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Tarsitano J, Bockor SS, Palomino MM, Fina Martin J, Ruzal SM, Allievi MC. [Deficiency in N-acetylglucosamine transport affects the sporulation process and increases the hemolytic activity of the S-layer protein in Lysinibacillus sphaericus ASB13052]. Rev Argent Microbiol 2024; 56:232-240. [PMID: 39218718 DOI: 10.1016/j.ram.2024.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 05/09/2024] [Accepted: 05/28/2024] [Indexed: 09/04/2024] Open
Abstract
Lysinibacillus sphaericus is a bacterium that, along with Bacillus thuringiensis var. israelensis, is considered the best biological insecticide for controlling mosquito larvae and an eco-friendly alternative to chemical insecticides. It depends on peptidic molecules such as N-acetylglucosamine to obtain carbon sources and possesses a phosphotransferase system (PTS) for their incorporation. Some strains carry S-layer proteins, whose involvement in metal retention and larvicidal activity against disease-carrying mosquitoes has been demonstrated. Alterations in the amino sugar incorporation system could affect the protein profile and functionality. Strain ASB13052 and the isogenic mutant in the ptsH gene, which is predominant in the PTS signaling pathway, were used in this study. For the first time, the presence of N-glycosylated S-layer proteins was confirmed in both strains, with a variation in their molecular weight pattern depending on the growth phase. In the exponential phase, an S-layer protein greater than 130 kDa was found in the ptsH mutant, which was absent in the wild-type strain. The mutant strain exhibited altered and incomplete low quality sporulation processes. Hemolysis analysis, associated with larvicidal activity, showed that the ptsH mutant has higher lytic efficiency, correlating with the high molecular weight protein. The results allow us to propose the potential effects that arise as a result of the absence of amino sugar transport on hemolytic activity, S-layer isoforms, and the role of N-acetylglucosamine in larvicidal activity.
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Affiliation(s)
- Julián Tarsitano
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Sabrina Sol Bockor
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires - Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN) - CONICET, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - María Mercedes Palomino
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires - Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN) - CONICET, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Joaquina Fina Martin
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires - Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN) - CONICET, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Sandra Mónica Ruzal
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires - Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN) - CONICET, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina
| | - Mariana Claudia Allievi
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires - Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN) - CONICET, Ciudad Universitaria, Ciudad Autónoma de Buenos Aires, Argentina.
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Herdman M, Isbilir B, von Kügelgen A, Schulze U, Wainman A, Bharat TAM. Cell cycle dependent coordination of surface layer biogenesis in Caulobacter crescentus. Nat Commun 2024; 15:3355. [PMID: 38637514 PMCID: PMC11026435 DOI: 10.1038/s41467-024-47529-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Accepted: 04/04/2024] [Indexed: 04/20/2024] Open
Abstract
Surface layers (S-layers) are proteinaceous, two-dimensional paracrystalline arrays that constitute a major component of the cell envelope in many prokaryotic species. In this study, we investigated S-layer biogenesis in the bacterial model organism Caulobacter crescentus. Fluorescence microscopy revealed localised incorporation of new S-layer at the poles and mid-cell, consistent with regions of cell growth in the cell cycle. Light microscopy and electron cryotomography investigations of drug-treated bacteria revealed that localised S-layer insertion is retained when cell division is inhibited, but is disrupted upon dysregulation of MreB or lipopolysaccharide. We further uncovered that S-layer biogenesis follows new peptidoglycan synthesis and localises to regions of high cell wall turnover. Finally, correlated cryo-light microscopy and electron cryotomographic analysis of regions of S-layer insertion showed the presence of discontinuities in the hexagonal S-layer lattice, contrasting with other S-layers completed by defined symmetric defects. Our findings present insights into how C. crescentus cells form an ordered S-layer on their surface in coordination with the biogenesis of other cell envelope components.
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Affiliation(s)
- Matthew Herdman
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK
| | - Buse Isbilir
- Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK
| | - Andriko von Kügelgen
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK
- Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK
| | - Ulrike Schulze
- Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK
| | - Alan Wainman
- Sir William Dunn School of Pathology, University of Oxford, Oxford, OX1 3RE, UK
| | - Tanmay A M Bharat
- Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK.
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Katak RDM, Cintra AM, Burini BC, Marinotti O, Souza-Neto JA, Rocha EM. Biotechnological Potential of Microorganisms for Mosquito Population Control and Reduction in Vector Competence. INSECTS 2023; 14:718. [PMID: 37754686 PMCID: PMC10532289 DOI: 10.3390/insects14090718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 08/11/2023] [Accepted: 08/19/2023] [Indexed: 09/28/2023]
Abstract
Mosquitoes transmit pathogens that cause human diseases such as malaria, dengue fever, chikungunya, yellow fever, Zika fever, and filariasis. Biotechnological approaches using microorganisms have a significant potential to control mosquito populations and reduce their vector competence, making them alternatives to synthetic insecticides. Ongoing research has identified many microorganisms that can be used effectively to control mosquito populations and disease transmission. However, the successful implementation of these newly proposed approaches requires a thorough understanding of the multipronged microorganism-mosquito-pathogen-environment interactions. Although much has been achieved in discovering new entomopathogenic microorganisms, antipathogen compounds, and their mechanisms of action, only a few have been turned into viable products for mosquito control. There is a discrepancy between the number of microorganisms with the potential for the development of new insecticides and/or antipathogen products and the actual available products, highlighting the need for investments in the intersection of basic research and biotechnology.
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Affiliation(s)
- Ricardo de Melo Katak
- Malaria and Dengue Laboratory, Instituto Nacional de Pesquisas da Amazônia-INPA, Manaus 69060-001, AM, Brazil;
| | - Amanda Montezano Cintra
- Multiuser Central Laboratory, Department of Bioprocesses and Biotechnology, School of Agricultural Sciences, São Paulo State University (UNESP), Botucatu 18610-034, SP, Brazil; (A.M.C.); (J.A.S.-N.)
| | - Bianca Correa Burini
- Florida Medical Entomology Laboratory, University of Florida, Vero Beach, FL 32962, USA;
| | - Osvaldo Marinotti
- Department of Biology, Indiana University, Bloomington, IN 47405, USA;
| | - Jayme A. Souza-Neto
- Multiuser Central Laboratory, Department of Bioprocesses and Biotechnology, School of Agricultural Sciences, São Paulo State University (UNESP), Botucatu 18610-034, SP, Brazil; (A.M.C.); (J.A.S.-N.)
| | - Elerson Matos Rocha
- Multiuser Central Laboratory, Department of Bioprocesses and Biotechnology, School of Agricultural Sciences, São Paulo State University (UNESP), Botucatu 18610-034, SP, Brazil; (A.M.C.); (J.A.S.-N.)
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Pantoja-Guerra M, Burkett-Cadena M, Cadena J, Dunlap CA, Ramírez CA. Lysinibacillus spp.: an IAA-producing endospore forming-bacteria that promotes plant growth. Antonie Van Leeuwenhoek 2023:10.1007/s10482-023-01828-x. [PMID: 37138159 DOI: 10.1007/s10482-023-01828-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 03/29/2023] [Indexed: 05/05/2023]
Abstract
Lysinibacillus is a bacterial genus that has generated recent interest for its biotechnological potential in agriculture. Strains belonging to this group are recognized for their mosquitocidal and bioremediation activity. However, in recent years some reports indicate its importance as plant growth promoting rhizobacteria (PGPR). This research sought to provide evidence of the PGP activity of Lysinibacillus spp. and the role of the indole-3-acetic acid (IAA) production associated with this activity. Twelve Lysinibacillus spp. strains were evaluated under greenhouse conditions, six of which increased the biomass and root architecture of corn plants. In most cases, growth stimulation was evident at 108 CFU/mL inoculum concentration. All strains produced IAA with high variation between them (20-70 µg/mL). The bioinformatic identification of predicted genes associated with IAA production allowed the detection of the indole pyruvic acid pathway to synthesize IAA in all strains; additionally, genes for a tryptamine pathway were detected in two strains. Extracellular filtrates from all strain's cultures increased the corn coleoptile length in an IAA-similar concentration pattern, which demonstrates the filtrates had an auxin-like effect on plant tissue. Five of the six strains that previously showed PGPR activity in corn also promoted the growth of Arabidopsis thaliana (col 0). These strains induced changes in root architecture of Arabidopsis mutant plants (aux1-7/axr4-2), the partial reversion of mutant phenotype indicated the role of IAA on plant growth. This work provided solid evidence of the association of Lysinibacillus spp. IAA production with their PGP activity, which constitutes a new approach for this genus. These elements contribute to the biotechnological exploration of this bacterial genus for agricultural biotechnology.
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Affiliation(s)
- Manuel Pantoja-Guerra
- Universidad de Antioquia, Instituto de Biología, Medellín, Colombia.
- Facultad de Ciencias Agropecuarias, Unilasallista Corporación Universitaria, Caldas - Antioquia, Colombia.
| | | | | | - Christopher A Dunlap
- United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, Crop Bioprotection Research Unit, 1815 N University, Peoria, IL, USA
| | - Camilo A Ramírez
- Universidad de Antioquia, Instituto de Biología, Medellín, Colombia
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Dunstand-Guzmán E, Hallal-Calleros C, Hernández-Velázquez VM, Dominguez-Roldan R, Peña-Chora G, Flores-Pérez I. Potential control of the infective stage of Taenia pisiformis using Bacillus thuringiensis GP526 strain. Exp Parasitol 2023; 249:108522. [PMID: 37011803 DOI: 10.1016/j.exppara.2023.108522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 03/23/2023] [Accepted: 03/29/2023] [Indexed: 04/03/2023]
Abstract
The GP526 strain of Bacillus thuringiensis has been referred as an in vitro helminthicide on various stages of Dipylidium caninum and Centrocestus formosanus. Our study addresses the in vitro ovicidal activity of GP526 strain spore-crystal complex on Taenia pisiformis eggs, evaluating induced damage microscopically. The eggs exposed to the total extract containing spores and crystals show damage after 24 hours, with loss of integrity on the eggshell, and an ovicidal activity of 33% at 1mg/ml. The destruction of the embryophore was observed after 120 h with a 72% of ovicidal activity at 1 mg/ml. The LC50 was 609.6 μg/ml, dose that causes a 50% of lethality on the hexacanth embryo, altering the oncosphere membrane. The spore-crystal proteins were extracted, and the protein profile was obtained by electrophoresis, finding a major band of 100 kDa suggestive of an S-layer protein, since an S-layer was immunodetected in both, spores and extracted proteins. The protein fraction containing the S-layer protein presents adhesion to the T. pisiformis eggs, and 0.4 mg/ml of the protein induces a lethality of 21.08% at 24 h. The characterization of molecular mechanisms of ovicidal activity will be an important contribution, so the characterization of the proteins that make up the extract of the GP526 strain, would be useful to support the biological potential for control of this cestodiasis and other parasitosis. B. thuringiensis is shown as a potent helminthicide on eggs, with useful potential for biological control of this cestodiasis.
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Multiple S-Layer Proteins of Brevibacillus laterosporus as Virulence Factors against Insects. Int J Mol Sci 2023; 24:ijms24021781. [PMID: 36675293 PMCID: PMC9864115 DOI: 10.3390/ijms24021781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 12/26/2022] [Accepted: 01/13/2023] [Indexed: 01/18/2023] Open
Abstract
S-layers are involved in the adaptation of bacteria to the outside environment and in pathogenesis, often representing special virulence factors. Vegetative cells of the entomopathogenic bacterium Brevibacillus laterosporus are characterized by an overproduction of extracellular surface layers that are released in the medium during growth. The purpose of this study was to characterize cell wall proteins of this bacterium and to investigate their involvement in pathogenesis. Electron microscopy observations documented the presence of multiple S-layers, including an outermost (OW) and a middle (MW) layer, in addition to the peptidoglycan layer covering the plasma membrane. After identifying these proteins (OWP and MWP) by mass spectrometry analyses, and determining their gene sequences, the cell wall multilayer-released fraction was successfully isolated and used in insect bioassays alone and in combination with bacterial spores. This study confirmed a central role of spores in bacterial pathogenicity to insects but also detected a significant virulence associated with fractions containing released cell wall multilayer proteins. Taken together, S-layer proteins appear to be part of the toxins and virulence factors complex of this microbial control agent of invertebrate pests.
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Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance. Toxins (Basel) 2021; 13:toxins13080523. [PMID: 34437394 PMCID: PMC8402332 DOI: 10.3390/toxins13080523] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/18/2021] [Accepted: 06/19/2021] [Indexed: 12/25/2022] Open
Abstract
Larvicides based on the bacteria Bacillus thuringiensis svar. israelensis (Bti) and Lysinibacillus sphaericus are effective and environmentally safe compounds for the control of dipteran insects of medical importance. They produce crystals that display specific and potent insecticidal activity against larvae. Bti crystals are composed of multiple protoxins: three from the three-domain Cry type family, which bind to different cell receptors in the midgut, and one cytolytic (Cyt1Aa) protoxin that can insert itself into the cell membrane and act as surrogate receptor of the Cry toxins. Together, those toxins display a complex mode of action that shows a low risk of resistance selection. L. sphaericus crystals contain one major binary toxin that display an outstanding persistence in field conditions, which is superior to Bti. However, the action of the Bin toxin based on its interaction with a single receptor is vulnerable for resistance selection in insects. In this review we present the most recent data on the mode of action and synergism of these toxins, resistance issues, and examples of their use worldwide. Data reported in recent years improved our understanding of the mechanism of action of these toxins, showed that their combined use can enhance their activity and counteract resistance, and reinforced their relevance for mosquito control programs in the future years.
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8
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Fina Martin J, Palomino MM, Cutine AM, Modenutti CP, Fernández Do Porto DA, Allievi MC, Zanini SH, Mariño KV, Barquero AA, Ruzal SM. Exploring lectin-like activity of the S-layer protein of Lactobacillus acidophilus ATCC 4356. Appl Microbiol Biotechnol 2019; 103:4839-4857. [PMID: 31053916 DOI: 10.1007/s00253-019-09795-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 03/22/2019] [Accepted: 03/23/2019] [Indexed: 02/06/2023]
Abstract
The surface layer (S-layer) protein of Lactobacillus acidophilus is a crystalline array of self-assembling, proteinaceous subunits non-covalently bound to the outmost bacterial cell wall envelope and is involved in the adherence of bacteria to host cells. We have previously described that the S-layer protein of L. acidophilus possesses anti-viral and anti-bacterial properties. In this work, we extracted and purified S-layer proteins from L. acidophilus ATCC 4356 cells to study their interaction with cell wall components from prokaryotic (i.e., peptidoglycan and lipoteichoic acids) and eukaryotic origin (i.e., mucin and chitin), as well as with viruses, bacteria, yeast, and blood cells. Using chimeric S-layer fused to green fluorescent protein (GFP) from different parts of the protein, we analyzed their binding capacity. Our results show that the C-terminal part of the S-layer protein presents lectin-like activity, interacting with different glycoepitopes. We further demonstrate that lipoteichoic acid (LTA) serves as an anchor for the S-layer protein. Finally, a structure for the C-terminal part of S-layer and possible binding sites were predicted by a homology-based model.
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Affiliation(s)
- Joaquina Fina Martin
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Maria Mercedes Palomino
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Anabella M Cutine
- Laboratorio de Glicómica Funcional y Molecular, Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), C1428, Buenos Aires, Argentina
| | - Carlos P Modenutti
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Dario A Fernández Do Porto
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
- Facultad de Ciencias Exactas y Naturales, Instituto de Cálculo, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Mariana C Allievi
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Sofia H Zanini
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
| | - Karina V Mariño
- Laboratorio de Glicómica Funcional y Molecular, Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), C1428, Buenos Aires, Argentina
| | - Andrea A Barquero
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Sandra M Ruzal
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Universidad de Buenos Aires, Cdad. Universitaria, Pabellón II, 4 piso, Lab QB40, C1428EGA, CABA, Buenos Aires, Argentina.
- Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina.
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Chalivendra S, DeRobertis C, Reyes Pineda J, Ham JH, Damann K. Rice Phyllosphere Bacillus Species and Their Secreted Metabolites Suppress Aspergillus flavus Growth and Aflatoxin Production In Vitro and In Maize Seeds. Toxins (Basel) 2018; 10:toxins10040159. [PMID: 29659522 PMCID: PMC5923325 DOI: 10.3390/toxins10040159] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 04/09/2018] [Accepted: 04/11/2018] [Indexed: 12/15/2022] Open
Abstract
The emergence of super-toxigenic strains by recombination is a risk from an intensive use of intraspecific aflatoxin (AF) biocontrol agents (BCAs). Periodical alternation with interspecific-BCAs will be safer since they preclude recombination. We are developing an AF-biocontrol system using rice-associated Bacilli reported previously (RABs). More than 50% of RABs inhibited the growth of multiple A. flavus strains, with RAB4R being the most inhibitory and RAB1 among the least. The fungistatic activity of RAB4R is associated with the lysis of A. flavus hyphal tips. In field trails with the top five fungistatic RABs, RAB4R consistently inhibited AF contamination of maize by Tox4, a highly toxigenic A. flavus strain from Louisiana corn fields. RAB1 did not suppress A. flavus growth, but strongly inhibited AF production. Total and HPLC-fractionated lipopeptides (LPs) isolated from culture filtrates of RAB1 and RAB4R also inhibited AF accumulation. LPs were stable in vitro with little loss of activity even after autoclaving, indicating their potential field efficacy as a tank-mix application. A. flavus colonization and AF were suppressed in RAB1- or RAB4R-coated maize seeds. Since RAB4R provided both fungistatic and strong anti-mycotoxigenic activities in the laboratory and field, it can be a potent alternative to atoxigenic A. flavus strains. On the other hand, RAB1 may serve as an environmentally safe helper BCA with atoxigenic A. flavus strains, due its lack of strong fungistatic and hemolytic activities.
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Affiliation(s)
- Subbaiah Chalivendra
- Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA.
| | - Catherine DeRobertis
- Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA.
| | - Jorge Reyes Pineda
- Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA.
| | - Jong Hyun Ham
- Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA.
| | - Kenneth Damann
- Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA.
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Hu Y, Cai Q, Tian S, Ge Y, Yuan Z, Hu X. Regulator DegU is required for multicellular behavior in Lysinibacillus sphaericus. Res Microbiol 2018; 169:177-187. [PMID: 29378340 DOI: 10.1016/j.resmic.2017.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 12/28/2017] [Accepted: 12/29/2017] [Indexed: 11/28/2022]
Abstract
DegS and DegU make up a two component system belonging to a class of signal transduction systems that play important roles in a broad range of bacterial responses to the environment. However, little study has been done to explore the physiological functions of DegS-DegU in mosquitocidal Lysinibacillus sphaericus. In this study, it was found that deletion of degU or degS-degU inhibited the swarming motility, biofilm formation, sporulation and binary toxin production through regulating the related genes, and phosphorylation was necessary for the functions of DegU. Based on the findings, a regulation network mediated by DegU was delineated. Both DegU-pi and Spo0A-pi positively regulates genes which are linked with the transition from stage Ⅱ to the end of the sporulation process and also influences the production of binary toxins via regulation on sigE. Both DegU-pi and Spo0A-pi negatively regulate abrB/sinR and influence the biofilm formation. DegU-pi can positively regulate the motility via the regulation on sigD. Whether the regulations are directly or indirectly need to be explored. Moreover, Spo0A-pi may indirectly regulate the swarming motility through negatively regulating DegU. It was concluded that DegU is a global transcriptional regulator on cell swarming motility, biofilm formation, sporulation and virulence in L. sphaericus.
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Affiliation(s)
- Yimin Hu
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China; University of Chinese Academy of Sciences, Beijing, 100039, China
| | - Quanxin Cai
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China
| | - Shen Tian
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China
| | - Yong Ge
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China
| | - Zhiming Yuan
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China.
| | - Xiaomin Hu
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, 430070, China.
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11
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Molecular Characterization of Mosquitocidal Toxin (Surface Layer Protein, SLP) from Bacillus cereus VCRC B540. Appl Biochem Biotechnol 2017; 184:1094-1105. [PMID: 28952017 DOI: 10.1007/s12010-017-2602-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 09/13/2017] [Indexed: 10/18/2022]
Abstract
A marine Bacillus cereus (VCRC B540) with mosquitocidal effect was recently reported from red snapper fish (Lutjanus sanguineous) gut and surface layer protein (S-layer protein, SLP) was reported to be mosquito larvicidal factor. In this present study, the gene encoding the surface layer protein was amplified from the genomic DNA and functionally characterized. Amplification of SLP-encoding gene revealed 1,518 bp PCR product, and analysis of the sequence revealed the presence of 1482 bp open reading frame with coding capacity for a polypeptide of 493 amino acids. Phylogenetic analysis revealed with homology among closely related Bacillus cereus groups of organisms as well as Bacillus strains. Removal of nucleotides encoding signaling peptide revealed the functional cloning fragment of length 1398 bp. Theoretical molecular weight (51.7 kDa) and isoelectric point (5.99) of the deduced functional SLP protein were predicted using ProtParam. The amplified PCR product was cloned into a plasmid vector (pGEM-T), and the open reading frame free off signaling peptide was subsequently cloned inpET-28a(+) and expressed in Escherichia coli BL21 (DE3). The isopropyl-β-D-thiogalactopyranoside (IPTG)-induced recombinant SLP was confirmed using western blotting, and functional SLP revealed mosquito larvicidal property. Therefore, the major findings revealed that SLP is a factor responsible for mosquitocidal activity, and the molecular characterization of this toxin was extensively studied.
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Contribution of Lysinibacillus sphaericus hemolysin and chitin-binding protein in entomopathogenic activity against insecticide resistant Aedes aegypti. World J Microbiol Biotechnol 2017; 33:181. [DOI: 10.1007/s11274-017-2348-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2017] [Accepted: 09/19/2017] [Indexed: 10/18/2022]
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Rezende TMT, Romão TP, Batista M, Berry C, Adang MJ, Silva-Filha MHNL. Identification of Cry48Aa/Cry49Aa toxin ligands in the midgut of Culex quinquefasciatus larvae. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2017; 88:63-70. [PMID: 28780070 DOI: 10.1016/j.ibmb.2017.08.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 07/15/2017] [Accepted: 08/01/2017] [Indexed: 06/07/2023]
Abstract
A binary mosquitocidal toxin composed of a three-domain Cry-like toxin (Cry48Aa) and a binary-like toxin (Cry49Aa) was identified in Lysinibacillus sphaericus. Cry48Aa/Cry49Aa has action on Culex quinquefasciatus larvae, in particular, to those that are resistant to the Bin Binary toxin, which is the major insecticidal factor from L. sphaericus-based biolarvicides, indicating that Cry48Aa/Cry49Aa interacts with distinct target sites in the midgut and can overcome Bin toxin resistance. This study aimed to identify Cry48Aa/Cry49Aa ligands in C. quinquefasciatus midgut through binding assays and mass spectrometry. Several proteins, mostly from 50 to 120 kDa, bound to the Cry48Aa/Cry49Aa toxin were revealed by toxin overlay and pull-down assays. These proteins were identified against the C. quinquefasciatus genome and after analysis a set of 49 proteins were selected which includes midgut bound proteins such as aminopeptidases, amylases, alkaline phosphatases in addition to molecules from other classes that can be potentially involved in this toxin's mode of action. Among these, some proteins are orthologs of Cry receptors previously identified in mosquito larvae, as candidate receptors for Cry48Aa/Cry49Aa toxin. Further investigation is needed to evaluate the specificity of their interactions and their possible role as receptors.
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Affiliation(s)
| | | | - Michel Batista
- Instituto Carlos Chagas-FIOCRUZ, Curitiba, PR 81350-010, Brazil
| | - Colin Berry
- Cardiff School of Biosciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom
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Gómez-Garzón C, Hernández-Santana A, Dussán J. A genome-scale metabolic reconstruction of Lysinibacillus sphaericus unveils unexploited biotechnological potentials. PLoS One 2017; 12:e0179666. [PMID: 28604819 PMCID: PMC5467902 DOI: 10.1371/journal.pone.0179666] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 06/01/2017] [Indexed: 01/25/2023] Open
Abstract
The toxic lineage (TL) of Lysinibacillus sphaericus has been extensively studied because of its potential biotechnological applications in biocontrol of mosquitoes and bioremediation of toxic metals. We previously proposed that L. sphaericus TL should be considered as a novel species based on a comparative genomic analysis. In the current work, we constructed the first manually curated metabolic reconstruction for this species on the basis of the available genomes. We elucidated the central metabolism of the proposed species and, beyond confirming the reported experimental evidence with genomic a support, we found insights to propose novel applications and traits to be considered in further studies. The strains belonging to this lineage exhibit a broad repertory of genes encoding insecticidal factors, some of them remain uncharacterized. These strains exhibit other unexploited biotechnological important traits, such as lactonases (quorum quenching), toxic metal resistance, and potential for aromatic compound degradation. In summary, this study provides a guideline for further research aimed to implement this organism in biocontrol and bioremediation. Similarly, we highlighted the unanswered questions to be responded in order to gain a deeper understanding of the L. sphaericus TL biology.
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Affiliation(s)
- Camilo Gómez-Garzón
- Centro de investigaciones microbiológicas (CIMIC), Universidad de los Andes, Bogotá, Colombia
| | | | - Jenny Dussán
- Centro de investigaciones microbiológicas (CIMIC), Universidad de los Andes, Bogotá, Colombia
- * E-mail:
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Rojas-Pinzón PA, Dussán J. Efficacy of the vegetative cells of Lysinibacillus sphaericus for biological control of insecticide-resistant Aedes aegypti. Parasit Vectors 2017; 10:231. [PMID: 28490350 PMCID: PMC5424284 DOI: 10.1186/s13071-017-2171-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 05/03/2017] [Indexed: 11/16/2022] Open
Abstract
Background The control of Aedes aegypti is usually based on chemical insecticides, but the overuse of these compounds has led to increased resistance. The binary toxin produced by Lysinibacillus sphaericus in the final stages of sporulation is used for mosquito control due to its specificity against the culicid larvae; however, it has been proved that Ae. aegypti is refractory for this toxin. Currently, there is no evidence of the use of L. sphaericus vegetative cells for mosquito biocontrol. Therefore, in this study, the vegetative cells of three L. sphaericus strains were assessed against a field-collected Ae. aegypti, resistant to temephos, and the reference Rockefeller strain. Results Vegetative cells of L. sphaericus 2362, III(3)7 and OT4b.25 produced between 90% and 100% of larvae mortality in the reference Rockefeller strain. Effective concentrations of each L. sphaericus strain for the four larval stages ranged from 1.4 to 2 × 107 CFU/ml. Likewise, a consortium of L. sphaericus assessed against a field-collected Ae. aegypti resistant to temephos and the Rockefeller strain caused 90% of larvae mortality. Concentrations of L. sphaericus consortium that resulted in larvae mortality of field-collected and Rockefeller Ae. aegypti ranged from 1.7 to 2.5 × 107 CFU/ml. The vegetative cells of L. sphaericus have no effect on the Ae. aegypti eggs and pupae. Conclusions The vegetative cells of L. sphaericus are effective against Ae. aegypti larvae, meaning that it could be used in the biological control of these mosquito species. Since the L. sphaericus consortium was effective against temephos-resistant Ae. aegypti, vegetative cells could be an alternative to overcome insecticide-resistant populations. Further studies, should be conducted to reveal the mode of action and the toxic principle of L. sphaericus vegetative cells.
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Affiliation(s)
- Paula Andrea Rojas-Pinzón
- Departamento de Ciencias Biológicas, Centro de Investigaciones Microbiológicas (CIMIC), Universidad de los Andes, Carrera 1 No. 18 A - 10, J-206, Bogotá, Colombia.
| | - Jenny Dussán
- Departamento de Ciencias Biológicas, Centro de Investigaciones Microbiológicas (CIMIC), Universidad de los Andes, Carrera 1 No. 18 A - 10, J-206, Bogotá, Colombia.
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Lozano LC, Dussán J. Synergistic Activity Between S-Layer Protein and Spore-Crystal Preparations from Lysinibacillus sphaericus Against Culex quinquefasciatus Larvae. Curr Microbiol 2017; 74:371-376. [PMID: 28168605 DOI: 10.1007/s00284-016-1185-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 12/21/2016] [Indexed: 01/25/2023]
Abstract
Lysinibacillus sphaericus is used for the biological control of mosquitoes. The main toxicity mechanism of pathogenic strains is a binary toxin produced during sporulation. S-layer is a proteinaceous structure on the surface of bacteria; its functions have been involved in the interaction between bacterial cells and the environment, for example, as protective coats, surface recognition, and biological control. In L. sphaericus, S-layer protein (SlpC) is expressed in vegetative cells, and is also found in spore-crystal preparations; it has larvicidal activity in Culex spp. In this study, partial and completed sporulated culture toxicities were compared; also, S-layer protein and spore-crystal proteins were tested against Culex quinquefasciatus larvae for possible interactions. Larvicidal activity obtained with a combination of SlpC and spore-crystal proteins from strain III(3)7 showed no significant interaction, whereas, combinations of both preparations from strain 2362 showed synergistic effect. The highest synergistic activity observed was between spore protein complex from strain 2362 and SlpC from III(3)7. S-layer protein could be considered a good alternative in formulation improvement, for biological control of mosquitoes.
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Affiliation(s)
- Lucía C Lozano
- Departamento de Ciencias Biológicas, Centro de Investigaciones Microbiológicas-CIMIC, Universidad de los Andes, Cra 1E No. 18A-10 J207, Bogotá, Colombia.,Departamento de Ciencias Básicas, Universidad de la Salle, Cra 2 No. 10-70, Bogotá, Colombia
| | - Jenny Dussán
- Departamento de Ciencias Biológicas, Centro de Investigaciones Microbiológicas-CIMIC, Universidad de los Andes, Cra 1E No. 18A-10 J207, Bogotá, Colombia.
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Schäffer C, Messner P. Emerging facets of prokaryotic glycosylation. FEMS Microbiol Rev 2016; 41:49-91. [PMID: 27566466 DOI: 10.1093/femsre/fuw036] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 02/17/2016] [Accepted: 08/01/2016] [Indexed: 12/16/2022] Open
Abstract
Glycosylation of proteins is one of the most prevalent post-translational modifications occurring in nature, with a wide repertoire of biological implications. Pathways for the main types of this modification, the N- and O-glycosylation, can be found in all three domains of life-the Eukarya, Bacteria and Archaea-thereby following common principles, which are valid also for lipopolysaccharides, lipooligosaccharides and glycopolymers. Thus, studies on any glycoconjugate can unravel novel facets of the still incompletely understood fundamentals of protein N- and O-glycosylation. While it is estimated that more than two-thirds of all eukaryotic proteins would be glycosylated, no such estimate is available for prokaryotic glycoproteins, whose understanding is lagging behind, mainly due to the enormous variability of their glycan structures and variations in the underlying glycosylation processes. Combining glycan structural information with bioinformatic, genetic, biochemical and enzymatic data has opened up an avenue for in-depth analyses of glycosylation processes as a basis for glycoengineering endeavours. Here, the common themes of glycosylation are conceptualised for the major classes of prokaryotic (i.e. bacterial and archaeal) glycoconjugates, with a special focus on glycosylated cell-surface proteins. We describe the current knowledge of biosynthesis and importance of these glycoconjugates in selected pathogenic and beneficial microbes.
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Affiliation(s)
- Christina Schäffer
- Department of NanoBiotechnology, Institute of Biologically Inspired Materials, NanoGlycobiology unit, Universität für Bodenkultur Wien, A-1180 Vienna, Austria
| | - Paul Messner
- Department of NanoBiotechnology, Institute of Biologically Inspired Materials, NanoGlycobiology unit, Universität für Bodenkultur Wien, A-1180 Vienna, Austria
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Rey A, Silva-Quintero L, Dussán J. Complete genome sequencing and comparative genomic analysis of functionally diverse Lysinibacillus sphaericus III(3)7. GENOMICS DATA 2016; 9:78-86. [PMID: 27419068 PMCID: PMC4932437 DOI: 10.1016/j.gdata.2016.06.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 06/16/2016] [Indexed: 01/25/2023]
Abstract
Lysinibacillus sphaericus III(3)7 is a native Colombian strain, the first one isolated from soil samples. This strain has shown high levels of pathogenic activity against Culex quinquefaciatus larvae in laboratory assays compared to other members of the same species. Using Pacific Biosciences sequencing technology we sequenced, annotated (de novo) and described the genome of strain III(3)7, achieving a complete genome sequence status. We then performed a comparative analysis between the newly sequenced genome and the ones previously reported for Colombian isolates L. sphaericus OT4b.31, CBAM5 and OT4b.25, with the inclusion of L. sphaericus C3-41 that has been used as a reference genome for most of previous genome sequencing projects. We concluded that L. sphaericus III(3)7 is highly similar with strain OT4b.25 and shares high levels of synteny with isolates CBAM5 and C3-41.
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Affiliation(s)
- Andrés Rey
- Centro de Investigaciones Microbiologicas (CIMIC), Universidad de los Andes, Bogotá D.C., Cundinamarca, Colombia
| | - Laura Silva-Quintero
- Centro de Investigaciones Microbiologicas (CIMIC), Universidad de los Andes, Bogotá D.C., Cundinamarca, Colombia
| | - Jenny Dussán
- Centro de Investigaciones Microbiologicas (CIMIC), Universidad de los Andes, Bogotá D.C., Cundinamarca, Colombia
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Complete Genome Sequence of Lysinibacillus sphaericus WHO Reference Strain 2362. GENOME ANNOUNCEMENTS 2016; 4:4/3/e00545-16. [PMID: 27284157 PMCID: PMC4901241 DOI: 10.1128/genomea.00545-16] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Lysinibacillus sphaericus is a species that contains strains widely used in the biological control of mosquitoes. Here, we present the complete 4.67-Mb genome of the WHO entomopathogenic reference strain L. sphaericus 2362, which is probably one of the most commercialized and studied strains. Genes coding for mosquitocidal toxin proteins were detected.
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Shrestha BK, Karki HS, Groth DE, Jungkhun N, Ham JH. Biological Control Activities of Rice-Associated Bacillus sp. Strains against Sheath Blight and Bacterial Panicle Blight of Rice. PLoS One 2016; 11:e0146764. [PMID: 26765124 PMCID: PMC4713167 DOI: 10.1371/journal.pone.0146764] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 12/22/2015] [Indexed: 11/19/2022] Open
Abstract
Potential biological control agents for two major rice diseases, sheath blight and bacterial panicle blight, were isolated from rice plants in this study. Rice-associated bacteria (RABs) isolated from rice plants grown in the field were tested for their antagonistic activities against the rice pathogens, Rhizoctonia solani and Burkholderia glumae, which cause sheath blight and bacterial panicle blight, respectively. Twenty-nine RABs were initially screened based on their antagonistic activities against both R. solani and B. glumae. In follow-up retests, 26 RABs of the 29 RABs were confirmed to have antimicrobial activities, but the rest three RABs did not reproduce any observable antagonistic activity against R. solani or B. glumae. According to16S rDNA sequence identity, 12 of the 26 antagonistic RABs were closest to Bacillus amyloliquefaciens, while seven RABs were to B. methylotrophicus and B, subtilis, respectively. The 16S rDNA sequences of the three non-antagonistic RABs were closest to Lysinibacillus sphaericus (RAB1 and RAB12) and Lysinibacillus macroides (RAB5). The five selected RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S, and RAB18) were closest to B. amyloliquefaciens in DNA sequence of 16S rDNA and gyrB, but to B. subtilis in that of recA. These RABs were observed to inhibit the sclerotial germination of R. solani on potato dextrose agar and the lesion development on detached rice leaves by artificial inoculation of R. solani. These antagonistic RABs also significantly suppressed the disease development of sheath blight and bacterial panicle blight in a field condition, suggesting that they can be potential biological control agents for these rice diseases. However, these antagonistic RABs showed diminished disease suppression activities in the repeated field trial conducted in the following year probably due to their reduced antagonistic activities to the pathogens during the long-term storage in -70C, suggesting that development of proper storage methods to maintain antagonistic activity is as crucial as identification of new biological control agents.
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Affiliation(s)
- Bishnu K. Shrestha
- Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, 70803, United States of America
| | - Hari Sharan Karki
- Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, 70803, United States of America
| | - Donald E. Groth
- Rice Research Station, Louisiana State University Agricultural Center, Rayne, Louisiana, 70578, United States of America
| | - Nootjarin Jungkhun
- Chiang Rai Rice Research Center, Bureau of Rice Research and Development, Rice Department, 474 Moo 9, Phaholyothin Rd., Muang Phan, Phan, Chiang Rai, 57120, Thailand
| | - Jong Hyun Ham
- Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, Louisiana, 70803, United States of America
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Lysinibacillus sphaericus binary toxin induces apoptosis in susceptible Culex quinquefasciatus larvae. J Invertebr Pathol 2015; 128:57-63. [PMID: 25958262 DOI: 10.1016/j.jip.2015.04.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Revised: 04/29/2015] [Accepted: 04/30/2015] [Indexed: 11/20/2022]
Abstract
During sporulation, a Gram-positive bacterium Lysinibacillus sphaericus (Ls) produces the mosquito larvicidal binary toxin composed of 2 subunits, BinA and BinB. Full toxicity against Culex and Anopheles mosquito larvae is achieved when both subunits are administered together at equimolar amounts. Although cellular responses to Bin toxin have been reported in previous studies, it remains essential to extensively examine the cytopathic effects in vivo to define the underlying mechanism of larval death. In this study, 4th instar Culex quinquefasciatus larvae fed with different doses of Bin toxin were analyzed both for ultrastructural as well as biochemical effects. Typical morphological changes consistent with apoptosis were observed in mosquito larvae exposed to Bin toxin, including mitochondrial swelling, chromatin condensation, cytoplasmic vacuolization and apoptotic cell formation. Bin toxin also induced the activation of caspase-9 and caspase-3 in larval midgut cells. Our current observations thus suggest that Bin toxin triggers apoptosis via an intrinsic or mitochondrial pathway in vivo, possibly contributing to larval death.
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