Methylobacterium nigriterrae sp. nov., isolated from black soil.

An aerobic, Gram-stain-negative, motile rod bacterium, designated as SYSU BS000021T, was isolated from a black soil sample in Harbin, Heilongjiang province, China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate belongs to the genus Methylobacterium, and showed the highest sequence similarity to Methylobacterium segetis KCTC 62267 T (98.51%) and Methylobacterium oxalidis DSM 24028 T (97.79%). Growth occurred at 20-37℃ (optimum, 28 °C), pH 6.0-8.0 (optimum, pH 7.0) and in the presence of 0% (w/v) NaCl. Polar lipids comprised of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified aminolipid and one unidentified polar lipid. The major cellular fatty acids (> 5%) were C18:0 and C18:1 ω7c and/or C18:1 ω6c. The predominant respiratory quinone was Q-10. The genomic G + C content was 68.36% based on the whole genome analysis. The average nucleotide identity (≤ 83.5%) and digital DNA-DNA hybridization (≤ 27.3%) values between strain SYSU BS000021T and other members of the genus Methylobacterium were all lower than the threshold values recommended for distinguishing novel prokaryotic species. Based on the results of phenotypic, chemotaxonomic and phylogenetic analyses, strain SYSU BS000021T represents a novel species of the genus Methylobacterium, for which the name Methylobacterium nigriterrae sp. nov. is proposed. The type strain of the proposed novel species is SYSU BS000021T (= GDMCC 1.3814 T = KCTC 8051 T).

Reclassification of Some Exiguobacterium Species Based on Genome Analysis.

The Exiguobacterium genus comprises Gram-stain-positive and facultatively anaerobic bacteria. Some Exiguobacterium species have previously shown significant high 16S rRNA gene sequence similarities with each other. This study evaluates the taxonomic classification of those Exiguobacterium species through comprehensive genome analysis. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were determined for various Exiguobacterium species pairs. The ANI and dDDH values between Exiguobacterium enclense and Exiguobacterium indicum, Exiguobacterium aquaticum and Exiguobacterium mexicanum, Exiguobacterium soli and Exiguobacterium antarcticum, and Exiguobacterium sibiricum and Exiguobacterium artemiae were above the cut-off level (95-96% for ANI and 70% for dDDH) for species delineation. Based on the findings, we propose to reclassify Exiguobacterium enclense as a later heterotypic synonym of Exiguobacterium indicum, Exiguobacterium aquaticum as a later heterotypic synonym of Exiguobacterium mexicanum, Exiguobacterium soli as a later heterotypic synonym of Exiguobacterium antarcticum and Exiguobacterium sibiricum as a later heterotypic synonym of Exiguobacterium artemiae.

Taxonomic Reframe of Some Species of the Genera Haloferax and Halobellus.

Haloferax and Halobellus are the representatives of the family Haloferacaceae and they are dominant in hypersaline ecosystems. Some Haloferax and Halobellus species exhibit a close evolutionary relationship. Genomic, phylogenetic (based on 16S rRNA gene sequence), and phylogenomic analysis were performed to evaluate the taxonomic positions of the genera Haloferax and Halobellus. Based on the results we propose to reclassify Halobellus ramosii as a later heterotypic synonym of Halobellus inordinatus; Haloferax lucentense and Haloferax alexandrinum as later heterotypic synonyms of Haloferax volcanii.

Oceanobacillus saliphilus sp. nov., Isolated from Saline-Alkali Soil in Heilongjiang Province, China.

A novel bacterium, designated strain APA_H-1(4)T, was isolated from the saline-alkaline soil, Zhaodong, Heilongjiang Province, China. Phenotypic and chemotaxonomic analyses, and whole-genome sequencing were used to determine the taxonomic position of the strain. Phylogenetic analysis indicated that the isolate belongs to the genus Oceanobacillus, and showed the highest sequence similarity to O. damuensis KCTC 33146T (98.35%, similarity) and 'O. massiliensis' DSM 24644 (98.32%). The average nucleotide identity values between strain APA_H-1(4)T and other members of the genus Oceanobacillus were lower than 82% recommended for distinguishing novel prokaryotic species. The digital DNA-DNA hybridization values of strain APA_H-1(4)T with O. damuensis KCTC 33146T and 'O. massiliensis' DSM 24644 were 13.60 and 17.60%, respectively. Cells of strain APA_H-1(4)T were Gram-staining positive, motile, aerobic, spore-forming rods (0.5-0.7 × 1.8-2.6 µm) with flagella. The growth was found to occur optimally at 37 °C. The whole-cell hydrolysate contained meso-diaminopimelic acid as the diagnostic cell wall diamino acid. The main detected polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, an unidentified phospholipid and an unidentified polar lipid. The predominant respiratory quinone was identified as menaquinone-7 (MK-7). The major cellular fatty acid (>10%) was anteiso-C15:0. The G + C content of the genomic DNA was determined to be 38.4% based on the draft genome sequence. Based on the comparative analysis of polyphasic taxonomic data, strain APA_H-1(4)T represents a novel species of the genus Oceanobacillus, for which the name Oceanobacillus saliphilus sp. nov. is proposed. The type strain is APA_H-1(4)T (=GDMCC 1.2239T = KCTC 43254T).

Alteribacter salitolerans sp. nov., isolated from a saline-alkaline soil.

A Gram-positive strain APA H-16(1)T was isolated from a saline-alkali soil sample collected from Heilongjiang Province, China. Cells were rod shaped, non-motile, endospore forming, and aerobic. Growth occurred at 10-45 °C (optimum, 35 °C), pH 7.0-10.5 (optimum, pH 9.5), and could tolerate NaCl up to 15.0% (w/v). Strain showed low 16S rRNA gene sequence similarities with Alteribacter natronophilus (97.8%), Alteribacter aurantiacus (97.7%), and Alteribacter populi (97.1%). The cell wall peptidoglycan was meso-diaminopimelic acid. The predominant menaquinone was MK-7. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, unidentified aminophospholipids, unidentified phospholipid, and unidentified lipid. The major fatty acids were anteiso-C15:0, and iso-C15:0. The genomic G + C content was 45.1%. The average nucleotide identity and digital DNA-DNA hybridization values between strain APA H-16(1)T and the most closely related species were below the cut-off level (95-96%; 70%) for species delineation. Based on phenotypic, phylogenetic, chemotaxonomic, and genome comparison, strain APA H-16(1)T represents a novel species of the genus Alteribacter, for which the name Alteribacter salitolerans sp. nov. is proposed. The type strain is APA H-16(1)T (= KCTC 43228T = CICC 25092T).

Micromonospora rubida sp. nov., a novel actinobacterium isolated from soil of Harbin.

A novel actinobacterium, designated strain NEAU-HG-1T, was isolated from soil collected from Harbin, Heilongjiang Province, Northeast China and characterised using a polyphasic approach. On the basis of 16S rRNA gene sequence analysis, strain NEAU-HG-1T belonged to the genus Micromonospora, and shared high sequence similarities with Micromonospora auratinigra DSM 44815T (98.9%) and Micromonospora coerulea DSM 43143T (98.7%). Morphological and chemotaxonomic characteristics of the strain also supported its assignment to the genus Micromonospora. Cell wall contained meso-diaminopimelic acid and the whole-cell sugars were arabinose and xylose. The polar lipid contained diphosphatidylglycerol, phosphatidylethanolamine, glycolipid and phosphatidylinositol. The predominant menaquinones were MK-10(H2), MK-10(H4) and MK-10(H6). The major fatty acids were C17:0 cycle, iso-C15:0, and iso-C16:0. Furthermore, strain NEAU-HG-1T displayed a DNA-DNA relatedness of 33.8 ± 2.2% with M. coerulea DSM 43143T. The level of digital DNA-DNA hybridization between strain NEAU-HG-1T and M. auratinigra DSM 44815T was 27.2% (24.8-29.7%). The value was well below the criteria for species delineation of 70% for dDDH. Whole-genome average nucleotide identity analyses result also indicated that the isolate should be assigned to a new species under the genus Micromonospora. Therefore, it is concluded that strain NEAU-HG-1T represents a novel species of the genus Micromonospora, for which the name Micromonospora rubida sp. nov. is proposed, with NEAU-HG-1T (= CGMCC 4.7479T = JCM 32386T) as the type strain.

Plantactinosporasoyae sp. nov., an endophytic actinomycete isolated from soybean root [Glycine max (L.) Merr].

A novel actinomycete, designated strain NEAU-gxj3T, was isolated from soybean root [Glycine max (L.) Merr.] collected from Harbin, Heilongjiang Province, China, and characterized using a polyphasic approach. The 16S rRNA gene sequence of strain NEAU-gxj3T showed highest similarity to those of Micromonospora equina Y22T (98.2 %) and Plantactinospora endophytica YIM 68255T (98.0 %). Phylogenetic analysis based on the 16S rRNA gene and gyrB gene demonstrated that the isolate clustered with the members of the genus Plantactinospora. The chemotaxonomic properties of strain NEAU-gxj3Twere also consistent with those of members of the genus Plantactinospora. The cell wall contained meso-diaminopimelic acid and whole-cell sugars were xylose, glucose and galactose. The predominant menaquinones were MK-10(H6), MK-9(H8), MK-10(H2) and MK-10(H4). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside. The major fatty acids were identified as anteiso-C17 : 0, iso-C16 : 0, iso-C15 : 0 and C15 : 0. A combination of DNA-DNA hybridization result and some phenotypic characteristics indicated that strain NEAU-gxj3Tcould be differentiated clearly from its closest phylogenetic relatives. Therefore, the strain is concluded to represent a novel species of the genus Plantactinospora, for which the name Plantactinospora soyae sp. nov. is proposed. The type strain is NEAU-gxj3T (=CGMCC 4.7221T=DSM 46832T).

Streptomyces bryophytorum sp. nov., an endophytic actinomycete isolated from moss (Bryophyta).

A novel endophytic actinomycete, designated strain NEAU-HZ10(T) was isolated from moss and characterised using a polyphasic approach. The strain was found to have morphological and chemotaxonomic characteristics typical of the genus Streptomyces. Strain NEAU-HZ10(T) formed grayish aerial mycelia, which differentiated into straight to flexuous chains of cylindrical spores. The cell wall peptidoglycan was found to contain LL-diaminopimelic acid. Predominant menaquinones were identified as MK-9(H6) and MK-9(H8). The polar lipid profile was found to consist of phosphatidylethanolamine, phosphatidylinositol and two unidentified phospholipids. The major fatty acids were identified as iso-C16:0, anteiso-C15:0 and C16:0. 16S rRNA gene sequence similarity studies showed that strain NEAU-HZ10(T) belongs to the genus Streptomyces and exhibits high sequence similarity to Streptomyces cocklensis DSM 42063(T) (98.9 %). Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain NEAU-HZ10(T) clustered with S. cocklensis DSM 42063(T), Streptomyces yeochonensis CGMCC 4.1882(T) (98.7 %), Streptomyces paucisporeus CGMCC 4.2025(T) (98.4 %) and Streptomyces yanglinensis CGMCC 4.2023(T) (98.1 %). However, a combination of DNA-DNA hybridisation results and some phenotypic characteristics indicated that strain NEAU-HZ10(T) can be distinguished from its phylogenetically closely related strains. Therefore, it is proposed that strain NEAU-HZ10(T) represents a novel species of the genus Streptomyces for which the name Streptomyces bryophytorum sp. nov. is proposed. The type strain is NEAU-HZ10(T) (= CGMCC 4.7151(T) = DSM 42138(T)).

Streptomyces songpinggouensis sp. nov., a Novel Actinomycete Isolated from Soil in Sichuan, China.

During a screening for novel and biotechnologically useful actinobacteria, a novel actinobacteria with weak antifungal activity, designated strain NEAU-Spg19T, was isolated from a soil sample collected from pine forest in Songpinggou, Sichuan, southwest China. The strain was characterized using a polyphasic taxonomic approach which confirmed that it belongs to the genus Streptomyces. Growth occurred at a temperature range of 10-30 °C, pH 5.0-11.0 and NaCl concentrations of 0-5 %. The cell wall peptidoglycan consisted of LL-diaminopimelic acid and glycine. The major menaquinones were MK-9(H6), MK-9(H8) and MK-9(H4). The phospholipid profile contained diphosphatidylglycerol (DPG), phosphatidylethanolamine and phosphatidylinositol. The major fatty acids were iso-C15:0, iso-C16:0, and C16:0. 16S rRNA gene sequence similarity studies showed that strain NEAU-Spg19T belongs to the genus Streptomyces with the highest sequence similarities to Streptomyces tauricus JCM 4837T (98.6 %) and Streptomyces rectiviolaceus JCM 9092T (98.3 %). Some physiological and biochemical properties and low DNA-DNA relatedness values enabled the strain to be differentiated from S. tauricus JCM 4837T and S. rectiviolaceus JCM 9092T. Hence, on the basis of phenotypic and genetic analyses, it is proposed that strain NEAU-Spg19T represents a novel species of the genus Streptomyces, for which the name Streptomyces songpinggouensis sp. nov. is proposed. The type strain is NEAU-Spg19T (=CGMCC 4.7140T=DSM 42141T).

Baia soyae gen. nov., sp. nov., a mesophilic representative of the family Thermoactinomycetaceae, isolated from soybean root [Glycine max (L.) Merr].

A mesophilic, endophytic, filamentous bacterium, designated strain NEAU-gxj18T, was isolated from soybean root [Glycine max (L.) Merr.] collected from Harbin, Heilongjiang Province, China and characterized using a polyphasic approach. Growth was observed at 20­40 °C (optimum 37 °C). Aerial mycelium was absent on all the media tested. Substrate mycelia were well-developed and formed abundant single endospores with smooth surfaces. The only menaquinone was MK-7.The diagnostic diamino acid was meso-diaminopimelic acid. The whole-cell sugars were ribose, glucose and galactose. The major fatty acids were iso-C15 : 0, C13 : 0 and iso-C17 : 0. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, one unidentified aminophospholipid and one undientified phospholipid. The DNA G+C content was 49.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NEAU-gxj18T was phylogenetically related to members of the family Thermoactinomycetaceae, with the highest sequence similarity to Geothermomicrobium terrae YIM 77562T (93.35 %). On the basis of morphological and chemotaxonomic characteristics, phylogenetic analysis and characteristic patterns of 16S rRNA gene signature nucleotides, strain NEAU-gxj18T represents a novel species of a new genus within the family Thermoactinomycetaceae, for which the name Baia soyae gen. nov., sp. nov. is proposed. The type strain of the type species is NEAU-gxj18T ( = CGMCC 4.7223T = DSM 46831T).

Streptomyces maoxianensis sp. nov., a novel actinomycete isolated from soil in Maoxian, China.

A novel actinomycete, designated strain NEAU-Spg16(T), was isolated from a soil sample from a pine forest in Songpinggou, Maoxian, southwest China. A polyphasic taxonomic study was carried out to establish the status of strain NEAU-Spg16(T). The cell wall peptidoglycan was found to contain LL-diaminopimelic acid and glycine. The major menaquinones were identified as MK-9(H8), MK-9(H4) and MK-9(H6). The phospholipid profile was found to contain diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and an unidentified phospholipid. The major fatty acids were identified as iso-C(16:0), C(18:0), C(16:0) and iso-C(15:0). 16S rRNA gene sequence similarity studies showed that strain NEAU-Spg16(T) belongs to the genus Streptomyces with the highest sequence similarity to Streptomyces nitrosporeus DSM 40023(T) (98.6%). However, phylogenetic analysis based on the 16S rRNA gene sequence indicated that it is most closely related to Streptomyces scopuliridis DSM 41917(T) (98.2% sequence similarity). A combination of DNA-DNA hybridization results and some phenotypic characteristics indicated that strain NEAU-Spg16(T) can be clearly differentiated from S. scopuliridis DSM 41917(T) and S. nitrosporeus DSM 40023(T). Therefore, it is concluded that strain NEAU-Spg16(T) represents a novel species of the genus of Streptomyces, for which the name Streptomyces maoxianensis sp. nov. is proposed. The type stain is NEAU-Spg16(T) (=CGMCC 4.7139(T) = DSM 42137(T)).

Actinoallomurus bryophytorum sp. nov., an endophytic actinomycete isolated from moss (Bryophyta).

A novel endophytic actinomycete, strain NEAU-TX1-15(T), was isolated from moss, collected from Wuchang, Heilongjiang province, north China. A polyphasic taxonomic study was carried out to establish the status of strain NEAU-TX1-15(T). Morphological and chemotaxonomic properties of strain NEAU-TX1-15(T) are consistent with the description of the genus Actinoallomurus. Strain NEAU-TX1-15(T) was observed to form short spiral or looped spore chains on aerial hyphae. The cell wall peptidoglycan was found to contain lysine and meso-diaminopimelic acid. The major menaquinones were identified as MK-9(H6) and MK-9(H8). The only phospholipid identified was phosphatidylglycerol. The major fatty acid was identified as iso-C16:0. Analysis of the 16S rRNA gene sequence supports the assignment of the novel strain to the genus Actinoallomurus, as it exhibits 99.2 % gene sequence similarity to that of Actinoallomurus yoronensis NBRC 103686(T). However, the low level of DNA-DNA relatedness allowed the strain to be differentiated from its close relative. Moreover, strain NEAU-TX1-15(T) could also be differentiated from A. yoronensis NBRC 103686(T) and other Actinoallomurus species showing high 16S rRNA gene sequence similarity (>98.0 %) by cultural and physiological characteristics. Therefore, the combination of phenotypic and chemotaxonomic data, and the DNA-DNA hybridization value, indicated that strain NEAU-TX1-15(T) represents a novel species of the genus Actinoallomurus for which the name Actinoallomurus bryophytorum sp. nov. is proposed. The type strain is NEAU-TX1-15(T) (=CGMCC 4.7200(T) = JCM 30340(T)).

Dactylosporangium cerinum sp. nov., a novel actinobacterium isolated from the rhizosphere of Pinus koraiensis Sieb. et Zucc.

A novel actinobacterium, designated strain NEAU-TPG4(T) was isolated from rhizosphere soil of Pinus koraiensis Sieb. et Zucc. collected from Luobei, Heilongjiang Province, north China, and characterized using a polyphasic approach. Morphological and chemotaxonomic properties of strain NEAU-TPG4(T) were consistent with the description of the genus Dactylosporangium. The strain formed finger-shaped sporangia on short sporangiophores that emerged directly from substrate hyphae. The cell-wall peptidoglycan consisted of meso- and 3-hydroxy-diaminopimelic acids; arabinose, xylose and glucose were found as whole-cell sugars. The phospholipid profile contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol. The predominant menaquinones were identified as MK-9(H8) and MK-9(H6). The predominant cellular fatty acids were identified as iso-C16:0, anteiso-C15:0, anteiso-C17:0 and C18:0. Phylogenetic analysis using 16S rRNA gene sequences also indicated that the strain should be classified in the genus Dactylosporangium and showed that the closest relatives were Dactylosporangium maewongense Japan Collection of Microorganism (JCM) 15933(T) (99.6 %), Dactylosporangium siamense NBRC 106093(T) (99.6 %), Dactylosporangium aurantiacum JCM 3083(T) (99.5 %) and Dactylosporangium luteum JCM 17685(T) (99.5 %). However, the low level of DNA-DNA relatedness and several cultural and physiological characteristics allowed the strain to be distinguished from its closest relatives. Thus, it is proposed that strain NEAU-TPG4(T) represents a novel Dactylosporangium species. Dactylosporangium cerinum sp. nov. The type strain of D. cerinum is NEAU-TPG4(T) (=CGMCC 4.7152(T) = DSM 46712(T)).

Two Novel Alkaliphilic Species Isolated from Saline-Alkali Soil in China: Halalkalibacter flavus sp. nov., and Halalkalibacter lacteus sp. nov.

The degradation of farmland in China underscores the need for developing and utilizing saline-alkali soil. Soil health relies on microbial activity, which aids in the restoration of the land's ecosystem, and hence it is important to understand microbial diversity. In the present study, two Gram-stain-positive strains HR 1-10T and J-A-003T were isolated from saline-alkali soil. Preliminary analysis suggested that these strains could be a novel species. Therefore, the taxonomic positions of these strains were evaluated using polyphasic analysis. Phylogenetic and 16S rRNA gene sequence analysis indicated that these strains should be assigned to the genus Halalkalibacter. Cell wall contained meso-2,6-diaminopimelic acid. The polar lipids present in both strains were diphosphatidyl-glycerol, phosphatidylglycerol, and an unidentified phospholipid. The major fatty acids (>10%) were anteiso-C15:0, C16:0 and iso-C15:0. Average nucleotide identity and digital DNA#x2013;DNA hybridization values were below the threshold values (95% and 70%, respectively) for species delineation. Based on the above results, the strains represent two novel species of the genus Halalkalibacter, for which the names Halalkalibacter flavus sp. nov., and Halalkalibacter lacteus sp. nov., are proposed. The type strains are HR 1-10T (=GDMCC 1.2946T = MCCC 1K08312T = JCM 36285T), and J-A-003T (=GDMCC 1.2949T = MCCC 1K08417T = JCM 36286T).

The shift of soil microbial community induced by cropping sequence affect soil properties and crop yield.

Rational cropping maintains high soil fertility and a healthy ecosystem. Soil microorganism is the controller of soil fertility. Meanwhile, soil microbial communities also respond to different cropping patterns. The mechanisms by which biotic and abiotic factors were affected by different cropping sequences remain unclear in the major grain-producing regions of northeastern China. To evaluate the effects of different cropping sequences under conventional fertilization practices on soil properties, microbial communities, and crop yield, six types of plant cropping systems were performed, including soybean monoculture, wheat-soybean rotation, wheat-maize-soybean rotation, soybean-maize-maize rotation, maize-soybean-soybean rotation and maize monoculture. Our results showed that compared with the single cropping system, soybean and maize crop rotation in different combinations or sequences can increase soil total organic carbon and nutrients, and promote soybean and maize yield, especially using soybean-maize-maize and maize-soybean-soybean planting system. The 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing showed that different cropping systems had different effects on bacterial and fungal communities. The bacterial and fungal communities of soybean monoculture were less diverse when compared to the other crop rotation planting system. Among the different cropping sequences, the number of observed bacterial species was greater in soybean-maize-maize planting setup and fungal species in maize-soybean-soybean planting setup. Some dominant and functional bacterial and fungal taxa in the rotation soils were observed. Network-based analysis suggests that bacterial phyla Acidobacteria and Actinobacteria while fungal phylum Ascomycota showed a positive correlation with other microbial communities. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) result showed the presence of various metabolic pathways. Besides, the soybean-maize-maize significantly increased the proportion of some beneficial microorganisms in the soil and reduced the soil-borne animal and plant pathogens. These results warrant further investigation into the mechanisms driving responses of beneficial microbial communities and their capacity on improving soil fertility during legume cropping. The present study extends our understanding of how different crop rotations effect soil parameters, microbial diversity, and metabolic functions, and reveals the importance of crop rotation sequences. These findings could be used to guide decision-making from the microbial perspective for annual crop planting and soil management approaches.

Mining and engineering exporters for titer improvement of macrolide biopesticides in Streptomyces.

Exporter engineering is a promising strategy to construct high-yield Streptomyces for natural product pharmaceuticals in industrial biotechnology. However, available exporters are scarce, due to the limited knowledge of bacterial transporters. Here, we built a workflow for exporter mining and devised a tunable plug-and-play exporter (TuPPE) module to improve the production of macrolide biopesticides in Streptomyces. Combining genome analyses and experimental confirmations, we found three ATP-binding cassette transporters that contribute to milbemycin production in Streptomyces bingchenggensis. We then optimized the expression level of target exporters for milbemycin titer optimization by designing a TuPPE module with replaceable promoters and ribosome binding sites. Finally, broader applications of the TuPPE module were implemented in industrial S. bingchenggensis BC04, Streptomyces avermitilis NEAU12 and Streptomyces cyaneogriseus NMWT1, which led to optimal titer improvement of milbemycin A3/A4, avermectin B1a and nemadectin α by 24.2%, 53.0% and 41.0%, respectively. Our work provides useful exporters and a convenient TuPPE module for titer improvement of macrolide biopesticides in Streptomyces. More importantly, the feasible exporter mining workflow developed here might shed light on widespread applications of exporter engineering in Streptomyces to boost the production of other secondary metabolites.

Mining and fine-tuning sugar uptake system for titer improvement of milbemycins in Streptomyces bingchenggensis.

Dramatic decrease of sugar uptake is a general phenomenon in Streptomyces at stationary phase, when antibiotics are extensively produced. Milbemycins produced by Streptomyces bingchenggensis are a group of valuable macrolide biopesticides, while the low yield and titer impede their broad applications in agricultural field. Considering that inadequate sugar uptake generally hinders titer improvement of desired products, we mined the underlying sugar uptake systems and fine-tuned their expression in this work. First, we screened the candidates at both genomic and transcriptomic level in S. bingchenggensis. Then, two ATP-binding cassette transporters named TP2 and TP5 were characterized to improve milbemycin titer and yield significantly. Next, the appropriate native temporal promoters were selected and used to tune the expression of TP2 and TP5, resulting in a maximal milbemycin A3/A4 titer increase by 36.9% to 3321 mg/L. Finally, TP2 and TP5 were broadly fine-tuned in another two macrolide biopesticide producers Streptomyces avermitilis and Streptomyces cyaneogriseus, leading to a maximal titer improvement of 34.1% and 52.6% for avermectin B1a and nemadectin, respectively. This work provides useful transporter tools and corresponding engineering strategy for Streptomyces.

Publisher Correction: Harnessing the intracellular triacylglycerols for titer improvement of polyketides in Streptomyces.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.