Phytohalomonas tamaricis gen. nov., sp. nov., an endophytic bacterium isolated from Tamarix ramosissima roots growing in Kumtag desert.

A gram-stain-negative, aerobic, non-spore-forming, rod-shaped, non-motile bacterium strain R4HLG17T was isolated from Tamarix ramosissima roots growing in Kumtag desert. The strain grew at salinities of 0-16% (w/v) NaCl (optimum 5-6%), pH 5-9 (optimum 7) and at 16-45 °C. Based on 16S rRNA gene sequence similarity, strain R4HLG17T belonged to the family Halomonadaceae and was most closely related to Halomonas lutea DSM 23508T(95.1%), followed by Halotalea alkalilenta AW-7T(94.8%), Salinicola acroporae S4-41T(94.8%), Salinicola halophilus CG4.1T(94.6%), and Larsenimonas salina M1-18T(94.4%). Multilocus sequence analysis (MLSA) based on the partial sequences of 16S rRNA, atpA, gyrB, rpoD, and secA genes indicated that the strain R4HLG17T formed an independent and monophyletic branch related to other genera of Halomonadaceae, supporting its placement as a new genus in this family. The draft genome of strain R4HLG17T was 3.6 Mb with a total G + C content of 55.1%. The average nucleotide identity to Halomonas lutea DSM 23508T was 83.5%. Q-9 was detected as the major respiratory quinone and summed feature 8 (C18:1ω7c/C18:1ω6c), summed feature 3 (C16:1ω7c/C16:1ω6c), and C16:0 as predominant cellular fatty acids. On the basis of chemotaxonomic, phylogenetic, and phenotypic evidence, strain R4HLG17T is concluded to represent a novel species of a new genus within Halomonadaceae, for which the name Phytohalomonas tamaricis gen. nov., sp. nov., is proposed. The type strain is R4HLG17T (=ACCC 19929T=KCTC 52415T).

Endophytic association of bioactive and halotolerant Humicola fuscoatra with halophytic plants, and its capability of producing anthraquinone and anthranol derivatives.

Halophytic plants growing in harsh desert environments are rich reservoirs of unique endophytic microorganisms. Here, healthy fresh plants of the families Tamaricaceae and Amarantaceae at three saline locations in Iran were investigated for their bioactive endophytic fungi. Among a vast number of isolates, eight isolates were identified as Humicola fuscoatra (Sordariomycetes, Pezizomycotina, Ascomycota) by microscopy and representative DNA sequences of the 5.8S rDNA (ITS) and partial ß-tubulin (TUB2). Those isolates were halotolerant, and highly bioactive, so that their intra- and extra-cellular metabolites possessed in vitro antifungal, antibacterial and antiproliferative activities, against a number of fungal and bacterial plant pathogens including the fungi Arthrobotrys conoides, Pyrenophora graminea, Pyricularia grisea and the bacteria Agrobacterium tumefaciens, Pseudomonas syringae and Xanthomonas oryzae. Chemical analyses of metabolites from the endophytes using HNMR, CNMR, NOESY, COSY, HMBC, HSQC, DEPT, TOCSY and EI MASS techniques identified 3,8-dihydroxy-1-methyl-9,10-anthracenedione (aloesaponarin II; an anthraquinone derivative), 1,8,9-anthracenetriol structure (chrysarobin; an anthranol derivative) and 2,4-di-tert-butylthiophenol in fungal extracts. To the best of our knowledge, this is the first report of endophytic association of halotolerant H. fuscoatra isolates with Tamaricaceae and Amarantaceae, and their bioactivity against plant pathogens. Also, the capability of chrysarobin and aloesaponarin II production is new to the fungal kingdom. These findings may find application in agriculture, pharmacology, and biotechnology.

A coumarin analogue NFA from endophytic Aspergillus fumigatus improves drought resistance in rice as an antioxidant.

BACKGROUND: Drought and its resulting oxidative damage are the major yield limiting factors for crops in arid and semi-arid regions. Recent studies have found that endophytic fungi coexisting in plants can alleviate biotic or abiotic damage to plant growth and development. In order to screen for the endophytes associated with drought stress, 12 strains of endophytic fungi with high antioxidant activity isolated from riparian plants Myricaria laxiflora were evaluated for their effects in rice by the crude extracts. RESULTS: Of the 12 endophytic fungi, Aspergillus fumigatus SG-17 functioned most effectively, with the crude extract exhibiting relatively higher antioxidant capacity both in vivo and in vitro. The subsequent MS and NMR analysis showed that the primary substance responsible for the antioxidant activity in the extract was (Z)-N-(4-hydroxystyryl) formamide (NFA), an analogue of coumarin. Enzyme activity assay in nerve cells SH-SY5Y showed that NFA could maintain the membrane integrity and regulate the antioxidase activity under oxidative stress. In rice suffering drought stress, NFA effectively alleviated the harm by regulating the contents of NADPH oxidases, antioxidants and heat shock proteins, all of which are closely related with the reactive oxygen species pathway. CONCLUSION: These findings indicated that some endophytes from plants often subjected to flooding and oxidative stress could enhance drought resistance by producing compounds such as NFA to regulate the oxidative pathway.

Nakamurella deserti sp. nov., isolated from rhizosphere soil of Reaumuria in the Taklamakan desert.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming, coccus-shaped actinobacterium, designated strain 12Sc4-1T, was isolated from a soil sample collected in the Taklamakan desert in Xinjiang Uygur Autonomous Region, China. Strain 12Sc4-1T grew at 8‒35 °C (optimum, 28‒30 °C), pH 6.0‒9.0 (optimum, pH 7.0) and in the presence of 0‒3 % (w/v) NaCl (optimum, 0 %). Phylogenetic analysis based on 16S rRNA gene sequence suggested that strain 12Sc4-1T belonged to the genus Nakamurella and shared the highest 16S rRNA gene sequence similarity to Nakamurella silvestris S20-107T (96.94 %). Strain 12Sc4-1T showed <96.0 % 16S rRNA gene sequence similarities to all other recognized members of the genus Nakamurella. Chemotaxonomic analyses showed that the isolate possessed meso-diaminopimelic acid as the diagnostic diamino acid of the peptidoglycan, glucose, mannose and galactose as whole-cell sugars, and MK-8(H4) as the predominant menaquinone. The polar lipids comprised diphosphatidylglycerol, phosphatidylethanolamine, an unidentified aminophospholipid, phosphatidylinositol, an unidentified phospholipid, an unidentified phosphoglycolipid and an unidentified glycolipid. The major fatty acids were C16 : 0 and anteiso-C15 : 0. The DNA G+C content was 72.1 mol% (draft genome sequence). On the basis of phylogenetic, phenotypic and chemotaxonomic analyses, strain 12Sc4-1T represents a novel species of the genus Nakamurella, for which the name Nakamurelladeserti sp. nov. is proposed. The type strain is 12Sc4-1T (=KCTC 49114T=CGMCC 1.16555T).

Pontibacter brevis sp. nov., isolated from rhizosphere soil of Tamarix ramosissima.

A Gram-stain-negative, oval-shaped and light pink pigmented bacterium, designated XAAS-2T, was isolated from rhizosphere soil of Tamarix ramosissima. The sole respiratory quinone of the type strain XAAS-2T was MK-7, and the principal cellular fatty acids were summed feature 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B) and iso-C15 : 0. The major polar lipids were phosphatidylethanolamine and two unidentified lipids. 16S rRNA gene sequence analysis indicated that strain XAAS-2T belonged to the genus Pontibacter within the family Cytophagaceae with sequence similarities of 93.9-97.1 % to other type species of the genus Pontibacter and to Pontibacter xinjiangensis CCTCC AB 207200T as the closest neighbour. The DNA G+C content of strain XAAS-2T was 50.6 mol%. The level of DNA-DNA relatedness of XAAS-2T and P. xinjiangensis CCTCC AB 207200T was 47.5 % (sd=3.27). Phenotypic and genotypic data suggested that strain XAAS-2T represents a novel species of the genus Pontibacter, for which the name Pontibacterbrevis sp. nov. is proposed, with the type strain XAAS-2T (=CCTCC AB 2016135T=JCM 31443T).

Bacillus tamaricis sp. nov., an alkaliphilic bacterium isolated from a Tamarix cone soil.

A Gram-stain-positive, alkaliphilic bacterium, designated EGI 80668T, was isolated from a Tamarix cone soil in Xinjiang, north-west China. Cells were facultatively anaerobic, terminal endospore-forming and motile by means of peritrichous flagella. Colonies were yellowish and the cells showed oxidase-negative and catalase-positive reactions. Strain EGI 80668T grew at pH 8.0-10.0 and with 0-10 % (w/v) NaCl (optimally at pH 9.0 and with 1-2 % NaCl) on marine agar 2216. The predominant menaquinone was MK-7. The major fatty acids were anteiso-C17 : 0 and anteiso-C15 : 0. The cellular polar lipids contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, four unknown phospholipids and one unknown aminophospholipid. The G+C content of the genomic DNA was 38.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain EGI 80668T was affiliated to the genus Bacillus. The highest 16S rRNA gene sequence similarity between strain EGI 80668T and a member of the genus Bacillus was 96.83 % with Bacillus cellulosilyticus JCM 9156T. A polyphasic taxonomic study based on morphological, physiological, biochemical and phylogenetic data indicated that strain EGI 80668T represents a novel species of the genus Bacillus, for which the name Bacillus tamaricis sp. nov. (type strain EGI 80668T=KCTC 33703T=CGMCC 1.15917T) is proposed.

The Impacts of Soil Fertility and Salinity on Soil Nitrogen Dynamics Mediated by the Soil Microbial Community Beneath the Halophytic Shrub Tamarisk.

Nitrogen (N) is one of the most common limiting nutrients for primary production in terrestrial ecosystems. Soil microbes transform organic N into inorganic N, which is available to plants, but soil microbe activity in drylands is sometimes critically suppressed by environmental factors, such as low soil substrate availability or high salinity. Tamarisk (Tamarix spp.) is a halophytic shrub species that is widely distributed in the drylands of China; it produces litter enriched in nutrients and salts that are thought to increase soil fertility and salinity under its crown. To elucidate the effects of tamarisks on the soil microbial community, and thus N dynamics, by creating "islands of fertility" and "islands of salinity," we collected soil samples from under tamarisk crowns and adjacent barren areas at three habitats in the summer and fall. We analyzed soil physicochemical properties, inorganic N dynamics, and prokaryotic community abundance and composition. In soils sampled beneath tamarisks, the N mineralization rate was significantly higher, and the prokaryotic community structure was significantly different, from soils sampled in barren areas, irrespective of site and season. Tamarisks provided suitable nutrient conditions for one of the important decomposers in the area, Verrucomicrobia, by creating "islands of fertility," but provided unsuitable salinity conditions for other important decomposers, Flavobacteria, Gammaproteobacteria, and Deltaproteobacteria, by mitigating salt accumulation. However, the quantity of these decomposers tended to be higher beneath tamarisks, because they were relatively unaffected by the small salinity gradient created by the tamarisks, which may explain the higher N mineralization rate beneath tamarisks.

Salinicola tamaricis sp. nov., a heavy-metal-tolerant, endophytic bacterium isolated from the halophyte Tamarix chinensis Lour.

A Gram-stain-negative, rod-shaped bacterium, strain F01T, was isolated from leaves of Tamarix chinensis Lour. The isolate grew optimally at 30 °C, at pH 7.0 and with 5.0 % (w/v) NaCl, and showed a high tolerance to manganese, lead, nickel, ferrous ions and copper ions. The major fatty acids were C18 : 1ω7c and C16 : 0, and the predominant respiratory quinone was Q-9. Polar lipids were dominated by diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, unidentified aminoglycolipids and phospholipids. The DNA G+C content was 65.8 %. Based on multilocus phylogenetic analysis, strain F01T belonged to the genus Salinicola, with highest 16S rRNA gene sequence similarity to Salinicola peritrichatus CGMCC 1.12381T (97.7 %). The level of DNA-DNA hybridization between strain F01T and closely related Salinicola strains was well below 70 %. According to the phenotypic, genetic and chemotaxonomic data, strain F01T is considered to represent a novel species in the genus Salinicola, for which the name Salinicola tamaricis sp. nov. is proposed. The type strain is F01T (=CCTCC AB 2015304T=KCTC 42855T).

Metagenomic Signatures of Bacterial Adaptation to Life in the Phyllosphere of a Salt-Secreting Desert Tree.

UNLABELLED: The leaves of Tamarix aphylla, a globally distributed, salt-secreting desert tree, are dotted with alkaline droplets of high salinity. To successfully inhabit these organic carbon-rich droplets, bacteria need to be adapted to multiple stress factors, including high salinity, high alkalinity, high UV radiation, and periodic desiccation. To identify genes that are important for survival in this harsh habitat, microbial community DNA was extracted from the leaf surfaces of 10 Tamarix aphylla trees along a 350-km longitudinal gradient. Shotgun metagenomic sequencing, contig assembly, and binning yielded 17 genome bins, six of which were >80% complete. These genomic bins, representing three phyla (Proteobacteria,Bacteroidetes, and Firmicutes), were closely related to halophilic and alkaliphilic taxa isolated from aquatic and soil environments. Comparison of these genomic bins to the genomes of their closest relatives revealed functional traits characteristic of bacterial populations inhabiting the Tamarix phyllosphere, independent of their taxonomic affiliation. These functions, most notably light-sensing genes, are postulated to represent important adaptations toward colonization of this habitat. IMPORTANCE: Plant leaves are an extensive and diverse microbial habitat, forming the main interface between solar energy and the terrestrial biosphere. There are hundreds of thousands of plant species in the world, exhibiting a wide range of morphologies, leaf surface chemistries, and ecological ranges. In order to understand the core adaptations of microorganisms to this habitat, it is important to diversify the type of leaves that are studied. This study provides an analysis of the genomic content of the most abundant bacterial inhabitants of the globally distributed, salt-secreting desert tree Tamarix aphylla Draft genomes of these bacteria were assembled, using the culture-independent technique of assembly and binning of metagenomic data. Analysis of the genomes reveals traits that are important for survival in this habitat, most notably, light-sensing and light utilization genes.

Egibacter rhizosphaerae gen. nov., sp. nov., an obligately halophilic, facultatively alkaliphilic actinobacterium and proposal of Egibaceraceae fam. nov. and Egibacterales ord. nov.

A novel obligately halophilic, facultatively alkaliphilic actinobacterium, designated EGI 80759T, was isolated from the rhizosphere of Tamarix hispida Willd, Karamay, Xinjiang province, north-west China. Cells of strain EGI 80759T were Gram-stain-positive, non-motile and non-endospore-forming rods. Strain EGI 80759T showed obligately halophilic growth with a tolerance to 8-25 % (w/v) NaCl (optimum growth at 10-12 %, w/v) and facultatively alkaliphilic growth within the pH range 7.0-11.0 (optimum growth at pH 9.0-10.0). Cell-wall hydrolysates of the isolate contained meso-diaminopimelic acid (peptidoglycan type A1γ), with glucose, glucosamine, ribose and mannose as the major sugars. The major fatty acids identified were 10-methyl-C17 : 0, C17 : 1ω8c and C17 : 0. The predominant menaquinone was MK-9(H4). The G+C content of the genomic DNA was 72.1 mol%. Phylogenetic analysis, based on 16S rRNA gene sequences, revealed that strain EGI 80759T clustered with members of the class Nitriliruptoria and showed highest 16S rRNA gene sequence similarities with Euzebya tangerina F10T (90.3 %) and Nitriliruptor alkaliphilus ANL-iso2T (88.1 %). On the basis of the data obtained from phenotypic and chemotaxonomic studies and the phylogenetic analysis, the isolate is proposed to be a representative of a novel genus and a novel species, Egibacter rhizosphaerae gen. nov., sp. nov., of a proposed novel family, Egibacteraceae fam. nov., and order, Egibacterales ord. nov., within the class Nitriliruptoria. The type strain of the type species, Egibacter rhizosphaerae, is EGI 80759T ( = CGMCC 1.14997T = KCTC 39588T).

Alleviating salt stress in tomato seedlings using Arthrobacter and Bacillus megaterium isolated from the rhizosphere of wild plants grown on saline-alkaline lands.

Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline-alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1-7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline-alkaline lands could be used for alleviating salt stress in crop plants.

Falsirhodobacter deserti sp. nov., isolated from sandy soil.

A Gram-stain-negative, non-motile, heterotrophic, rod-shaped bacterium, designated strain W402(T), was isolated from an enrichment culture of a Tamarix ramosissima rhizosphere soil sample from the Xinjiang desert in the PR China. Analysis of the almost-complete 16S rRNA gene sequence showed that the isolate was phylogenetically related to a species of the genus Falsirhodobacter, having a close relationship to Falsirhodobacter halotolerans JA744(T) (97 % similarity). However, DNA-DNA relatedness between W402(T) and F. halotolerans JA744(T) was 43.2±1.2 %. Strain W402(T) grew in 0-10 % (w/v) NaCl. The temperature and pH ranges for growth were 10-40 °C and pH 5.5-10.0, respectively. Optimal growth occurred at 1-3 % (w/v) NaCl, 30 °C and pH 7.0. The predominant cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c, 61.4 %), C18 : 0 (9.8 %) and 11-methyl C18 : 1ω7c (8.2 %). The major quinone of strain W402(T) was Q-10. Phosphatidylethanolamine was predominant in the polar lipid profile. The DNA G+C content of strain W402(T) was 67.3 mol%. Taken together, these results confirm that W402(T) represents a novel species of the genus Falsirhodobacter, for which the name Falsirhodobacter deserti sp. nov. is proposed. The type strain is W402(T) ( = ACCC 05851(T) = KCTC 32408(T)).

Allosalinactinospora lopnorensis gen. nov., sp. nov., a new member of the family Nocardiopsaceae isolated from soil.

A novel actinomycete, designated strain CA15-2(T), was isolated from a soil sample collected from the rhizosphere of tamarisk in the Lop Nor region, Xinjiang, China, and was characterized by using a polyphasic taxonomic approach. Optimal growth occurred at 37 °C and pH 7.5-8.0 and with 5% (w/v) NaCl. Strain CA15-2(T) formed white to pale-yellow branched substrate mycelium without fragmentation and sparse aerial mycelium with wavelike curves. Whole-cell hydrolysates of the isolate contained meso-diaminopimelic acid as the diagnostic diamino acid of the cell wall but no diagnostic sugars. The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylmethylethanolamine, phosphatidylethanolamine, one unidentified glycolipid, one unidentified phospholipid and other unidentified lipids. MK-9(H8), MK-10(H8) and MK-10(H6) were the predominant menaquinones. The major fatty acids were iso-C16:0 and C16:0. The G+C content of the genomic DNA was 69.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CA15-2(T) formed a distinct subclade in the family Nocardiopsaceae, with less than 95% 16S rRNA gene sequence similarity to all known members of the family Nocardiopsaceae. On the basis of the evidence from our polyphasic study, a novel genus, Allosalinactinospora gen. nov., is proposed, with the type species Allosalinactinospora lopnorensis gen. nov., sp. nov. The type strain of Allosalinactinospora lopnorensis is strain CA15-2(T) ( = DSM 45697(T) =CGMCC 4.7074(T)).

Tamaricihabitans halophyticus gen. nov., sp. nov., an endophytic actinomycete of the family Pseudonocardiaceae.

A novel actinomycete strain, designated KLBMP 1356T, was isolated from the root of halophyte Tamarix chinensis Lour. collected from the coastal area of Jiangsu province, PR China. The isolate was characterized using a polyphasic approach. Comparative analysis of the 16S rRNA gene sequence indicated that strain KLBMP 1356T was phylogenetically related to members of the family Pseudonocardiaceae and formed a distinct monophyletic clade between the genera Amycolatopsis (93.1-94.7 % 16S rRNA gene sequence similarity), Prauserella (93.6-95.1 %) and Saccharomonospora (93.2-94.3 %). The isolate displayed long spore chains containing rod-shaped and smooth-surfaced spores. Strain KLBMP 1356T contained meso-diaminopimelic acid as the diagnostic diamino acid, and galactose, arabinose and glucose as the whole-cell sugars. The major menaquinone was MK-9(H4) and the fatty acid profile was characterized by the predominance of iso-C16 : 0, C17 : 1ω8c, C17 : 1ω6c and C17 : 0. The polar lipids comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, unknown aminophospholipids and an unknown glycolipid. Mycolic acids were not present. The G+C content of the genomic DNA was 67.2 mol%. On the basis of the evidence from this polyphasic study, strain KLBMP 1356T is considered to represent a novel species of a new genus in the family Pseudonocardiaceae, for which the name Tamaricihabitans halophyticus gen. nov., sp. nov. is proposed. The type strain of the type species is KLBMP 1356T ( = DSM 45765T = NBRC 109361T).

Prauserella endophytica sp. nov., an endophytic actinobacterium isolated from Tamarix taklamakanensis.

A novel endophytic actinobacterium, designated strain SP28S-3(T), was isolated from a surface-sterilized stem of Tamarix taklamakanensis collected from the southern edge of Taklamakan desert, Xinjiang, China. Strain SP28S-3(T) was found to show chemotaxonomic and morphological properties consistent with its classification in the genus Prauserella. The polar lipids were found to consist of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphoglycolipid, phosphatidylcholine, phosphatidylinositol, a glycolipid, an aminolipid and unidentified phospholipids. The major fatty acids (>10 %) were identified as iso-C16:0 and C16:0. The genomic DNA G+C content was determined to be 69.7 mol%. Phylogenetic analysis of strain SP28S-3(T) clearly showed that the strain had the highest similarity of 16S rRNA gene sequence with Prauserella coralliicola SCSIO 11529(T) (99.9 %), followed by Prauserella marina DSM 45268(T) (97.0 %) and is affiliated with the genus Prauserella. The low level (47.8 ± 5.5 %) of DNA-DNA relatedness between strain SP28S-3(T) and P. coralliicola SCSIO 11529(T) combined with other polyphasic taxonomic evidence clearly support the conclusion that strain SP28S-3(T) represents a novel Prauserella species, for which the name Prauserella endophytica sp. nov. is proposed. The type strain is SP28S-3(T) (=DSM 46655(T) = CGMCC 4.7182 (T)).

Diversity of endophytic fungi of Myricaria laxiflora grown under pre- and post-flooding conditions.

Myricaria laxiflora is distributed along the riverbanks of the Yangtze River valley. The Three Gorges Dam has dramatically changed the habitat of M. laxiflora, which has evolved to develop increased resistance to flooding stress. In order to elucidate the relationship between plant endophytic fungi and flooding stress, we isolated and taxonomically characterized the endophytic fungi of M. laxiflora. One hundred and sixty-three fungi were isolated from healthy stems, leaves and roots of M. laxiflora grown under pre- and post-flooding conditions. Culture and isolation were carried out under aerobic and anaerobic conditions. Based on internal transcribed spacer sequence analysis and morphological characteristics, the isolates exhibited abundant biodiversity; they were classified into 5 subphyla, 7 classes, 12 orders, 17 families, and 26 genera. Dominant endophytes varied between pre- and post-flooding plants, among different plant tissues, and between aerobic and anaerobic culture conditions. Aspergillus and Alternaria accounted for more than 55% of all isolates. Although the number of isolates from post-flooding plants was greater, endophytes from pre-flooding plants were more diverse and abundant. Endophytes were distributed preferentially in particular tissues; this affinity was constrained by both the host habitat and the oxygen availability of the host.

Diverse microhabitats experienced by Halomonas variabilis on salt-secreting leaves.

The leaf surfaces of the salt-excreting tree Tamarix aphylla harbor a wide diversity of halophilic microorganisms, including Halomonas sp., but little is known of the factors that shape community composition in this extreme habitat. We isolated a strain of Halomonas variabilis from the leaf surface of T. aphylla and used it to determine the heterogeneity of salt concentrations experienced by bacteria in this environment. This halophilic strain was transformed with a proU::gfp reporter gene fusion, the fluorescence of which was responsive to NaCl concentrations up to 200 g liter(-1). These bioreporting cells were applied to T. aphylla leaves and were subsequently recovered from dew droplets adhering to the leaf surface. Although cells from within a given dew droplet exhibited similar green fluorescent protein fluorescence, the fluorescence intensity varied between droplets and was correlated with the salt concentration measured in each drop. Growth of H. variabilis was observed in all droplets, regardless of the salt concentration. However, cells found in desiccated microniches between dew drops were low in abundance and generally dead. Other bacteria recovered from T. aphylla displayed higher desiccation tolerance than H. variabilis, both in culture and on inoculated plants, despite having lower osmotic tolerance. Thus, the Tamarix leaf surface can be described as a salty desert with occasional oases where water droplets form under humid conditions. While halotolerant bacteria such as Halomonas grow in high concentrations of salt in such wet microniches, other organisms are better suited to survive desiccation in sites that are not wetted.

Streptomyces halophytocola sp. nov., an endophytic actinomycete isolated from the surface-sterilized stems of a coastal halophyte Tamarix chinensis Lour.

A novel actinomycete, designated KLBMP 1284(T), was isolated from the surface-sterilized stems of a coastal halophyte Tamarix chinensis Lour. collected from the city of Nantong, Jiangsu Province, east China. The strain was found to have morphological and chemotaxonomic characteristics typical of members of the genus Streptomyces. Analysis of the 16S rRNA gene sequence of strain KLBMP 1284(T) revealed that the strain formed a distinct clade within the phylogenetic tree based on 16S rRNA gene sequences and the highest sequence similarity (99.43 %) was to Streptomyces sulphureus NRRL B-1627(T). 16S rRNA gene sequence similarity to other species of the genus Streptomyces was lower than 97 %. Based on DNA-DNA hybridization values and comparison of morphological and phenotypic data, KLBMP 1284(T) could be distinguished from the closest phylogenetically related species, Streptomyces sulphureus NRRL B-1627(T). Thus, based on these data, it is evident that strain KLBMP 1284(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces halophytocola sp. nov. is proposed. The type strain is KLBMP 1284(T) (= KCTC 19890(T) = NBRC 108770(T)).

Distance-decay relationships partially determine diversity patterns of phyllosphere bacteria on Tamarix trees across the Sonoran Desert [corrected].

Dispersal limitation in phyllosphere communities was measured on the leaf surfaces of salt-excreting Tamarix trees, which offer unique, discrete habitats for microbial assemblages. We employed 16S rRNA gene pyrosequencing to measure bacterial community dissimilarity on leaves of spatially dispersed Tamarix specimens in sites with uniform climatic conditions across the Sonoran Desert in the Southwestern United States. Our analyses revealed diverse bacterial communities with four dominant phyla that exhibited differential effects of environmental and geographic variables. Geographical distance was the most important parameter that affected community composition, particularly that of betaproteobacteria, which displayed a statistically significant, distance-decay relationship.

Disrupting mycorrhizal mutualisms: a potential mechanism by which exotic tamarisk outcompetes native cottonwoods.

The disruption of mutualisms between plants and mycorrhizal fungi is a potentially powerful mechanism by which invasives can negatively impact native species, yet our understanding of this mechanism's role in exotic species invasion is still in its infancy. Here, we provide several lines of evidence indicating that invasive tamarisk (Tamarix sp.) negatively affects native cottonwoods (Populus fremontii) by disrupting their associations with arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. At a field site in the early stages of tamarisk invasion, cottonwoods with tamarisk neighbors had reduced EM colonization and altered EM fungal community composition relative to cottonwoods with native neighbors, leading to reductions in EM propagule abundance in the soil beneath tamarisk. Similarly, AM colonization of cottonwoods was reduced with a tamarisk neighbor, but there were no significant changes in AM fungal spore communities or propagule abundance. Root colonization by nonmycorrhizal fungi, including potential pathogens, was higher in cottonwoods with tamarisk neighbors. A greenhouse experiment in which AM and EM inoculation and plant neighbor were manipulated in a fully factorial design showed that cottonwoods benefited from mycorrhizas, especially EM, in terms of shoot biomass when grown with a conspecific, but shoot biomass was similar to that of nonmycorrhizal controls when cottonwoods were grown with a tamarisk neighbor. These results are partially explained by a reduction in EM but not AM colonization of cottonwoods by a tamarisk neighbor. Tamarisk neighbors negatively affected cottonwood specific leaf area, but not chlorophyll content, in the field. To pinpoint a mechanism for these changes, we measured soil chemistry in the field and the growth response of an EM fungus (Hebeloma crustuliniforme) to salt-amended media in the laboratory. Tamarisk increased both NO3- concentrations and electrical conductivity 2.5-fold beneath neighboring cottonwoods in the field. Salt-amended media did not affect the growth of H. crustuliniforme. Our findings demonstrate that a nonnative species, even in the early stages of invasion, can negatively affect a native species by disrupting its mycorrhizal symbioses. Some of these changes in mycorrhizal fungal communities may remain as legacy effects of invasives, even after their removal, and should be considered in management and restoration efforts.