Heptabladed β‐propeller lectins PLL2 and PHL from Photorhabdus spp. recognize O ‐methylated sugars and influence the host immune system

Systematics and phylogeny of the entomopathogenic nematobacterial complexes Steinernema-Xenorhabdus and Heterorhabditis-Photorhabdus

Entomopathogenic nematodes of the genera Steinernema and Heterorhabditis, along with their bacterial symbionts from the genera Xenorhabdus and Photorhabdus, respectively, are important biological control agents against agricultural pests. Rapid progress in the development of genomic tools has catalyzed a transformation of the systematics of these organisms, reshaping our understanding of their phylogenetic and cophlylogenetic relationships. In this review, we discuss the major historical events in the taxonomy and systematics of this group of organisms, highlighting the latest advancements in these fields. Additionally, we synthesize information on nematode-bacteria associations and assess the existing evidence regarding their cophylogenetic relationships.

Cyclodepsipeptides: Isolation from Endophytic Fungi of Sarcophyton ehrenbergi and Verification of Their Larvicidal Activity via In-Vitro and In-Silico Studies

Culex pipiens mosquitoes are vectors to many viruses and can transmit diseases such as filariasis and avian malaria. The present study evaluated the larvicidal activity of marine-derived endophytic fungi Aspergillus nomius and Aspergillus flavus from the soft coral Sarcophyton ehrenbergi along with two known cyclodepsipeptide compounds, scopularide A (1) and B (2), isolated from A. flavus extract, against third-instar larvae of C. pipiens, using distilled water as a negative control and toosenedanin as a positive control. The structures of the isolated compounds were confirmed by various spectroscopic analyses. The lethal concentrations (LC₅₀ and LC₉₀) were calculated by probit analysis. Scopularide A was the most potent after 96 h treatment, with LC₅₀ and LC₉₀ values of 58.96 and 994.31 ppm, respectively, and with 82.66% mortality at a concentration of 300 ppm. To unravel the biochemical mechanism of the tested extracts and compounds, their effects against protease, chitinase, phenoloxidases and lipase enzymes from the whole-body tissue of C. pipiens were evaluated after 72 h treatment at LC₅₀ dose. Superior activity was observed for A. flavus extract against all tested enzymes. A molecular docking study was conducted for scopularide A and B on the four tested enzymes, to further verify the observed activity. Results revealed good binding affinities for both compounds as compared to the docked ligands, mainly via a number of hydrogen bonds. This was the first study to report the isolation of endophytic fungi A. flavus and A. nomius from the marine soft coral S. ehrenbergi. The endophytic fungal extract of A. flavus was found to be a promising source for a natural larvicidal agent against C. pipiens populations.

Towards better syntheses of partially methylated carbohydrates?

We give an overview of the reported synthetic strategies towards partially methylated glycosides and discuss how better protocols could stem from catalytic site-selective transformations of carbohydrates and cleaner methylation reagents.

Photorhabdus hindustanensis sp. nov., Photorhabdus akhurstii subsp. akhurstii subsp. nov., and Photorhabdus akhurstii subsp. bharatensis subsp. nov., isolated from Heterorhabditis entomopathogenic nematodes

Two Gram-negative, rod-shaped bacteria, H1^T and H3^T, 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 H1^T and H3^T are closely related to P. akhurstii DSM 15138^T, to P. hainanensis DSM 22397^T, and to P. namnaonensis PB45.5^T. In silico genomic comparisons confirm these observations and show that strain H1^T shares 70.6, 66.8, and 63.5 % digital DNA-DNA hybridization (dDDH) with P. akhurstii DSM 15138^T, P. hainanensis DSM 22397^T, and P. namnaonensis PB45.5^T, respectively, and that strain H3^T shares 76.6, 69.4, and 59.2 % dDDH with P. akhurstii DSM 15138^T, P. hainanensis DSM 22397^T, and P. namnaonensis PB45.5^T, 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 H1^T and H3^T differ physiologically and biochemically from their more closely related taxa, we propose to classify H1^T and H3^T into new taxa as follows: H3^T as a new subspecies within the species P. akhurstii, and H1^T as a new species within the Photorhabdus genus, in spite that H1^T shares 70.6 % dDDH with P. akhurstii DSM 15138^T, score that is slightly higher than the 70 % threshold that delimits species boundaries. The reason for this is that H1^T and P. akhurstii DSM 15138^T cluster apart in the phylogenetic trees and that dDDH scores between strain H1^T and other P. akhurstii strains are lower than 70 %. Hence, the following names are proposed: Photorhabdus hindustanensis sp. nov. with the type strain H1^T (=IARI-SGMG3^T,=KCTC 82683^T=CCM 9150^T=CCOS 1975^T) and P. akhurstii subsp. bharatensis subsp. nov. with the type strain H3^T (=IARI-SGHR2^T=KCTC 82684^T=CCM 9149^T=CCOS 1976^T). These propositions automatically create P. akhurstii subsp. akhurstii subsp. nov. with DSM 15138^T as the type strain (currently classified as P. akhurstii).

Visualization of hydrogen atoms in a perdeuterated lectin-fucose complex reveals key details of protein-carbohydrate interactions

Carbohydrate-binding proteins from pathogenic bacteria and fungi have been shown to be implicated in various pathological processes, where they interact with glycans present on the surface of the host cells. These interactions are part of the initial processes of infection of the host and are very important to study at the atomic level. Here, we report the room temperature neutron structures of PLL lectin from Photorhabdus laumondii in its apo form and in complex with deuterated L-fucose, which is, to our knowledge, the first neutron structure of a carbohydrate-binding protein in complex with a fully deuterated carbohydrate ligand. A detailed structural analysis of the lectin-carbohydrate interactions provides information on the hydrogen bond network, the role of water molecules, and the extent of the CH-π stacking interactions between fucose and the aromatic amino acids in the binding site.