A marine lipopeptides-producing Bacillus amyloliquefaciens HY2-1 with a broad-spectrum antifungal and antibacterial activity and its fermentation kinetics study.

The antagonistic Bacillus amyloliquefaciens HY2-1 was a marine microbiology that was isolated previously from the seabed silt of Beibu Gulf in China by dual culture with Penicillium digitatum. As a continuous study, the present work focused on evaluating the antimicrobial activity, identifying the produced active components, and revealing the fermentation characteristics of B. amyloliquefaciens HY2-1, respectively. It was found that B. amyloliquefaciens HY2-1 exhibited a broad-spectrum antimicrobial activity against the tested seven phytopathogenic fungi and five pathogenic bacteria by producing Bacillus lipopeptides such as fengycin A (C14 to C19 homologues) and surfactin (C14 and C15 homologues). Morphological observation of P. digitatum under light microscope, scanning electron microscopy, transmission electron microscopy, and fluorescence microscope inferred that B. amyloliquefaciens exerted the antagonistic activity by damaging the fungal cell membrane, thus inhibiting the mycelium growth and sporification of phytopathogenic fungi. As a marine microbiology, our results showed that B. amyloliquefaciens could survive and metabolize even at the culture condition with 110 g/L of NaCl concentration, and the produced antimicrobial compounds exhibited excellent thermostability and acid-alkali tolerance. The dynamic models were further constructed to theoretically analyze the fermentation process of B. amyloliquefaciens HY2-1, suggesting that the synthesis of antimicrobial compounds was coupled with both cell growth and cell biomass. In conclusion, the marine lipopeptides-producing B. amyloliquefaciens HY2-1 showed a promising prospect to be explored as a biocontrol agent for plant disease control of crops and postharvest preservation of fruits and vegetables, especially due to its outstanding stress resistance and the broad-spectrum and effective antagonist on various phytopathogenic fungi.

Exopolysaccharides from Lactobacillus plantarum reduces cadmium uptake and mitigates cadmium toxicity in rice seedlings.

Exopolysaccharides (EPSs) can be used as effective exogenous substances to alleviate the toxic effect of cadmium (Cd) on rice and other crops, thus improving plant growth characteristics under stress conditions, and reducing the accumulation of Cd in grains, but the underlying mechanism is still unclear. In the present work, the effects of EPSs from Lactobacillus plantarum on the efficiency of Cd absorption and distribution in rice seedlings under Cd stress were investigated. The results revealed that growth of rice seedlings was severely inhibited by exposure to Cd, resulting in the decrease of plant height, leaf length and biomass. This inhibition phenomenon was alleviated by the addition of EPSs from L. plantarum LPC-1. The underlying mechanism might be that EPSs could facilitate the accumulation efficiency of Cd in rice roots and reduce the transportation rate of Cd from root to leaves, therefore decreasing the Cd content in leaves. Further research showed that Cd contents in the cell wall fraction of the rice seedling root were increased by the addition of EPSs, while the proportions of Cd in the cell organelle and cell soluble component were reduced. Application of EPSs promotes the proportion of pectate- and protein- integrated Cd in rice roots. While the content of water-soluble Cd, which is more toxic to plants, decreased continuously both in roots and leaves. Our study clearly confirmed the positive effects of EPSs on alleviating Cd toxicity and decreasing Cd translocation in rice above-ground parts. Furthermore, the subcellular distribution and chemical forms of Cd in different rice seedlings parts were also affected by the addition of EPSs, which might be an important potential mechanism for EPSs in respect of alleviating Cd toxicity for rice. These findings provided a foundation for the application of exogenous substances on improving the growth performance of crops under heavy metal stress.

Dynamics of the Bacterial Community's Soil During the In-Situ Degradation Process of Waste Chicken Feathers.

Bacteria play an important role in the biodegradation of feather waste. The exploration of the related microbial community structure and diversity is essential to improve the performance of feather waste treatment processes. In the present work, an in-situ soil sampled from a poultry farm was directly used to simulate and accelerate the natural degradation processes of feather waste under laboratory conditions, in which the dynamics of the microbial communities was further analyzed by Illumina HiSeq high-throughput 16S rRNA gene sequencing. Biochemical factors, including pH, feather degradation rate and soluble protein content were also determined in this study. The biochemical results showed that the in-situ soil exhibited an effective degradability on chicken feathers, and the degradation rate of feathers reached 57.95 ± 3.09% at 120 h of cultivation. Meanwhile, soluble protein content and pH reached 33.62 ± 1.45 mg/mL 8.99 ± 0.08, respectively. The results of bacterial diversity analysis showed that bacterial community structure and composition significantly varied in each phase of degradation. Additionally, the bacteria system with feather degradability might consist of Bacillus, Chryseobacterium, Lysobacter, Brevibacillus, and Stenotrophomonas genera. This system may include the following key pathways: carbohydrate metabolism, amino acid metabolism, nucleotide metabolism, membrane transport, replication and repair, translation, signal transduction and energy metabolism. Moreover, the bacterial communities may occur community succession during the degradation processes of chicken feathers. In summary, the present work provided valuable insights into the understanding of microbial community and metabolic functions for feather degradation, although the in-situ biodegradation process was conducted under laboratory conditions. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-021-00996-6.

Antifungal Action of Antifungalmycin N2 Against Rhizoctonia solani by Disrupting Cell Membrane and Inhibiting Succinate Dehydrogenase.

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) was a novel structural antifungal metabolite produced by Streptomyces sp. strain N2. Our previous study reported that the antagonistic interaction between antifungalmycin N2 and Rhizoctonia solani was accompanied by an oxidative stress in R. solani cell, indicating a probable damage occurred in the cell membranes and mitochondria. To verify this, the present study focused on investigating the effects of antifungalmycin N2 on the structure and function of cell membranes and mitochondria of R. solani. Morphological observations in transmission electron microscopy and fluorescence microscope showed that cell membranes of R. solani were damaged, and its cytoplasmic organelles were disorganized when treated with antifungalmycin N2. Meanwhile, the kinetics of membrane-related physiological and biochemical parameters, such as the increased malondialdehyde level, dropped ergosterol formation, and enhanced electrical conductivity in R. solani mycelia, further confirmed that antifungalmycin N2 would disrupt the cell membrane structure and function. More significantly, antifungalmycin N2 had a significantly inhibitory effect on the succinate dehydrogenase (SDH) activity of R. solani, and indicated that the mode and site of action of antifungalmycin N2 against R. solani might be similar to the existing succinate dehydrogenase inhibitors fungicides by binding in the ubiquinone-binding site. In conclusion, the above results demonstrated that the mode and site of action of antifungalmycin N2 targeted to cell membrane and SDH of R. solani, thus exerting the antifungal activity by damaging cell membrane structure and function, together with inhibiting the SDH activity.

The peculiar physiological responses of Rhizoctonia solani under the antagonistic interaction coupled by a novel antifungalmycin N2 from Streptomyces sp. N2.

A novel antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) was previously discovered from Streptomyces sp. N2, which exerted a broad-spectrum antagonistic activity against phytopathogenic fungi. To provide comprehensive insights into the antagonistic mechanisms and biocontrol efficacy of antifungalmycin N2, the present work investigated the physiological responses of Rhizoctonia solani under interaction with antifungalmycin N2. First, the mycelial growth of R. solani was significantly inhibited by antifungalmycin N2 during liquid shake-flask culture. Morphological observations showed that the morphogenesis of R. solani was influenced by antifungalmycin N2, in which the hyphae became severely shriveled and flattened, irregularly folded and branched. Additionally, an obvious accumulation of reactive oxygen species (ROS) was detected in R. solani hyphae, indicating oxidative stress induced by antifungalmycin N2. Further results showed that chitinase activity and its hydrolytic N-acetylglucosamine were significantly accelerated by antifungalmycin N2, demonstrating the cell wall of R. solani was damaged. Interestingly, the enzymatic antioxidant activities of R. solani were significantly induced in response to a relatively low concentration of antifungalmycin N2 (1.44-5.77 µg/mL). However, all antioxidant enzymes became highly inactive when the antifungalmycin N2 was increased to 11.53 µg/mL, suggesting that the enzymatic antioxidant system in R. solani was probably collapsed by the oxidative stress beyond its acceptance scope. In conclusion, antifungalmycin N2 exerted its antagonistic activity by inducing both cell wall degradation and oxidative stress in R. solani, thus leading to fungal morphogenesis and autolysis. Meanwhile, R. solani could induce and activate its antioxidant enzymes as a defence response to the oxidative stress caused by antifungalmycin N2.

Antioxidant activity changes of exopolysaccharides with different carbon sources from Lactobacillus plantarum LPC-1 and its metabolomic analysis.

The effects of different carbon sources on the antioxidant activity changes of exopolysaccharides (EPSs) were determined for the strains Lactobacillus plantarum LPC-1 with glucose, sucrose and its mixture as carbon sources, respectively. Meanwhile, GC-MS datasets coupled with multivariate statistical methods were used to investigate metabolic changes of EPSs-producing L. plantarum cultured with different carbon source. Among carbon sources examined, both of glucose and sucrose were favorable for the cell growth, while the maximum EPSs yield was achieved when sucrose was employed. EPSs cultured with different carbon sources showed remarkable different antioxidant activities, and EPSs with sucrose or mixed sugar as carbon source exhibited a promising antioxidant activity, such as hydroxyl scavenging activity and DPPH radical scavenging activity. Results from rice cultivation showed a similar conclusion that there were also significant differences in the antioxidant activities of EPSs obtained from different carbon sources in inducing rice resistance to chromium stress, but addition of EPSs had no significant impact on the uptake of Cr metals. Principal component analysis showed clear differences in metabolites among different treatment, and the glycolysis and tricarboxylic acid cycle were decreased when sucrose or mixed sugar was used as carbon source, and the production of lactic acid was also reduced, which might be the main reasons for the overproduction of EPSs. Our results indicated that Lactobacillus strain, depending on the carbon source in the medium, could produce EPSs of different biological properties, and the metabolomic analysis findings provided the first omics view of cell growth and EPSs synthesis in L. plantarum, which would be a theoretical basis for further improving the production of EPSs.

Antagonistic activity and mechanism of an isolated Streptomyces corchorusii stain AUH-1 against phytopathogenic fungi.

The various diseases that occur during the growth of plants usually cause a significant reduction in production and quality of agricultural products. Actinomycetes, especially Streptomyces spp., become a valuable biological control resource due to their preponderant abilities to produce various secondary metabolites with novel structure and remarkable biological activity. The present work aimed to isolate an effective antagonistic actinomycete against various soilborne phytopathogenic fungi. By dual culture with Fusarium oxysporum f. sp. niveum, an antagonistic actinomycete named Streptomyces corchorusii stain AUH-1 was screened out from 26 soil samples. The in vitro bioassay results showed that S. corchorusii stain AUH-1 had a broad-spectrum antagonistic activity against a range of fungal plant pathogens, such as F. oxysporum f. sp. niveum, Phytophthora parasitica var. nicotianae, Rhizoctonia solani, P. capsica, Botryosphaeria dothidea, F. oxysporum f. sp. vasinfectum, Verticillium dahliae, and F. oxysporum f. sp. cucumerinum. According to the morphological observations in scanning electron microscopy (SEM) and fluorescence microscope (FM), it was found that the cell membranes of F. oxysporum f. sp. niveum were damaged when treated with the antifungal metabolite form S. corchorusii stain AUH-1. Meanwhile, the dropped ergosterol formation and increased malondialdehyde levels further confirmed that S. corchorusii strain AUH-1 exerted its antagonistic activity against F. oxysporum f. sp. niveum via damaging the structure and function of cell membranes. In conclusion, S. corchorusii strain AUH-1 showed a promising prospect for the development of biological agent, especially due to its broad-spectrum and effective antagonist on various soil-borne plant pathogens.

Metabolic differences of industrial acarbose-producing Actinoplanes sp. A56 under various osmolality levels.

Many investigations have revealed that a certain concentration of osmolality was indispensable for efficient acarbose production, but little information was available on the response mechanism of acarbose-producing strains to osmotic stress. By using the gas chromatography-mass spectrometry (GC-MS) analysis coupled with the enzyme activity determination of central carbon metabolism, the present work investigated the metabolic characteristics of industrial acarbose-producing Actinoplanes sp. A56 under various osmolality levels. Relatively high osmolality (450-500 mOsm/kg) appeared to favor efficient acarbose production by Actinoplanes sp. A56, although it inhibited cell growth. Further GC-MS analysis showed that fatty acids were the uppermost differential intracellular metabolites under various osmolality levels, and the relatively high osmolality resulted in increases in levels of fatty acids.

Interactive performances of betaine on the metabolic processes of Pseudomonas denitrificans.

The performances of betaine on the metabolic processes of vitamin B12-producing Pseudomonas denitrificans were investigated in this paper. The results showed that betaine was an indispensable methyl-group donor for vitamin B12 biosynthesis, but large amounts of the extracellular glycine accompanied by betaine metabolism would impose a severe restriction on the cell growth of P. denitrificans. By further using a comparative metabolomics approach coupled with intracellular free amino acids analysis for the fermentation processes with betaine addition (10 g/l) or not, it was found that betaine could highly strengthen the formation of some key precursors and intermediates facilitating vitamin B12 biosynthesis, such as δ-aminolevulinic acid (ALA, the first precursor of vitamin B12), glutamate (an intermediate of ALA via C5 pathway), glycine (an intermediate of ALA via C4 pathway), and methionine (directly participating in the methylation reaction involved in vitamin B12 biosynthetic pathway). Therefore, the performances of betaine on P. denitrificans metabolic processes were not only serving as a decisive methyl-group donor for vitamin B12 biosynthesis, but also playing a powerfully promoting role in the generation of vitamin B12 precursors and intermediates.

Industrial vitamin B12 production by Pseudomonas denitrificans using maltose syrup and corn steep liquor as the cost-effective fermentation substrates.

The aerobic Pseudomonas denitrificans is widely used for industrial and commercial vitamin B12 fermentation, due to its higher productivity compared to the anaerobic vitamin B12-producing microorganisms. This paper aimed to develop a cost-effective fermentation medium for industrial vitamin B12 production by P. denitrificans in 120,000-l fermenter. It was found that maltose syrup (a low-cost syrup from corn starch by means of enzymatic or acid hydrolysis) and corn steep liquor (CSL, a by-product of starch industry) were greatly applicable to vitamin B12 production by P. denitrificans. Under the optimal fermentation medium performed by response surface methodology, 198.27 ± 4.60 mg/l of vitamin B12 yield was obtained in 120,000-l fermenter, which was close to the fermentation with the refined sucrose (198.80 mg/l) and was obviously higher than that obtained under beet molasses utilization (181.75 mg/l). Therefore, maltose syrups and CSL were the efficient and economical substrates for industrial vitamin B12 fermentation by P. denitrificans.

A novel osmolality-shift fermentation strategy for improving acarbose production and concurrently reducing byproduct component C formation by Actinoplanes sp. A56.

Component C (Acarviosy-1,4-Glc-1,1-Glc) was a highly structural acarbose analog, which could be largely formed during acarbose fermentation process, resulting in acarbose purification being highly difficult. By choosing osmolality level as the key fermentation parameter of acarbose-producing Actinoplanes sp. A56, this paper successfully established an effective and simplified osmolality-shift strategy to improve acarbose production and concurrently reduce component C formation. Firstly, the effects of various osmolality levels on acarbose fermentation were firstly investigated in a 50-l fermenter. It was found that 400-500 mOsm/kg of osmolality was favorable for acarbose biosynthesis, but would exert a negative influence on the metabolic activity of Actinoplanes sp. A56, resulting in an obviously negative increase of acarbose and a sharp formation of component C during the later stages of fermentation (144-168 h). Based on this fact, an osmolality-shift fermentation strategy (0-48 h: 250-300 mOsm/kg; 49-120 h: 450-500 mOsm/kg; 121-168 h: 250-300 mOsm/kg) was further carried out. Compared with the osmolality-stat (450-500 mOsm/kg) fermentation process, the final accumulation amount of component C was decreased from 498.2 ± 27.1 to 307.2 ± 9.5 mg/l, and the maximum acarbose yield was increased from 3,431.9 ± 107.7 to 4,132.8 ± 111.4 mg/l.

Root cell wall remodeling: A way for exopolysaccharides to mitigate cadmium toxicity in rice seedling.

Exopolysaccharides (EPS) are macromolecules with environment beneficial properties. Currently, numerous studies focus on the absorption of heavy metals by EPS, but less attention has been paid to the effects of EPS on the plants. This study explored the effects of EPS from Lactobacillus plantarum LPC-1 on the structure and function of cell walls in rice seedling roots under cadmium (Cd) stress. The results showed that EPS could regulate the remodeling process of the cell walls of rice roots. EPS affects the synthesis efficiency and the content of the substances that made up the cell wall, and thus plays an essential role in limiting the uptake and transport of Cd in rice root. Furthermore, EPS could induce plant resistance to heavy metals by regulating the lignin biosynthesis pathway in rice roots. Finally, the cell wall remodeling induced by EPS likely contributes to plant stress responses by activating the reactive oxygen species (ROS) signaling.

An effective and simplified scale-up strategy for acarbose fermentation based on the carbon source control.

The scale-up strategy for acarbose fermentation by Actinoplanes sp. A56 was explored in this paper. The results obtained in shake-flask cultivation demonstrated that the ratio of maltose and glucose had significant effects on the biosynthesis of acarbose, and the feeding medium containing 3:1 (mass ratio) of maltose and glucose was favorable for acarbose production. Then the correlation of the carbon source concentration with acarbose production was further investigated in 100-l fermenter, and the results showed that 7.5-8.0 g of total sugar/100 ml and 4.0-4.5 g of reducing sugar/100 ml were optimal for acarbose production. Based on the results in 100-l fermenter, an effective and simplified scale-up strategy was successfully established for acarbose fermentation in a 30-m(3) fermenter, by using total sugar and reducing sugar as the scale-up parameter. As a result, 4,327 mg of acarbose/l was obtained at 168 h of fermentation.

Revealing the Promoting Effect of Betaine on Vitamin B12 Biosynthetic Pathway of Pseudomonas denitrificans by Using a Proteomics Analysis.

BACKGROUND: Our previous comparative metabolomics research revealed that betaine (N,N,Ntrimethylglycine, a typically essential methyl-group donor for vitamin B12 biosynthesis) had powerful promoting effect on the generation of vitamin B12 precursors and intermediates in vitamin B12-producing Pseudomonas denitrificans. However, the integral effect of betaine on the vitamin B12 biosynthetic pathway is still unclear. OBJECTIVES: Considering the vitamin B12 biosynthetic pathway of P. denitrificans as a whole, this work aimed to reveal the biological function of betaine on the vitamin B12 biosynthetic pathway in P. denitrificans, which would sharpen and expand understanding of betaine as the methyl-group donor for vitamin B12 biosynthesis. MATERIALS AND METHODS: By using a proteomics method based on the iTRAQ technique, the present study compared and analyzed the differential expression of proteins involved in vitamin B12 biosynthetic pathway under 10 g/L betaine in addition to P. denitrificans fermentation medium. RESULTS: The results showed that betaine could significantly up-regulate the expression of proteins related to the vitamin B12 biosynthetic pathway, which was mainly reflected in the following three aspects: 1) the δ-aminolevulinic acid (ALA) synthase and porphobilinogen synthase that were responsible for the formation of the committed precursors for tetrapyrrole-derived macrocycle in vitamin B12 molecule; 2) the C-methylation-related enzymes (such as precorrin-4 C(11)-methyltransferase, precorrin-2 C(20)- methyltransferase, precorrin-8X methylmutase, and precorrin-6Y C5,15-methyltransferase) and methionine synthase that were crucial to the C-methylation reactions for vitamin B12 biosynthesis; 3) the latestage key enzymes (Cobaltochelatase, and Cob(I)yrinic acid a,c-diamide adenosyltransferase) that were related to cobalt chelation of vitamin B12 molecule. CONCLUSION: The present study demonstrated clearly that betaine could significantly promote the expression of the integral enzymes involved in the vitamin B12 biosynthetic pathway of P. denitrificans, thus promoting vitamin B12 biosynthesis.

Isolation, characterization, and genome sequencing of a novel chitin deacetylase producing Bacillus aryabhattai TCI-16.

Chitin deacetylase (CDA) is a chitin degradation enzyme that catalyzes the conversion of chitin to chitosan by the deacetylation of N-acetyl-D-glucosamine residues, playing an important role in the high-value utilization of waste chitin. The shells of shrimp and crab are rich in chitin, and mangroves are usually recognized as an active habitat to shrimp and crab. In the present study, a CDA-producing bacterium, strain TCI-16, was isolated and screened from the mangrove soil. Strain TCI-16 was identified and named as Bacillus aryabhattai TCI-16, and the maximum CDA activity in fermentation broth reached 120.35 ± 2.40 U/mL at 36 h of cultivation. Furthermore, the complete genome analysis of B. aryabhattai TCI-16 revealed the chitin-degrading enzyme system at genetic level, in which a total of 13 putative genes were associated with carbohydrate esterase 4 (CE4) family enzymes, including one gene coding CDA, seven genes encoding polysaccharide deacetylases, and five genes encoding peptidoglycan-N-acetyl glucosamine deacetylases. Amino acid sequence analysis showed that the predicted CDA of B. aryabhattai TCI-16 was composed of 236 amino acid residues with a molecular weight of 27.3 kDa, which possessed a conserved CDA active like the known CDAs. However, the CDA of B. aryabhattai TCI-16 showed low homology (approximately 30%) with other microbial CDAs, and its phylogenetic tree belonged to a separate clade in bacteria, suggesting a high probability in structural novelty. In conclusion, the present study indicated that the novel CDA produced by B. aryabhattai TCI-16 might be a promising option for bioconversion of chitin to the value-added chitosan.

Discovery and evaluation on the antibacterial and cytotoxic activities of a novel antifungalmycin N2 produced from Streptomyces sp. strain N2.

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) was a novel metabolite produced from Streptomyces sp. strain N2, and the present study aimed to evaluate its antibacterial and cytotoxic properties. By using Oxford cup method, the obtained results revealed that antifungalmycin N2 exhibited a significant antibacterial activity against the pathogenic bacteria such as Staphylococcus aureus, Escherichia coli, and Micrococcus kristinae, especially the Gram-positive S. aureus. Meanwhile, the MTT assay showed that antifungalmycin N2 could exert a marked inhibitory action on tumor cell lines, such as the cell lines of BEL-7402 (human hepatocellular carcinoma), Hela (human cervical carcinoma), HCT116 (human colon cancer), and SW620 (human colon cancer). And the IC50 values antifungalmycin N2 against the above cell lines ranged from 11.23 to 15.37 µg/mL. In conclusion, the antibacterial and cytotoxic activities suggested that the novel antifungalmycin N2 was a promising active structure to be developed as new drug for treating infectious diseases and cancers.

Medium optimization for the feather-degradation by Streptomyces fradiae Var S-221 using the response surface methodology.

In order to accelerate biodegradation of feather into more amino acids, the fermentation medium of feather-biodegrading Streptomyces fradiae Var S-221 was optimized in this paper. In the first optimization step, the effects of feather powder, beet molasses, (NH(4))(2)SO(4) and KH(2)PO(4) on amino acids formation were evaluated by using full factorial design. The results showed that feather powder and (NH(4))(2)SO(4) had significant and positive effects on feather-biodegradation into amino acids. Then, the method of the steepest ascent was used to access the optimal region of the two significant factors. In the third step, the concentration of feather powder and (NH(4))(2)SO(4) were further optimized with central composite design and response surface analysis. As a result, the composition of the optimal medium for S. fradiae Var S-221 fermentation were as follows (g/100 ml): feather powder, 19.504; beet molasses, 4.0; (NH(4))(2)SO(4), 1.467; KH(2)PO(4), 0.3; MgSO(4), 0.15; FeSO(4), 0.001; ZnSO(4), 0.0001; and MnSO(4), 0.0001. Using this optimal fermentation medium, the amino acids concentration was increased from 4.61 to 6.13 g/100 ml.

Structural characterization and induced copper stress resistance in rice of exopolysaccharides from Lactobacillus plantarum LPC-1.

Excessive accumulation of copper could decrease growth and quality of crops, and little information was currently available on the role of exopolysaccharides (EPS) from Lactobacillus plantarum in inducing copper stress resistance in plants. The main objective of this work was to purify and characterize the EPS produced by our isolated L. plantarum LPC-1, and evaluate its potential protection for rice against copper stress. Firstly, two fractions (EPS-1 and EPS-2) were separated and purified from L. plantarum LPC-1 by DEAE-52 cellulose and Sephadex G-100 cellulose column chromatography. According to the further scanning electron microscope (SEM), ultraviolet-visible (UV), fourier-transform infrared spectroscopy (FTIR) spectroscopy and gas chromatography (GC) analyses, it was observed that EPS-1 and EPS-2 were heteropolysaccharides that were composed of mannose and glucose with molar ratio of 2.40:15.01 and 3.02:11.63, respectively. Additionally, the two fractions possessed considerable antioxidant activities, and EPS-1 had a stronger antioxidant activity than EPS-2 in vitro. Furthermore, exogenous addition of EPS significantly alleviated the toxic effects by copper on rice seedlings. In conclusion, this study provided evidence of the EPS-mediated reduction of copper toxicity in rice seedlings at physiological and biochemical levels, suggesting that EPS could be considered as novel and effective plant immune inducers in crops.

Antagonistic activity of a novel antifungalmycin N2 from Streptomyces sp. N2 and its biocontrol efficacy against Rhizoctonia solani.

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) is a novel bioactive substance produced by Streptomyces sp. N2. In this present work, the antagonistic activity of antifungalmycin N2 and its biocontrol efficacy on Rhizoctonia solani were carried out to evaluate its potential as a biocontrol agent against fungal plant diseases. By using potato dextrose agar media for in vitro cultivation of phytopathogenic fungi, the results showed that antifungalmycin N2 not only displayed broad-spectrum antifungal activities against various plant pathogenic fungi, but also had a strong antagonism to the sclerotial germination of R. solani. In a detached leaf assay, it was found that antifungalmycin N2 could effectively protect the rice leaves form the infection of R. solani, resulting in a significantly reduced sheath blight severity on the surfaces of rice leaves. In the pot experiments, the results also revealed that significantly lower sheath blight infections occurred in the tissues of the treated rice plants, which further confirmed that antifungalmycin N2 had a favorable biocontrol efficacy on rice sheath blight. In conclusion, the above results indicated that the novel antifungalmycin N2 was one of promising biocontrol agents for plant disease control.

Improved large-scale production of vitamin B12 by Pseudomonas denitrificans with betaine feeding.

The strategy of betaine control for vitamin B12 large-scale fermentation by Pseudomonas denitrificans was investigated in this paper. The results obtained in shake-flask experiments demonstrated that betaine could greatly stimulate vitamin B12 biosynthesis but had an inhibition to cell growth. Based on the influence of betaine on the fermentation of P. denitrificans, betaine feeding was a beneficial strategy to solve the inconsistency between cell growth and vitamin B12 production. As a result, an effective and economical strategy of betaine feeding was established for vitamin B12 fermentation in 120-m3 fermenter, in which betaine was continuously fed to maintain betaine concentration of the broth at the range of 5-7g/l during 50-140h of fermentation.