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Machado RAR, Somvanshi VS, Muller A, Kushwah J, Bhat CG. Photorhabdus hindustanensis sp. nov., Photorhabdus akhurstii subsp. akhurstii subsp. nov. , and Photorhabdus akhurstii subsp. bharatensis subsp. nov. , isolated from Heterorhabditis entomopathogenic nematodes. Int J Syst Evol Microbiol 2021; 71. [PMID: 34524954 DOI: 10.1099/ijsem.0.004998] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Two Gram-negative, rod-shaped bacteria, H1T and H3T, isolated from the digestive tract of Heterorhabditis entomopathogenic nematodes were biochemically and molecularly characterized to determine their taxonomic positions. The 16S rRNA gene sequences of these strains indicate that they belong to the Gammaproteobacteria, to the family Morganellaceae, and to the Photorhabdus genus. Deeper analyses using whole genome-based phylogenetic reconstructions show that strains H1T and H3T are closely related to P. akhurstii DSM 15138T, to P. hainanensis DSM 22397T, and to P. namnaonensis PB45.5T. In silico genomic comparisons confirm these observations and show that strain H1T shares 70.6, 66.8, and 63.5 % digital DNA-DNA hybridization (dDDH) with P. akhurstii DSM 15138T, P. hainanensis DSM 22397T, and P. namnaonensis PB45.5T, respectively, and that strain H3T shares 76.6, 69.4, and 59.2 % dDDH with P. akhurstii DSM 15138T, P. hainanensis DSM 22397T, and P. namnaonensis PB45.5T, respectively. Physiological and biochemical characterization reveals that these two strains differ from most of the validly described Photorhabdus species and from their more closely related taxa. Given the clear phylogenetic separations, that the threshold to discriminate species and subspecies is 70 and 79% dDDH, respectively, and that strains H1T and H3T differ physiologically and biochemically from their more closely related taxa, we propose to classify H1T and H3T into new taxa as follows: H3T as a new subspecies within the species P. akhurstii, and H1T as a new species within the Photorhabdus genus, in spite that H1T shares 70.6 % dDDH with P. akhurstii DSM 15138T, score that is slightly higher than the 70 % threshold that delimits species boundaries. The reason for this is that H1T and P. akhurstii DSM 15138T cluster apart in the phylogenetic trees and that dDDH scores between strain H1T and other P. akhurstii strains are lower than 70 %. Hence, the following names are proposed: Photorhabdus hindustanensis sp. nov. with the type strain H1T (=IARI-SGMG3T,=KCTC 82683T=CCM 9150T=CCOS 1975T) and P. akhurstii subsp. bharatensis subsp. nov. with the type strain H3T (=IARI-SGHR2T=KCTC 82684T=CCM 9149T=CCOS 1976T). These propositions automatically create P. akhurstii subsp. akhurstii subsp. nov. with DSM 15138T as the type strain (currently classified as P. akhurstii).
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Affiliation(s)
- Ricardo A R Machado
- Experimental Biology Research Group, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland
| | - Vishal S Somvanshi
- Division of Nematology, Indian Council of Agricultural Research, Indian Agricultural Research Institute (ICAR-IARI), New Delhi, India
| | - Arthur Muller
- Experimental Biology Research Group, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland
| | - Jyoti Kushwah
- Division of Nematology, Indian Council of Agricultural Research, Indian Agricultural Research Institute (ICAR-IARI), New Delhi, India
| | - Chaitra G Bhat
- Division of Nematology, Indian Council of Agricultural Research, Indian Agricultural Research Institute (ICAR-IARI), New Delhi, India
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Photorhabdus spp.: An Overview of the Beneficial Aspects of Mutualistic Bacteria of Insecticidal Nematodes. PLANTS 2021; 10:plants10081660. [PMID: 34451705 PMCID: PMC8401807 DOI: 10.3390/plants10081660] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 07/29/2021] [Accepted: 08/03/2021] [Indexed: 11/17/2022]
Abstract
The current approaches to sustainable agricultural development aspire to use safer means to control pests and pathogens. Photorhabdus bacteria that are insecticidal symbionts of entomopathogenic nematodes in the genus Heterorhabditis can provide such a service with a treasure trove of insecticidal compounds and an ability to cope with the insect immune system. This review highlights the need of Photorhabdus-derived insecticidal, fungicidal, pharmaceutical, parasiticidal, antimicrobial, and toxic materials to fit into current, or emerging, holistic strategies, mainly for managing plant pests and pathogens. The widespread use of these bacteria, however, has been slow, due to cost, natural presence within the uneven distribution of their nematode partners, and problems with trait stability during in vitro culture. Yet, progress has been made, showing an ability to overcome these obstacles via offering affordable mass production and mastered genome sequencing, while detecting more of their beneficial bacterial species/strains. Their high pathogenicity to a wide range of arthropods, efficiency against diseases, and versatility, suggest future promising industrial products. The many useful properties of these bacteria can facilitate their integration with other pest/disease management tactics for crop protection.
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Ahuja A, Kushwah J, Mathur C, Chauhan K, Dutta TK, Somvanshi VS. Identification of Galtox, a new protein toxin from Photorhabdus bacterial symbionts of Heterorhabditis nematodes. Toxicon 2021; 194:53-62. [PMID: 33610634 DOI: 10.1016/j.toxicon.2021.02.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 02/02/2021] [Accepted: 02/16/2021] [Indexed: 01/25/2023]
Abstract
The Gram-negative bacteria Photorhabdus lives in a symbiotic relationship with the insect-pathogenic Heterorhabditis nematodes and produces numerous hydrolytic enzymes, secondary metabolites and protein toxins. Seven Photorhabdus strains were previously isolated from the Heterorhabditis nematodes collected from different geographical regions of India. The strains IARI-SGMG3, IARI-SGHR2, IARI-SGHR4, IARI-SGMS1 and IARI-SGGJ2 were identified as P. akhurstii, whereas IARI-SGLDK1 and IARI-SGHP1 were identified as P. laumondii subsp. laumondii and P. laumondii subsp. clarkeii, respectively. A new and previously unreported 35 kDa molecular weight protein toxin 'Galtox' was identified from these Photorhabdus strains. The nucleotide sequences of the toxin gene from seven Photorhabdus strains were PCR amplified, sequenced, cloned into pET protein expression vector, and the protein toxin was expressed and purified. The Galtox sequence from various strains showed variations in sequence and toxicity against Galleria mellonella. The injection of purified Galtox protein into the 4th instar larvae showed median lethal dose (LD50) values of 2.39-26.08 ng toxin/g G. mellonella bodyweight after 48 h. The protein injection killed the insects quickly and exhibited a median lethal time (LT50) of 12-60 h when injected at the rate of 3.1-31.2 ng toxin/g G. mellonella bodyweight. Galtox protein sequence analysis indicated similarity to several bacterial toxin-related protein domains, such as 6rgnA domain of Bordetella membrane targeting toxin BteA, 6gy6 domain of Xenorhabdus α-Xenorhabdolysins, 4mu6A and 4xa9a domains similar to effector protein LegC3 from Legionella pneumophila and 1cv8.1 domain of staphylococcal cysteine proteinase staphopain B. The mode of action of Galtox needs to be understood to enable its use for the management of agricultural insect-pests.
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Affiliation(s)
- Amit Ahuja
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Jyoti Kushwah
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Chetna Mathur
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Khushbu Chauhan
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Tushar Kanti Dutta
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Vishal Singh Somvanshi
- Division of Nematology, ICAR - Indian Agricultural Research Institute, New Delhi, 110012, India.
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Dutta TK, Mathur C, Mandal A, Somvanshi VS. The differential strain virulence of the candidate toxins of Photorhabdus akhurstii can be correlated with their inter-strain gene sequence diversity. 3 Biotech 2020; 10:299. [PMID: 32550116 DOI: 10.1007/s13205-020-02288-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 06/01/2020] [Indexed: 02/06/2023] Open
Abstract
Photorhabdus akhurstii is an insect-parasitic bacterium that symbiotically associates with the nematode, Heterorhabditis indica. The bacterium possesses several pathogenicity islands that aids in conferring toxicity to different insects. Herein, we constructed the plasmid clones of coding sequences of four toxin genes (pirA, tcaA, tccA and tccC; each was isolated from four P. akhurstii strains IARI-SGMG3, IARI-SGGJ2, IARI-SGHR2 and IARI-SGMS1) in Escherichia coli and subsequently, their biological activity were investigated against the fourth-instar larvae of the model insect, Galleria mellonella via intra-hemocoel injection. Bioinformatics analyses indicated inter-strain amino acid sequence difference at several positions of the candidate toxins. In corroboration, differential insecticidal activity of the identical toxin protein (PirA, TcaA, TccA and TccC conferred 15-59, 27-100, 25-100 and 33-98% insect mortality, respectively, across the strains) derived from the different bacterial strains was observed, suggesting that the diverse gene pool in Indian strains of P. akhurstii leads to strain-specific virulence in this bacterium. These toxin candidates appear to be an attractive option to deploy them in biopesticide development for managing the insect pests globally.
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Affiliation(s)
- Tushar K Dutta
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012 India
| | - Chetna Mathur
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012 India
| | - Abhishek Mandal
- Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012 India
| | - Vishal S Somvanshi
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012 India
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Mathur C, Phani V, Kushwah J, Somvanshi VS, Dutta TK. TcaB, an insecticidal protein from Photorhabdus akhurstii causes cytotoxicity in the greater wax moth, Galleria mellonella. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2019; 157:219-229. [PMID: 31153472 DOI: 10.1016/j.pestbp.2019.03.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 03/22/2019] [Accepted: 03/31/2019] [Indexed: 06/09/2023]
Abstract
Photorhabdus akhurstii can produce a variety of proteins that aid this bacterium and its mutualistic nematode vector, Heterorhabditis indica to kill the insect host. Herein, we characterized (by heterologously expressing in E. coli) an open reading frame (1713 bp) of the toxin complex protein, TcaB from P. akhurstii strains IARI-SGHR2 and IARI-SGMS1 and assessed its toxic effect on G. mellonella larvae. The intra-hemocoel injection of purified TcaB (molecular weight-63 kDa) caused fourth instar larval bodies to blacken and die with LD50 values of 67.25 (IARI-SGHR2) and 52.08 (IARI-SGMS1) ng per larva at 12 h. Additionally, oral administration of the toxin caused larval mortality with LD50 values of 709.55 (IARI-SGHR2) and 598.44 (IARI-SGMS1) ng per g diet per larva at 7 days post feeding. Injection of purified TcaB caused loss of viability of fourth instar G. mellonella hemocytes at 6 h post incubation; cells displayed morphological changes typical of apoptosis, including cell shrinkage, membrane blebbing, nuclear condensation and disintegration. Injection of TcaB also elevated the phenoloxidase activity in insect hemolymph which triggers an extensive immune response that potentially leads to larval death. Similar to other bacterial toxins TcaB possesses potent biological activity which may enable it to be used as an efficient agent for pest management.
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Affiliation(s)
- Chetna Mathur
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Victor Phani
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Jyoti Kushwah
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Vishal S Somvanshi
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India
| | - Tushar K Dutta
- Division of Nematology, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
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Draft Genome Sequences for Five Photorhabdus Bacterial Symbionts of Entomopathogenic Heterorhabditis Nematodes Isolated from India. Microbiol Resour Announc 2019; 8:MRA01404-18. [PMID: 30701235 PMCID: PMC6346184 DOI: 10.1128/mra.01404-18] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Accepted: 12/17/2018] [Indexed: 11/20/2022] Open
Abstract
Photorhabdus bacteria exhibit contrasting lifestyles; they are virulent insect pathogens but symbionts of the entomopathogenic Heterorhabditis nematodes. Photorhabdus genomes encode several secondary metabolites and insecticidal protein toxins. Photorhabdus bacteria exhibit contrasting lifestyles; they are virulent insect pathogens but symbionts of the entomopathogenic Heterorhabditis nematodes. Photorhabdus genomes encode several secondary metabolites and insecticidal protein toxins. Here, we present the draft genome sequences for five Photorhabdus strains isolated from Heterorhabditis nematodes collected from various geographical regions of India.
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A 37 kDa Txp40 protein characterized from Photorhabdus luminescens sub sp. akhurstii conferred injectable and oral toxicity to greater wax moth, Galleria mellonella. Toxicon 2018; 154:69-73. [PMID: 30278182 DOI: 10.1016/j.toxicon.2018.09.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 09/15/2018] [Accepted: 09/25/2018] [Indexed: 11/22/2022]
Abstract
Photorhabdus luminescens is a gram-negative bacterium that symbiotically associates with insect-parasitic nematode, Heterorhabditis indica. Herein, we have characterized an insecticidal gene, Txp40 (1008 bp) from the indigenous isolates of P. luminescens, and tested its bioefficacy against Galleria mellonella via injectable and oral bioassay. The recombinant protein characterized from P. luminescens strain H3 exhibited comparatively greater insect toxicity than strain H1 in terms of LD50 and LT50 values. Txp40 holds great potential to replace Bt toxins in global agriculture.
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