Polyoxin B

In this paper, fermentation dynamics process of Streptomyces aureochromogenes was researched. The production of polyoxins in culture medium with moderate concentration sucrose was at a relative high level. And, when the carbon source changed to glucose, the mycelium grew in a better condition, while no poloxins was produced. This phenomenon also happened when increasing the initial concentration of sucrose to three times. To evaluate the regulatory mechanism of polyoxin production, comparative proteomic analysis of S. aureochromogenes was conducted. The result showed that tricarboxylic acid cycle (TCA) cycle, amino metabolism, and fatty acid metabolism were active and glycolysis was repressed. And, the fact that stress and stress-related protein like superoxide dismutase (SOD), Clp protease, and catalase were highly expressed indicated a higher regulator level in synthesis of polyoxins. In addition, enzymes related to transcription or translation processes also revealed a correlation between specific cell growth rate and polyoxin production.

BACKGROUND: Polyoxin, a peptidyl nucleoside antibiotic, consists of three building blocks including a nucleoside skeleton, polyoximic acid (POIA), and carbamoylpolyoxamic acid (CPOAA), however, little is known about the "pathway redundancy" of the metabolic networks directing the CPOAA biosynthesis in the cell factories of the polyoxin producer.

Polyoxin and nikkomycin are naturally occurring peptidyl nucleoside antibiotics with potent antifungal bioactivity. Both exhibit similar structural features, having a nucleoside skeleton and one or two peptidyl moieties. Combining the refactoring of the polyoxin producer Streptomyces aureochromogenes with import of the hydroxypyridylhomothreonine pathway of nikkomycin allows the targeted production of three designer nucleoside antibiotics designated as nikkoxin E, F, and G. These structures were determined by NMR and/or high resolution mass spectrometry. Remarkably, the introduction of an extra copy of the nikS gene encoding an ATP-dependent ligase significantly enhanced the production of the designer antibiotics. Moreover, all three nikkoxins displayed improved bioactivity against several pathogenic fungi as compared with the naturally-occurring antibiotics. These data provide a feasible model for high efficiency generation of nucleoside antibiotics related to polyoxins and nikkomycins in a polyoxin cell factory via synthetic biology strategy.