Production of transglutaminase by Streptomyces isolates in solid-state fermentation

Aims:  To screen Streptomyces isolates for transglutaminase (TGase) production in solid-state fermentation (SSF) on various substrates.
Methods and Results:  Streptomyces mobaraensis NRRL B-3729, Streptomyces paucisporogenes ATCC 12596 and Streptomyces platensis NRRL 2364 strains were screened for extracellular TGase production in SSF on different substrates. High-protein-content beans, peas and lentils proved to be the best substrates. Good TGase production was obtained on liver kidney beans and green mung beans in a 4- to 6-day SSF. Temperature optima of the enzymes varied between 45 to 50°C. Molecular weight determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS PAGE) indicated similar size (∼37 kDa) for all three enzymes. TGase was the dominating protein band on SDS PAGE for two Streptomyces strains in SSF extracts. Other enzymes were present in smaller quantities.
Conclusions:  Streptomyces mobaraensis NRRL B-3729, S. paucisporogenes ATCC 12596 and S. platensis NRRL 2364 strains were successfully propagated under SSF conditions on crushed/milled liver kidney bean and green mung bean to obtain good level of TGase.
Significance and Impact of the Study:  Owing to much reduced production cost and direct applicability, SSF TGase without downstream processing (cheap in situ enzyme, crude enzyme) may be an excellent candidate for some nonfood applications.     

Statistical optimization of l-leucine amino peptidase production from Streptomyces gedanensis IFO 13427 under submerged fermentation using response surface methodology

Response surface methodology (RSM) employing the central composite design (CCD) was used to optimize the fermentation medium for the production of l-leucine amino peptidase (LAP) from Streptomyces gedanensis IFO13427 under submerged fermentation. The design was employed by selecting substrate concentration, NaCl concentration and initial pH as model factors by ‘one variable at a time’ experiment. A second-order quadratic model and response surface method showed that the optimum conditions (soy bean 0.3%, NaCl, 0.03 M, and initial pH 7) resulted in the improvement of LAP production (25.69 IU/ml) as compared to the initial level (12.17 ± 0.23 IU/ml) after 72 h of fermentation, whereas its value predicted by the quadratic model was 24.56 IU/ml. Analysis of variance (ANOVA) showed a high coefficient of determination (R²) value of 0.9799, ensuring a satisfactory adjustment of the quadratic model with the experimental data. This is first report on LAP production by S. gedanensis using statistical experimental design and response surface methodology in submerged fermentation.     

Engineered production of iso-migrastatin in heterologous Streptomyces hosts

Glutarimide-containing polyketides such as migrastatin (MGS) are well known for their ability to inhibit tumor cell migration. We have previously shown that MGS is derived from iso-migrastatin (iso-MGS) via a H₂O-mediated ring-expansion rearrangement. A bacterial artificial chromosome (BAC) library of Streptomyces platensis NRRL18993, an iso-MGS producer, was constructed. From this library, pBS11001, a BAC clone harboring the intact iso-MGS biosynthetic gene cluster, was identified. Mobilization of pBS11001 into five heterologous Streptomyces hosts afforded recombinant strains, SB11001, SB11002, SB11003, SB11004, and SB11005, respectively. Under a standard set of media and fermentation conditions, the recombinant strains all produced the same profile of iso-MGS as that of S. platensis NRRL18993. These findings highlight the strength and flexibility of the BAC-based technology for natural product production and engineering in heterologous Streptomyces model hosts.     

The <Emphasis Type="Italic">Streptomyces violaceusniger</Emphasis> clade: a home for streptomycetes with rugose ornamented spores

The taxonomic status of 16 strains received as Streptomyces hygroscopicus, Streptomyces melanosporofaciens, Streptomyces sparsogenes, Streptomyces sporoclivatus and Streptomyces violaceusniger was evaluated in a polyphasic study. Eleven of the organisms formed a distinct clade in the Streptomyces 16S rRNA gene tree with the type strains of Streptomyces asiaticus, Streptomyces cangkringensis, Streptomyces indonesiensis, Streptomyces javensis, Streptomyces malaysiensis, Streptomyces rhizosphaericus, Streptomyces yatensis and Streptomyces yogyakartensis, the members of this group produced rugose ornamented spores in spiral spore chains. The eleven strains were assigned to three established and four novel species, namely Streptomyces albiflaviniger sp. nov., Streptomyces demainii sp. nov., Streptomyces geldanamycininus sp. nov., Streptomyces griseiniger sp. nov., and Streptomyces hygroscopicus, Streptomyces melanosporofaciens and Streptomyces violaceusniger. It is also proposed that S. sporoclivatus becomes a subjective synonym of S. melanosporofaciens. S. sparsogenes NRRL 2940^T, which produced ridged ornamented spores in spiral spore chains, formed a distinct phyletic line in the Streptomyces 16S rRNA gene tree and was readily distinguished from the other strains using a range of phenotypic properties. S. violaceusniger strains NRRL 8097, NRRL B-5799, NRRL 2834 and ISP 5182 fell outside the S. violaceusniger 16S rRNA gene clade and formed either smooth or ridged ornamented spores in either flexuous or spiral spore chains. These organisms were distinguished from one another and from their closest phylogenetic neighbors and were considered to merit species status as Streptomyces auratus sp. nov., Streptomyces phaeoluteichromatogenes sp. nov., Streptomyces phaeogriseichromatogenes sp. nov., and Streptomyces phaeoluteigriseus sp. nov., respectively. The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of the tested strains are S. albiflaviniger NRRL B-1356^T (AJ391812), S. auratus NRRL 8097^T (AJ391816), S. geldanamycininus NRRL 3602^T (DQ334781), S. griseiniger NRRL B-1865^T (AJ391818), S. hygroscopicus NRRL 2387^T (AJ391820), NRRL 2339 (AJ391821) and NRRL B-1477 (AJ391819), S. demainii NRRL B-1478^T (DQ334782), S. melanosporofaciens NRRL B-12234^T (AJ391837), S. phaeogriseichromatogenes NRRL 2834^T (AJ391813), S. phaeoluteichromatogenes NRRL B-5799^T (AJ391814), S. phaeoluteigriseus ISP 5182^T (AJ391815), S. sparsogenes NRRL 2940^T (AJ391817), S. sporoclivatus NRRL B-24330^T (AJ 781369), S. violaceusniger ISP 5563^T (AJ 391823) and NRRL B-1476^T (AJ 391822).     

Streptomyces deserti sp. nov., isolated from hyper-arid Atacama Desert soil

The taxonomic position of a Streptomyces strain isolated from a hyper-arid desert soil was established using a polyphasic approach. The organism had chemical and morphological properties typical of the genus Streptomyces and formed a phyletic line at the periphery of the Streptomyces coeruleorubidus subcluster in the 16S rRNA gene tree. DNA:DNA relatedness values between the isolate and its nearest phylogenetic neighbours, Streptomyces lomondensis NRRL 3252^T and Streptomyces lusitanus NRRL B-12501^T were 42.5 (±0.48)% and 25.0 (±1.78)%, respectively. The isolate was readily distinguished from these organisms using a combination of morphological and phenotypic properties. On the basis of these results, it is proposed that isolate C63^T (CGMCC 4.6997^T, = KACC 15425^T) be classified as the type strain of Streptomyces deserti sp. nov.     

Molecular and culture dependent characterization of endolithic bacteria in two beach sand samples and description of Rhizobium endolithicum sp. nov.

The taxonomic position of a streptomycete isolated from a potato tubercle was determined by using a polyphasic approach. The organism had chemotaxonomic and morphological properties consistent with its classification in the genus Streptomyces and formed a distinct phyletic line in the Streptomyces 16S rRNA gene tree. It was found to be closely related to Streptomyces celluloflavus NRRL B-2493^T (99.4 % 16S rRNA gene similarity) and shared a 99.0 % 16S rRNA gene similarity value with Streptomyces albolongus NRRL B-3604^T and Streptomyces cavourensis subsp. cavourensis NBRC 13026^T; low levels of DNA–DNA relatedness with these organisms showed that the isolate belonged to a distinct genomic species. The isolate was distinguished readily from the type strains of these species using a combination of morphological and other phenotypic properties. On the basis of these results, it is proposed that isolate ASBV-1^T (= CBMAI 1465^T = CCMA 894^T = NRRL B-24922^T) be classified as the type strain of Streptomyces araujoniae sp. nov.     

Isolation and Physiological Activities of Piericidin A,A Natural Insecticide Produced by Streptomyces

In the course of screening research on new insecticides among metabolites of microorganisms, two active components were isolated from mycellia of Streptomyces sp. 16–22. The names, Piericidin A and B, were proposed to these active metabolites. Isolation procedure, physical and chemical properties and physiological activities of Piericidin A were presented. From the results of taxonomic study on Streptomyces sp. 16–22, it was found that this is a new species, to which the name, Streptomyces mobaraensis Nagatsu et Suzuki, was proposed.     

Conserved Organization of Genes for Biosynthesis of Chlortetracycline in Streptomyces Strains

By genomic Southern blot analysis, the DNA sequences homologous to the gene cluster responsible for biosynthesis of 6-demethylchlortetracycline in Streptomyces aureofaciens NRRL3203 were shown to be highly conserved in independent chlortetracycline- or tetracycline producing Streptomyces strains. By contrast, oxytetracycline-producing Streptomyces strains had no hybridization with the cluster DNA.     

Streptomyces species with madurose (3-O-methyl-D-galactose) as a whole-cell sugar

Madurose, an actinomycete whole-cell sugar, was found in the strains of the genus Streptomyces: three strains of S. platensis, one strain each of S. platensis subsp. malvinus, and S. albus subsp. albus. The sugar was isolated from the hydrolysate of S. platensis IFO 14008 cells, and was identified as madurose (3-O-methyl-D-galactose) by chromatographic analyses, ¹H-NMR spectrometry, mass spectrometry as its alditol acetate, and demethylation with boron trichloride. Cell walls of the strain contained peptidoglycan and teichoic acids. ll-Diaminopimelic acid, glycine, glutamic acid, and alanine were present in the peptidoglycan fraction in molar ratios of 1.0:1.3:1.2:2.3. Madurose was detected in the teichoic acid fraction, which was composed of phosphorus, glycerol, galactose, and madurose in molar ratios of 9.3:8.5:2.9:1.0. Thus, madurose was found in the glycerol teichoic acid moiety of the cell walls of this strain.Abbreviations PC paper chromatography - TLC thin-layer chromatography - HPLC high performance liquid chromatography - GLC gas-liquid chromatography - TCA trichloroacetic acid     

Streptomyces endocoffeicus sp. nov., an endophytic actinomycete isolated from Coffea arabica (L.)

An aerobic, non-motile, Gram-stain positive actinomycete, designated strain CA3R110^T, was isolated from the surface-sterilised root of Coffea arabica L. collected from Lampang Province, Thailand. 16S rRNA gene sequence analysis indicated that strain CA3R110^T was a member of the genus Streptomyces and showed the closest similarities to Streptomyces buecherae AC541^T (99.2%), followed by Streptomyces rapamycinicus NRRL B-5491^T (99.1%), Streptomyces luteoverticillatus NBRC 3840^T (99.1%), Streptomyces coerulescens NBRC 12758^T (99.1%), and Streptomyces iranensis HM 35^T (99.0%). Strain CA3R110^T contained LL-diaminopimelic acid in cell peptidoglycan, MK-9(H₆), and MK-9(H₈) as major menaquinone, iso-C_16:0, iso-C_15:0, C_16:0 as major fatty acids. Diphosphatidylglycerol, phosphatidylethanolamine, hydroxy-phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositolmannoside were detected in the cell. The chemotaxonomic characteristics possessed the typical properties of the genus Streptomyces. A low digital DNA–DNA hybridization (<?55.7%) and average nucleotide identity-blast (ANIb) (<?92.2%) values revealed that strain CA3R110^T could be distinguished from any known Streptomyces species. With the differences in phenotypic and genotypic data, strain CA3R110^T represents a novel species of genus Streptomyces, for which the name Streptomyces endocoffeicus sp. nov. is proposed. The type strain is CA3R110^T (=?TBRC 11245^T?=?NBRC 114296^T).

     

Isolation and characterization of fatty acid methyl ester (FAME)‐producing Streptomyces sp. S161 from sheep (Ovis aries) faeces

An actinomycete producing oil‐like mixtures was isolated and characterized. The strain was isolated from sheep faeces and identified as Streptomyces sp. S161 based on 16S rRNA gene sequence analysis. The strain showed cellulase and xylanase activities. The ¹H nuclear magnetic resonance (NMR) spectra of the mixtures showed that the mixtures were composed of fatty acid methyl esters (52·5), triglycerides (13·7) and monoglycerides (9·1) (mol.%). Based on the gas chromatography–mass spectrometry (GC‐MS) analysis, the fatty acid methyl esters were mainly composed of C14‐C16 long‐chain fatty acids. The results indicated that Streptomyces sp. S161 could produce fatty acid methyl esters (FAME) directly from starch. To our knowledge, this is the first isolated strain that can produce biodiesel (FAME) directly from starch.

Significance and Impact of the Study

Nowadays, production of biodiesel is based on plant oils, animal fats, algal oils and microbial oils. Lipid mostly consists of triacylglycerols (TAG), and conversion of these lipids into fatty acid short‐chain alcohol esters (methanol or ethanol) is the final step in biodiesel production. In this study, an oil‐producing Streptomyces strain was isolated from sheep faeces. The oil was composed of C₁₄‐C₁₆ long‐chain fatty acid methyl esters, triglycerides and monoglycerides. This is the first isolated strain‐producing biodiesel (FAME) directly from starch. Due to showing cellulase and xylanase activities, the strain would be helpful for converting renewable lignocellulose into biodiesel directly.     

<Emphasis Type="Italic">Streptomyces sudanensis</Emphasis> sp. nov., a new pathogen isolated from patients with actinomycetoma

Nine strains isolated from mycetoma patients and received as Streptomyces somaliensis were the subject of a polyphasic taxonomic study. The organisms shared chemical markers consistent with their classification in the genus Streptomyces and formed two distinct monophyletic subclades in the Streptomyces 16S rRNA gene tree. The first subclade contained four organisms, including the type strain of S. somaliensis, and the second clade the remaining five strains which had almost identical 16S rRNA sequences. Members of the two subclades were sharply separated using DNA:DNA relatedness and phenotypic data which also showed that the subclade 1 strains formed an heterogeneous group. In contrast, the subclade 2 strains were assigned to a single genomic species and had identical phenotypic profiles. It is evident from these data that the subclade 2 strains should be recognised as a new species of Streptomyces. The name proposed for this new species is Streptomyces sudanensis sp. nov. The type strain is SD 504^T (DSM = 41923^T = NRRL B-24575^T). Erika T. Quintana and Katarzyna Wierzbicka contributed equally to this work. The GenBank accession numbers for the 16S rRNA gene sequences of Streptomyces somaliensis DSM 40738^T and Streptomyces sudanensis DSM 41607, DSM 41608, DSM 41609, SD 504^T and SD 509 are EF540897, EF540898, EF540999, EF515876 and EF540900.     

Streptomyces spp. alleviate Rhizoctonia solani‐mediated oxidative stress in Solanum lycopersicon

The ability of Streptomyces species to act as biocontrol agents for plant pathogens via induced systemic resistance has been demonstrated and considerable efforts have been made in elucidating the underlying mechanisms of Streptomyces–host plant–phytopathogen interactions. Here, we have assessed the ability of Streptomyces coelicolor, Streptomyces griseus, Streptomyces albus, Streptomyces antibioticus and Streptomyces champavatii to provide disease protection against Rhizoctonia solani in Solanum lycopersicon and have also examined associated changes in hydrogen peroxide (H₂O₂) production, lipid peroxidation (LPO) and antioxidant enzymes. The production of H₂O₂ at the second day after pathogen inoculation (dapi) was observed to be 1.1‐fold higher in Streptomyces‐treated plants, when compared to untreated inoculated control plants. A similar increase in catalase and ascorbate peroxidase activity was observed at fourth dapi whereas increased activities of guaiacol reductase and glutathione peroxidase were observed at fifth dapi. Likewise, LPO reached a maximum at sixth dapi in untreated inoculated plants while in Streptomyces‐treated plants it was observed to be 1.3–1.5‐fold less when compared to untreated inoculated control plants. This study offers novel insights into the mechanisms of priming by Streptomyces and highlights their capacity to activate plant defence responses generated by biotic stress through induction of antioxidant enzymes along with improved reactive oxygen species management.     

Titer improvement of iso-migrastatin in selected heterologous <Emphasis Type="Italic">Streptomyces</Emphasis> hosts and related analysis of mRNA expression by quantitative RT–PCR

iso-Migrastatin (iso-MGS) has been actively pursued recently as an outstanding candidate of antimetastasis agents. Having characterized the iso-MGS biosynthetic gene cluster from its native producer Streptomyces platensis NRRL 18993, we have recently succeeded in producing iso-MGS in five selected heterologous Streptomyces hosts, albeit the low titers failed to meet expectations and cast doubt on the utility of this novel technique for large-scale production. To further explore and capitalize on the production capacity of these hosts, a thorough investigation of these five engineered strains with three fermentation media for iso-MGS production was undertaken. Streptomyces albus J1074 and Streptomyces lividans K4-114 were found to be preferred heterologous hosts, and subsequent analysis of carbon and nitrogen sources revealed that sucrose and yeast extract were ideal for iso-MGS production. After the initial optimization, the titers of iso-MGS in all five hosts were considerably improved by 3–18-fold in the optimized R2YE medium. Furthermore, the iso-MGS titer of S. albus J1074 (pBS11001) was significantly improved to 186.7 mg/L by a hybrid medium strategy. Addition of NaHCO₃ to the latter finally afforded an optimized iso-MGS titer of 213.8 mg/L, about 5-fold higher than the originally reported system. With S. albus J1074 (pBS11001) as a model host, the expression of iso-MGS gene cluster in four different media was systematically studied via the quantitative RT–PCR technology. The resultant comparison revealed the correlation of gene expression and iso-MGS production for the first time; synchronous expression of the whole gene cluster was crucial for optimal iso-MGS production. These results reveal new insights into the iso-MGS biosynthetic machinery in heterologous hosts and provide the primary data to realize large-scale production of iso-MGS for further preclinical studies.     

Novel aromatic polyketides from soil <Emphasis Type="Italic">Streptomyces</Emphasis> spp.: purification,characterization and bioactivity studies

Aromatic polyketides are important therapeutic compounds which include front line antibiotics and anticancer drugs. Since most of the aromatic polyketides are known to be produced by soil dwelling Streptomyces, 54 Streptomyces strains were isolated from the soil samples. Five isolates, R1, B1, R3, R5 and Y8 were found to be potent aromatic polyketide producers and were identified by 16S rRNA gene sequencing as Streptomyces spectabilis, Streptomyces olivaceus, Streptomyces purpurascens, Streptomyces coeruleorubidus and Streptomyces lavendofoliae respectively. Their sequences have been deposited in the GenBank under the accession numbers KF468818, KF681280, KF395224, KF527511 and KF681281 respectively. The Streptomyces strains were cultivated in the media following critically optimised culture conditions. The resulting broth extracts were fractionated on a silica gel column and preparative TLC to obtain pure compounds. The pure compounds were tested for bioactivity and the most potent compound from each isolate was identified by UV–Vis, IR and NMR spectroscopic methods. Isolated S. spectabilis (R1), yielded one potent compound identified as dihydrodaunomycin with an MIC of 4 µg/ml against Bacillus cereus and an IC₅₀ value of 24 µM against HeLa. S. olivaceus (B1), yielded a comparatively less potent compound, elloramycin. S. purpurascens (R3) yielded three compounds, rhodomycin, epelmycin and obelmycin. The most potent compound was rhodomycin with an MIC of 2 µg/ml against B. cereus and IC₅₀ of 15 µM against HeLa. S. coeruleorubidus (R5), yielded daunomycin showing an IC₅₀ of 10 µM and also exhibiting antimetastatic properties against HeLa. S. lavendofoliae (Y8), yielded a novel aclacinomycin analogue with IC₅₀ value of 2.9 µM and potent antimetastatic properties at 1 µM concentration against HeLa. The study focuses on the characterization of aromatic polyketides from soil Streptomyces spp., which can serve as potential candidates for development of chemotherapeutic drugs in future.     

Streptomyces bullii sp. nov., isolated from a hyper-arid Atacama Desert soil

A Streptomyces strain isolated from a hyper-arid Atacama Desert soil was characterised using a polyphasic taxonomic approach. The strain, designated C2^T, had chemical and morphological properties typical of the genus Streptomyces. The isolate formed a branch in the Streptomyces 16S rRNA gene tree together with the type strain of Streptomyces chromofuscus and was also loosely related to Streptomyces fragilis NRRL 2424^T. DNA:DNA relatedness values between the isolate and its two phylogenetic neighbours showed that it formed a distinct genomic species. The strain was readily distinguished from these organisms using a combination of morphological and phenotypic data. Based on the genotypic and phenotypic results, isolate C2^T represents a novel species in the genus Streptomyces, for which the name Streptomyces bullii sp. nov. is proposed. The type strain is C2^T (=CGMCC 4.7019^T = KACC 15426^T).     

Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single‐cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N₀) on A. platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass‐made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0·04–0·44 day^?1) and urea concentrations (0·5 and 5 mmol l^?1). With N₀ = 5 mmol l^?1, the maximum steady‐state biomass concentration was1415 mg l^?1, achieved with D = 0·04 day^?1, but the highest protein content (71·9%) was obtained by applying D = 0·12 day^?1, attaining a protein productivity of 106·41 mg l^?1 day^?1. Nitrogen removal reached 99% on steady‐state conditions. Conclusions: The best results were achieved by applying N₀ = 5 mmol l^?1; however, urea led to inhibitory conditions at D ≥ 0·16 day^?1, inducing the system wash‐out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.     

Conversion of biomass hydrolysates and other substrates to ethanol and other chemicals by Lactobacillus buchneri*

Aims: A Lactobacillus buchneri strain NRRL B‐30929 can convert xylose and glucose into ethanol and chemicals. The aims of the study were to survey three strains (NRRL B‐30929, NRRL 1837 and DSM 5987) for fermenting 17 single substrates and to exam NRRL B‐30929 for fermenting mixed substrates from biomass hydrolysates. Methods and Results: Mixed acid fermentation was observed for all three L. buchneri strains using various carbohydrates; the only exception was uridine which yielded lactate, acetate and uracil. Only B‐30929 is capable of utilizing cellobiose, a desired trait in a potential biocatalyst for biomass conversion. Flask fermentation indicated that the B‐30929 strain can use all the sugars released from pretreated hydrolysates, and producing 1·98–2·35 g l^?1 ethanol from corn stover hydrolysates and 2·92–3·01 g l^?1 ethanol from wheat straw hydrolysates when supplemented with either 0·25× MRS plus 1% corn steep liquor or 0·5× MRS. Conclusions: The L. buchneri NRRL B‐30929 can utilize mixed sugars in corn stover and wheat straw hydrolysates for ethanol and other chemical production. Significance and Impact of the Study: These results are valuable for future research in engineering L. buchneri NRRL B‐30929 for fermentative production of ethanol and chemicals from biomass.     

Iso-migrastatin titer improvement in the engineered <Emphasis Type="Italic">Streptomyces lividans</Emphasis> SB11002 strain by optimization of fermentation conditions

The heterologous production of iso-migrastatin (iso-MGS) was successfully demonstrated in an engineered S. lividans SB11002 strain, which was derived from S. lividans K4-114, following introduction of pBS11001, which harbored the entire mgs biosynthetic gene cluster. However, under similar fermentation conditions, the iso-MGS titer in the engineered strain was significantly lower than that in the native producer — Streptomyces platensis NRRL 18993. To circumvent the problem of low iso-MGS titers and to expand the utility of this heterologous system for iso-MGS biosynthesis and engineering, systematic optimization of the fermentation medium was carried out. The effects of major components in the cultivation medium, including carbon, organic and inorganic nitrogen sources, were investigated using a single factor optimization method. As a result, sucrose and yeast extract were determined to be the best carbon and organic nitrogen sources, resulting in optimized iso-MGS production. Conversely, all other inorganic nitrogen sources evaluated produced various levels of inhibition of iso-MGS production. The final optimized R2YE production medium produced iso-MGS with a titer of 86.5 mg/L, about 3.6-fold higher than that in the original R2YE medium, and 1.5 fold higher than that found within the native S. platensis NRRL 18993 producer.     

Streptomyces polyrhachii sp. nov., a novel actinomycete isolated from an edible Chinese black ant (Polyrhachis vicina Roger)

A novel actinomycete, designated strain NEAU-ycm1^T, was isolated from an edible Chinese black ant (Polyrhachis vicina Roger) and characterized with a polyphasic approach. The organism was found to have morphological and chemotaxonomic characteristics typical of streptomycetes. Phylogenetic analysis based on the almost complete 16S rRNA gene sequence show that the novel isolate belongs to the genus Streptomyces and forms a separate subclade. The closest phylogenetic relatives were identified as the type strains of Streptomyces intermedius NBRC 13049^T (97.74 %), Streptomyces aureoverticillatus NRRL B-3326^T (97.69 %), Streptomyces rutgersensis NBRC 12819^T (97.68 %), Streptomyces gougerotii NBRC 3198^T (97.68 %) and Streptomyces diastaticus subsp. diastaticus NBRC 3714^T (97.68 %). Similarities to other type strains of the genus Streptomyces were lower than 97.55 %. A comparison between strain NEAU-ycm1^T and the closest related Streptomyces type strains revealed that it is different from them in morphological, physiological and biochemical characteristics. Therefore, it is proposed that NEAU-ycm1^T (=CGMCC 4.7094^T = DSM 42102^T) represents a novel species of the genus of Streptomyces, for which the name Streptomyces polyrhachii sp. nov. is proposed.