Isolation and identification of actinomycetes from Fire Mountain, China, and the elicitation of antimicrobial production

Abstract

The increasing emergence of antimicrobial resistance alongside the decrease of novel compounds being discovered is an emerging worldwide health threat. The discovery of novel antibiotics, especially from natural products, is an important area of research for all. Natural products from secondary metabolites produced by actinomycetes are a recognised and established source of antimicrobial compounds, with many clinically relevant drugs on the market. This thesis aimed to investigate several approaches to the discovery of novel antimicrobial compounds from putative streptomycetes, using classical methodology alongside elicitation techniques. In chapter 3, selective isolation and classical whole cell approaches were investigated to isolate putatively novel strains of Streptomyces spp. from a soil sample taken from Fire Mountain in China, which were subsequently tested for their ability to produce bioactive secondary metabolites. The results showed incidences of broad-spectrum activity from >7% of isolates tested. The known compounds streptothricin and wailupemyin were purified and identified from the Fire Mountain isolates, as well as a compound that inhibited the growth of multidrug resistant strains. In chapter 4, various chemical, biological, and co-culturing techniques were carried out to investigate how these methods could induce the production of antimicrobial compounds from non-active isolates. Ferrioxaime E, a siderophore commonly isolated from Streptomyces spp., was identified from DEM60169 and DEM60164. DEM60169 was also found to produce lipozalidinone A, a broad-spectrum antimicrobial compound, and gentamicins C1 and C1a. Additionally, the use of solid scaffolds was investigated to simulate the natural soil environment that the strains were isolated from. Co-culturing techniques were employed to stimulate the production of antimicrobial secondary metabolites. Six-hundred and twenty incidences of antimicrobial action were observed using this method, and twenty strain combinations transferred to liquid media to investigate further. It is concluded that elicitation techniques should be utilised to further investigate the production of antimicrobial compounds from Streptomyces spp.