Microbial diversity in polyextreme salt flats and their potential applications

Recent geological, hydrochemical, and mineralogical studies performed on hypersaline salt flats have given insights into similar geo-morphologic features on Mars. These salt-encrusted depressions are widely spread across the Earth, where they are characterized by high salt concentrations, intense UV radiation, high evaporation, and low precipitation. Their surfaces are completely dry in summer; intermittent flooding occurs in winter turning them into transitory hypersaline lakes. Thanks to new approaches such as culture-dependent, culture-independent, and metagenomic-based methods, it is important to study microbial life under polyextreme conditions and understand what lives in these dynamic ecosystems and how they function. Regarding these particular features, new halophilic microorganisms have been isolated from some salt flats and identified as excellent producers of primary and secondary metabolites and granules such as halocins, enzymes, carotenoids, polyhydroxyalkanoates, and exopolysaccharides. Additionally, halophilic microorganisms are implemented in heavy metal bioremediation and hypersaline wastewater treatment. As a result, there is a growing interest in the distribution of halophilic microorganisms around the world that can be looked upon as good models to develop sustainable biotechnological processes for all fields. This review provides insights into diversity, ecology, metabolism, and genomics of halophiles in hypersaline salt flats worldwide as well as their potential uses in biotechnology.

Aliibacillus thermotolerans gen. nov., sp. nov.: a thermophilic and heterotrophic ammonia-oxidizing bacterium from compost

A novel moderately thermophilic and heterotrophic ammonia-oxidizing bacterium, designated strain BM62^T, was isolated from compost in the thermophilic stage in Harbin, China. Phylogenetic analysis based on the 16S rRNA gene indicated that strain BM62^T belongs to the family Bacillaceae within the class Bacilli and was most closely related to Alteribacillus iranensis X5B^T (only 94.6% sequence similarity). Cells of strain BM62^T were Gram-positive, rod-shaped, motile by periflagella, catalase-positive and oxidase-negative. Growth of strain BM62^T was observed at salinities of 0-4% (optimum 2-3%), temperatures of 35-65 °C (optimum 50 °C) and pH values of 5-9 (optimum pH 7). The major cellular fatty acid was iso-C_16:0, and the predominant ubiquinone was MK-7. The peptidoglycan type is A1γ, and meso-diaminopimelic acid was the diagnostic diamino acid. The major polar lipids were diphosphatidylglycerol, phospholipid and phosphatidylglycerol. The G + C content of its genomic DNA was 36.5 mol%. Data from this polyphasic taxonomy study suggested that strain BM62^T should be classified as the type strain of the type species of a new genus within the family Bacillaceae for which the name Aliibacillus thermotolerans gen. nov., sp. nov. is proposed. The type strain of the species Aliibacillus thermotolerans sp. nov. is BM62^T (= DSM 101851^T = CGMCC 1.15790^T). The respective DPD Taxon Number is GA00057.

Epidermidibacterium keratini gen. nov., sp. nov., a member of the family Sporichthyaceae, isolated from keratin epidermis

A novel actinobacterial strain, designated EPI-7^T, was isolated on R2A agar from human skin (keratinocytes) and subjected to a taxonomic study using a polyphasic approach. Strain EPI-7^T showed a Gram-positive reaction, was non-motile, non-spore-forming, and cells had a rod-shape. Colonies were round, convex and pale yellow. Phylogenetic analysis based on 16S rRNA gene sequences showed that the novel isolate formed a cluster with several uncultured bacterial clones and with cultured members of the genera Modestobacter and Sporichthya. The 16S rRNA gene sequence similarities with respect to the type strains of recognized species from the above genera and other phylogenetic neighbours ranged from 92.6 to 93.4 %. The G+C content of the genomic DNA was 68.9 mol%. The only isoprenoid quinone was MK-9(H4), and the major fatty acids detected were C17 : 1ω8c, C16 : 0, iso-C15 : 0 and summed feature 3. The major polar lipids were found to be phosphatidylethanolamine, phosphatidylinositol, three unidentified phospholipids, phosphatidylglycerol, phosphatidylcholine, two unidentified amino lipids and three unidentified lipids. The cell-wall peptidoglycan contained meso-diaminopimelic acid, glutamic acid and alanine. Whole-cell sugars present included rhamnose, glucose and galactose. The combination of the genotypic and phenotypic data allowed differentiation of strain EPI-7^T from its closest phylogenetic neighbours and provided evidence that strain EPI-7^T represents a novel genus and species in the family Sporichthyaceae. The name Epidermidibacterium keratini gen. nov., sp. nov. is proposed with the type strain being EPI-7^T (=KCCM 90264^T=JCM 31644^T).

Aidingibacillus halophilus gen. nov., sp. nov., a novel member of the family Bacillaceae

A Gram-positive, non-motile, asporogenous and aerobic bacterium, designated YIM 98012^T, was isolated from a salt lake in China. Strain YIM 98012^T was found to be catalase and oxidase positive. Optimal growth of strain YIM 98012^T was observed at 37 °C and pH 7.0 and it was found to grow in the presence of 5-20% (w/v) NaCl (optimum 10% NaCl). Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the novel strain is affiliated with the family Bacillaceae of the phylum Firmicutes and that it shares high (94.7%) sequence similarity with Alteribacillus persepolensis DSM 21632^T and does not show sequence similarities of more than 94.0% to known members of other related genera. The major fatty acids (> 10%) were identified as anteiso-C_15:0, anteiso-C_17:0, iso-C_16:0 and C_16:0. The genomic DNA G+C content was determined to be 41.0 mol% and the dominated respiratory quinone was identified as MK-7. The cell wall peptidoglycan of strain YIM 98012^T was found to contain meso-diaminopimelic acid, while the polar lipids profile was found to include diphosphatidylglycerol, phosphatidylglycerol and phosphatidylcholine. Based on physiological and chemotaxonomic characteristics, strain YIM 98012^T is concluded to be the type strain of the type species of a novel genus in the family Bacillaceae for which the name Aidingibacillus halophilus gen. nov., sp. nov. is proposed. The type strain is YIM 98012^T (= KCTC 33868^T = DSM 104332^T).

Bacillus ectoiniformans sp. nov., a halotolerant bacterium isolated from deep-sea sediments

A halotolerant, Gram-positive bacterium (strain NE-14T), which was isolated from sediment samples of the South China Sea, was subjected to a taxonomic study. Strain NE-14T grew well at wide temperature and pH ranges, 10.0-45.0 °C and pH 6-10, with an optimum at 30 °C and pH 8.0, respectively. Growth of strain NE-14T was observed at total salt concentrations of 0-10 % (w/v) with optimum at 2 % (w/v). Phylogenetic analysis based on 16S rRNA gene sequence comparison indicated that the isolate belongs to the genus Bacillus. Strain NE-14T was related most closely to Bacillus shackletonii LMG 18435T, Bacillus bataviensis LMG 21833T, Bacillus idriensis SMC 4352-2T and Bacillus drentensis LMG 21831T with 16S rRNA gene sequence similarities of 96.2, 95.9, 95.8 and 95.7 %, respectively. DNA-DNA hybridization between strain NE-14T and B. shackletonii LMG 18435T, B. bataviensis LMG 21833T, B. idriensis SMC 4352-2T and B. drentensis LMG 21831T gave reassociation values of about 27.4, 22.4, 16.4 and 15.9 %, respectively. The DNA G+C content of strain NE-14T was 39.2 mol%. The predominant isoprenoid quinone was menaquinone 7 (MK-7). The cell-wall peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. The predominant cellular fatty acids of strain NE-14T were iso-C15 : 0 and anteiso-C15 : 0. The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phospholipid. Based on the phenotypic and phylogenetic characteristics, it is proposed that strain NE-14T be classified as representing a novel species of the genus Bacillus, for which the name Bacillus ectoiniformans sp. nov. is proposed. The type strain is NE-14T ( = DSM 28970T = JCM 30397T).

Aquibacillus halophilus gen. nov., sp. nov., a moderately halophilic bacterium from a hypersaline lake, and reclassification of Virgibacillus koreensis as Aquibacillus koreensis comb. nov. and Virgibacillus albus as Aquibacillus albus comb. nov

A novel Gram-stain-positive, moderately halophilic bacterium, designated strain B6BT, was isolated from the water of an Iranian hypersaline lake, Aran-Bidgol, and characterized taxonomically using a polyphasic approach. Cells of strain B6BT were rod-shaped, motile and produced ellipsoidal endospores in terminal positions in non-swollen sporangia. Strain B6BT was a strictly aerobic bacterium and catalase- and oxidase-positive. The strain was able to grow at NaCl concentrations of 0.5–20.0 % (w/v), with optimum growth occurring at 10.0 % (w/v) NaCl. The optimum temperature and pH for growth were 35 °C and pH 7.0. On the basis of 16S rRNA gene sequence analysis, strain B6BT was shown to belong to the phylum Firmicutes and its closest phylogenetic similarities were with the species Virgibacillus koreensis BH30097T (97.5 %), Virgibacillus albus YIM 93624T (97.4 %), Sediminibacillus halophilus EN8dT (96.8 %), Sediminibacillus albus NHBX5T (96.6 %), Virgibacillus carmonensis LMG 20964T (96.3 %) and Paraliobacillus quinghaiensis YIM-C158T (96.0 %), respectively. Phylogenetic analysis revealed that strain B6BT, along with V. koreensis BH30097T and V. albus YIM 93624T, clustered in a separate clade in the family Bacillaceae . The DNA G+C content of the novel isolate was 35.8 mol%. DNA–DNA hybridization experiments revealed low levels of relatedness between strain B6BTand V. koreensis BH30097T (13 %) and V. albus YIM 93624T (33 %). The major cellular fatty acid of strain B6BT was anteiso-C15 : 0 (75.1 %) and its polar lipid pattern consisted of phosphatidylglycerol, diphosphatidylglycerol, an unknown phospholipid and an unknown glycolipid. The isoprenoid quinones were MK-7 (90 %) and MK-6 (3 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. All of these features support the placement of isolate B6BT within the phylum Firmicutes . It is closely related to V. koreensis and V. albus , but with features that clearly distinguish it from species of the genus Virgibacillus or of other related genera. On the basis of the polyphasic evidence derived in this study, we propose that strain B6BT be placed within a new genus, as Aquibacillus halophilus gen. nov., sp. nov., with B6BT as the type strain ( = IBRC-M 10775T = KCTC 13828T). We also propose that V. koreensis and V. albus should be transferred to this new genus and be named Aquibacillus koreensis comb. nov. and Aquibacillus albus comb. nov., respectively. The type strain of Aquibacillus koreensis comb. nov. is BH30097T ( = KCTC 3823T = IBRC-M 10657T = JCM 12387T) and the type strain of Aquibacillus albus comb. nov. is YIM 93624T ( = DSM 23711T = IBRC-M 10798T = JCM 17364T).

Evolution in the Bacillaceae

The family Bacillaceae constitutes a phenotypically diverse and globally ubiquitous assemblage of bacteria. Investigation into how evolution has shaped, and continues to shape, this family has relied on several widely ranging approaches from classical taxonomy, ecological field studies, and evolution in soil microcosms to genomic-scale phylogenetics, laboratory, and directed evolution experiments. One unifying characteristic of the Bacillaceae , the endospore, poses unique challenges to answering questions regarding both the calculation of evolutionary rates and claims of extreme longevity in ancient environmental samples.

Bacillus ligniniphilus sp. nov., an alkaliphilic and halotolerant bacterium isolated from sediments of the South China Sea

An alkaliphilic and halotolerant Gram-stain-positive bacterium, which was isolated from sediment samples from the South China Sea, was subjected to a taxonomic study. The isolate, strain L1T, grew well at a wide range of temperatures and pH values, 10.0-45.0 °C and pH 6-11, with optima at 30 °C and pH 9.0, respectively. The growth of strain L1T occurred at total salt concentrations of 0-10% (w/v) with an optimum at 2% (w/v). Phylogenetic analysis based on 16S rRNA sequence comparison indicated that the isolate represented a member of the genus Bacillus. The strains most closely related to strain L1T were Bacillus nanhaiisediminis JCM 16507T, Bacillus halodurans DSM 497T and Bacillus pseudofirmus DSM 8715T, with 16S rRNA similarities of 96.5%, 95.9% and 95.7%, respectively. DNA-DNA hybridization of strain L1T with the type strains of the most closely related species, B. nanhaiisediminis JCM 16507T, B. halodurans DSM 497T and B. pseudofirmus DSM 8715T, showed reassociation values of about 21.7%, 14.3% and 13.9%, respectively. The DNA G+C content of strain L1T was 40.76 mol%. The predominant isoprenoid quinone was menaquinone 7 (MK-7). The cell-wall peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. The predominant cellular fatty acids of strain L1T were iso-C14 : 0 and anteiso-C15:0. The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. Based on the phenotypic and phylogenetic characteristics, it is proposed that strain L1T (=JCM 18543T=DSM 26145T) should be classified as the type strain of Bacillus ligniniphilus sp. nov.

Saliterribacillus persicus gen. nov., sp. nov., a moderately halophilic bacterium isolated from a hypersaline lake

A novel Gram-positive, moderately halophilic bacterium, designated strain X4BT, was isolated from soil around the hypersaline lake Aran-Bidgol in Iran and characterized taxonomically using a polyphasic approach. Cells of strain X4BT were motile rods and formed ellipsoidal endospores at a terminal or subterminal position in swollen sporangia. Strain X4BT was a strictly aerobic bacterium, catalase- and oxidase-positive. The strain was able to grow at NaCl concentrations of 0.5–22.5 % (w/v), with optimum growth occurring at 7.5 % (w/v) NaCl. The optimum temperature and pH for growth were 35 °C and pH 7.0. Analysis of 16S rRNA gene sequence revealed that strain X4BT is a member of the family Bacillaceae , constituting a novel phyletic lineage within this family. Highest sequence similarities were obtained with the 16S rRNA gene sequences of the type strains of Sediminibacillus albus (96.0 %), Paraliobacillus ryukyuensis (95.9 %), Paraliobacillus quinghaiensis (95.8 %) and Sediminibacillus halophilus (95.7 %), respectively. The DNA G+C content of this novel isolate was 35.2 mol%. The major cellular fatty acids of strain X4BT were anteiso-C15 : 0 and anteiso-C17 : 0 and its polar lipid pattern consisted of diphosphatidylglycerol, phosphatidylglycerol, two aminolipids, an aminophospholipid and an unknown phospholipid. The isoprenoid quinones were MK-7 (89 %) and MK-6 (11 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. On the basis of 16S rRNA gene sequence analysis in combination with chemotaxonomic and phenotypic data, strain X4BT represents a novel species in a new genus in the family Bacillaceae , order Bacillales for which the name Saliterribacillus persicus gen. nov., sp. nov. is proposed. The type strain of the type species (Saliterribacillus persicus) is X4BT ( = IBRC-M 10629T = KCTC 13827T).

Alteribacillus bidgolensis gen. nov., sp. nov., a moderately halophilic bacterium from a hypersaline lake, and reclassification of Bacillus persepolensis as Alteribacillus persepolensis comb. nov

A novel Gram-stain-positive, moderately halophilic bacterium, designated strain P4BT, was isolated from water of the hypersaline Aran-Bidgol lake in Iran and characterized taxonomically by using a polyphasic approach. Cells of strain P4BT were non-motile rods producing ellipsoidal endospores at a central position in non-swollen sporangia. Strain P4BT was strictly aerobic and catalase- and oxidase-positive. It was able to grow at NaCl concentrations of 0.5–12.5 % (w/v), with optimum growth occurring at 5–7.5 % (w/v) NaCl. The optimum temperature and pH for growth were 35 °C and pH 7.0. On the basis of 16S rRNA gene sequence analysis, strain P4BT was shown to belong to the phylum Firmicutes and shared highest similarity with Bacillus persepolensis HS136T (97.1 %) and Bacillus salarius BH169T (95.1 %). However, it shared only 91.3 % 16S rRNA gene sequence similarity with Bacillus subtilis subsp. subtilis DSM 10T, indicating that strain P4BT might not be a member of the genus Bacillus . The DNA G+C content of this new isolate was 38.9 mol%. DNA–DNA hybridization experiments revealed a low level of relatedness between strain P4BT and B. persepolensis HS136T (6 %). The major cellular fatty acids of strain P4BT were iso-C15 : 0 and anteiso-C15 : 0, as for B. persepolensis HS136T but in contrast to B. salarius DSM 16461T and B. subtilis subsp. subtilis DSM 10T. Its polar lipid pattern consisted of phosphatidylglycerol, an aminoglycolipid and an unknown phospholipid. This polar lipid profile was similar to that obtained for B. persepolensis DSM 21632T but different from those of B. salarius DSM 16461T and B. subtilis subsp. subtilis DSM 10T. The isoprenoid quinones were MK-7 (88 %) and MK-8 (2 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. All these features indicate placement of strain P4BT within the Firmicutes , closely related to B. persepolensis but with features clearly distinct from those of the genus Bacillus and other related genera. On the basis of these data, strain P4BT is considered to represent a novel species of a new genus, for which the name Alteribacillus bidgolensis gen. nov., sp. nov. is proposed. The type strain of Alteribacillus bidgolensis is P4BT ( = CCM 7963T = CECT 7998T = DSM 25260T = IBRC-M 10614T = KCTC 13821T). It is also suggested to transfer B. persepolensis to this new genus, as Alteribacillus persepolensis comb. nov. The type strain of Alteribacillus persepolensis is HS136T ( = CCM 7595T = DSM 21632T = JCM 15720T = LMG 25222T).

Bacillus luteolus sp. nov., a halotolerant bacterium isolated from a salt field

A novel Gram-stain-positive, motile, strictly aerobic bacterium, designated YIM 93174T, was isolated from a salt field in Korea. Cells of this strain were rod-shaped and formed pale tangerine colonies and grew at pH 6.0–8.0 (optimal growth at pH 7.0), at 15–45 °C (optimum 28–37 °C) and at salinities of 0–10 % (w/v) NaCl (optimum 0–2 % NaCl). Some phenotypic characters allowed differentiation of strain YIM 93174T from its nearest phylogenetic relatives. Comparative 16S rRNA gene sequence analysis showed that strain YIM 93174T belongs to the genus Bacillus, exhibiting the highest level of sequence similarity with the type strain of Bacillus humi (95.7 %), followed by those of Bacillus alkalitelluris (94.9 %) and Bacillus litoralis (94.5 %). The major fatty acids were iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0. The cell-wall peptidoglycan was of the A1γ type, containing meso-diaminopimelic acid as the diagnostic diamino acid. The genomic DNA G+C content was 36.9 mol% and the predominant respiratory quinone was MK-7. The major polar lipids of strain YIM 93174T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and two unknown phospholipids. On the basis of the evidence from this polyphasic study, strain YIM 93174T represents a novel species of the genus Bacillus, for which the name Bacillus luteolus sp. nov. is proposed, with YIM 93174T ( = DSM 22388T  = KCTC 13210T  = CCTCC AA 208068T) as the type strain.

Bacillus iranensis sp. nov., a moderate halophile from a hypersaline lake

A Gram-positive, moderately halophilic rod, designated X5BT, was isolated from saline mud of the hypersaline lake Aran-Bidgol in Iran. Strain X5BT was a strictly aerobic, motile bacterium that produced ellipsoidal endospores at a central-subterminal position in non-swollen sporangia. The isolate grew at pH 7.0-10.0 (optimum pH 7.5), at 25-45 °C (optimum 35 °C) and with 2.5-15 % (w/v) NaCl (optimum 5-7.5 %). On the basis of 16S rRNA gene sequences, strain X5BT belonged to the genus Bacillus and showed highest similarity with Bacillus persepolensis HS136T (95.6 % 16S rRNA gene sequence similarity) and Bacillus salarius BH169T (95.5 %). The DNA G+C content was 42.4 mol%. The major cellular fatty acids were anteiso-C15:0 and iso-C15:0 and the polar lipid profile consisted of phosphatidylglycerol, diphosphatidylglycerol, three phospholipids and two glycolipids. The diamino acid found in the cell-wall peptidoglycan was meso-diaminopimelic acid and the isoprenoid quinones were MK-7 (92 %), MK-6 (6 %) and MK-5 (2 %). On the basis of phylogenetic, chemotaxonomic and phenotypic data, a novel species of the genus Bacillus is proposed, with the name Bacillus iranensis sp. nov. The type strain is X5BT (=IBRC 10446T=DSM 23995T).