Antimicrobial activity and biosynthesis of indole antibiotics produced by Xenorhabdus nematophilus

Abstract

~We have investigated the mechanism of action and physiology of production of the indole derivative antibiotics produced by the nematode-associated, entomopathogenic bacterium Xenorhabdus nernatophilus. Maximum antibiotic concentration was reached during the late stationary phase of growth, and the antibiotic yield was appreciably enhanced by supplementation with tryptophan. Antibiotic biosynthesis apparently involved the removal of the side-chain carboxyl (C-1) carbon of tryptophan. The C-3 methylene carbon of tryptophan, on the other hand, was retained. The purified indole antibiotic was effective against both Gram-positive and Gram-negative bacteria at low to moderate concentrations causing a severe inhibition of RNA synthesis, accompanied by a less severe effect on protein synthesis. An isogenic pair of Eschevichia coli strains differing at the velA locus was used to demonstrate that the swift reduction in total RNA synthesis is related to an antibiotic-induced accumulation of the regulatory nucleotide, ppGpp, in susceptible bacteria. The E. coli veZA mutant, which does not exhibit any discernible increase in ppGpp upon antibiotic treatment, showed no decrease in growth or RNA synthesis. Using this antibiotic, it was also observed that ppGpp may be employed as a metabolic regulator in bacteria such as Pseudomonasputida, which have not previously been reported to employ ppGpp as a regulatory molecule. We propose that the indole derivative antibiotic exerts growth inhibitory control in susceptible bacteria by greatly enhancing synthesis of ppGpp, resulting in a rapid inhibition of RNA synthesis.

Transcriptional Analysis and Functional Characterization of a Gene Pair Encoding Iron-Regulated Xenocin and Immunity Proteins of Xenorhabdus nematophila

“…nematophila produces antibacterial peptides to control the growth of other bacterial strains associated with the larval prey (1,26,43,45). These antibiotics serve two critical functions: (i) they prevent putrefaction of the larval carcass by eliminating competing bacterial strains, and (ii) they provide the host strain unrestricted access to the available nutrients.…”

Inactivation of a Novel Gene Produces a Phenotypic Variant Cell and Affects the Symbiotic Behavior of Xenorhabdus nematophilus

“…ANV2 did not produce antibiotics, crystal proteins, or OpnB (Table 2). These products have been previously shown to be induced during the post-exponential-growth phase (23,24,25,42). ANV2 also possessed dramatically reduced levels of fimbriae, was unable to stimulate hemagglutination, lacked hemolytic activity, and did not swarm on agar plates.…”

“…However, the biochemical properties of these products are very different. The antibiotics produced by Xenorhabdus are either indole derivatives or belong to the xenocoumacin or xenorhabdin family of compounds, while the antibiotics of Photorhabdus are hydroxystilbenes (2,24,42). The biochemical properties of the crystal proteins of the respective bacteria are also very different (7,14).…”

“…X. nematophilus proliferates within the hemolymph and eventually enters stationary phase. Under stationary-phase conditions, the bacterium produces numerous products that play roles in providing a nutrient base for the developing nematodes (25,42,45). During the final stages of nematode development, the bacteria and nematode reassociate, and the symbiotic pair leaves the insect cadaver in search of a new host (4,25,36).…”

GC-MS analysis and antimicrobial effects of methanol stem bark extract of Trilepisium madagascriense DC.

“…Paramomycin, indole, ethyl iso-allocholate and phenol have been reported to possess strong antimicrobial properties (Sundar and Chang, 1993;Meyer et al, 1999;Huang et al, 2011). Paramomycin which was originally isolated from the fermentation of Streptomyces in 1956 (Lu et al, 1997) has been reported to possess broad spectrum activity against Gram-negative and Gram-positive bacteria (Stead, 2000) such as E. coli, S. aureus, S. pyogenes, P. vulgaris and K. Pneumoniae (Francois et al, 2004) as well as some protozoa and cestodes (Davidson et al, 2009).…”