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.

Klenkia sesuvii sp. nov., isolated from leaves of halophyte Sesuvium portulacastrum.

During a study on the diversity of culturable actinobacteria from coastal halophytes in Thailand, strain LSe6-5T was isolated from leaves of sea purslane (Sesuvium portulacastrum L.), and a polyphasic approach was employed to determine its taxonomic position. The 16S rRNA gene sequences analysis indicated that the strain was most closely related to Klenkia brasiliensis Tu 6233T (99.2 %), Klenkia marina YIM M13156T (99.1 %), and Klenkia terrae PB261T (98.7 %). The genome of strain LSe6-5T was estimated to be 4.33 Mbp in size, with DNA G+C contents of 74.3%. A phylogenomic tree based on whole-genome sequences revealed that strain LSe6-5T formed a clade with Klenkia marina DSM 45722T, indicating their close relationship. However, the average nucleotide identity (ANI)-blast, ANI-MUMmer, and dDDH values between strain LSe6-5T with K. marina DSM 45722T (87.1, 88.9, and 33.0 %) were below the thresholds of 95-96 % ANI and 70 % dDDH for identifying a novel species. Furthermore, strain LSe6-5T showed morphological and chemotaxonomic characteristics of the genus Klenkia. Cells were motile, rod-shaped, and Gram-stain-positive. Optimal growth of strain LSe6-5T occurred at 28 °C, pH 7.0, and 0-3 % NaCl. The whole-cell hydrolysates contained meso-diaminopimelic acid as the diagnostic diamino acid, with galactose, glucose, mannose, and ribose as whole-cell sugars. The predominant menaquinones were MK-9(H4) and MK-9(H0). The polar lipid profile was composed of diphosphatidylglycerol, hydroxyphosphatidylethanolamine, phosphatidylinositol, glycophosphatidylinositol, an unidentified phospholipid, and an unidentified lipid. Major cellular fatty acids were iso-C15 : 0, iso-C16 : 0, and iso-C17 : 0. From the distinct phylogenetic position and combination of genotypic and phenotypic characteristics, it is supported that strain LSe6-5T represents a novel species of the genus Klenkia, for which the name Klenkia sesuvii sp. nov. is proposed. The type strain is strain LSe6-5T (=TBRC 16417T= NBRC 115929T).

Gordonia prachuapensis sp. nov. and Gordonia sesuvii sp. nov., two novel actinobacteria isolated from mangrove sediments and leaves of halophyte Sesuvium portulacastrum in Thailand.

A polyphasic approach was used to characterize two novel actinobacterial strains, designated PKS22-38T and LSe1-13T, which were isolated from mangrove soils and leaves of halophyte Sesuvium portulacastrum (L.), respectively. Phylogenetic analyses based on 16S rRNA gene sequences showed that they belonged to the genus Gordonia and were most closely related to three validly published species with similarities ranging from 98.6 to 98.1 %. The genomic DNA G+C contents of strains PKS22-38T and LSe1-13T were 67.3 and 67.2 mol%, respectively. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains were 93.3 and 54.9 %, respectively, revealing that they are independent species. Meanwhile, the ANI and dDDH values between the two novel strains and closely related type strains were below 80.5 and 24.0 %, respectively. Strains PKS22-38T and LSe1-13T contained C16 : 0, C18 : 1 ω9c and C18 : 0 10-methyl (TBSA) as the major fatty acids and diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol as the main phospholipids. The predominant menaquinone was MK-9(H2). Based on phenotypic, chemotaxonomic, phylogenetic and genomic data, strains PKS22-38T and LSe1-13T are considered to represent two novel species within the genus Gordonia, for which the names Gordonia prachuapensis sp. nov. and Gordonia sesuvii sp. nov. are proposed, with strain PKS22-38T (=TBRC 17540T=NBRC 116256T) and strain LSe1-13T (=TBRC 17706T=NBRC 116396T) as the type strains, respectively.

Enhancing quinoa (Chenopodium quinoa) growth in saline environments through salt-tolerant rhizobacteria from halophyte biotope.

The use of plant growth-promoting rhizobacteria (PGPR) in agriculture is one of the most promising approaches to improve plants' growth under salt stress and to support sustainable agriculture under climate change. In this context, our goal was to grow and enhance quinoa growth using native rhizobacteria that can withstand salt stress. To achieve this objective, we isolated rhizobacteria from three saline localities in a semi-arid region in Tunisia, which are characterized by different halophyte species and tested their plant growth-promoting (PGP) activities. Then, we inoculated quinoa seedlings cultivated on 300 mM NaCl with the three most efficient rhizobacteria. A positive effect of the three-salt tolerant rhizobacteria on the growth of quinoa under salinity was observed. In fact, the results of principal component analysis indicated that the inoculation of quinoa by salt-tolerant PGPR under high salinity had a prominent beneficial effect on various growth and physiological parameters of stressed plant, such as the biomass production, the roots length, the secondary roots number, proline content and photosynthesis activities. Three rhizobacteria were utilized in this investigation, and the molecular identification revealed that strain 1 is related to the Bacillus inaquosorum species, strain 2 to Bacillus thuringiensis species and strain 3 to Bacillus proteolyticus species. We can conclude that the saline soil, especially the halophytic rhizosphere, is a potential source of salt-tolerant plant growth-promoting rhizobacteria (ST-PGPR), which stimulate the growth of quinoa and improve its tolerance to salinity.

Planting halophytes increases the rhizosphere ecosystem multifunctionality via reducing soil salinity.

Soil salinization poses a significant global challenge, exerting adverse effects on both agriculture and ecosystems. Planting halophytes has the potential ability to improve saline-alkali land and enhance ecosystem multifunctionality (EMF). However, it remains unclear which halophytes are effective in improving saline-alkali land and what impact they have on the rhizosphere microbial communities and EMF. In this study, we evaluated the Na+ absorption capability of five halophytes (Grubovia dasyphylla, Halogeton glomeratus, Suaeda salsa, Bassia scoparia, and Reaumuria songarica) and assessed their rhizosphere microbial communities and EMF. The results showed that S. salsa possessed the highest shoot (3.13 mmol g-1) and root (0.92 mmol g-1) Na+ content, and its soil Na+ absorption, along with B. scoparia, was significantly higher than that of other plants. The soil pH, salinity, and Na+ content of the halophyte rhizospheres decreased by 6.21%, 23.49%, and 64.29%, respectively, when compared to the bulk soil. Extracellular enzymes in the halophyte rhizosphere soil, including α-glucosidase, ß-glucosidase, ß-1,4-N-acetyl-glucosaminidase, neutral phosphatase, and alkaline phosphatase, increased by 70.1%, 78.4%, 38.5%, 79.1%, and 64.9%, respectively. Furthermore, the halophyte rhizosphere exhibited higher network complexity of bacteria and fungi and EMF than bulk soil. The relative abundance of the dominant phyla Proteobacteria, Firmicutes, and Ascomycota in the halophyte rhizosphere soil increased by 9.4%, 8.3%, and 22.25%, respectively, and showed higher microbial network complexity compared to the bulk soil. Additionally, keystone taxa, including Muricauda, Nocardioides, and Pontibacter, were identified with notable effects on EMF. This study confirmed that euhalophytes are the best choice for saline-alkali land restoration. These findings provided a theoretical basis for the sustainable use of saline-alkali cultivated land.

Salt-tolerant plant growth-promoting Pseudomonas atacamensis KSS-6 in combination with organic manure enhances rice yield, improves nutrient content and soil properties under salinity stress.

In the current study salt tolerant-plant growth-promoting rhizobacteria (ST-PGPR) Pseudomonas atacamensis KSS-6, selected on the basis of prominent plant growth-promoting (PGP) and stress tolerance properties was tested as bioinoculant to improve yield of rice grown in saline soil. The ST-PGPR KSS-6 was capable of maintaining the PGP traits up to 200 mM NaCl, however, higher salt stress conditions affected these activities. The study was designed to determine the effect of developed talc-based bioformulation using KSS-6 along with organic manure (OM) on growth and yield of paddy under saline conditions. Bioformulation broadcasting was also done to examine the effect on soil properties. It was found that the combinatorial treatment showed positive impact on growth and yield of rice under saline conditions. Co-application of KSS-6 with OM showed maximum increment in growth, chlorophyll content, plant fresh weight, and dry weight as compared to untreated control plants. Furthermore, the combinatorial treatment improved the nutrient content (P, K, Zn, Fe, Mg, and Mn) by more than 35% and enhanced the biochemical parameters such as proline, flavonoids, carbohydrates, protein, dietary fiber, and antioxidant content of rice grains by more than 32%. Soil parameters including pH and electrical conductivity (EC), moisture content, total organic carbon, OM, sodium, and chloride ions were also improved upon treatment. There was significant lowering of EC from 7.43 to 4.3 dS/m when combination of OM and bacteria were applied. These findings suggest that the application of KSS-6 in the form of bioinoculant could be a promising strategy to mitigate negative impacts of salt stress and enhance the yield and nutritional properties of rice grown in degraded and saline soil.

Fungal endophytes from salt-adapted plants confer salt tolerance and promote growth in wheat (Triticum aestivum L.) at early seedling stage.

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt-sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants' roots and their ability to withstand in vitro salt stress was evaluated. The fungal endophytes could withstand up to 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt-sensitive wheat seeds/seedlings, several of the endophytes showed a positive impact on germination and biomass-related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolates from dicot plants (identified as Microsphaeropsis arundinis) could successfully colonize wheat and promote its growth under salt and no-salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate and has previously been reported to be an effective biocontrol agent. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for enhancing the salt stress tolerance of wheat crop.

Bacterial diversity and community structure in the rhizosphere of the halophyte Halocnemum strobilaceum in an Algerian arid saline soil.

Hypersaline ecosystems host a particular microbiota, which can be specifically recruited by halophytes. In order to broaden our knowledge of hypersaline ecosystems, an in natura study was conducted on the microbiota associated with the halophyte Halocnemum strobilaceum from alkaline-saline arid soil in Algeria. We collected and identified a total of 414 strains isolated from root tissues (RT), root-adhering soil (RAS), non-adhering rhizospheric soil (NARS) and bulk soil (BS) using different NaCl concentrations. Our data showed that halophilic and halotolerant bacterial isolates in BS and the rhizosphere belonged to 32 genera distributed in Proteobacteria (49%), Firmicutes (36%), Actinobacteria (14%) and Bacteroidetes (1%). Bacterial population size and species diversity were greatly increased in the rhizosphere (factor 100). The reservoir of diversity in BS was dominated by the genera Bacillus and Halomonas. Bacillus/Halomonas ratio decreased with the proximity to the roots from 2.2 in BS to 0.3 at the root surface. Salt screening of the strains showed that species belonging to nine genera were able to grow up to 5.1 M NaCl. Thus, we found that H. strobilaceum exerted a strong effect on the diversity of the recruited microbiota with an affinity strongly attributed to the genus Halomonas.

Rare ß-Resorcylic Acid Derivatives from a Halophyte-Associated Fungus Colletotrichum gloeosporioides JS0419 and Their Antifungal Activities.

Six new ß-resorcylic acid derivatives (1-5 and 7) were isolated from a halophyte-associated fungus, Colletotrichum gloeosporioides JS0419, together with four previously reported ß-resorcylic acid lactones (RALs). The relative and absolute stereochemistry of 1 was completely established by a combination of spectroscopic data and chemical reactions. The structures of the isolated compounds were elucidated by analysis of HRMS and NMR data. Notably, compounds 1-3 had a ß-resorcylic acid harboring a long unesterified aliphatic side chain, whereas the long aliphatic chains were esterified to form macrolactones in 4-9. Among the isolated compounds, monocillin I and radicicol showed potent antifungal activities against Cryptococcus neoformans, comparable to clinically available antifungal agents and radicicol showed weak antifungal activity against Candida albicans. These findings provide insight into the chemical diversity of fungal RAL-type compounds and their pharmacological potential.

Insights into the endophytic bacterial community comparison and their potential role in the dimorphic seeds of halophyte Suaeda glauca.

BACKGROUND: Seed dimorphism has been thought to be a bet-hedging strategy that helps plants survive in the disturbed environment and has been widely studied for its ecological adaptation mechanism. Many studies showed that seed-associated microorganisms play an important role in enhancing plant fitness, but information regarding endophytic bacteria associated with dimorphic seeds is limited. This study explores the influence of seed coat structure and seed phytochemical properties on the community composition and diversity of endophytic bacteria of dimorphic seeds of Suaeda glauca. In this study, we used 16S rRNA high-throughput gene sequencing method to compare the community composition and bacterial diversity between brown and black seeds of Suaeda glauca. RESULTS: A significant difference was observed in seed coat structure and phytochemical properties between brown and black seeds of S. glauca. Total 9 phyla, 13 classes, 31 orders, 53 families, 102 genera were identified in the dimorphic seeds. The dominant phyla were Proteobacteria, Firmicutes, and Actinobacteria. The results showed that seed dimorphism had little impact on the diversity and richness of endophytic bacterial communities but significantly differs in the relative abundance of the bacterial community between brown and black seeds. At the phylum level, Actinobacteria tend to be enriched significantly in brown seeds. At the genus level, Rhodococcus, Ralstonia, Pelomonas and Bradyrhizobium tend to be enriched significantly in brown seeds, while Marinilactibacillus was mainly found in black seeds. Besides, brown seeds harbored a large number of bacteria with plant-growth-promoting traits, whereas black seeds presented bacteria with enzyme activities (i.e., pectinase, cellulolytic and xylanolytic activities). CONCLUSION: The endophytic bacterial community compositions were significantly different between dimorphic seeds of Suaeda glauca, and play an important role in the ecological adaptation of dimorphic seeds by performing different biological function roles. The endophytic bacterial communities of the dimorphic seeds may be influenced mainly by the seed coat structureand partly by the seed phytochemical characteristics. These findings provide valuable information for better understanding of the ecological adaptation strategy of dimorphic seeds in the disturbed environment.

Hongsoonwoonella zoysiae gen. nov., sp. nov., a new member of the family Stappiaceae isolated from a tidal mudflat.

A Gram stain-negative bacterial strain, designated SY4-7T, was isolated from rhizosphere mudflat of a halophyte (Zoysia sinica) collected around Seonyu Island, Republic of Korea. Cells of the organism were strictly aerobic, non-sporulating, non-motile rods and grew at 20-42 °C, pH 6-8 and 1-6% (w/v) NaCl. The 16S rRNA gene-based phylogenetic analyses revealed that strain SY4-7T formed an independent cluster separated from the recognized genera of the family Stappiaceae, which was also supported by phylogenomic analysis-based 92-core gene sequences. The type stains of the phylogenetically closest relatives were Stappia indica (95.6% sequence similarity), Stappia stellulata (95.1%) and Roseibium hamelinense (95.1%). The isoprenoid quinone was Q-10. The polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, three unidentified aminophospholipids, an unidentified phosphoglycolipid, an unidentified aminolipid, two unidentified phospholipids and an unidentified lipid. The major cellular fatty acids are C18:1ω7c and C19:1 cyclo ω8c. The G + C content of the genomic DNA is 60.7%. Discrimination of the organism from all the recognized genera of the family Stappiaceae was apparent by the chemotaxonomic and phylogenetic features. Based on the results presented here, strain SY4-7T (= KCTC 72226T = NBRC 113902T) represents a novel species of a new genus in the family Stappiaceae, for which the name Hongsoonwoonella zoysiae sp. nov. is proposed.

Microbacterium karelineae sp. nov. isolated from a halophyte plant in the Taklamakan desert.

A bacterial strain, designated TRM 80801T, was isolated from the Karelinea in Taklamakan desert, Xinjiang Uygur Autonomous Region, north-west China. Cells were Gram-stain-positive, aerobic, non-motile, short rods. Strain TRM 80801T grew at 4-50 °C, with optimum growth at 28 °C, and grew at pH 6.0-11.0 and 1-15 % (w/v) NaCl. Phylogenetic analyses of the 16S rRNA gene sequences placed strain TRM 80801T within the genus Microbacterium with the highest similarities to Microbacterium suaedae YZYP 306T (98.97 %) and Microbacterium indicum BBH6T (98.17 %), respectively. The DNA G+C content of TRM 80801T is 69.38 mol%. The cell-wall peptidoglycan contained the amino acids ornithine, glutamic acid, glycine and alanine, the diagnostic diamino acid was ornithine. The acyl type of the peptidoglycan was glycolyl. Whole-cell sugars were ribose, mannose, glucose, rhamnose and galactose. The major cellular fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The predominant menaquinones were MK-10, MK-11 and MK-12. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol. The whole-genome average nucleotide identity (ANI) value between strain TRM 80801T and Microbacterium suaedae YZYP 306T is 70.2 %. On the basis of the evidence presented in this study, strain TRM 80801T is representative of a novel species in the genus Microbacterium, for which the name Microbacterium karelineae sp. nov. is proposed. The type strain is TRM 80801T (=CCTCC AB 2019248T=KCTC 49357T).

Metabolomics Analyses Reveal Metabolites Affected by Plant Growth-Promoting Endophytic Bacteria in Roots of the Halophyte Mesembryanthemum crystallinum.

Mesembryanthemum crystallinum L. (common ice plant) is an edible halophyte. However, if ice plants are used to phytoremediate salinity soil, there are problems of slow initial growth, and a long period before active NaCl uptake occurs under higher salinity conditions. Application of endophytic bacteria may improve the problem, but there remain gaps in our understanding of how endophytic bacteria affect the growth and the biochemical and physiological characteristics of ice plants. The aims of this study were to identify growth-promoting endophytic bacteria from the roots of ice plants and to document the metabolomic response of ice plants after application of selected endophytic bacteria. Two plant growth-promoting endophytic bacteria were selected on the basis of their ability to promote ice plant growth. The two strains putatively identified as Microbacterium spp. and Streptomyces spp. significantly promoted ice plant growth, at 2-times and 2.5-times, respectively, compared with the control and also affected the metabolome of ice plants. The strain of Microbacterium spp. resulted in increased contents of metabolites related to the tricarboxylic acid cycle and photosynthesis. The effects of salt stress were alleviated in ice plants inoculated with the endobacterial strains, compared with uninoculated plants. A deeper understanding of the complex interplay among plant metabolites will be useful for developing microbe-assisted soil phytoremediation strategies, using Mesembryanthemum species.

Performance of halotolerant bacteria associated with Sahara-inhabiting halophytes Atriplex halimus L. and Lygeum spartum L. ameliorate tomato plant growth and tolerance to saline stress: from selective isolation to genomic analysis of potential determinants.

The use of halotolerant beneficial plant-growth-promoting (PGP) bacteria is considered as a promising eco-friendly approach to improve the salt tolerance of cash crops. One strategy to enhance the possibility of obtaining stress-alleviating bacteria is to screen salt impacted soils. In this study, amongst the 40 endophytic bacteria isolated from the roots of Sahara-inhabiting halophytes Atriplex halimus L. and Lygeum spartum L., 8 showed interesting NaCl tolerance in vitro. Their evaluation, through different tomato plant trials, permitted the isolate IS26 to be distinguished as the most effective seed inoculum for both plant growth promotion and mitigation of salt stress. On the basis of 16S rRNA gene sequence, the isolate was closely related to Stenotrophomonas rhizophila. It was then screened in vitro for multiple PGP traits and the strain-complete genome was sequenced and analysed to further decipher the genomic basis of the putative mechanisms underlying its osmoprotective and plant growth abilities. A remarkable number of genes putatively involved in mechanisms responsible for rhizosphere colonization, plant association, strong competition for nutrients, and the production of important plant growth regulator compounds, such as AIA and spermidine, were highlighted, as were substances protecting against stress, including different osmolytes like trehalose, glucosylglycerol, proline, and glycine betaine. By having genes related to complementary mechanisms of osmosensing, osmoregulation and osmoprotection, the strain confirmed its great capacity to adapt to highly saline environments. Moreover, the presence of various genes potentially related to multiple enzymatic antioxidant processes, able to reduce salt-induced overproduction of ROS, was also detected.

Fungi in mangrove ecosystems and their potential applications.

Mangrove fungi, their ecological role in mangrove ecosystems, their bioproducts, and potential applications are reviewed in this article. Mangrove ecosystems can play an important role in beach protection, accretion promotion, and sheltering coastlines and creeks as barriers against devastating tropical storms and waves, seawater, and air pollution. The ecosystems are characterized by high average and constant temperatures, high salinity, strong winds, and anaerobic muddy soil. The mangrove ecosystems also provide the unique habitats for the colonization of fungi which can produce different kinds of enzymes for industrial uses, recycling of plants and animals in the ecosystems, and the degradation of pollutants. Many mangrove ecosystem-associated fungi also can produce exopolysaccharides, Ca2+-gluconic acid, polymalate, liamocin, polyunsaturated fatty acids, biofuels, xylitol, enzymes, and bioactive substances, which have many potential applications in the bioenergy, food, agricultural, and pharmaceutical industries. Therefore, mangrove ecosystems are rich bioresources for bioindustries and ecology. It is necessary to identify more mangrove fungi and genetically edit them to produce a distinct array of novel chemical entities, enzymes, and bioactive substances.

Amelioration effect of salt-tolerant plant growth-promoting bacteria on growth and physiological properties of rice (Oryza sativa) under salt-stressed conditions.

For sustainable agriculture in saline soil, extensive exploitation of salt-tolerant plant growth-promoting (PGP) bacteria and other symbiotic bacteria is required. This study was carried out to evaluate the efficiency of native salt-tolerant rice rhizobacteria for plant growth promotion under salt stress. A total of 188 bacteria were screened for assessing salt-tolerant capacity and nine isolates tolerating 12% NaCl (w/v) concentration were selected. Biochemical and molecular identification revealed that the salt-tolerant bacteria belonged to Bacillus sp, Exiguobacterium sp, Enterobacter sp, Lysinibacillus sp, Stenotrophomonas sp, Microbacterium sp, and Achromobacter sp. The increase in NaCl concentration from 2 to 4% decreases the PGP activities such as IAA production, P solubilization, K solubilization, and nitrate reduction. The effects of inoculation of salt-tolerant bacteria on the growth and different physiological properties of rice (Oryza sativa) were studied. It was found that the salinity affected the root and shoot length of the control plants; however, bacterial inoculant were found to effectively promote the growth of paddy under salinity stress. Further, bacterial inoculants substantially enhanced total chlorophyll, proline, total phenol, and oxidative damage such as electrolyte leakage and membrane stability index under salt stress. This study suggests that salt-tolerant PGP bacteria may be used for cultivation of O. sativa in salinized agricultural lands.

Sphingobacterium endophyticum sp. nov., a novel endophyte isolated from halophyte.

A bacterial strain designated NYYP31T was isolated from the leaves of an annual halophytes, Suaeda corniculata Bunge, collected from the southern edge of the Gurbantunggut desert, north-west China. Strain NYYP31T was Gram-staining negative, strictly aerobic, rod-shaped, non-motile, and non-spore-forming. Growth was observed at 4-42 °C, at pH 5.0-10.0, in the presence of up to 8% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences and coding sequences of 92 protein clusters showed that strain NYYP31T should be assigned to the genus Sphingobacterium. 16S rRNA gene sequence similarity analysis showed that strain NYYP31T was most closely related to the type strain of Sphingobacterium daejeonense (97.9%) and Sphingobacterium lactis (97.7%). The predominant isoprenoid quinone was MK-7. The major fatty acids were identified as iso-C15:0, iso-C17:0 3-OH and summed feature 3 (C16:1 ω7c and/or C16:1 ω6c). The polar lipids were phosphatidylethanolamine, two unidentified phospholipids, three unidentified lipids, three unidentified amino phospholipids, and two unidentified glycolipids. The genomic DNA G + C content was 36.4 mol%. The average nucleotide identity (ANI) values for strain NYYP31T to the type strains of S. daejeonense and S. lactis were 77.9 and 74.1%, respectively, which were below the cut-off level (95-96%) for species delineation. Based on the above results, strain NYYP31T represents a novel species of the genus Sphingobacterium, for which the name Sphingobacterium endophyticum sp. nov. is proposed. The type strain is NYYP31T (= CGMCC 1.16979T = NBRC 114258T).

Aurantiacibacter rhizosphaerae sp. nov., isolated from a rhizosphere mudflat of a halophyte and proposal to reclassify Erythrobacter suaedae Lee et al. 2019. and Erythrobacter flavus Yoon et al. 2003 as Aurantiacibacter suaedae comb. nov. and Qipengyuania flava comb. nov., respectively.

A marine alphaproteobacterium, designated as strain GH3-10T, was isolated from the rhizosphere mud of a halophyte (Suaeda japonica) collected at the seashore of Gangwha Island, Republic of Korea. The isolate was found to be Gram-stain-negative, strictly aerobic, catalase- and oxidase-positive, non-motile, short rods and produced orange-coloured colonies. The 16S rRNA gene- and whole genome-based phylogenetic analyses exhibited that strain GH3-10T belonged to the genus Aurantiacibacter and was most closely related to Aurantiacibacter atlanticus s21-N3T (98.7 % 16S rRNA gene sequence similarity) and Aurantiacibacter marinus KCTC 23554T (98.4 %). The major respiratory quinone was ubiquinone-10. The polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingoglycolipid and an unidentified lipid. The major fatty acids were C18 : 1 ω7c, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and C18 : 1 ω7c 10-methyl. The DNA G+C content was 61.3 mol% (by genome). Average nucleotide identity and DNA-DNA relatedness values between the isolate and its phylogenetically closest relatives, together with phenotypic distinctness warranted the taxonomic description of a new species. On the basis of data obtained by a polyphasic approach, strain GH3-10T (=KCTC 62379T=JCM 32444T) represents a novel species of the genus Aurantiacibacter, for which the name Aurantiacibacter rhizosphaerae sp. nov. is proposed. According to phylogenetic coherence based on 16S rRNA genes and core genomes, it is also proposed that Erythrobacter suaedae Lee et al. 2019. and Erythrobacter flavus Yoon et al. 2003 be transferred to Aurantiacibacter suaedae comb. nov. and Qipengyuania flava comb. nov., respectively.

Pseudoalteromonas rhizosphaerae sp. nov., a novel plant growth-promoting bacterium with potential use in phytoremediation.

Strain RA15T was isolated from the rhizosphere of the halophyte plant Arthrocnemum macrostachyum growing in the Odiel marshes (Huelva, Spain). RA15T cells were Gram stain-negative, non-spore-forming, aerobic rods and formed cream-coloured, opaque, mucoid, viscous, convex, irregular colonies with an undulate margin. Optimal growth conditions were observed on tryptic soy agar (TSA) plates supplemented with 2.5 % NaCl (w/v) at pH 7.0 and 28 °C, although it was able to grow at 4-32 °C and at pH values of 5.0-9.0. The NaCl tolerance range was from 0 to 15 %. The major respiratory quinone was Q8 but Q9 was also present. The most abundant fatty acids were summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), C17 : 1 ω8c and C16 : 0. The polar lipids profile comprised phosphatidylglycerol and phosphatidylethanolamine as the most abundant representatives. Phylogenetic analyses confirmed the well-supported affiliation of strain RA15T within the genus Pseudoalteromonas, close to the type strains of Pseudoalteromonas neustonica, Pseudoalteromonas prydzensis and Pseudoalteromonas mariniglutinosa. Results of comparative phylogenetic and phenotypic studies between strain RA15T and its closest related species suggest that RA15T could be a new representative of the genus Pseudoalteromonas, for which the name Pseudoalteromonas rhizosphaerae sp. nov. is proposed. The type strain is RA15T (=CECT 9079T=LMG 29860T). The whole genome has 5.3 Mb and the G+C content is 40.4 mol%.

Halomonas radicis sp. nov., isolated from Arthrocnemum macrostachyum growing in the Odiel marshes(Spain) and emended descriptions of Halomonas xinjiangensis and Halomonas zincidurans.

Strain EAR18T was isolated as an endophyte from the roots of a halophyte plant, Arthrocnemum macrostachyum, growing in the Odiel marshes (Huelva, Spain). Cells of strain EAR18T were Gram- stain-negative, motile, non-spore-forming aerobic rods. It grew optimally on tryptic soy agar supplemented with 2.5 % NaCl (w/v), at pH 7 and 30 °C for 48 h. It tolerated NaCl from 0 to 25 % (w/v). It presented Q9 as the major quinone and C19 : 0 cyclo ω8c, summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0 as the predominant fatty acids. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and four unidentified phospholipids. The results of phylogenetic analysis based on 16S rRNA gene sequences revealed that strain EAR18T formed a well-supported clade with species Halomonas zincidurans B6T and Halomonas xinjiangensis TRM 0175T (similarities of 98.3 and 96.1 % respectively). Furthermore, digital DNA-DNA hybridization analysis resulted in values of 20.4 % with H. xinjiangensis TRM 0175T and 35.50 % with H. zincidurans B6T, and ANIb/ANIm results in values of 73.8 %/84.2 % with H. xinjiangensis TRM 0175T and 86.8 %/89.4 % with H. zincidurans B6T. Based on phylogeny and differential phenotypic properties in comparison with its closest related species, strain EAR18T is suggested to represent a new species in the genus Halomonas, for which the name Halomonas radicis sp. nov. is proposed. The type strain is EAR18T (=CECT 9077T=LMG 29859T). The whole genome was sequenced, and it had a total length of 4.6 Mbp and a G+C content of 64.9 mol%.