Abstract
Fungal-bacterial associations are present in nature, playing important roles in ecological, evolutionary and medicinal processes. Here we report a fungus-bacterial symbiont from marine sediment. The bacterium lives inside the fungal mycelium yet is robust enough to survive independent of its host; the independently grown bacterium can infect the fungal host in vitro and continue to grow progenitively. The bacterial symbiont modulates the fungal host to biosynthesize a polyketide antimicrobial, spiromarmycin. Spiromarmycin appears to endow upon the symbiont pair a protective/defensive means of warding off competitor organisms, be they prokaryotic or eukaryotic microorganisms. Genomic analyses revealed the spiromarmycin biosynthetic machinery to be encoded, not by the bacterium, but rather the fungal host. This unique fungal-bacterial symbiotic relationship and the molecule/s resulting from it dramatically expand our knowledge of marine microbial diversity and shed important insights into endosymbionts and fungal-bacterial relationships.
Highlights
Fungal-bacterial associations are present in nature, playing important roles in ecological, evolutionary and medicinal processes
To recapitulate the actinomycete richness of the oceanic environment, a sediment sample collected from the northern South China Sea was diluted and coated onto a fucose-proline agar plate containing the antibacterial trimethoprim and antifungal nystatin
After 2 weeks, a single colony was isolated and the purity of the culture was ensured by three rounds of purification using different media; ISP2, malt extract agar medium and potato dextrose agar containing trimethoprim were successively employed to ensure the purity of the isolated microorganism
Summary
Fungal-bacterial associations are present in nature, playing important roles in ecological, evolutionary and medicinal processes. In line with earlier 16S rRNA gene sequencing data for the intact symbiont pairing, the bacterium was identified as A. faecali SCSIO B001
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