Persistent microbial communities in hyperarid subsurface habitats of the Atacama Desert: Insights from intracellular DNA analysis

Desert environments constitute one of the largest and yet most fragile ecosystems on Earth. Under the absence of regular precipitation, microorganisms are the main ecological component mediating nutrient fluxes by using soil components, like minerals and salts, and atmospheric gases as a source for energy and water. While most of the previous studies on microbial ecology of desert environments have focused on surface environments, little is known about microbial life in deeper sediment layers. Our study is extending the limited knowledge about microbial communities within the deeper subsurface of the hyperarid core of the Atacama Desert. By employing intracellular DNA extraction and subsequent 16S rRNA sequencing of samples collected from a soil pit in the Yungay region of the Atacama Desert, we unveiled a potentially viable microbial subsurface community residing at depths down to 4.20 m. In the upper 80 cm of the playa sediments, microbial communities were dominated by Firmicutes taxa showing a depth-related decrease in biomass correlating with increasing amounts of soluble salts. High salt concentrations are possibly causing microbial colonization to cease in the lower part of the playa sediments between 80 and 200 cm depth. In the underlying alluvial fan deposits, microbial communities reemerge, possibly due to gypsum providing an alternative water source. The discovery of this deeper subsurface community is reshaping our understanding of desert soils, emphasizing the need to consider subsurface environments in future explorations of arid ecosystems.

Bacillales: From Taxonomy to Biotechnological and Industrial Perspectives

For a long time, the genus Bacillus has been known and considered among the most applicable genera in several fields. Recent taxonomical developments resulted in the identification of more species in Bacillus-related genera, particularly in the order Bacillales (earlier heterotypic synonym: Caryophanales), with potential application for biotechnological and industrial purposes such as biofuels, bioactive agents, biopolymers, and enzymes. Therefore, a thorough understanding of the taxonomy, growth requirements and physiology, genomics, and metabolic pathways in the highly diverse bacterial order, Bacillales, will facilitate a more robust designing and sustainable production of strain lines relevant to a circular economy. This paper is focused principally on less-known genera and their potential in the order Bacillales for promising applications in the industry and addresses the taxonomical complexities of this order. Moreover, it emphasizes the biotechnological usage of some engineered strains of the order Bacillales. The elucidation of novel taxa, their metabolic pathways, and growth conditions would make it possible to drive industrial processes toward an upgraded functionality based on the microbial nature.

Radiobacillus deserti gen. nov., sp. nov., a UV-resistant bacterium isolated from desert soil

A Gram-stain-positive, aerobic, rod-shaped, non-motile, endospore-forming and UV-resistant bacterial strain, designated strain TKL69^T, was isolated from sandy soil sampled in the Taklimakan Desert. The strain grew at 20-50 °C, pH 6-9 and with 0-12 % (w/v) NaCl. The major fatty acids were anteiso-C_15 : 0, iso-C_15 : 0 and C_16 : 0. The only respiratory quinone was MK-7. The cell-wall peptidoglycan was meso-diaminopimelic acid. Diphosphatidyl glycerol, two unidentified aminophospholipids and one unidentified phospholipid were identified as the major polar lipids. Genomic DNA analysis revealed a G+C content of 38.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain TKL69^T has the highest similarity to Salinibacillus xinjiangensis CGMCC 1.12331^T (96.9 %) but belongs to an independent taxon separated from other genera of the family Bacillaceae. Phylogenetic, phenotypic and chemotaxonomic analyses suggested that strain TKL69^T represents a novel species of a new genus, for which the name Radiobacillus gen. nov., sp. nov. is proposed, with the type strain being Radiobacillus deserti TKL69^T (=JCM 33497^T=CICC 24779^T).

Peculiarities and biotechnological potential of environmental adaptation by Geobacillus species

The genus Geobacillus comprises thermophilic bacilli capable of endospore formation. The members of this genus provide thermostable proteins and can be used in whole cell applications at elevated temperatures; therefore, these organisms are of biotechnological importance. While these applications have been described in previous reviews, the present paper highlights the environmental adaptations and genome diversifications of Geobacillus spp. and their applications in evolutionary-protein engineering. Despite their obligate thermophilic properties, Geobacillus spp. are widely distributed in nature. Because several isolates demonstrate remarkable properties for cell reproduction in their respective niches, they seem to exist not only as endospores but also as vegetative cells in diverse environments. This suggests their excellence in environmental adaptation via genome diversification; in fact, evidence suggests that Geobacillus spp. were derived from Bacillus spp. while diversifying their genomes via horizontal gene transfer. Moreover, when subjected to an environmental stressor, Geobacillus spp. diversify their genomes using inductive mutations and transposable elements to produce derivative cells that are adaptive to the stressor. Notably, inductive mutations in Geobacillus spp. occur more rapidly and frequently than the stress-induced mutagenesis observed in other microorganisms. Owing to this, Geobacillus spp. can efficiently generate mutant genes coding for thermostable enzyme variants from the thermolabile enzyme genes under appropriate selection pressures. This phenomenon provides a new approach to generate thermostable enzymes, termed as thermoadaptation-directed enzyme evolution, thereby expanding the biotechnological potentials of Geobacillus spp. In this review, we have discussed this approach using successful examples and major challenges yet to be addressed.

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.

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).

Examination into the taxonomic position of Bacillus thermotolerans Yang et al., 2013, proposal for its reclassification into a new genus and species Quasibacillus thermotolerans gen. nov., comb. nov. and reclassification of B. encimensis Dastager et al., 2015 as a later heterotypic synonym of B. badius

Two novel Gram-staining positive, rod-shaped, moderately halotolerant, endospore forming bacterial strains 5.5LF 38TD and 5.5LF 48TD were isolated and taxonomically characterized from a landfill in Chandigarh, India. The analysis of 16S rRNA gene sequences of the strains confirmed their closest identity to Bacillus thermotolerans SgZ-8T with 99.9% sequence similarity. A comparative phylogenetic analysis of strains 5.5LF 38TD, 5.5LF 48TD and B. thermotolerans SgZ-8^T confirmed their separation into a novel genus with B. badius and genus Domibacillus as the closest phylogenetic relatives. The major fatty acids of the strains are iso-C_15:0 and iso-C_16:0 and MK-7 is the only quinone. The major polar lipids are diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The digital DNA-DNA hybridization (DDH) and ortho average nucleotide identity (ANI) values calculated through whole genome sequences indicated that the three strains showed low relatedness with their phylogenetic neighbours. Based on evidences from phylogenomic analyses and polyphasic taxonomic characterization we propose reclassification of the species B. thermotolerans into a novel genus named Quasibacillus thermotolerans gen. nov., comb. nov with the type strain SgZ-8^T (=CCTCC AB2012108^T=KACC 16706^T). Further our analyses also revealed that B. encimensis SGD-V-25^T is a later heterotypic synonym of Bacillus badius DSM 23^T.

Ecology of Bacillaceae

Members of the family Bacillaceae are among the most robust bacteria on Earth, which is mainly due to their ability to form resistant endospores. This trait is believed to be the key factor determining the ecology of these bacteria. However, they also perform fundamental roles in soil ecology (i.e., the cycling of organic matter) and in plant health and growth stimulation (e.g., via suppression of plant pathogens and phosphate solubilization). In this review, we describe the high functional and genetic diversity that is found within the Bacillaceae (a family of low-G+C% Gram-positive spore-forming bacteria), their roles in ecology and in applied sciences related to agriculture. We then pose questions with respect to their ecological behavior, zooming in on the intricate social behavior that is becoming increasingly well characterized for some members of Bacillaceae. Such social behavior, which includes cell-to-cell signaling via quorum sensing or other mechanisms (e.g., the production of extracellular hydrolytic enzymes, toxins, antibiotics and/or surfactants) is a key determinant of their lifestyle and is also believed to drive diversification processes. It is only with a deeper understanding of cell-to-cell interactions that we will be able to understand the ecological and diversification processes of natural populations within the family Bacillaceae. Ultimately, the resulting improvements in understanding will benefit practical efforts to apply representatives of these bacteria in promoting plant growth as well as biological control of plant pathogens.

A heavy metal tolerant novel bacterium, Bacillus malikii sp. nov., isolated from tannery effluent wastewater

The taxonomic position of a Gram-stain positive and heavy metal tolerant bacterium, designated strain NCCP-662(T), was investigated by polyphasic characterisation. Cells of strain NCCP-662(T) were observed to be rod to filamentous shaped, motile and strictly aerobic, and to grow at 10-50 °C (optimum 30-37 °C) and at pH range of 6-10 (optimum pH 7-8). The strain was found to be able to tolerate 0-12 % NaCl (w/v) and heavy metals (Cr 1200 ppm, Pb 1800 ppm and Cu 1200 ppm) in tryptic soya agar medium. The phylogenetic analysis based on the 16S rRNA gene sequence of strain NCCP-662(T) showed that it belongs to the genus Bacillus and showed high sequence similarity (98.2 and 98.0 %, respectively) with the type strains of Bacillus niabensis 4T19(T) and Bacillus halosaccharovorans E33(T). The chemotaxonomic data showed that the major quinone is MK-7; the predominant cellular fatty acids are anteiso-C15 :0, iso-C14:0, iso-C16:0 and C16:0 and iso-C15:0; the major polar lipids are diphosphatidylglycerol, phosphatidylglycerol along with several unidentified glycolipids, phospholipids and polar lipids. The DNA G+C content was determined to be 36.9 mol%. These data also support the affiliation of strain NCCP-662(T) with the genus Bacillus. The level of DNA-DNA relatedness between strain NCCP-662(T) and B. niabensis JCM 16399(T) was 20.5 ± 0.5 %. On the basis of physiological and biochemical characteristics, phylogenetic analyses and DNA-DNA hybridization data, strain NCCP-662(T) can be clearly differentiated from the validly named Bacillus species and thus represents a new species, for which the name Bacillus malikii sp. nov. is proposed with the type strain NCCP-662(T) (= LMG 28369(T) = DSM 29005(T) = JCM 30192(T)).

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).

Salinibacillus xinjiangensis sp. nov., a halophilic bacterium from a hypersaline lake

A Gram-positive, endospore-forming, rod-shaped bacterium, designated isolate J4T, was isolated from a neutral saline lake sample from Xinjiang Uyghur Autonomous Region, China, and subjected to a polyphasic taxonomic investigation. Phylogenetic analysis based on 16S rRNA gene sequence revealed that strain J4T is most closely related to Salinibacillus aidingensis 25-7T (with 96.7 % similarity), Salinibacillus kushneri 8-2T (96.5 %), Ornithinibacillus scapharcae TW25T (96.4 %), Salirhabdus euzebyi CVS-14T (96.4 %) and Ornithinibacillus californiensis MB-9T (96.2 %). Chemotaxonomic analysis showed menaquinone-7 (MK-7) to be the major isoprenoid quinone of strain J4T; diphosphatidylglycerol and phosphatidylglycerol were the major cellular polar lipids and the cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid. The major cellular fatty acids were iso-C15 : 0 and anteiso-C15 : 0. The genomic DNA G+C content of strain J4T was determined to be 36.2 mol%. Strain J4T was positive for catalase activity and negative for oxidase activity. Strain J4T was observed to grow at 25–50 °C (optimal 35–42 °C), pH 6.5–8.0 (optimal 7.0–7.5) and in media containing 1–21 % (w/v) NaCl (optimal 9–12 %). Based on these data, strain J4T represents a novel species of the genus Salinibacillus and the name Salinibacillus xinjiangensis sp. nov. is proposed. The type strain is J4T ( = CGMCC 1.12331T = JCM 18732T).

Bacillus salsus sp. nov., a halophilic bacterium from a hypersaline lake

A Gram-staining-positive, endospore-forming, rod-shaped, strictly aerobic, slightly halophilic bacterium, designated strain A24T, was isolated from the hypersaline lake Aran-Bidgol in Iran. Cells of strain A24T were motile rods and produced oval endospores at a terminal position in swollen sporangia. Strain A24T was catalase and oxidase positive. Growth occurred with between 0.5 and 7.5 % (w/v) NaCl and the isolate grew optimally at 3 % (v/w) NaCl. The optimum temperature and pH for growth were 35 °C and pH 8.0, respectively. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain A24T belonged to the genus Bacillus within the phylum Firmicutes and showed the closest phylogenetic similarity with the species Bacillus alkalitelluris BA288T (97.2 %), Bacillus herbersteinensis D-1,5aT (96.0 %) and Bacillus litoralis SW-211T (95.6 %). The G+C content of the genomic DNA of this strain was 35.9 mol%. The polar lipid pattern of strain A24T consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and two unknown phospholipids. The major cellular fatty acids of strain A24T were anteiso-C15 : 0 and iso-C15 : 0. The respiratory quinones were MK-7 (94 %) and MK-6 (4 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. All these features confirm the placement of isolate A24T within the genus Bacillus . DNA–DNA hybridization experiments revealed a relatedness of 8 % between strain A24T and Bacillus alkalitelluris IBRC-M 10596T, supporting its placement as a novel species. Phenotypic characteristics, phylogenetic analysis and DNA–DNA relatedness data suggest that this strain represents a novel species of the genus Bacillus , for which the name Bacillus salsus sp. nov. is proposed. The type strain is strain A24T ( = IBRC-M 10078 T = KCTC 13816T).

Bacillus halosaccharovorans sp. nov., a moderately halophilic bacterium from a hypersaline lake

A novel Gram-stain-positive, moderately halophilic bacterium, designated strain E33(T), was isolated from water of the hypersaline lake Aran-Bidgol in Iran and characterized taxonomically using a polyphasic approach. Cells of strain E33(T) were motile rods and produced ellipsoidal endospores at a central or subterminal position in swollen sporangia. Strain E33(T) was a strictly aerobic bacterium, catalase- and oxidase-positive. The strain was able to grow at NaCl concentrations of 0.5-25 % (w/v), with optimum growth occurring at 5-15 % (w/v) NaCl. The optimum temperature and pH for growth were 40 °C and pH 7.5-8.0, respectively. On the basis of 16S rRNA gene sequence analysis, strain E33(T) was shown to belong to the genus Bacillus within the phylum Firmicutes and showed the closest phylogenetic similarity with the species Bacillus niabensis 4T19(T) (99.2 %), Bacillus herbersteinensis D-1-5a(T) (97.3 %) and Bacillus litoralis SW-211(T) (97.2 %). The DNA G+C content of the type strain of the novel species was 42.6 mol%. The major cellular fatty acids of strain E33(T) were anteiso-C15 : 0 and iso-C15 : 0, and the polar lipid pattern consisted of diphosphatidylglycerol, phosphatidylglycerol, two unknown glycolipids, an unknown lipid and an unknown phospholipid. The isoprenoid quinones were MK-7 (97 %), MK-6 (2 %) and MK-8 (0.5 %). The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. All these features confirm the placement of isolate E33(T) within the genus Bacillus. DNA-DNA hybridization experiments revealed low levels of relatedness between strain E33(T) and Bacillus niabensis IBRC-M 10590(T) (22 %), Bacillus herbersteinensis CCM 7228(T) (38 %) and Bacillus litoralis DSM 16303(T) (19 %). On the basis of polyphasic evidence from this study, a novel species of the genus Bacillus, Bacillus halosaccharovorans sp. nov. is proposed, with strain E33(T) (= IBRC-M 10095(T) = DSM 25387(T)) as the type strain.

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).