Identification of Galtox, a new protein toxin from Photorhabdus bacterial symbionts of Heterorhabditis nematodes. (30th April 2021)

• Record Type: Journal Article
• Authors: Ahuja, Amit; Kushwah, Jyoti; Mathur, Chetna; Chauhan, Khushbu; Dutta, Tushar Kanti; Somvanshi, Vishal Singh
• Is Part Of: Toxicon. Volume 194(2021)
• Page Start: 53
• Page End: 62
• Publication Date: 2021-04-30
• Subjects: Photorhabdus -- Photox -- Galtox -- Heterorhabditis -- Protein toxins -- Rapid virulence annotation; Toxins -- Periodicals; Venom -- Periodicals; 615.9
• DOI: 10.1016/j.toxicon.2021.02.011
• Languages: English
• ISSNs: 0041-0101

Abstract

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. Graphical abstract: Image 1 Highlights: Photorhabdus bacteria are symbiont of the entomopathogenic Heterorhabditis nematodes and produce numerous protein toxins. Here we report Galtox, a new and previously unreported protein toxin of 35 KiloDalton molecular weight from Photorhabdus . Several known bacterial toxin related domains were found in the protein sequence of Galtox. Galtox exhibited injectable toxicity and median lethal dose of 2.39–26.08 ng toxin/gram Galleria bodyweight. Galtox showed median lethal time of 12–60 h at the rate of 3.1–31.2 ng toxin/gram Galleria bodyweight.