Dynamics of the cytosol soluble carbohydrates and membrane lipids in response to ambient pH in alkaliphilic and alkalitolerant fungi

Comparative composition of lipids and cytosol soluble carbohydrates at different ambient pH values was studied for two obligately alkaliphilic fungi (Sodiomyces magadii and S. alkalinus) and for two alkalitolerant ones (Acrostalagmus luteoalbus and Chordomyces antarcticus). The differences and common patterns were revealed in responses to pH stress for the fungi with different types of adaptation to ambient pH. While trehalose was one of the major cytosol carbohydrates in alkaliphilic fungi under optimal growth conditions (pH 10.2), pH decrease to 7.0 resulted in doubling its content. In alkalitolerant fungi trehalose was a minor component and its level did not change significantly at different pH. In alkalitolerant fungi, arabitol and mannitol were the major carbohydrate components, with their highest ratio observed under alkaline conditions and the lowest one, under neutral and acidic conditions. In alkaliphiles, significant levels of arabitol were revealed only under alkaline conditions, which indicated importance of trehalose and arabitol for alkaliphily. Decreased pH resulted in the doubling of the proportion of phosphatidic acids among the membrane lipids, which was accompanied by a decrease in the fractions of phosphatidylcholines and sterols. Alkalitolerant fungi also exhibited a decrease in sterol level at decreased pH, but against the background of increased proportion of one of phospholipids. Decreased unsaturation degree in the fatty acids of the major phospholipids was a common response to decreased ambient pH.     

Sucrose Lipids of Arthrobacteria,Corynebacteria and Nocardia Grown on Sucrose

Arthrobacter paraffineus KY 4303, when grown on sucrose as the sole carbon source, produced novel glycolipids, either of which was different from trehalose lipid produced from n-alkane by the same microorganism. Two kinds of glycolipids were isolated by chromatography on silicic acid columns. Major components of these lipids were sucrose and α-branched β-hydroxy fatty acid. One of the lipid (SL–1, having high polarity) was identified as 6-O-monofattyacyl glucosly-β-fructoside. Another (SL–2, having low polarity) was partly characterized as sucrose ester of at least two moles of the fatty acid.

Formation of sucrose lipids was also demonstrated in sucrose-grown cells of several microorganisms of Corynebacteria, Nocardia and Brevibacteria, which were isolated as hydrocarbon-utilizing bacteria and could produce a considerable amount of trehalose lipid from n-alkane.     

Trehalose Lipid and α-Branched-β-hydroxy Fatty Acid Formed by Bacteria Grown on n-Alkanes

A bacterium isolated in our laboratory, Arthrobacter paraffineus KY 4303. when grown on n-paraffin as the sole source of carbon, produced anthrone-positive lipid in the emulsion layer (holding bacterial cells, lipids and n-paraffin remained) of the culture medium. This was isolated and identified as α-branched-β-hydroxy fatty acid trehalose ester.

The addition of penicillin to the growing culture caused a significant suppression of trehalose lipid formation and led consequently to the accumulation of both the precursors, α, α-trehalose and α-branched-β-hydroxy fatty acid, in the culture medium.

The formation of trehalose lipid was also observed in other bacteria which can utilize n-paraffin as the sole source of carbon. In addition, a possible role of this trehalose lipid in the utilization of n-paraffin by these bacteria was discussed.     

Trehalose Biosynthesis in Response to Abiotic Stresses

Trehalose is a non‐reducing disaccharide that is present in diverse organisms ranging from bacteria and fungi to invertebrates, in which it serves as an energy source, osmolyte or protein/membrane protectant. The occurrence of trehalose and trehalose biosynthesis pathway in plants has been discovered recently. Multiple studies have revealed regulatory roles of trehalose‐6‐phosphate, a precursor of trehalose, in sugar metabolism, growth and development in plants. Trehalose levels are generally quite low in plants but may alter in response to environmental stresses. Transgenic plants overexpressing microbial trehalose biosynthesis genes have been shown to contain increased levels of trehalose and display drought, salt and cold tolerance. In‐silico expression profiling of all Arabidopsis trehalose‐6‐phosphate synthases (TPSs) and trehalose‐6‐phosphate phosphatases (TPPs) revealed that certain classes of TPS and TPP genes are differentially regulated in response to a variety of abiotic stresses. These studies point to the importance of trehalose biosynthesis in stress responses.     

The ethanol-induced global alteration in Arthrobacter simplex and its mutants with enhanced ethanol tolerance

Arthrobacter simplex has received considerable interests due to its superior Δ¹-dehydrogenation ability. Ethanol used as co-solvent is a stress commonly encountered during biotransformation. Therefore, studies of ethanol tolerance of A. simplex are of great importance to improve the biotransformation efficiency. In this paper, the combined analysis of physiological properties, cell compositions, stress-responsive metabolites, and proteome profiles was carried out to achieve a global view of ethanol tolerance of A. simplex. Under sublethal conditions, cell permeability and membrane fluidity exhibited concentration-dependent increase by affecting the contents or compositions of cell peptidoglycan, lipids, phospholipids, and fatty acids. Among them, cis–trans isomerization of unsaturated fatty acids was a short-term and reversible process, while the changes in phospholipid headgroups and increase in saturation degree of fatty acids were long-term and irreversible processes, which collectively counteracted the elevated membrane fluidity caused by ethanol and maintained the membrane stability. The decreased intracellular ATP content was observed at high ethanol concentration since proton motive force responsible for driving ATP synthesis was dissipated. The involvement of trehalose and glycerol, oxidative response, and DNA damage were implicated due to their changes in positive proportion to ethanol concentration. Proteomic data supported that ethanol invoked a global alteration, among which, the change patterns of proteins participated in the biosynthesis of cell wall and membrane, energy metabolism, compatible solute metabolism, and general stress response were consistent with observations from cell compositions and stress-responsive metabolites. The protective role of proteins participated in DNA repair and antioxidant system under ethanol stress was validated by overexpression of the related genes. This is the first demonstration on ethanol tolerance mechanism of A. simplex, and the current studies also provide targets to engineer ethanol tolerance of A. simplex.

     

Biosorption of Copper(II) by Live and Dried Biomass of the White Rot Fungi Phanerochaete chrysosporium and Funalia trogii

Biosorption is an innovative and alternative technology to remove heavy metal pollutants from aqueous solution using live, inactive and dead biomasses such as algae, bacteria and fungi. In this study, live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was applied as heavy metal adsorbent material. Biosorption of copper(II) cations in aqueous solution by live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was investigated to study the effects of initial heavy metal concentration, pH, temperature, contact time, agitation rate and amount of fungus. Copper(II) was taken up quickly by fungal biomass (live or dried) during the first 15 min and the most important factor which affected the copper adsorption by live and dried biomass was the pH value. An initial pH of around 5.0 allowed for an optimum adsorption performance. Live biomass of two white rot fungi showed a high copper adsorption capacity compared with dried biomass. Copper(II) uptake was found to be independent of temperature in the range of 20–45 °C. The initial metal ion concentration (10–300 mg/L) significantly influenced the biosorption capacity of these fungi. The results indicate that a biosorption as high as 40–60 % by live and dried biomass can be obtained under optimum conditions.     

Expression of the Grifola frondosa Trehalose Synthase Gene and Improvement of Drought-Tolerance in Sugarcane （Saccharum officinarum L.）

Trehalose Is a nonreduclng dlsaccharlde of glucose that functions as a protectant In the stabilization of blologlcal structures and enhances stress tolerance to abiotic stresses in organisms. We report here the expression of a Grlfola frondosa trehalose synthase （TSase） gene for Improving drought tolerance In sugarcane （Saccharum offlclnarum L.）. The expression of the transgene was under the control of two tandem copies of the CaMV35S promoter and transferred Into sugarcane by Agrobacterium tumefaciens EHA105. The transgenlc plants accumulated high levels of trehalose, up to 8.805-12.863 mg/g fresh weight, whereas It was present at undetectable level in nontransgenlc plants. It has been reported that transgenlc plants transformed with Escherlchla coil TPS （trehalose-6-phosphatesynthase） and/or TPP （trehalose-6-phosphate phosphatase） are severely stunted and have root morphologlc alterations. Interestingly, our transgenlc sugarcane plants had no obvious morphological changes and no growth Inhibition in the field. Trehalose accumulation in 35S-35S：TSase plants resulted In In- creased drought tolerance, as shown by the drought and the drought physiological Indexes, such as the rate of bound water/free water, plasma membrane permeability, malondlaldehyde content, chlorophyll a and b contents, and activity of SOD and POD of the excised leaves. These results suggest that transgenlc plants transformed with the TSase gene can accumulate high levels of trehalose and have enhanced tolerance to drought.     

Additive roles of two TPS genes in trehalose synthesis,conidiation, multiple stress responses and host infection of a fungal insect pathogen

Intracellular trehalose accumulation is relevant to fungal life and pathogenicity. Trehalose-6-phosphate synthase (TPS) is known to control the first step of trehalose synthesis, but functions of multiple TPS genes in some filamentous fungi are variable. Here, we examined the functions of two TPS genes (tpsA and tpsB) in Beauveria bassiana, a fungal insect pathogen widely applied in arthropod pest control. Intracellular TPS activity and trehalose content decreased by 71–75 and 72–80% in ΔtpsA, and 21–30 and 15–45% in ΔtpsB, respectively, and to undetectable levels in ΔtpsAΔtpsB, under normal and stressful conditions. The three mutants lost 33, 50, and 98% of conidiation capacity in standard cultures. Conidial quality indicated by viability, density, intracellular trehalose content, cell wall integrity, and hydrophobicity was more impaired in ΔtpsA than in ΔtpsB and mostly in ΔtpsAΔtpsB, which was also most sensitive to nutritional, chemical, and environmental stresses and least virulent to Galleria mellonella larvae. Almost all of phenotypic defects in ΔtpsAΔtpsB approached to the sums of those observed in ΔtpsA and ΔtpsB and were restored by targeted gene complementation. Altogether, TpsA and TpsB play complementary roles in sustaining trehalose synthesis, conidiation capacity, conidial quality, multiple stress tolerance, and virulence, highlighting a significance of both for the fungal adaptation to environment and host.

     

Environmental drivers of ectomycorrhizal communities in Europe's temperate oak forests

Ectomycorrhizal fungi are major ecological players in temperate forests, but they are rarely used in measures of forest condition because large‐scale, high‐resolution, standardized and replicated belowground data are scarce. We carried out an analysis of ectomycorrhizas at 22 intensively monitored long‐term oak plots, across nine European countries, covering complex natural and anthropogenic environmental gradients. We found that at large scales, mycorrhizal richness and evenness declined with decreasing soil pH and root density, and with increasing atmospheric nitrogen deposition. Shifts in mycorrhizas with different functional traits were detected; mycorrhizas with structures specialized for long‐distance transport related differently to most environmental variables than those without. The dominant oak‐specialist Lactarius quietus, with limited soil exploration abilities, responds positively to increasing nitrogen inputs and decreasing pH. In contrast, Tricholoma, Cortinarius and Piloderma species, with medium‐distance soil exploration abilities, show a consistently negative response. We also determined nitrogen critical loads for moderate (9.5–13.5 kg N/ha/year) and drastic (17 kg N/ha/year) changes in belowground mycorrhizal root communities in temperate oak forests. Overall, we generated the first baseline data for ectomycorrhizal fungi in the oak forests sampled, identified nitrogen pollution as one of their major drivers at large scales and revealed fungi that individually and/or in combination with others can be used as belowground indicators of environmental characteristics.     

Heat shock response in the thermophilic fungus Rhizomucor miehei

Changes in the composition of the membrane lipids and cytosol carbohydrates of the thermophilic fungus Rhizomucor miehei in response to heat shock were studied. Under optimal conditions (41–43°C), high trehalose content (8–11%) was found at all stages of growth of submerged culture. Heat shock (51–53°C) for 1 h did not result in enhanced trehalose synthesis, while increase in shock duration to 3 h resulted in a significant increase in trehalose content. The share of sterols and phosphatidic acids in the membrane lipids increased, while the share of phosphatidylcholines and phosphatidylethanolamines decreased. These processes resulted in increased content of non-bilayer lipids, while the unsaturation degree of the fatty acids of the major phospholipids did not decrease. Comparison of resistance to lethal heat shock in the control and experimental variants of R. miehei revealed that this thermophilic fungus exhibited no acquired heat resistance.     

Biochemical characterization of a thermostable endomannanase/endoglucanase from Dictyoglomus turgidum

Dictyoglomus turgidum is a hyperthermophilic, anaerobic, gram-negative bacterium that shows an array of putative glycoside hydrolases (GHs) encoded by its genome, a feature that makes this microorganism very interesting for biotechnological applications. The aim of this work is the characterization of a hyperthermophilic GH5, Dtur_0671, of D. turgidum, annotated as endoglucanase and herein named DturCelB in agreement to DturCelA, which was previously characterized. The synthetic gene was expressed in Escherichia coli. The purified recombinant enzyme is active as a monomer (40 kDa) and CD structural studies showed a conserved α/β structure at different temperatures (25 and 70 °C) and high thermoresistance (Tm of 88 °C). Interestingly, the enzyme showed high endo-β-1,4-mannanase activity vs various mannans, but low endo-β-1,4 glucanase activity towards carboxymethylcellulose. The K _M and V _max of DturCelB were determined for both glucomannan and CMC: they were 4.70 mg/ml and 473.1 μmol/min mg and 1.83 mg/ml and 1.349 μmol/min mg, respectively. Its optimal activity towards temperature and pH resulted to be 70 °C and pH 5.4, respectively. Further characterization highlighted good thermal stability (~ 50% of enzymatic activity after 2 h at 70 °C) and pH stability over a broad range (> 90% of activity after 1 h in buffer, ranging pH 5–9); resistance to chemicals was also observed.

     

秦岭辛家山林区落叶松外生菌根真菌多样性

【目的】以秦岭辛家山林区落叶松为研究对象,观察鉴定与其共生的外生菌根真菌。【方法】通过野外调查结合形态学和分子生物学鉴定方法。【结果】鉴定出31种外生菌根真菌,分属2门4目11科11属,分别有毛革菌属(Tomentella)、丝盖伞属(Inocybe)、红菇属(Russula)、Amphinema、蜡蘑属(Laccaria)、蜡壳耳属(Sebacina)、鹅膏菌属(Amanita)、牛肝菌属(Boletus)、丝膜菌属(Cortinarius)、乳菇属(Lactarius)和硬皮马勃属(Scleroderma),丝盖伞属是优势类群。阳坡外生菌根真菌多样性高于阴坡。对菌根根际土与非根际土化学性质分析表明,pH值显著低于非根际,速效磷、速效钾含量显著高于非根际。对根际土化学性质与外生菌根侵染率相关性分析表明,落叶松外生菌根侵染率与土壤pH值呈显著正相关;与速效钾呈极显著正相关;与全氮、速效磷呈显著负相关。【结论】落叶松外生菌根真菌多样性丰富,且受坡向影响。外生菌根真菌可降低根际pH,提高根际有机质、全氮、速效磷、速效钾、水溶性钙和水溶性镁的含量。外生菌根侵染率受土壤pH值、全氮、速效磷、速效钾的影响。     

Kangiella shandongensis sp. nov., a novel species isolated from saltern in Yantai,China

A Gram-stain-negative, wheat, rod-shaped, non-motile, non-spore forming, and facultatively anaerobic bacterium strain, designated as PI^T, was isolated from saline silt samples collected in saltern in Yantai, Shandong, China. Growth was observed within the ranges 4–45 °C (optimally at 33 °C), pH 6.0–9.0 (optimally at pH 7.0) and 1.0–11.0% NaCl (optimally at 3.0%, w/v). Strain PI^T showed highest 16S rRNA gene sequence similarity to Kangiella sediminilitoris BB-Mw22^T (98.3%) and Kangiella taiwanensis KT1^T (98.3%). The major cellular fatty acids (>?10% of the total fatty acids) were iso-C_15:0 (52.7%) and summed featured 9 (iso-C_17:1ω9c/C_16:0 10-methyl, 11.8%). The major polar lipids identified were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine and phosphatidylglycerol. The major respiratory isoprenoid quinone was Q-8. The G?+?C content of the genomic DNA was 45.8%. Average Nucleotide Identity values between whole genome sequences of strain PI^T and next related type strains supported the novel species status. Based on physiological, biochemical, chemotaxonomic characteristics and genomic analysis, strain PI^T is considered to represent a novel species within the genus Kangiella, for which the name Kangiella shandongensis sp. nov. is proposed. The type strain is PI^T (=?KCTC 82509 ^T?=?MCCC 1K04352^T).

     

A new function of trehalose and the peculiarities of lipid formation in mycelial fungi

This work deals with lipid formation in ascomycete fungi and the effect of preservatives on them. A new biological function of trehalose was revealed, and of particular interest was the fact that the effect of this disaccharide depended on its concentration in the growth medium. In the presence of a preservative such as potassium sorbate (PS), low trehalose concentrations suppressed the growth of mycelial fungi contaminating hard cheeses and contributed to the prolongation of the preservative’s effect. A tenfold increase in trehalose concentration in the medium, conversely, resulted in a drastic increase in growth activity and removed the PS effect. Therefore, trehalose can function as an inhibitor or a stimulator of growth processes, depending on its concentration. It was established that the secondary growth of Penicillium fungi during their ontogeny is accompanied by consumption of accumulated reserve lipids. In contrast, this phenomenon does not occur in mucorous fungi, and this probably accounts for the fact that Mucorales representatives can accumulate significant triacylglyceride amounts during the idiophase.     

Trehalose‐6‐phosphate phosphatases from Arabidopsis thaliana: identification by functional complementation of the yeast tps2 mutant

It is currently thought that most flowering plants lack the capacity to synthesize trehalose, a common disaccharide of bacteria, fungi and invertebrates that appears to play a major role in desiccation tolerance. Attempts have therefore been made to render plants more drought-resistant by the expression of microbial genes for trehalose synthesis. It is demonstrated here that Arabidopsis thaliana itself possesses genes for at least one of the enzymes required for trehalose synthesis, trehalose-6-phosphate phosphatase. The yeast tps2 mutant, which lacks this enzyme, is heat-sensitive, and Arabidopsis cDNA able to complement this effect has been screened for. Half of the yeast transformants that grew at 38.6°C were also able to produce trehalose. All of these expressed one of two Arabidopsis cDNA, either AtTPPA or AtTPPB, which are both homologous to the C-terminal part of the yeast TPS2 gene and other microbial trehalose-6-phosphate phosphatases. Yeast tps2 mutants expressing AtTPPA or AtTPPB contained trehalose-6-phosphate phosphatase activity that could be measured both in vivo and in vitro. The enzyme dephosphorylated trehalose-6-phosphate but not glucose-6-phosphate or sucrose-6-phosphate. Both genes are expressed in flowers and young developing tissue of Arabidopsis. The finding of these novel Arabidopsis genes for trehalose-6-phosphate phosphatase strongly indicates that a pathway for trehalose biosynthesis exists in plants.     

Cloning,expression and characterization of the esterase estUT1 from Ureibacillus thermosphaericus which belongs to a new lipase family XVIII

A new esterase gene from thermophilic bacteria Ureibacillus thermosphaericus was cloned into the pET32b vector and expressed in Escherichia coli BL21(DE3). Alignment of the estUT1 amino acid sequence revealed the presence of a novel canonical pentapeptide (GVSLG) and 41–47% identity to the closest family of the bacterial lipases XIII. Thus the esterase estUT1 from U. thermosphaericus was assigned as a member of the novel family XVIII. It also showed a strong activity toward short-chain esters (C2–C8), with the highest activity for C2. When p-nitrophenyl butyrate is used as a substrate, the temperature and pH optimum of the enzyme were 70–80 °C and 8.0, respectively. EstUT1 showed high thermostability and 68.9 ± 2.5% residual activity after incubation at 70 °C for 6 h. Homology modeling of the enzyme structure showed the presence of a putative catalytic triad Ser93, Asp192, and His222. The activity of estUT1 was inhibited by PMSF, suggesting that the serine residue is involved in the catalytic activity of the enzyme. The purified enzyme exhibited high stability in organic solvents. EstUT1 retained 85.8 ± 2.4% residual activity in 30% methanol at 50 °C for 6 h. Stability at high temperature and tolerance to organic solvents make estUT1 a promising enzyme for biotechnology application.

     

Gottfriedia endophyticus sp. nov., a novel indole-acetic acid producing bacterium isolated from the roots of rice plant

A Gram-stain-positive, aerobic, motile and rod-shaped bacterium, designated RG28^T, was isolated from the roots of rice plant collected from paddy fields in Ilsan, South Korea. Cells of the strain were oxidase-negative but catalase-positive. Strain RG28^T was found to grow at 10–50 °C (optimum, 25–30 °C), pH 5.0–10.0 (optimum, pH 7.0) and in 1.0–5.0% (w/v) NaCl (optimum, 0%). The cell-wall peptidoglycan contained meso-diaminopimelic acid and the predominant menaquinones were MK-7 and MK-6. The predominant cellular fatty acids were C_16:0, iso-C_15:0 and anteiso-C_15:0. The major polar lipids included phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, four unidentified aminophosphoglycolipids, four unidentified aminophospholipids, two unidentified glycolipids, one unidentified aminoglycolipid and four unidentified lipids. The genomic DNA G?+?C content was 33.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain was closely related to Gottfriedia acidiceleris CBD 119^T (98.6%), Gottfriedia solisilvae LMG 18422^T (98.5%) and Gottfriedia luciferensis LMG 18422^T (98.4%). The average nucleotide identity (ANI) and in silico DNA–DNA hybridization (isDDH) values between strain RG28^T and type strains of Gottfriedia species were lower than the cut-offs (≥?95–96% for ANI and?≥?70% for is DDH) required to define a bacterial species. Meanwhile, the strain has the ability to produce indole-acetic acid (40.5 µg/mL). Phylogenetic, physiological and chemotaxonomic data suggested that strain RG28^T represented a novel species of the genus Gottfriedia, for which the name Gottfriedia endophyticus sp. nov. is proposed, with the type strain RG28^T (=?KCTC 43327^T?=?TBRC 15151^T).

     

Characterization of Probiotic Properties of Antifungal Lactobacillus Strains Isolated from Traditional Fermenting Green Olives

The aim of this work is to characterize the potential probiotic properties of 14 antifungal Lactobacillus strains isolated from traditional fermenting Moroccan green olives. The molecular identification of strains indicated that they are composed of five Lactobacillus brevis, two Lactobacillus pentosus, and seven Lactobacillus plantarum. In combination with bile (0.3%), all the strains showed survival rates (SRs) of 83.19–56.51% at pH 3, while 10 strains showed SRs of 31.67–64.44% at pH 2.5. All the strains demonstrated high tolerance to phenol (0.6%) and produced exopolysaccharides. The autoaggregation, hydrophobicity, antioxidant activities, and surface tension value ranges of the strains were 10.29–41.34%, 15.07–34.67%, 43.11–52.99%, and 36.23–40.27 mN/m, respectively. Bacterial cultures exhibited high antifungal activity against Penicillium sp. The cell-free supernatant (CFS) of the cultures showed important inhibition zones against Candida pelliculosa (18.2–24.85 mm), as well as an antibacterial effect against some gram-positive and gram-negative bacteria (10.1–14.1 mm). The neutralized cell-free supernatant of the cultures displayed considerable inhibitory activity against C. pelliculosa (11.2–16.4 mm). None of the strains showed acquired or horizontally transferable antibiotic resistance or mucin degradation or DNase, hemolytic, or gelatinase activities. Lactobacillus brevis S82, Lactobacillus pentosus S75, and Lactobacillus plantarum S62 showed aminopeptidase, β-galactosidase, and β-glucosidase activities, while the other enzymes of API-ZYM were not detected. The results obtained revealed that the selected antifungal Lactobacillus strains are considered suitable candidates for use both as probiotic cultures for human consumption and for starters and as biopreservative cultures in agriculture, food, and pharmaceutical industries.

     

Nocardioides lacusdianchii sp. nov., an attached bacterium of Microcystis aeruginosa

Attached bacteria of Microcystis play important roles in the occurence, outbreak and decline of Microcystis water blooms. In this study, a novel actinobacterium, designated strain JXJ CY 38 ^T, was isolated from the culture mass of Microcystis aeruginosa FACHB-905 (MAF), collected from Lake Dianchi, south-west, China. The strain was found to be a Gram-stain positive, short rod, catalase positive and oxidase negative. The isolate was found to be able to grow at 5.0–38.0 °C (optimum, 28.0 °C), pH 4.0–11.0 (optimum, 7.0–8.0) and 0–3.0% (w/v, optimum, 0%) NaCl. Based on 16S rRNA gene sequences, strain JXJ CY 38 ^T shows high similarities to Nocardioides furvisabuli JCM 13813 ^T (99.0%) and Nocardioides alpinus JCM 18960 ^T (98.7%), and less than 98.2% similarities to other members of the genus. The major cellular fatty acids (>?10.0%) were identified as iso-C_16:0 (23.6%), C_18:1ω9c (18.2%) and C_17:1ω8c (16.4%), while the predominant menaquinone was found to be MK-8 (H₄). The diagnostic diamino acids in the cell wall peptidoglycan were identified as aspartic acid, glutamic acid, glycine and alanine, with mannose, ribose and arabinose as whole cell sugars. The polar lipids were found to be diphosphatidylglycerol, phosphatidylglycerol, a phospholipid, phosphatidylcholine and an unidentified lipid. The DNA G?+?C content was determined to be 71.3%. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 38 ^T and the type strains N. furvisabuli JCM 13813 ^T and N. alpinus JCM 18960 ^T were 49.4% and 37.7%, and 92.0% and 83.4%, respectively. On the basis of the above taxonomic data and differences in physiological characteristics from the closely related type strains, strain JXJ CY 38 ^T was determined to represent a novel species of genus Nocardioides, for which the name Nocardioides lacusdianchii sp. nov. is proposed. The type strain is JXJ CY 38 ^T (=?KCTC 49381 ^T?=?CGMCC 4.7665 ^T). Strain JXJ CY 38 ^T apparently exhibits complex effects on the interactions between MAF and other attached bacteria, including the promotion or inhibition of the growth of MAF and bacteria, and the synthesis and release of microcystins by MAF.

     

Functional roles of microbial symbionts in plant cold tolerance

In this review, we examine the functional roles of microbial symbionts in plant tolerance to cold and freezing stresses. The impacts of symbionts on antioxidant activity, hormonal signaling and host osmotic balance are described, including the effects of the bacterial endosymbionts Burkholderia, Pseudomonas and Azospirillum on photosynthesis and the accumulation of carbohydrates such as trehalose and raffinose that improve cell osmotic regulation and plasma membrane integrity. The influence of root fungal endophytes and arbuscular mycorrhizal fungi on plant physiology at low temperatures, for example their effects on nutrient acquisition and the accumulation of indole‐3‐acetic acid and antioxidants in tissues, are also reviewed. Meta‐analyses are presented showing that aspects of plant performance (shoot biomass, relative water content, sugar and proline concentrations and F_v/F_m) are enhanced in symbiotic plants at low (?1 to 15 °C), but not at high (20–26 °C), temperatures. We discuss the implications of microbial symbionts for plant performance at low and sub‐zero temperatures in the natural environment and propose future directions for research into the effects of symbionts on the cold and freezing tolerances of plants, concluding that further studies should routinely incorporate symbiotic microbes in their experimental designs.