Wheat endophytes and their potential role in managing abiotic stress under changing climate

Wheat (Triticum aestivum L.) cultivation differs considerably in respect of soil type, temperature, pH, organic matter, moisture regime, etc. Among these, rising atmospheric temperature due to global warming is most important as it affects grain yield drastically. Studies have shown that for every 1°C rise in temperature above wheat's optimal growing temperature range of 20-25°C, there is a decrease in 2.8 days and 1.5 mg in the grain filling period and kernel weight, respectively, resulting in wheat yield reduction by 4-6 quintal per hectare. Growing demand for food and multidimensional issues of global warming may further push wheat crop to heat stress environments that can substantially affect heading duration, percent grain setting, maturity duration, grain growth rate and ultimately total grain yield. Considerable genetic variation exists in wheat gene pool with respect to various attributes associated with high temperature and stress tolerance; however, only about 15% of the genetic variability could be incorporated into cultivated wheat so far. Thus, alternative strategies have to be explored and implemented for sustainable, more productive and environment friendly agriculture. One of the feasible and environment friendly option is to look at micro-organisms that reside inside the plant without adversely affecting its growth, known as 'endophytes', and these colonize virtually all plant organs such as roots, stems, leaves, flowers and grains. The relationship between plant and endophytes is vital to the plant health, productivity and overall survival under abiotic stress conditions. Thus, it becomes imperative to enlist the endophytes (bacterial and fungal) isolated till date from wheat cultivars, their mechanism of ingression and establishment inside plant organs, genes involved in ingression, the survival advantages they confer to the plant under abiotic stress conditions and the potential benefits of their use in sustainable wheat cultivation.

Saccharopolyspora karakumensis sp. nov., Saccharopolyspora elongata sp. nov., Saccharopolyspora aridisoli sp. nov., Saccharopolyspora terrae sp. nov. and their biotechnological potential revealed by genome analysis

Exploration of unexplored habitats for novel actinobacteria with high bioactivity potential holds great promise in the search for novel entities. During the course of isolation of actinobacteria from desert soils, four actinobacteria, designated as 5K548^T, 7K502^T, 16K309^T and 16K404^T, were isolated from the Karakum Desert and their bioactivity potential as well as taxonomic provenances were revealed by comprehensive genome analyses. Pairwise sequence analyses of the 16S rRNA genes indicated that the four strains are representatives of putatively novel taxa within the prolific actinobacterial genus Saccharopolyspora. The strains have typical chemotaxonomic characteristics of the genus Saccharopolyspora by having meso-diaminopimelic acid as diagnostic diaminoacid, arabinose, galactose and ribose as whole-cell sugars. Consistent with this assignment, all of the isolates contained phosphatidylcholine in their polar lipid profiles and MK-9(H₄) as the predominant menaquinone. The sizes of the genomes of the isolates ranged from 6.0 to 10.2 Mb and the associated G + C contents from 69.6 to 69.7 %. Polyphasic characterizations including determination of overall genome relatedness indices revealed that the strains are representatives of four novel species in the genus Saccharopolyspora. Consequently, isolates 5K548^T, 7K502^T, 16K404^T and 16K309^T are proposed as novel Saccharopolyspora species for which the names of Saccharopolyspora karakumensis sp. nov., Saccharopolyspora elongata sp. nov., Saccharopolyspora aridisoli sp. nov. and Saccharopolyspora terrae sp. nov. are proposed, respectively. Comprehensive genome analysis for biosynthetic gene clusters showed that the strains have high potential for novel secondary metabolites. Moreover, the strains harbour many antimicrobial resistance genes providing more evidence for their potentiality for bioactive metabolites.

Endophytic microbes: biodiversity, plant growth-promoting mechanisms and potential applications for agricultural sustainability

Endophytic microbes are known to live asymptomatically inside their host throughout different stages of their life cycle and play crucial roles in the growth, development, fitness, and diversification of plants. The plant-endophyte association ranges from mutualism to pathogenicity. These microbes help the host to combat a diverse array of biotic and abiotic stressful conditions. Endophytic microbes play a major role in the growth promotion of their host by solubilizing of macronutrients such as phosphorous, potassium, and zinc; fixing of atmospheric nitrogen, synthesizing of phytohormones, siderophores, hydrogen cyanide, ammonia, and act as a biocontrol agent against wide array of phytopathogens. Endophytic microbes are beneficial to plants by directly promoting their growth or indirectly by inhibiting the growth of phytopathogens. Over a long period of co-evolution, endophytic microbes have attained the mechanism of synthesis of various hydrolytic enzymes such as pectinase, xylanases, cellulase, and proteinase which help in the penetration of endophytic microbes into tissues of plants. The effective usage of endophytic microbes in the form of bioinoculants reduce the usage of chemical fertilizers. Endophytic microbes belong to different phyla such as Actinobacteria, Acidobacteria, Bacteroidetes, Deinococcus-thermus, Firmicutes, Proteobacteria, and Verrucomicrobia. The most predominant and studied endophytic bacteria belonged to Proteobacteria followed by Firmicutes and then by Actinobacteria. The most dominant among reported genera in most of the leguminous and non-leguminous plants are Bacillus, Pseudomonas, Fusarium, Burkholderia, Rhizobium, and Klebsiella. In future, endophytic microbes have a wide range of potential for maintaining health of plant as well as environmental conditions for agricultural sustainability. The present review is focused on endophytic microbes, their diversity in leguminous as well as non-leguminous crops, biotechnological applications, and ability to promote the growth of plant for agro-environmental sustainability.

Saccharopolyspora spongiae sp. nov., a novel actinomycete isolated from the marine sponge Scopalina ruetzleri (Wiedenmayer, 1977)

A novel marine actinomycete, designated strain CMAA 1452T, was isolated from the sponge Scopalina ruetzleri collected from Saint Peter and Saint Paul Archipelago, in Brazil, and subjected to a polyphasic taxonomic investigation. The organism formed a distinct phyletic line in the Saccharopolyspora 16S rRNA gene tree and had chemotaxonomic and morphological properties consistent with its classification in this genus. It was found to be closely related to Saccharopolyspora dendranthemae KLBMP 1305T (99.5% 16S rRNA gene sequence similarity) and shared similarities of 99.3, 99.2 and 99.0 % with 'Saccharopolyspora endophytica' YIM 61095, Saccharopolyspora tripterygii YIM 65359T and 'Saccharopolyspora pathumthaniensis' S582, respectively. DNA-DNA relatedness values between the isolate and its closest phylogenetic neighbours, namely S. dendranthemae KLBMP 1305T, 'S. endophytica' YIM 61095 and S. tripterygii YIM 65359T, were 53.5, 25.8 and 53.2 %, respectively. Strain CMAA 1452T was also distinguished from the type strains of these species using a range of phenotypic features. On the basis of these results, it is proposed that strain CMAA 1452T (=DSM 103218T=NRRL B-65384T) merits recognition as the type strain of a novel Saccharopolyspora species, Saccharopolyspora spongiae sp. nov.

Herbihabitans rhizosphaerae gen. nov., sp. nov., a member of the family Pseudonocardiaceae isolated from rhizosphere soil of the herb Limonium sinense (Girard)

The taxonomic position of an actinobacterium, designated CPCC 204279T, which was isolated from a rhizosphere soil sample of the herb Limonium sinense collected from Xinjiang Province, China, was established using a polyphasic approach. Whole-cell hydrolysates of strain CPCC 204279T contained galactose and arabinose as diagnostic sugars and meso-diaminopimelic acid as the diamino acid. The muramic acid residues in the peptidoglycan were N-acetylated. The predominant menaquinone was MK-9(H4). The phospholipids consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides. The major fatty acids were iso-C16 : 0, iso-C16 : 0 2-OH, C16 : 1ω9c, iso-C16 : 1 and C16 : 0. The genomic DNA G+C content was 73.2 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CPCC 204279T should be placed in the family Pseudonocardiaceae, in which the strain formed a distinct lineage next to the genus Actinophytocola. Signature nucleotides in the 16S rRNA gene sequence showed that the strain contained the Pseudonocardiaceae family-specific 16S rRNA signature nucleotides and a genus-specific diagnostic nucleotide signature pattern. The combination of phylogenetic analysis and phenotypic characteristics supported the conclusion that strain CPCC 204279T represents a novel species of a new genus in the family Pseudonocardiaceae, for which the name Herbihabitans rhizosphaerae gen. nov., sp. nov. is proposed. Strain CPCC 204279T (=NBRC 111774T=DSM 101727T) is the type strain of the type species.

Saccharopolyspora halotolerans sp. nov., a halophilic actinomycete isolated from a hypersaline lake

A novel actinomycete strain, designated TRM 45123T, was isolated from a hypersaline habitat in Xinjiang Province (40° 20′ N 90° 49′ E), north-west China. The isolate was characterized using a polyphasic approach. 16S rRNA gene sequence analysis indicated that strain TRM 45123T belonged to the genus Saccharopolyspora and was closely related to Saccharopolyspora gloriosae (96.7 % similarity). The G+C content of the DNA was 69.07 mol%. The isolate contained meso-diaminopimelic acid as the diagnostic diamino acid, and arabinose and ribose as the major whole-cell sugars. The diagnostic phospholipids were phosphatidylethanolamine, phosphatidylcholine and phosphatidylglycerol. The predominant menaquinone was MK-9(H4). The major fatty acids were iso-C16 : 0, anteiso-C17 : 0, iso-C15 : 0 and anteiso-C15 : 0. On the basis of the evidence from this polyphasic study, a novel species, Saccharopolyspora halotolerans sp. nov., is proposed. The type strain of Saccharopolyspora halotolerans is TRM 45123T ( = CCTCC AA 2013006T = DSM 45990T).

Saccharopolyspora indica sp. nov., an actinomycete isolated from the rhizosphere of Callistemon citrinus (Curtis)

A novel actinomycete strain, designated VRC122T, was isolated from a Callistemon citrinus rhizosphere sample collected from New Delhi, India, and its taxonomic status was determined by using a polyphasic approach. Strain VRC122T was a Gram-stain-positive, aerobic, non-motile, non-acid–alcohol-fast strain. Phylogenetic analysis based on 16S rRNA gene sequences showed the strain was placed in a well-separated sub-branch within the genus Saccharopolyspora . The highest levels of 16S rRNA gene sequence similarity were found with Saccharopolyspora hirsuta subsp. kobensis JCM 9109T (98.71 %), Saccharopolyspora antimicrobica I05-00074T (98.69 %) and Saccharopolyspora jiangxiensis W12T (98.66 %); 16S rRNA gene sequence similarities with type strains of all other species of the genus Saccharopolyspora were below 98 %. Chemosystematic studies revealed that it contained meso-diaminopimelic acid. Arabinose and galactose were the predominant whole-cell sugars. Diagnostic polar lipids were diphosphatidylglycerol, phosphatidylinositol and phosphatidylcholine. MK-9(H6) was the predominant menaquinone. C14 : 0, C16 : 0, iso-C15 : 0, iso-C16 : 0, iso-C17 : 0, anteiso-C15 : 0, anteiso-C17 : 0, C17 : 0 cyclo and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) were the major cellular fatty acids. The G+C content of the genomic DNA was 69.5 mol%. The results of DNA–DNA hybridization (30 %, 22 % and 25 %, respectively) with type strains of the above-mentioned species, in combination with differences in physiological and biochemical data supported that strain VRC122T represents a novel species of the genus Saccharopolyspora , for which the name Saccharopolyspora indica sp. nov., is proposed. The type strain is VRC122T ( = KCTC 29208T = MTCC 11564T = MCC 2206T = ATCC BAA-2551T).

Saccharopolyspora pathumthaniensis sp. nov., a novel actinomycetes isolated from termite guts (Speculitermes sp.)

Morphological and chemotaxonomic characterization of actinomycete strain S582 isolated from the gut of a termite (Speculitermes sp.) in Pathum Thani Province, Thailand, clearly demonstrated that this strain is a member of the genus Saccharopolyspora. 16S rDNA sequence analysis for the strain supported the assignment of the strain to the genus Saccharopolyspora. The similarity value of sequences between this strain and the closely related species Saccharopolyspora endophytica was 99.5%. The DNA G+C content was 70.2 mol%. DNA-DNA hybridization results (53.3%) and some physiological and biochemical properties indicated that strain S582(T) was distinguished from the phylogenetically closest relatives. Based on these genotypic and phenotypic data, strain S582(T) should be a new species in the genus Saccharopolyspora and the name Saccharopolyspora pathumthaniensis sp. nov. is proposed for the strain. The type strain is S582(T) (=NBRC 104112(T) =BCC 28624(T)).

Bacillus oceanisediminis sp. nov., isolated from marine sediment

A Gram-stain-positive, spore-forming, rod-shaped and aerobic bacterium was isolated from a sediment sample from the South Sea in China. The isolate, designated H2T, grew at 4–45 °C (optimum 37 °C) and pH 6–10 (optimum pH 7.0). The cell-wall peptidoglycan contained meso-diaminopimelic acid. The major isoprenoid quinone was MK-7 and the polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unknown aminophospholipid. The major fatty acid was iso-C15 : 0. The genomic DNA G+C content of strain H2T was 44.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate formed a monophyletic clade with Bacillus firmus IAM 12464T. DNA–DNA relatedness between the isolate and B. firmus ATCC 14575T was low (27.5 %). Strain H2T also had a phenotypic profile that readily distinguished it from its closest phylogenetic neighbours. It is evident from the combination of genotypic and phenotypic data that the organism should be classified in a novel species of the genus Bacillus, for which the name Bacillus oceanisediminis sp. nov. is proposed. The type strain is H2T (=CGMCC 1.10115T =JCM 16506T).

Saccharopolyspora phatthalungensis sp. nov., isolated from rhizosphere soil of Hevea brasiliensis

The taxonomic position of a rhizosphere soil isolate, designated strain SR8.15T, was determined by using a polyphasic approach. Phylogenetic analysis based on an almost-complete 16S rRNA gene sequence of the strain showed that it formed a well-separated sub-branch within the radiation encompassing the genus Saccharopolyspora. Highest levels of 16S rRNA gene sequence similarity were found between strain SR8.15T and Saccharopolyspora shandongensis CGMCC 4.3530T (98.9 %) and Saccharopolyspora spinosa DSM 44228T (98.5 %). However, these strains shared low levels of DNA–DNA relatedness (<26 %). Strain SR8.15T had chemical characteristics consistent with its classification in the genus Saccharopolyspora. It contained meso-diaminopimelic acid as the diagnostic diamino acid. Whole-cell hydrolysates contained arabinose and galactose. The diagnostic phospholipids were phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol. The main menaquinone was MK-9(H4). No mycolic acid was detected. The predominant cellular fatty acid was iso-C16 : 0. The G+C content of the genomic DNA of strain SR8.15T was 70.3 mol%. Strain SR8.15T had a phenotypic profile that readily distinguished it from recognized representatives of the genus Saccharopolyspora. It is evident from its combined genotypic and phenotypic properties that strain SR8.15T represents a novel species of the genus Saccharopolyspora, for which the name Saccharopolyspora phatthalungensis sp. nov. is proposed. The type strain is SR8.15T (=TISTR 1921T=BCC 35844T=NRRL B-24798T).

Saccharopolyspora gloriosae sp. nov., an endophytic actinomycete isolated from the stem of Gloriosa superba L

A Gram-stain-positive, aerobic actinomycete, strain YIM 60513T, was isolated from the stem of Gloriosa superba L. collected from tropical rainforest at Xishuangbanna, Yunnan Province, south-west China. 16S rRNA gene sequence analysis indicated that strain YIM 60513T belonged to the genus Saccharopolyspora and was closely related to Saccharopolyspora gregorii NCIB 12823T (99.1 % similarity) and Saccharopolyspora cebuensis SPE 10-1T (97.3 % similarity). Data for the predominant quinone [MK-9(H4)], major fatty acids (iso-C16 : 0, anteiso-C17 : 0 and C17 : 1 cis9) and G+C content of the genomic DNA (71.6 mol%) were similar to those for members of the genus Saccharopolyspora. The level of DNA–DNA relatedness between strain YIM 60513T and S. gregorii NCIB 12823T was 43 %. The combination of phylogenetic analysis, phenotypic differences, chemotaxonomic characteristics and DNA–DNA hybridization data supported the view that strain YIM 60513T should be distinguished from S. gregorii NCIB 12823T and S. cebuensis SPE 10-1T. Strain YIM 60513T therefore represents a novel species of the genus Saccharopolyspora, for which the name Saccharopolyspora gloriosae sp. nov. is proposed. The type strain is YIM 60513T (=KCTC 19243T =CCTCC AA 207006T).

Yuhushiella deserti gen. nov., sp. nov., a new member of the suborder Pseudonocardineae

A thermotolerant, Gram-stain-positive, aerobic, sporangium-forming actinomycete, strain RA45(T), was isolated from a desert region in Xinjiang Uigur Autonomous Region, north-western China. Comparative analysis of the 16S rRNA gene sequence and phenotypic characterization revealed that strain RA45(T) belonged phylogenetically to the family Pseudonocardiaceae of the suborder Pseudonocardineae. Strain RA45(T) showed more than 5  % 16S rRNA gene sequence divergence from recognized species of genera in the family Pseudonocardiaceae, forming a distinct lineage within the evolutionary radiation occupied by the genera Amycolatopsis, Prauserella, Thermocrispum, Saccharomonospora, Saccharopolyspora and Sciscionella, but distinct from each of them. The affiliation to the family was supported by the presence of suborder- and family-specific 16S rRNA signature nucleotides, a DNA G+C content of 69.9 mol%, the presence of meso-diaminopimelic acid, ribose, arabinose, glucose and galactose, which are characteristic components of cell-wall chemotype IV of actinomycetes, the presence of menaquinone MK-9(H₄) as the major respiratory lipoquinone, a lack of mycolic acids and the presence of an N-acetylated type of muramic acid. However, strain RA45(T) differed from known genera of the family in its polar lipid composition: the major phospholipids were phosphatidylethanolamine, phosphatidylinositol mannosides, phosphatidylmethylethanolamine, diphosphatidylglycerol, phospholipids of unknown structure and phospholipids of unknown structure containing glucosamine (phospholipid type IV). Based on its morphological, chemotaxonomic and phylogenetic characteristics, strain RA45(T) is considered to represent a novel species of a new genus in the family Pseudonocardiaceae, for which the name Yuhushiella deserti gen. nov., sp. nov. is proposed. The type strain of Yuhushiella deserti is RA45(T) (=CGMCC 4.5579(T) =JCM 16584(T)).

Saccharopolyspora rosea sp. nov., isolated from a patient with bronchial carcinoma

The taxonomic status of a bacterium isolated from a patient with bronchial carcinoma was established using a polyphasic taxonomic approach. The strain had morphological and chemotaxonomic characteristics consistent with those of members of the genus Saccharopolyspora. The generic assignment was confirmed by comparative analysis of the 16S rRNA gene sequence, which showed that the strain constituted a distinct phyletic line, displaying 93.5-96.9 % sequence similarity with respect to members of the genus Saccharopolyspora. The isolate was distinguished from the type strains of recognized members of the genus Saccharopolyspora by means of various biochemical tests. The genotypic and phenotypic data obtained demonstrated that strain IMMIB L-1070(T) represents a novel species of the genus Saccharopolyspora, for which the name Saccharopolyspora rosea sp. nov. is proposed. The type strain is IMMIB L-1070(T) (=DSM 45226(T)=CCUG 56401(T)).

Saccharopolyspora endophytica sp. nov., an endophytic actinomycete isolated from the root of Maytenus austroyunnanensis

A Gram-positive, aerobic, non-motile, non-acid-alcohol-fast strain, designated YIM 61095(T), was isolated from the root of Maytenus austroyunnanensis collected from a tropical rainforest of Xishuangbanna in Yunnan Province, south-west China. Strain YIM 61095(T) exhibited chemotaxonomic and morphological characteristics that were consistent with members of the genus Saccharopolyspora. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 61095(T) was a member of the genus Saccharopolyspora and was most closely related to Saccharopolyspora flava AS 4.1520(T) (97.7% sequence similarity). The major fatty acids were iso-C(15:0), iso-C(16:0), iso-C(17:0) and anteiso-C(17:0). The predominant quinone detected was MK-9(H(4)). The DNA G+C content was 66.2 mol%. The phenotypic characteristics and DNA-DNA hybridization relatedness data indicated that strain YIM 61095(T) should be distinguished from Saccharopolyspora flava AS 4.1520(T). On the basis of the evidence presented in this study, strain YIM 61095(T) represents a novel species of the genus Saccharopolyspora, for which the name Saccharopolyspora endophytica sp. nov. is proposed. The type strain is YIM 61095(T) (=KCTC 19397(T)=CCTCC AA 208003(T)).