Salt-tolerant plant growth-promoting bacteria as a versatile tool for combating salt stress in crop plants.

Soil salinization poses a great threat to global agricultural ecosystems, and finding ways to improve the soils affected by salt and maintain soil health and sustainable productivity has become a major challenge. Various physical, chemical and biological approaches are being evaluated to address this escalating environmental issue. Among them, fully utilizing salt-tolerant plant growth-promoting bacteria (PGPB) has been labeled as a potential strategy to alleviate salt stress, since they can not only adapt well to saline soil environments but also enhance soil fertility and plant development under saline conditions. In the last few years, an increasing number of salt-tolerant PGPB have been excavated from specific ecological niches, and various mechanisms mediated by such bacterial strains, including but not limited to siderophore production, nitrogen fixation, enhanced nutrient availability, and phytohormone modulation, have been intensively studied to develop microbial inoculants in agriculture. This review outlines the positive impacts and growth-promoting mechanisms of a variety of salt-tolerant PGPB and opens up new avenues to commercialize cultivable microbes and reduce the detrimental impacts of salt stress on plant growth. Furthermore, considering the practical limitations of salt-tolerant PGPB in the implementation and potential integration of advanced biological techniques in salt-tolerant PGPB to enhance their effectiveness in promoting sustainable agriculture under salt stress are also accentuated.

Optimization of fermentation conditions, purification and rheological properties of poly (γ-glutamic acid) produced by Bacillus subtilis 1006-3.

This study aimed to investigate the optimal fermentation condition, purification and rheological properties of extracellular polymers produced by Bacillus subtilis 1006-3. An optimum temperature of 30.2 °C, inoculation amount of 6.1%, and pH of 8.2 were determined via Response Surface Methodology. The result of amino acid analysis and gel electrophoresis indicated that the obtained polymer contained only glutamic acid, with a wide molecular weight range. This polymer was finally determined as γ-PGA by infrared spectroscopy. The γ-PGA solution displayed a behavior of pseudoplastic non-Newtonian fluid with shear thinning properties, which can be described by the Ostward-de Waele power law model. The apparent viscosity of γ-PGA solution increased with the increase in its concentration from 1% to 10%. The deviation in pH from neutral value, and the addition of NaCl or MgCl2 can reduce the apparent viscosity of γ-PGA solution, and it was more sensitive to Mg2+ than to Na+ addition. At the concentration of 4, 6, and 8%, γ-PGA solution showed predominantly viscous response in the range of 0.1-100 rad/s angular frequency (G″>G'). These results indicated the potential application of the γ-PGA as a thickening agent.

Leucobacter chromiisoli sp. nov., isolated from chromium-containing chemical plant soil.

A Gram-stain-positive, rod-shaped, aerobic, non-motile, non-sporulating bacterial strain, designated CSA1T, was isolated from chromium-containing soil sampled at a chemical plant. Growth of strain CSA1T occurred at pH 6-10 (optimum, pH 7), 15-45 °C (optimum, 30 °C) and in the presence of 0.5-6.5 % (w/v) NaCl (optimum, 2 %). The 16S rRNA gene sequence of strain CSA1T revealed the highest similarity to Leucobacter ruminantium A2T (97.5 %), Leucobacter tardus K 70/01T (97.3 %), Leucobacter humi Re6T (96.6 %), Leucobacter kyeonggiensis F3-P9T (96.2 %), Leucobacter zeae CC-MF41T (96.1 %) and Leucobacter weissii S27T (96.0 %). The draft genome of CSA1T was approximately 3 350 931 bp in size with a G+C content of 70.6 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values among strain CSA1T and the selected Leucobacter species were 74.0-79.2 % (ANIb), 84.3-87.1 % (ANIm) and 21.5-25.4 % (dDDH), which are below the recommended cutoff values for species delineation. The major fatty acids were anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unknown glycolipid. The predominant menaquinones were MK-11, MK-8 and MK-6. The cell-wall amino acids were 2,4-diaminobutyric acid, alanine, glycine, glutamic acid and threonine. From the phenotypic, chemotaxonomic and molecular features, strain CSA1T was considered to represent a novel species of the genus Leucobacter, for which the name Leucobacter chromiisoli sp. nov. is proposed. The type strain is CSA1T (=JCM 34359T=CGMCC 1.18746T).

Genomic insights into the salt tolerance and cold adaptation of Planococcus halotolerans SCU63T.

Planococcus halotolerans, recently described as a novel species with SCU63T as the type strain, is capable of thriving in up to 15% NaCl and temperatures as low as 0 °C. To better understand its adaptation strategies at the genomic level, strain SCU63T was subjected to whole-genome sequencing and data mining. The high-quality assembly yielded 17 scaffolds with a genome size of 3,622,698 bp. Its genome harbors 3683 protein-coding sequences and 127 RNA genes, as well as three biosynthetic gene clusters and 25 genomic islands. The phylogenomic tree provided compelling insights into the evolutionary relationships of Planococcus. Comparative genomic analysis revealed key similarities and differences in the functional gene categories among Planococcus species. Strain SCU63T was shown to have diverse stress response systems for high salt and cold habitats. Further comparison with three related species showed the presence of numerous unique gene clusters in the SCU63T genome. The strain might serve as a good model for using extremozymes in various biotechnological processes.

Ornithinibacillus caprae sp. nov., a moderate halophile isolated from the hides of a white goat.

A novel Gram-stain-positive, motile, moderate halophile, strain L9T, was isolated from hides of white goat in China. The isolate grew optimally at 30 °C, at pH 7 and with 5-10% (w/v) NaCl. The predominant menaquinone was MK-7, and the major cellular fatty acids were identified as iso-C15:0 and anteiso-C15:0. The peptidoglycan amino acid type was determined to be A4ß, containing L-ornithine and D-aspartic as diagnostic amino acids. The phospholipids were dominated by diphosphatidylglycerol, phosphatidylglycerol, one unidentified aminophospholipid and two unidentified phospholipids. Genome sequencing resulted in a genome size of 4.0 Mbp and a DNA G + C content of 35.9 mol%. Phylogenetic trees based on the 16S rRNA gene sequences showed the isolate to be closely related to Oceanobacillus limi H9BT (98.2% similarity) and Ornithinibacillus halophilus G8BT (97.5% similarity). The ANI and dDDH values between strain L9T and the closely related species were 69.8-76.1% and 13.0-20.5%, respectively. On the basis of the data presented, strain L9T represents a novel species of the genus Ornithinibacillus, for which the name Ornithinibacillus caprae sp. nov. is proposed. The type strain is L9T (= KCTC 43176T = CGMCC 1.17659T).

Halomonas pellis sp. nov., a moderately halophilic bacterium isolated from wetsalted hides.

A Gram-stain-negative, moderately halophilic strain, designated strain L5T, was isolated from wetsalted hides collected from Chengdu, south-west PR China. The cells were motile, facultative aerobic, short rod-shaped and non-endospore-forming. Growth of strain L5T occurred at pH 6-10 (optimum, pH 8), 10-45 °C (optimum, 30 °C) and in the presence of 1-17 % (w/v) NaCl (optimum, 10 %). Results of phylogenetic analyses based on 16S rRNA, gyrB and rpoD gene sequences and its genome revealed that strain L5T belonged to the genus Halomonas. Strain L5T was found to be most closely related to the type strains of Halomonas saliphila, Halomonas lactosivorans, Halomonas kenyensis, Halomonas daqingensis and Halomonas desiderata (98.8, 98.6, 98.3, 97.9 and 97.4 % 16S rRNA gene sequence similarity, respectively). The draft genome was approximately 4.2 Mb in size with a G+C content of 63.5 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization values among strain L5T and the selected Halomonas species were 83.3-88.9 % (ANIm), 71.1-87.3 % (ANIb) and 20.2-34.6 %, which are below the recommended cutoff values. Major fatty acids were C16 : 0, C16 : 1 ω7c, C18 : 1 ω7c and C19 : 0 cyclo ω8c and the predominant ubiquinone was Q-9, with minor ubiquinone Q-8 also present. The phospholipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, four unidentified aminophospholipids and three unidentified phospholipids. Based on the mentioned polyphasic taxonomic evidence, strain L5T represents a novel species within the genus Halomonas, for which Halomonas pellis sp. nov. is proposed. The type strain is L5T (=CGMCC 1.17335T=KCTC 72573T).

Gracilibacillus salitolerans sp. nov., a moderate halophile isolated from saline soil in Northwest China.

A moderately halophilic strain, designated SCU50T, was recovered from a saline soil sample and characterized by a polyphasic approach. The 16S rRNA gene sequence analysis showed that strain SCU50T belonged to the genus Gracilibacillus and was most closely related to Gracilibacillus thailandensis TP2-8T (98.1 % similarity) and Gracilibacillus orientalis XH-63T (97.7 %). Genomic average nucleotide identity and digital DNA-DNA hybridization analyses confirmed the separate species status of the new isolate relative to other recognized Gracilibacillus species. The genome size was about 5.09 Mbp and the DNA G+C content was 36.7 mol%. The strain grew optimally at 10-15 % (w/v) NaCl, pH 6.5-7.5 and 25-30 °C. It contained anteiso-C15 : 0, iso-C15 : 0 and anteiso-C17 : 0 as the dominant fatty acids and menaquinone-7 as the major respiratory quinone. The polar lipid profile was examined and found to comprise diphosphatidylglycerol, phosphatidylglycerol, one unidentified phospholipid and one unidentified lipid. The cell-wall peptidoglycan type was A1γ based on meso-diaminopimelic acid. Combining the data from phenotypic, chemotaxonomic, genomic and phylogenetic characterization, it was concluded that strain SCU50T should be assigned as representing a novel species within the genus Gracilibacillus. Thus, a novel taxon named Gracilibacillus salitolerans sp. nov. was first established, with SCU50T (=CGMCC 1.17336T=KCTC 43107T) as the type strain.

Description of Salinicola corii sp. nov., a Halotolerant Bacterium Isolated from Wetsalted Hides.

A novel Gram-stain-negative, moderately halotolerant, rod-shaped bacterium, designated strain L3T, was isolated from a wetsalted hide in Chengdu, China. The organism grew optimally at 30 °C, at pH 8 and with 5-10% (w/v) NaCl. The major cellular fatty acids were C16:0, C16:1ω7c, C18:1ω7c and C19:0 cyclo ω8c; the predominant respiratory quinone was Q-9; the phospholipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and three unidentified phospholipids. Phylogenetic trees based on the 16S rRNA, gyrB and rpoD genes' sequences, obtained using three different algorithms, clearly revealed the isolate belonged to the genus Salinicola, and was found to be closely related to Salinicola acroporae JCM 30412T, Salinicola socius CGMCC 1.12383T and Salinicola lusitanus CR50T. The draft genome was approximately 4.5 Mb in size with 4486 predicted coding sequences, and the G+C content was 62.6 mol%. The maximum values of ANI and dDDH between strain L3T and the three above-mentioned type species were 89.2% and 63.8%, respectively. Differential phenotypic properties, together with the genome analysis, support the view that strain L3T represents a novel species, Salinicola corii sp. nov., with the type strain L3T (=CGMCC 1.17272T=KCTC 72572T).

Halomonas saliphila sp. nov., a moderately halophilic bacterium isolated from a saline soil.

A novel, Gram-stain-negative, aerobic, rod-shaped, motile and moderately halophilic bacterium, designated strain LCB169T, was isolated from a saline soil sample from Gansu Province, PR China. The cells of LCB169T grew at 10-52 °C (optimum 30 °C), at pH 6.0-10.0 (optimum pH 8.0) and in the presence of 0-17 % (w/v) NaCl (optimum 10-15 %). Phylogenetic analysis based on 16S rRNA gene sequences and concatenated 16S rRNA, gyrB and rpoD genes sequences revealed that LCB169T represented a member of the genus Halomonas in the class Gammaproteobacteria. The most closely related species were Halomonas daqingensis DQD2-30T (98.0 % 16S rRNA gene sequence similarity), Halomonas kenyensis AIR-2T (97.8 %) and Halomonas desiderata FB2T (97.5 %). DNA-DNA relatedness values between LCB169T and H. daqingensis CGMCC 1.6443T, H. desiderata DSM 9502T and H. kenyensis DSM 17331T were 33, 35 and 38 %, respectively. The polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and three unidentified phospholipids. The major fatty acids were C18 : 1ω7c, C16 : 0, C16 : 1ω7c and C12 : 0 3-OH. The genomic DNA G+C content was 66.1 mol% and the predominant respiratory quinone was Q-9. On the basis of the results of phenotypic, phylogenetic and chemotaxonomic analyses and DNA-DNA hybridization relatedness values, LCB169T is considered to represent a novel species of the genus Halomonas, for which the name Halomonas saliphila sp. nov. is proposed. The type strain is LCB169T (=CGMCC 1.15818T=KCTC 52618T).

Streptomyces geranii sp. nov., a novel endophytic actinobacterium isolated from root of Geranium carolinianum L.

A novel endophytic actinomycete, designated A301T, was isolated from the root of Geranium carolinianum Linn collected from Mount Emei in China and characterized using a polyphasic approach. Growth occurred at 10-37 °C, pH 6-11 and in the presence of 0-5 % NaCl (w/v). Strain A301T contained ll-diaminopimelic acid as the diagnostic diamino acid in the cell-wall peptidoglycan. The whole-cell hydrolysates included galactose and ribose. The predominant menaquinones were MK-9(H6) and MK-9(H8). The major cellular fatty acids were C15 : 0, C16 :  0, anteiso-C15 : 0 and iso-C16 : 0. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, two unidentified phospholipids, three unidentified lipids and two unidentified aminophospholipids. Strain A301T shared the highest 16S rRNA gene sequence similarity to Streptomyces cinereorubersubsp. fructofermentans NBRC 15396T (98.1 %) and Streptomyces turgidiscabies ATCC 700248T (98.1 %). The DNA-DNA relatedness values between strain A301T and the two above-mentioned members of the genus Streptomyces were 42.6 % and 47.2 %, respectively. The G+C content of the DNA was 70.5 mol%. On the basis of the polyphasic approach and DNA-DNA hybridization data, strain A301T represents a novel species within the genus Streptomyces, for which the name Streptomyces geranii sp. nov. is proposed. The type strain is A301T (=CGMCC 4.7422T=JCM 32177T).

Streptomyces populi sp. nov., a novel endophytic actinobacterium isolated from stem of Populus adenopoda Maxim.

A novel endophytic actinobacterium strain, designated A249T, was isolated from the stem of Populus adenopoda collected at Mount Qingcheng in south-west China. Its taxonomic position was determined by using a polyphasic approach. The cultural and morphological characteristics of isolate A249T were consistent with members of the genus Streptomyces. Growth occurred at 10-37 °C, pH 6.0-12.0 and in the presence of 0-4 % (w/v) NaCl. Analysis of the 16S rRNA gene sequence and phylogenetic trees showed the closest phylogenetic relatives to strain A249T were Streptomyces shaanxiensis JCM 16925T (98.0 % 16S rRNA gene sequence similarity) and Streptomyces lanatus JCM 4332T (97.9 %). The DNA-DNA hybridization values between the strain A249T and the two reference strains ranged from 41.4 to 49.4 %. The DNA G+C content was 71.7 mol%. The range of average nucleotide identity values was 81.5-86.7 %. Chemical analysis of cellular components indicated that strain A249T contained ll-diaminopimelic acid, xylose and galactose. The predominant menaquinones were MK-9(H6) and MK-9(H8). The polar lipids were diphosphatidylglycerol, phosphatidylinositol mannosides, phosphatidylethanolamine, two unidentified lipids, one unidentified phospholipid, one unidentified aminolipid and one unidentified aminophospholipid. The major fatty acids comprised C16 : 0, iso-C14 : 0, iso-C15 : 0, iso-C16 : 0, anteiso-C15 : 0 and C16 : 1ω7c. On the basis of the phenotypic and genotypic differentiation of the three tested strains, isolate A249T is proposed to represent a novel species of the genus Streptomyces, named Streptomyces populi sp. nov. The type strain is A249T (=CGMCC 4.7417T=JCM 32175T).

Planococcus halotolerans sp. nov., isolated from a saline soil sample in China.

A novel Gram-stain-positive, coccoid or short rod-shaped, moderate-orange-pigmented, halotolerant and psychrotolerant bacterium, designated strain SCU63T, was isolated from a saline soil sample in China, and characterized by a polyphasic taxonomic approach. 16S rRNA gene sequence similarity of strain SCU63T to species in the genera Planococcus and Planomicrobium ranged from 96.5 to 98.6 %. Phylogenetic trees as well as diagnostic signature nucleotides in the 16S rRNA gene sequence supported the view that this strain should be assigned to the genus Planococcus. Further, average nucleotide identity and digital DNA-DNA hybridization analyses confirmed the separate species status of strain SCU63T relative to the closely related taxa. The isolate grew at 0-40 °C (optimum, 30-35 °C), at pH 6.5-9.0 (pH 7.0-7.5) and in the presence of 0-15 % (w/v) NaCl (3 %). The principal fatty acids were anteiso-C15 : 0, C16 : 1ω7c alcohol, iso-C16 : 0 and iso-C14 : 0, and the dominant isoprenoid quinones were MK-8 and MK-7. The peptidoglycan type was determined to be A4α (l-Lys-d-Glu), and the polar lipids contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminophospholipid and one unidentified lipid. The DNA G+C content was 44.6 mol%. Based on the genotypic, phenotypic and chemotaxonomic data, strain SCU63T can be classified as a novel species in the genus Planococcus, for which the name Planococcushalotolerans sp. nov. is proposed. The type strain is SCU63T (=CGMCC 1.13628T=KCTC 43001T).

Planococcus salinus sp. nov., a moderately halophilic bacterium isolated from a saline-alkali soil.

A novel aerobic, Gram-stain-positive, motile, moderately halophilic and coccoid bacterial strain, designated LCB217T, was isolated from a saline-alkali soil in north-western China and identified using a polyphasic taxonomic approach. Growth occurred with 3-15 % (w/v) NaCl (optimum 3-5 %), at 10-45 °C (optimum 30 °C) and at pH 7.0-9.0 (optimum pH 9.0). Strain LCB217T contained MK-7 and MK-8 as the predominant menaquinones and anteiso-C15 : 0, iso-C14 : 0 and iso-C16 : 0 as the major fatty acids. The polar lipids from strain LCB217T consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, one unidentified phospholipid, one unidentified aminophospholipid and one unidentified lipid. The peptidoglycan type was A4α (l-Lys-d-Glu). Phylogenetic analysis of the 16S rRNA gene sequence showed that strain LCB217T belonged to the genus Planococcus and was closely related to the type strains Planococcus plakortidis AS/ASP6 (II)T (98.2 % similarity), Planococcus maitriensis S1T (97.7 %) and Planococcus salinarum ISL-16T (97.2 %). The G+C content of the genomic DNA was 49.4 mol%. DNA-DNA relatedness values between strain LCB217T andPlanococcusplakortidis AS/ASP6 (II)T, Planococcusmaitriensis S1T andPlanococcussalinarum ISL-16T were 29.5, 38.1 and 39.5 %, respectively. On the basis of the phenotypic, phylogenetic and genomic data, strain LCB217T represents a novel species of the genus Planococcus, for which the name Planococcus salinus sp. nov. is proposed. The type strain is LCB217T (=CGMCC 1.15685T=KCTC 33861T).

Ornithinibacillus salinisoli sp. nov., a moderately halophilic bacterium isolated from a saline-alkali soil.

A taxonomic study was performed on strain LCB256T, which was isolated from a saline-alkali soil sample taken from northwestern China. Cells of strain LCB256T were Gram-stain-positive, aerobic, rod-shaped and grew at 3-17 % (w/v) NaCl (optimum 10-15 %), 10-52 °C (optimum 25-30 °C) and pH 7.0-9.0 (optimum 8.0). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain LCB256T was most closely related to the two genera of Ornithinibacillus and Oceanobacillus, showing highest sequence similarity to Oceanobacillus limi KCTC 13823T (97.8 %) and Ornithinibacillus bavariensis WSBC 24001T (97.2 %). The peptidoglycan amino acid type was found to be A4ß and the major respiratory quinone was determined to be MK-7. The polar lipid profile of strain LCB256T contained diphosphatidylglycerol, phosphatidylglycerol, one unidentified phospholipid and two unidentified aminolipids. The dominant cellular fatty acids were anteiso-C15 : 0 and iso-C15 : 0. The G+C content of genomic DNA was 39.3 mol%. DNA-DNA relatedness values between strain LCB256T and Ornithinibacillus halophilus KCTC 13822T and Oceanobacillus limi KCTC 13823T were 46.2 and 34.8 %, respectively. Based on this polyphasic taxonomic study, a novel species of the genus Ornithinibacillus, Ornithinibacillussalinisoli sp. nov. is proposed. The type strain is LCB256T (=CGMCC 1.15809T=KCTC 33862T).

Pedobacter chitinilyticus sp. nov., a chitin-degrading bacterium isolated from wheat leaf tissue.

A bacterium, designated strain CM134L-2T, was isolated from a chitin-enriched wheat leaf microbiome in Chengdu, Sichuan province, China. It was Gram-stain-negative, strictly aerobic, non-spore-forming, motile, rod-shaped, and bright yellow in colour. Strain CM134L-2T grew at 4-35 °C, at pH 6.0-9.0 and could use chitin as the only carbon resource. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CM134L-2T was most closely related to Pedobacter nanyangensis Q-4T (97.7 %) and Pedobacter zeaxanthinifaciens TDMA-5T (97.4 %). Digital DNA-DNA hybridization (dDDH) values between strain CM134L-2T with these two type strains were 26.8  and 20.8 %, respectively, and average nucleotide identity (ANI) values were 83.2 and 76.2 %; these values are lower than the proposed and generally accepted species boundaries of 70 % for dDDH and 95-96 % for ANI, which suggests strain CM134L-2T represents a novel species. The genomic DNA G+C content of strain CM134L-2T was 39.3 mol%, menaquinone-7 was the major respiratory quinone, phosphatidylethanolamine was the major polar lipid and the major components of the cellular fatty acids were iso-C15 : 0, and C16 : 1ω7c/C16 : 1ω6c (summed feature 3); these features supported the affiliation of strain CM134L-2T to the genus Pedobacter. Overall, strain CM134L-2T belongs to the genus Pedobacter, but can be classified as a novel species, for which the name Pedobacter chitinilyticus sp. nov. is proposed. The type strain is CM134L-2T (=CGMCC 1.16520T=KCTC 62643T).

Streptomyces dioscori sp. nov., a Novel Endophytic Actinobacterium Isolated from Bulbil of Dioscorea bulbifera L.

A novel endophytic actinobacterium strain, A217T, was isolated from the bulbil of Dioscorea bulbifera L. Its taxonomic position was characterized using a polyphasic study. Morphological and chemotaxonomic characteristics of strain A217T were consistent with those of members of the genus Streptomyces: long straight to flexuous spore chain; cellular components contained LL-diaminopimelic acid, ribose, and small traces of glucose in whole-cell hydrolysates; MK-9(H6) and MK-9(H8) as predominant menaquinones. The patterns of major fatty acids are C16:0, anteiso-C15:0, C15:0, iso-C14:0, C16:1 ω7c, anteiso-C17:0, and iso-C17:1 ω5c. The polar lipids comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol mannoside, and glycolipid, as well as two unidentified phospholipids, one unidentified aminolipid, and one unidentified aminophospholipid. The DNA G + C content of draft genome is 70.7 mol%. Analysis of the 16S rRNA gene sequence and phylogenetic trees revealed that the isolate was most closely related to S. aurantiacus JCM 4453T (99.0%), S. glomeroaurantiacus JCM 4677T (99.0%), and S. tauricus JCM 4837T (98.8%). The DNA-DNA hybridization values between the strain A217T and three reference strains ranged from 34.6% to 51.7%. On the basis of phenotypic and genotypic differentiation from all tested strains, isolate A217T is proposed to represent a novel species of the genus Streptomyces, named Streptomyces dioscori sp. nov. The type strain is A217T (= CGMCC 4.7415T = JCM 32173T).

Biosynthesis, characterization and antimicrobial activity of silver nanoparticles by a halotolerant Bacillus endophyticus SCU-L.

We have conducted a thorough study on extracellular biosynthesis of silver nanoparticles (AgNPs) by a halotolerant bacterium Bacillus endophyticus SCU-L, which was identified by 16S rRNA gene sequencing analysis. This strain was selected during an ongoing research programme aimed at finding a novel biological method for green nanosynthetic routes using the extremophiles in unexplored hypersaline habitats. The biosynthesized AgNPs were characterized and analyzed with UV-vis spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Further, the AgNPs were found to be spherical in shape with an average particle size of about 5.1 nm, and it was stable in aqueous solution for three months period of storage at room temperature under dark condition. Also, the synthesized AgNPs significantly presented antimicrobial activity against Candida albicans, Escherichia coli, Salmonella typhi and Staphylococcus aureus. The above results suggested that the present work may provide a valuable reference and theoretical basis for further exploration on microbial biosynthesis of AgNPs by halotolerant bacteria.

Paracoccusacridae sp. nov., isolated from the insect Acrida cinerea living in deserted cropland.

A Gram-stain-negative, aerobic, rod-shaped, non-motile bacterial strain, designated SCU-M53T, was isolated from the insect Acrida cinerea. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain SCU-M53T belonged to the genus Paracoccus, having Paracoccus chinensisNBRC 104937T (97.04 % 16S rRNA gene sequence similarity) and Paracoccus niistensis KCTC 22789T (96.70 %) as the most closely related phylogenetic neighbours. Growth occurred at 10-40 °C (optimum 25-30 °C), pH 5.0-10.0 (optimum pH 6.5-7.5) and with 0-4 % (w/v) NaCl (optimum 0-1 % NaCl). The fatty acids of strain SCU-M53T were C18 : 1ω7c, C18 : 0, C16 : 0, C14 : 0 3-OH, C14 : 0 and C10 : 0 3-OH. The polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, an unknown aminolipid, two unknown phospholipids and two unknown lipids. The isoprenoid quinone was ubiquinone-10. The DNA G+C content was 60.6 mol%. Strain SCU-M53T exhibited 36.5 and 28.6 % DNA-DNA relatedness to P. chinensis NBRC 104937T and P. niistensis KCTC 22789T, respectively. According to these results, strain SCU-M53T represents a novel species of the genus Paracoccus, for which the name Paracoccus acridae sp. nov. is proposed. The type strain is SCU-M53T (=KCTC 42932T=CGMCC 1.15419T).

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects.

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Development and characterization of levan/pullulan/chitosan edible films enriched with ε-polylysine for active food packaging.

The levan/pullulan/chitosan edible films, enriched with ε-polylysine, as an antimicrobial agent, were successfully fabricated by the casting method, and their applicability for food packaging was systematically evaluated by several analytical techniques. An increase in the levan/pullulan ratios (ranged from 0:6 to 3:3) in the films showed a decreased water solubility (from 72.21% to 26.64%) and oxygen permeability (from 48.75 × 10-2 g·mm·m-2·d-1·kPa-1 to 4.45 × 10-2 g·mm·m-2·d-1·kPa-1), and increased elongation at break (from 10.92% to 46.61%). All the films showed a strong inhibitory effect on two typical food-borne pathogens and good biodegradability in the soil. These films were employed as edible coatings on strawberries, and the storage stability was investigated by means of physical and biochemical parameters. Compared to control, the weight loss, firmness, and total soluble solids of the coated strawberries showed a downward trend. Overall, these findings suggest that the developed edible films could be a potential approach for sustainable active food packaging.