Bacillus altitudinis strain AMCC 101304: a novel potential biocontrol agent for potato common scab

ABSTRACT

Potato common scab, caused by Streptomyces spp., is one of the leading causes of heavy commercial losses in the potato industry and is thus one of the most serious plant diseases worldwide. This study identified and assessed potential biocontrol agents against potato common scab. In total, 110 isolates were obtained through antagonistic tests; among which, Bacillus sp. strain AMCC 101304 was found to be most effective at inhibiting the potato common scab pathogen, Streptomyces scabies. Bacillus sp. strain AMCC 101304 was finally identified as Bacillus altitudinis by morphological observation, physiological and biochemical experimentation, as well as 16S rRNA sequencing and phylogenetic analysis. Pot experiments were conducted twice (in spring and autumn) to verify the biocontrol effect of B. altitudinis AMCC 101304 against potato common scab. In spring, the control efficiency reached 76.34%. In autumn, the disease incidence was reduced from 100% to 34.19% (one treatment with strain AMCC 101304) and 38.42% (two treatments with strain AMCC 101304), and the control efficiency reached 82.50% (one application) and 78.43% (two applications). The present study demonstrated the potential of an isolate, identified as B. altitudinis AMCC 101304, as an effective biocontrol agent for future use in the field.     

Substituted benzoic and picolinic acids as foliar sprays against potato common scab

Glasshouse tests on potato cv. Arran Banner measured the effects of single early foliar sprays of 18 substituted benzoic and two dichloropicolinic acids on the severity of common scab, caused by soil-borne Streptomyces scabies. The monosubstituted benzoic acids tested (25 mM) did not affect scab. However, anti-scab action was shown by some 2,5-disubstituted acids. Decreases in scab severity were about 35% from 1·6 mM 5-bromo-2-chloro- and 2,5-dimethylbenzoic acids, and over 50% from 1·6 mM 2,5-dichloro-, 2,5-dibromo- and 5-chloro-2-nitrobenzoic acids and from 0·05 mM 3,6-dichloropicolinic acid (clopyralid), which is structurally similar to 2,5-dichlorobenzoic acid. None of the spray treatments affected yield or shape of tubers. No visible effects on foliage were caused by two of the benzoic acids active against scab (5-chloro-2-nitro- and 2,5-dimethyl-), but the other active acids caused some distortion. In tests of the six dichlorobenzoic acids against S. scabies in culture, the 2,5-isomer (which was the most effective against the disease in plants) was one of the least toxic. With other 2,5-disubstituted benzoic acids, it probably decreased scab indirectly by altering the response of the host to infection.     

Vegetative cells of Bacillus pumilus entrapped in chitosan beads as a product for hydrocarbon biodegradation

The aim of this work was to develop a product using a bacterial strain entrapped in chitosan beads and evaluate its potential to degrade hexadecane. Among 41 isolates obtained from petroleum-contaminated sediments, two isolates, UFPEDA 831 and UFPEDA 840, were selected due to high growth potential utilizing hexadecane. Both isolates were cultivated under different conditions of pH, temperature, osmotic pressure and their susceptibility to antibiotics and resistance to ultraviolet radiation were evaluated. UFPEDA 831 and UFPEA 840 were identified as Ochrobactrum anthropic and Bacillus pumilus, respectively, based on their fatty acid profile and rDNA 16S sequencing. The effect of chitosan on cell viability and production of chitosanase by the selected strains were also evaluated. After these preliminary tests, only B. pumilus showed promising characteristics for immobilisation, and was subsequently entrapped in chitosan beads to be used to degrade hexadecane. The immobilised cells removed 90.8% of hexadecane from a 1% (v/v) solution within 144 h. The beads were analysed by SEM and revealed a homogeneous porous surface with a bacterial biofilm inside. The mechanical resistance of the beads associated with their reuse highlighted the potential of the product to be used for treatment of hexadecane from industrial effluents and/or contaminated environments.     

A Bjerkandera adust new strain as a potential biocontrol agent against wheat scab

International Microbiology - Bjerkandera adusta can decompose polycyclic aromatic hydrocarbons including cellulose and lignin, but its roles in inhibiting plant pathogens are unclear. Here, the...     

Effect of Streptomyces melanosporofaciens strain EF-76 and of chitosan on common scab of potato

The efficiency of Streptomyces melanosporofaciens strain EF-76, a geldanamycin producer, and of chitosan, a polymer derived from chitin that elicits plant defense mechanisms, to protect potato tubers against common scab was evaluated under both controlled and field conditions (years 2000 and 2001). S. melanosporofaciens EF-76 reduced disease incidence in the greenhouse assay and in the 2001 field assay. EF-76 also reduced symptom severity on potato tubers grown under field conditions. Chitosan provided a protective effect against S. scabies,the causal agent of potato common scab during the 2000 field assay by reducing both disease incidence and symptom severity. Combination of S. melanosporofaciensEF-76 and chitosan ensures a level of protection that was at least equivalent to the protection conferred by one of the two products used alone. In some instances, an additive effect of protection was observed when both products were used in combination. Combination of S. melanosporofaciensEF-76 and of chitosan thus represents a promising method of biocontrol against common scab.     

Glasshouse tests of quinones, polyhydroxybenzenes and related compounds against potato common scab

Forty quinones, polyhydroxybenzenes and related compounds were tested for possible control of potato common scab, caused by Streptomyces scabies. They were incorporated, at 50 μg/g or less, into scab-infected soil in which potato plants were then grown in the glasshouse. Quintozene at 50/μ g/g was used as standard. The chemicals varied very widely in their effects on scab, and in their phytotoxicity, as measured by decrease in yield of tubers. Corresponding 1,4-benzoquinones and hydroquinones behaved similarly. The unsubstituted and the phenyl-, chloro-,2,5- and 2,6-dichloro-com-pounds were as effective as quintozene; with the exception of chloro-hydroquinone, they did not decrease yield. Chloranil and chloroneb (the dimethylether of 2,5-dichlorohydroquinone) were much less effective, and chloroneb decreased yield as well. 4-terf-butyl catechol was more effective than any other compound tested, including quintozene, and at suitable rates (25 or 12-5 μg/g) did not decrease yield. Other hydroxybenzenes and some 1,4-naphthaquinones (including dichlone) and anthraquinones were almost ineffective.     

Interactions and biocontrol of pathogenic Streptomyces strains co-occurring in potato scab lesions

Aims:  To test interactions between pathogenic strains of Streptomyces turgidiscabies , S. scabies and S. aureofaciens . To study biological control of S. turgidiscabies and S. scabies using the nonpathogenic Streptomyces strain (346) isolated from a scab lesion and a commercially available biocontrol agent ( S. griseoviridis strain K61; 'Mycostop').
Methods and Results:  Pathogenic strains of S. turgidiscabies and S. aureofaciens inhibited growth of S. scabies in vitro , whereas strain 346 and S. griseoviridis inhibited the pathogenic strains and were subsequently tested for control of scab in the greenhouse and field. Strains 346 and K61 suppressed development of common scab disease caused by S. turgidiscabies in the greenhouse. Strain 346 reduced incidence of S. turgidiscabies in scab lesions on potato tubers in the field.
Conclusions:  Streptomyces turgidiscabies shows antagonism against S. scabies that occurs in the same scab lesions and shares the ecological niche in the field. Biocontrol of S. turgidiscabies is possible with nonpathogenic Streptomyces strains but interactions may be complicated.
Significance and Impact of the Study:  Streptomyces turgidiscabies may have potential to displace S. scabies under the Scandinavian potato growing conditions. Biological control of the severe potato scab pathogen, S. turgidiscabies , is demonstrated for the first time. The results can be applied to enhance control of common scab.     

马铃薯疮痂病拮抗菌YN-2-2的分离与鉴定

【背景】近年来,疮痂病在全国马铃薯各主要产区普遍发生,危害呈逐年加重趋势,有效防控手段匮乏,给种植者造成严重的经济损失。利用拮抗微生物抑制病原菌繁殖,降低其危害程度,已成为马铃薯植保领域的研究热点。【目的】筛选对疮痂病原菌具有拮抗作用的菌株,为研制高效复合功能菌剂、有效防控马铃薯疮痂病提供菌种资源。【方法】从疮痂病发生严重的云南昭通马铃薯大田采集近根际土壤,分离、筛选代谢产物具有明显拮抗效果的菌株,通过形态学观察、生理生化特征分析和16SrRNA基因序列测定等方法进行菌种鉴定,并对其代谢产物的稳定性和抑菌效果进行分析。【结果】获得一株拮抗效果明显的细菌YN-2-2,其菌落圆形,淡黄色,边缘整齐、光滑、干燥,中间有凹陷,菌体杆状,大小为(2.51-4.09)μm×(1.09-1.68)μm,革兰氏染色阳性,16SrRNA基因序列与Bacillus thuringiensis ATCC 10792T (ACNF01000156)的相似性达到99.79%。YN-2-2的代谢产物热稳定性较好,pH耐受范围广(3.0-13.0),对蛋白酶K敏感度较低,对疮痂链霉菌的抑菌圈直径最大为22.8 mm。盆栽试验结果表明:浇施100 mL浓度为1×107 CFU/mL的培养液,可显著降低马铃薯微型薯疮痂病病情指数,防效达36.11%。【结论】菌株YN-2-2经鉴定为苏云金芽孢杆菌(Bacillus thuringiensis),可以作为高效复合功能菌剂的候选菌株。     

Chemical control of potato common scab disease under field conditions

The aim of this study was to evaluate certain fungicides against Streptomyces scabies (Thaxter), the main causal agent of common scab disease in potato and other crops, in vitro and in vivo. Fourteen isolates of S. scabies were isolated from naturally infected potato tubers showing common scab symptoms. All isolates were pathogenic to potato tubers and produced typical symptoms of common scab. Isolate (No. 11) caused highest disease index (DSI) followed by isolates 10, 8 and 5 (61.13%). Seven fungicides (Rizolex, Capitan, Moncut, Ridomil, Maxim, Topsin, and Oxyplus) were screened in vitro for their toxicity against the pathogen isolate (No. 11). Results showed that four of them (Rizolex, Capitan, Moncut, and Ridomil) exhibited inhibition zone ranging from 5.33 to 26.33?mm. Capitan, Ridomil, and Rizolex were able to reduce DSI under field condition but they varied in their effects. Capitan was the best fungicide which aids in the reduction of disease (33.8%) followed by Ridomil (31.5%) while Rizolex (21.2%) was the lowest one.     

Glasshouse tests of chemicals for control of potato common scab

Quintozene is the only chemical used successfully in practice to control soil-borne Streptomyces scabies, the cause of potato common scab. However it may be carcinogenic, and the aim of this work was to find a substitute for it. About 100 chemicals, most of which had known fungitoxic action or were related to such chemicals, were tested in the glasshouse by growing potato plants in soil with which the chemicals had been mixed, usually at 50 ppm. Many of the chemicals failed to decrease the incidence of scab, or decreased the yield of tubers, or both. The most effective chemical was captafol, which was as effective as quintozene and, unlike quintozene, did not decrease yield. Captan and folpet, which are very closely related to captafol, were ineffective.     

Effect of chitosan and a biocontrol streptomycete on field and potato tuber bacterial communities

Four treatments applied on potato seed tubers i.e. talc only, chitosan only, Streptomyces melanosporofaciens strain EF-76 in talc and S. melanosporofaciens strain EF-76 in chitosan were compared for their efficiency to reduce common scab incidence. As previously reported the joint application of the geldanamycin-producing S. melanosporofaciens strain EF-76 and chitosan was effective to control common scab of potato. Nevertheless, field application of S. melanosporofaciens EF-76 did not allow the selection of geldanamycin-resistant actinomycetes (GRA) in the bulk soil during the potato growing season. The number of GRA on harvested potato tubers was, however, significantly higher in treatments that contained chitosan than in other treatments suggesting that chitosan might promote the establishment of the antagonistic actinomycete on progeny tubers. Biolog EcoPlates were used to determine the metabolic profiles of the bacterial soil communities. A permutation MANOVA analysis detected significant differences within the metabolic profiles of the bacterial communities at the potato flowering period but not at the beginning of the season or a week before harvest. A combination of S. melanosporofaciens EF-76 and chitosan thus represents a promising tool against common scab, with low short-term impact on soil bacterial communities.     

Characterization of cross-linked hydroxycinnamic acid amides isolated from potato common scab lesions

Four feruloyl amides, N-trans-feruloyloctopamine (1), N-cis-feruloyloctopamine (2), N-trans-feruloyltyramine (3), N-cis-feruloyltyramine (4), a cross-linked N-trans-feruloyltyramine dimer (5), and a cross-linked N-cis-feruloyltyramine dimer (6) were isolated from potato common scab lesions. The compounds were purified by TLC and characterized by a combination of (1)H and (13)C NMR spectroscopic techniques. The presence of an accompanying minor complex of cross-linked dimers containing both feruloyltyramines and feruloyloctopamines was also demonstrated. This is the first characterization of cross-linked hydroxycinnamic acid amides associated with wound healing in potato (Solanum tuberosum) tubers.     

A non-replicating oncolytic vector as a novel therapeutic tool against cancer

Cancers are still difficult targets despite recent advances in cancer therapy. Due to the heterogeneity of cancer, a single-treatment modality is insufficient for the complete elimination of cancer cells. Therapeutic strategies from various aspects are needed. Gene therapy has been expected to bring a breakthrough to cancer therapy, but it has not yet been successful. Gene therapy also should be combined with other treatments to enhance multiple therapeutic pathways. In this view, gene delivery vector itself should be equipped with intrinsic anti-cancer activities. HVJ (hemagglutinating virus of Japan; Sendai virus) envelope vector (HVJ-E) was developed to deliver therapeutic molecules. HVJ-E itself possessed anti-tumor activities such as the generation of anti-tumor immunities and the induction of cancer-selective apoptosis. In addition to the intrinsic anti-tumor activities, therapeutic molecules incorporated into HVJ-E enabled to achieve multi-modal therapeutic strategies in cancer treatment. Tumor-targeting HVJ-E was also developed. Thus, HVJ-E will be a novel promising tool for cancer treatment.     

Efficiency of Trichoderma harzianum as a biocontrol agent in combination with humate and chitosan against Meloidogyne incognita on tomato

Abstract

A pot trial was conducted to estimate the role of Trichoderma harzianum alone or in combination with two organic substances, potassium humate and chitosan in controlling Meloidogyne incognita on tomato. All treatments caused greater decreases in parameters of M. incognita in comparison to the control treatment (nematode only) and this led to noticeable enhancements in growth and yield of tomato. The lowest numbers of eggmasses, eggs/eggmass, galls/root, females/root, and second stage juveniles/250?g soil were recorded due to the combination of T. harzianum (10¹⁰ spore/ml) with chitosan and potassium humate after 120 days from the transplanting of tomato seedlings. Also, this treatment showed the best promotion for all tomato parameters (lengths and weights of shoots and roots, and productivity). So, mixing chitosan, potassium and T. harzianum is highly recommended to be used as an effective bio-nematicide against M. incognita on tomato plants.     

Genetic diversity of Streptomyces spp. causing common scab of potato in eastern Canada

Common scab is an important disease of potato caused by Streptomyces scabies and other closely related species. In this study, the genetic diversity of Streptomyces spp. causing common scab of potato in eastern Canada was for the first time investigated. Forty-one Streptomyces spp. isolates were retrieved from necrotic lesions of potato tubers harvested from different regions of the Canadian provinces New-Brunswick, Nova Scotia and Prince-Edward-Island. Most isolates were closely related to known pathogenic S. scabies strains on the basis of partial 16S ribosomal (r) RNA and rpoB gene sequence analyses. Two isolates were identified as pathogenic species of Streptomyces acidiscabies. To our knowledge, this species has never been previously isolated in these areas. Genome fingerprinting studies using repetitive elements (rep) polymerase chain reactions (PCR) revealed 10 distinct genetic groups in eastern Canada. The geographical distribution of the genetic groups was region-dependant. Pathogenicity- and virulence-related genes (txtA, txtC, and tomA) were PCR-amplified from each isolate, and nucleotide sequence analysis of partial gene fragments revealed slight polymorphisms in both txtA and txtC genes. No genetic variation was noted in the partial tomA gene sequences.     

Effects of foliar sprays of daminozide on the incidence of potato common scab

Single foliar sprays of the growth retardant daminozide (1.5–12 g/l) approximately halved the incidence of common scab, caused by soil-borne Streptomyces scabies, on potted potato plants in the glasshouse. Two analogues of daminozide (N-dimethylaminomaleamic and N-(dimethylamino)-methylsuccinamic acids) also decreased scab, but others were inactive. Of 22 other unrelated growth regulators and translocated chemicals tested as foliar sprays, only gibberellic acid (0.1 g/l) decreased scab incidence, but many of the tubers were distorted. Chlormequat chloride and chlorphonium chloride, as root treatments, were inactive. In other experiments with daminozide, scab incidence was decreased after application to soil. In tests with two plants per pot, spraying one of each pair decreased its rate of stem extension, but did not affect the other, indicating that little or no daminozide passed into the soil from the roots of the sprayed plant. The decrease in scab brought about by foliar sprays was not altered by varying their timing during the period before symptom development (1 to 5 wk after potting). In agar plate tests, daminozide was only weakly toxic to S. scabies. It is concluded that daminozide probably decreased scab by altering the physiology of the plants, so that scab symptoms did not develop.     

Short-duration low-direct-current electrical field treatment is a practical tool for considerably reducing counts of gram-negative bacteria entrapped in gel beads

Application of a direct-current electrical field for very short times can serve as a practical nonthermal procedure to reduce or modify the microbial distribution in gel beads. The viability of Escherichia coli and Serratia marcescens entrapped in alginate and agarose beads decreases as the field intensity and duration of electrical field increase.     

TxtH is a key component of the thaxtomin biosynthetic machinery in the potato common scab pathogen Streptomyces scabies

Streptomyces scabies causes potato common scab disease, which reduces the quality and market value of affected tubers. The predominant pathogenicity determinant produced by S. scabies is the thaxtomin A phytotoxin, which is essential for common scab disease development. Production of thaxtomin A involves the nonribosomal peptide synthetases (NRPSs) TxtA and TxtB, both of which contain an adenylation (A-) domain for selecting and activating the appropriate amino acid during thaxtomin biosynthesis. The genome of S. scabies 87.22 contains three small MbtH-like protein (MLP)-coding genes, one of which (txtH) is present in the thaxtomin biosynthesis gene cluster. MLP family members are typically required for the proper folding of NRPS A-domains and/or stimulating their activities. This study investigated the importance of TxtH during thaxtomin biosynthesis in S. scabies. Biochemical studies showed that TxtH is required for promoting the soluble expression of both the TxtA and TxtB A-domains in Escherichia coli, and amino acid residues essential for this activity were identified. Deletion of txtH in S. scabies significantly reduced thaxtomin A production, and deletion of one of the two additional MLP homologues in S. scabies completely abolished production. Engineered expression of all three S. scabies MLPs could restore thaxtomin A production in a triple MLP-deficient strain, while engineered expression of MLPs from other Streptomyces spp. could not. Furthermore, the constructed MLP mutants were reduced in virulence compared to wild-type S. scabies. The results of our study confirm that TxtH plays a key role in thaxtomin A biosynthesis and plant pathogenicity in S. scabies.