significance of Horizontal Gene Transfer

Some sulfate-reducing bacteria (SRB), mainly belonging to the Desulfovibrionaceae family, have evolved the capability to conserve energy through microbial extracellular electron transfer (EET), suggesting that this process may be more widespread than previously believed. While previous evidence has shown that mobile genetic elements drive the plasticity and evolution of SRB and iron-reducing bacteria (FeRB), few have investigated the shared molecular mechanisms related to EET. To address this, we analyzed the prevalence and abundance of EET elements and how they contributed to their differentiation among 42 members of the Desulfovibrionaceae family and 23 and 59 members of Geobacteraceae and Shewanellaceae, respectively. Proteins involved in EET, such as the cytochromes PpcA and CymA, the outer membrane protein OmpJ, and the iron-sulfur cluster-binding CbcT, exhibited widespread distribution within Desulfovibrionaceae. Some of these showed modular diversification. Additional evidence revealed that horizontal gene transfer was involved in the acquiring and losing of critical genes, increasing the diversification and plasticity between the three families. The results suggest that specific EET genes were widely disseminated through horizontal transfer, where some changes reflected environmental adaptations. These findings enhance our comprehension of the evolution and distribution of proteins involved in EET processes, shedding light on their role in iron and sulfur biogeochemical cycling.

Whole-Genome Sequencing Redefines Shewanella Taxonomy

The genus Shewanella encompasses a diverse group of Gram negative, primarily aquatic bacteria with a remarkable ecological relevance, an outstanding set of metabolic features and an emergent clinical importance. The rapid expansion of the genus over the 2000 s has prompted questions on the real taxonomic position of some isolates and species. Recent work by us and others identified inconsistencies in the existing species classification. In this study we aimed to clarify such issues across the entire genus, making use of the genomic information publicly available worldwide. Phylogenomic analyses, including comparisons based on genome-wide identity indexes (digital DNA-DNA hybridization and Average Nucleotide Identity) combined with core and accessory genome content evaluation suggested that the taxonomic position of 64 of the 131 analyzed strains should be revisited. Based on the genomic information currently available, emended descriptions for some Shewanella species are proposed. Our study establishes for the first time a whole-genome based phylogeny for Shewanella spp. including a classification at the subspecific level.

Multilocus Sequence Analysis, a Rapid and Accurate Tool for Taxonomic Classification, Evolutionary Relationship Determination, and Population Biology Studies of the Genus Shewanella

The genus Shewanella comprises a group of marine-dwelling species with worldwide distribution. Several species are regarded as causative agents of food spoilage and opportunistic pathogens of human diseases. In this study, a standard multilocus sequence analysis (MLSA) based on six protein-coding genes (gyrA, gyrB, infB, recN, rpoA, and topA) was established as a rapid and accurate identification tool in 59 Shewanella type strains. This method yielded sufficient resolving power in regard to enough informative sites, adequate sequence divergences, and distinct interspecies branches. The stability of phylogenetic topology was supported by high bootstrap values and concordance with different methods. The reliability of the MLSA scheme was further validated by identical phylogenies and high correlations of genomes. The MLSA approach provided a robust system to exhibit evolutionary relationships in the Shewanella genus. The split network tree proposed twelve distinct monophyletic clades with identical G+C contents and high genetic similarities. A total of 86 tested strains were investigated to explore the population biology of the Shewanella genus in China. The most prevalent Shewanella species was Shewanella algae, followed by Shewanella xiamenensis, Shewanella chilikensis, Shewanella indica, Shewanella seohaensis, and Shewanella carassii The strains frequently isolated from clinical and food samples highlighted the importance of increasing the surveillance of Shewanella species. Based on the combined genetic, genomic, and phenotypic analyses, Shewanella upenei should be considered a synonym of S. algae, and Shewanella pacifica should be reclassified as a synonym of Shewanella japonica IMPORTANCE The MLSA scheme based on six housekeeping genes (HKGs) (gyrA, gyrB, infB, recN, rpoA, and topA) is well established as a reliable tool for taxonomic, evolutionary, and population diversity analyses of the genus Shewanella in this study. The standard MLSA method allows researchers to make rapid, economical, and precise identification of Shewanella strains. The robust phylogenetic network of MLSA provides profound insight into the evolutionary structure of the genus Shewanella The population genetics of Shewanella species determined by the MLSA approach plays a pivotal role in clinical diagnosis and routine monitoring. Further studies on remaining species and genomic analysis will enhance a more comprehensive understanding of the microbial systematics, phylogenetic relationships, and ecological status of the genus Shewanella.

Methods for identification and differentiation of different Shewanella spp. isolates for diagnostic use

Shewanella spp. are Gram-negative, rod-shaped, motile bacteria that are widely distributed in marine and freshwater environments. The bacteria are present in the physiological microflora of fish from temperate waters and are known as fish spoilage species. From clinically healthy fish and from fish with skin ulcerations, Shewanella spp. is regularly isolated, indicating a possible role as fish pathogen. In this study, 74 isolates of Shewanella spp. were analysed. For species identification, biochemical techniques, 16S rRNA sequencing, MALDI-TOF MS and the Sherlock Microbial Identification System (MIS) based on the composition of fatty acid ethyl esters were compared. The phylogenetic relationship, cytotoxicity in vitro and resistance against antibiotics were tested. The most reliable method for species identification was 16S rRNA sequencing. From diseased fish, clinically healthy fish and the aquatic environment, different Shewanella species were isolated. This indicates that Shewanella spp. is widespread in the aquatic milieu and acts as a secondary pathogen. The virulence of Shewanella spp. is probably not depending on the species but on the isolate itself. Many isolates of Shewanella spp. were showing multiresistances against antibiotic substances, especially in samples derived from retailers and in routine diagnostics, all Shewanella spp. should therefore be tested for resistances against antibiotic agents.

Shewanella carassii sp. nov., isolated from surface swabs of crucian carp and faeces of a diarrhoea patient

Two strains, 08MAS2251^T and LZ2016-166, were isolated from diverse samples in China collected from the surface of crucian carp and the faeces of a diarrhoea patient, respectively. Both strains were pink-orange coloured, Gram-negative, oxidase- and catalase-positive, facultative anaerobic and motile bacteria, produced H2S and reduced nitrates to nitrites. Growth occurred in the presence of 0-9 % (w/v) NaCl and at 10-42 °C. The optimum conditions were with 1 % (w/v) NaCl and at 35 °C. The phylogenetic tree of 16S rRNA gene demonstrated that strains 08MAS2251^T and LZ2016-166 clustered in a distinctive clade next to the species Shewanella chilikensis JC5^T within the genus Shewanella. Meanwhile, gyrB gene sequence analysis indicated that the two strains formed an independent branch that was clearly separate from all the other Shewanella species with sequence similarities from 68.49 to 95.74 %. The DNA G+C content of strain 08MAS2251^T was 52.68 mol%. Genomic relatedness of in silico DNA-DNA hybridization between strain 08MAS2251^T and phylogenetic neighbours ranged from 50.5-51.8 %, below the cutoff of 70 %. In addition, corresponding average nucleotide identity values were between 93.01 to 93.49%, which were lower than 95 % threshold. The major fatty acids of strain 08MAS2251^T were C17 : 1ω8c (27.2 %), iso-C15 : 0 (22.5 %), summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c; 8.7 %), C16 : 0 (6.2 %), iso-C13 : 0 (5.6 %) and C17 : 0 (4.5 %). Based on phenotypic and genetic analysis, strains 08MAS2251^T and LZ2016-166 are identified as a novel species of the genus Shewanella, for which the name Shewanellacarassii sp. nov. is proposed. The type strain is 08MAS2251^T (=DSM 104682^T=CGMCC 1.16033^T).

Shewanella algicola sp. nov., a marine bacterium isolated from brown algae

A Gram-stain-negative, aerobic, rod-shaped bacterium motile by means of a single polar flagella, strain ST-6T, was isolated from a brown alga (Sargassum thunbergii) collected in Jeju, Republic of Korea. Strain ST-6T was psychrotolerant, growing at 4-30 °C (optimum 20 °C). Phylogenetic analysis based on 16S rRNA and gyrB gene sequences revealed that strain ST-6T belonged to a distinct lineage in the genus Shewanella. Strain ST-6T was related most closely to Shewanella basaltis J83T, S. gaetbuli TF-27T, S. arctica IT12T, S. vesiculosa M7T and S. aestuarii SC18T, showing 96-97 % and 85-70 % 16S rRNA and gyrB gene sequences similarities, respectively. DNA-DNA relatedness values between strain ST-6T and the type strains of two species of the genus Shewanella were <22.6 %. The major cellular fatty acids (>5 %) were summed feature 3 (comprising C16:1ω7c and/ or iso-C15:0 2-OH), C16:0, iso-C13:0 and C17:1ω8c. The DNA G+C content of strain ST-6Twas 42.4 mol%, and the predominant isoprenoid quinones were menaquinone MK-7 and ubiquinones Q-7 and Q-8. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain ST-6T is considered to represent a novel species of the genus Shewanella, for which the name Shewanella algicola sp. nov. is proposed. The type strain is ST-6T (= KCTC 23253T = JCM 31091T).

Shewanella mangrovi sp. nov., an acetaldehyde-degrading bacterium isolated from mangrove sediment

A taxonomic study was carried out on strain YQH10T, which was isolated from mangrove sediment collected from Zhangzhou, China during the screening of acetaldehyde-degrading bacteria. Cells of strain YQH10T were Gram-stain-negative rods and pale brown-pigmented. Growth was observed at salinities from 0 to 11 % and at temperatures from 4 to 42 °C. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YQH10T is affiliated to the genus Shewanella, showing the highest similarity with Shewanella haliotis DW01T (95.7 %) and other species of the genus Shewanella (91.4–95.6 %). The principal fatty acids were iso-C15 : 0 and C17 : 1ω8c. The major respiratory quinone was Q-8. The polar lipids comprised phosphatidylethanolamine and phosphatidylglycerol. The genomic DNA had a G+C content of 48.3 mol%. Strain YQH10T can completely degrade 0.02 % (w/v) acetaldehyde on 2216E at 28 °C within 48 h. Based on these phenotypic and genotypic data, strain YQH10T represents a novel species of the genus Shewanella, for which the name Shewanella mangrovi sp. nov. is proposed. The type strain is YQH10T ( = MCCC 1A00830T = JCM 30121T).

Enzymatic exploration of catalase from a nanoparticle producing and biodecolorizing algae Shewanella xiamenensis BC01

Shewanella xiamenensis (SXM) was found to produce nanoparticles (NPs) under aerobic condition. The oxidoreductase enzymatic activities including of catalase, manganese peroxidase, laccase, NADH dehydrogenase, flavin reductase, azoreductase and Fe reductase are first investigated. Catalase showed the greatest enzymatic activity among all oxidoreductases in SXM, which with strong activities in multiple substrates of ABTS, guaiacol and 2,6-DMP. The optimum temperature, pH, concentrations of H2O2 and 2,6-DMP for this enzyme were found to be 65 °C, pH 4.0, 128.7 mM and 10 mM, respectively. Finally, from the kinetic parameters and structure simulation of catalase, implied that SXM would potentially apply in bioremediation, microbe fuel cells (MFCs) and nano-biotechnology based on its distinguished enzymatic system.

Psychrobium conchae gen. nov., sp. nov., a psychrophilic marine bacterium isolated from the Iheya North hydrothermal field

A novel psychrophilic, marine, bacterial strain designated BJ-1(T) was isolated from the Iheya North hydrothermal field in the Okinawa Trough off Japan. Cells were Gram-negative, rod-shaped, non-spore-forming, aerobic chemo-organotrophs and motile by means of a single polar flagellum. Growth occurred at temperatures below 16 °C, with the optimum between 9 and 12 °C. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the closest relatives of strain BJ-1(T) were Shewanella denitrificans OS-217(T) (93.5% similarity), Shewanella profunda DSM 15900(T) (92.9%), Shewanella gaetbuli TF-27(T) (92.9%), Paraferrimonas sedimenticola Mok-106(T) (92.1%) and Ferrimonas kyonanensis Asr22-7(T) (91.7%). The major respiratory quinone was Q-8. The predominant fatty acids were C(16:1)ω7c and C(16:0). The G+C content of the novel strain was 40.5 mol%. Based on phylogenetic, phenotypic and chemotaxonomic evidence, it is proposed that strain BJ-1(T) represents a novel species in a new genus, for which the name Psychrobium conchae gen. nov., sp. nov. is proposed. The type strain of Psychrobium conchae is BJ-1(T) ( =JCM 30103(T) =DSM 28701(T)).

Shewanella aestuarii sp. nov., a marine bacterium isolated from a tidal flat

A Gram-stain-negative, non-spore-forming, facultatively anaerobic bacterium, designated strain SC18T, was isolated from a tidal flat of Suncheon bay in South Korea. Cells were rod-shaped and motile by means of a polar flagellum. Cells were catalase-, oxidase- and β-haemolysis-positive. Growth was observed at 4–37 °C (optimum, 25–30 °C), at pH 5.0–9.0 (optimum, pH 7.0) and in the presence of 0–5.0 % (w/v) NaCl (optimum, 0–2 %). The major cellular fatty acids were summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c), iso-C15 : 0 and C16 : 0. The polar lipid pattern indicated the presence of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmethylethanolamine, an unidentified aminolipid and three unidentified lipids. Strain SC18T contained Q-7, Q-8, MK-7 and MMK-7 as the dominant respiratory quinones and the G+C content of the genomic DNA was 41.3 mol%. Phylogenetic analysis based on 16S rRNA and gyrase B (gyrB) gene sequences showed that strain SC18T formed a tight phyletic lineage with members of the genus Shewanella . Strain SC18T was related most closely to Shewanella denitrificans OS217T (97.3 % 16S rRNA gene sequence similarity) and Shewanella gaetbuli TF-27T (97.1 %), but the DNA–DNA relatedness levels between strain SC18T and the type strains of S. denitrificans and S. gaetbuli were 18.3±2.8 and 22.5±1.6 % (mean±sd), respectively. On the basis of phenotypic, chemotaxonomic and molecular features, strain SC18T represents a novel species of the genus Shewanella , for which the name Shewanella aestuarii sp. nov. is proposed. The type strain is SC18T ( = KACC 16187T = JCM 17801T).

Shewanella dokdonensis sp. nov., isolated from seawater

A novel bacterial strain, designated UDC329T, was isolated from a sample of seawater collected at Dong-do, on the coast of Dokdo Island, in the East Sea of the Republic of Korea. The Gram-staining-negative, motile, facultatively anaerobic, non-spore-forming rods of the strain developed into dark orange–yellow colonies. The strain grew optimally between 25 and 30 °C, with 1 % (w/v) NaCl and at pH 7. It grew in the absence of NaCl, but not with NaCl at >7 % (w/v). The predominant menaquinone was MK-7, the predominant ubiquinones were Q-7 and Q-8, and the major fatty acids were iso-C15 : 0 (33.52 %) and C17 : 1ω8c (11.73 %). The genomic DNA G+C content of strain UDC329T was 50.2 mol%. In phylogenetic analyses based on 16S rRNA and gyrB gene sequences, strain UDC329T was grouped with members of the genus Shewanella and appeared most closely related to Shewanella fodinae JC15T (97.9 % 16S rRNA gene sequence similarity), Shewanella indica KJW27T (95.0 %), Shewanella algae ATCC 51192T (94.8 %), Shewanella haliotis DW01T (94.5 %) and Shewanella chilikensis JC5T (93.9 %). The level of DNA–DNA relatedness between strain UDC329T and S. fodinae JC15T was, however, only 27.4 %. On the basis of phenotypic, genotypic and DNA–DNA relatedness data, strain UDC329T represents a novel species in the genus Shewanella , for which the name Shewanella dokdonensis sp. nov. is proposed. The type strain is UDC329T ( = KCTC 22898T = DSM 23626T).

Shewanella indica sp. nov., isolated from sediment of the Arabian Sea

A Gram-negative, facultatively anaerobic, rod-shaped, catalase- and oxidase-positive bacterium, motile by means of a single polar flagellum and designated strain KJW27(T), was isolated from the marine sediment of Karwar jetty, west coast of India. The strain was β-haemolytic and grew with 0-10 % (w/v) NaCl, at 10-45 °C and at pH 6.5-10, with optimum growth with 2 % (w/v) NaCl, at 37 °C and at pH 7.5. The major fatty acids were iso-C₁₅:₀ (22.2 %), C₁₇:₁ω8c (21 %), summed feature 3 (comprising C₁₆:₁ω7c and/or C₁₆:₁ω6c; 10.2 %), C₁₆:₀ (7.1 %), iso-C₁₃:₀ (5.6 %) and C₁₇:₀ (4.4 %). The DNA G+C content was 51.2 mol%. Phylogenetic analysis based on 16S rRNA and gyrB gene sequences showed that strain KJW27(T) forms a lineage within the genus Shewanella and is closely related to Shewanella algae ATCC 51192(T) (98.8 %), Shewanella haliotis DW01(T) (98.8 %) and Shewanella chilikensis JC5(T) (98.2 %). Sequence identity with other members of this genus ranges from 92.2 to 96.4 %. The DNA-DNA relatedness of strain KJW27(T) with S. algae ATCC 51192(T), S. haliotis DW01(T) and S. chilikensis JC5(T) was 52, 44 and 33 %, respectively. The phenotypic, genotypic and DNA-DNA relatedness data indicate that strain KJW27(T) should be distinguished from S. algae ATCC 51192(T), S. haliotis DW01(T) and S. chilikensis JC5(T). On the basis of the data presented in this study, strain KJW27(T) represents a novel species, for which the name Shewanella indica sp. nov. is proposed. The type strain is KJW27(T) ( = KCTC 23171(T)  = BCC 41031(T)  = NCIM 5388(T)).

The periplasmic nitrate reductase in Shewanella: the resolution, distribution and functional implications of two NAP isoforms, NapEDABC and NapDAGHB

In the bacterial periplasm, the reduction of nitrate to nitrite is catalysed by a periplasmic nitrate reductase (NAP) system, which is a species-dependent assembly of protein subunits encoded by the nap operon. The reduction of nitrate catalysed by NAP takes place in the 90 kDa NapA subunit, which contains a Mo-bis-molybdopterin guanine dinucleotide cofactor and one [4Fe-4S] iron-sulfur cluster. A review of the nap operons in the genomes of 19 strains of Shewanella shows that most genomes contain two nap operons. This is an unusual feature of this genus. The two NAP isoforms each comprise three isoform-specific subunits - NapA, a di-haem cytochrome NapB, and a maturation chaperone NapD - but have different membrane-intrinsic subunits, and have been named NAP-alpha (NapEDABC) and NAP-beta (NapDAGHB). Sixteen Shewanella genomes encode both NAP-alpha and NAP-beta. The genome of the vigorous denitrifier Shewanella denitrificans OS217 encodes only NAP-alpha and the genome of the respiratory nitrate ammonifier Shewanella oneidensis MR-1 encodes only NAP-beta. This raises the possibility that NAP-alpha and NAP-beta are associated with physiologically distinct processes in the environmentally adaptable genus Shewanella.

Shewanella fodinae sp. nov., isolated from a coal mine and from a marine lagoon

Strains JC15(T) and JC19 were isolated from samples collected from different locations in India, including a coal mine and a marine lagoon. Both strains were Gram-stain-negative rods, motile by means of a single polar flagellum, catalase- and oxidase-positive, and hydrolysed casein, produced H(2)S and showed beta-haemolysis. Strain JC15(T) grew optimally at pH 6 (range pH 5-8) while strain JC19 grew optimally at pH 7 (range pH 6-9) and both had a growth temperature optimum of 30-37 degrees C (range 22-40 degrees C). Both strains could grow chemo-organoheterotrophically and chemolithoautotrophically. Neither strain required NaCl for growth and both could tolerate up to 9 % (w/v) NaCl, with optimum growth at 5 % NaCl. Vitamin B(12) was required as a growth factor by both strains. The major fatty acids were iso-C(15 : 0), C(17 : 1)omega8c and iso-C(13 : 0) 3-OH. The DNA G+C contents of strains JC15(T) and JC19 were 53.6 and 54.3 mol%, respectively. A phylogenetic tree based on 16S rRNA gene sequence analysis showed that strains JC15(T) and JC19 were most closely related to Shewanella haliotis DW01(T) (approximately 94 % sequence similarity) and to other members of the genus Shewanella. Genomic relatedness (DNA-DNA hybridization) between strains JC15(T) and JC19 is 88 %. On the basis of phenotypic and molecular genetic evidence, strain JC15(T) represents a novel species of the genus Shewanella, for which the name Shewanella fodinae sp. nov. is proposed. The type strain is JC15(T) (=CCUG 57102(T) =NBRC 105216(T) =KCTC 22506(T)).

Shewanella chilikensis sp. nov., a moderately alkaliphilic gammaproteobacterium isolated from a lagoon

A Gram-negative, motile, rod-shaped, facultatively anaerobic bacterium was isolated from sediment of Chilika Lagoon, a brackish water lagoon in India. The strain, designated JC5(T), was able to grow in the presence of 0-8.0 % NaCl and at pH 7.0-10.0. The isolate was positive for oxidase and catalase and exhibited alpha-haemolysis. The major fatty acids were iso-C(15 : 0) (18.3 %), C(16 : 0) (11.3 %), C(17 : 1)omega8c (13.1 %) and a summed feature, C(16 : 1)omega7c and/or C(16 : 1)omega6c (15.1 %). The genomic DNA G+C content was 54.6 mol%. A phylogenetic tree based on the 16S rRNA gene sequences showed that strain JC5(T) forms a lineage within the genus Shewanella and is closely related to Shewanella haliotis DW01(T) (98.0 %), Shewanella algae ATCC 51192(T) (97.6 %) and Shewanella marina C4(T) (95.8 %). Further, genomic DNA-DNA hybridization of strain JC5(T) with S. haliotis DW01(T) and S. algae ATCC 51192(T) showed relatedness of only 42 and 23 %, respectively. On the basis of phenotypic and molecular genetic evidence, strain JC5(T) represents a novel species of the genus Shewanella, for which the name Shewanella chilikensis sp. nov. is proposed. The type strain is JC5(T) (=CCUG 57101(T) =NBRC 105217(T) =KCTC 22540(T)).