Angucycline-Like Aromatic Polyketide from a Novel <i>Streptomyces</i> Species Reveals Freshwater Snail <i>Physa acuta</i> as Underexplored Reservoir for Antibiotic-Producing Actinomycetes

• Main Authors: Nasim Safaei, Yvonne Mast, Michael Steinert, Katharina Huber, Boyke Bunk, Joachim Wink
• Format: Article
• Language: English
• Published: MDPI AG 2021-12-01
• Series: Antibiotics
• Subjects: Actinobacteria; <i>Physa acuta</i>; <i>Streptomyces</i>; antibiotics; angucycline
• Online Access: https://www.mdpi.com/2079-6382/10/1/22

Antibiotic producers have mainly been isolated from soil, which often has led to the rediscovery of known compounds. In this study, we identified the freshwater snail<i> Physa acuta</i> as an unexplored source for new antibiotic producers. The bacterial diversity associated with the snail was characterized by a metagenomic approach using cultivation-independent high-throughput sequencing. Although Actinobacteria represented only 2% of the bacterial community, the focus was laid on the isolation of the genus <i>Streptomyces</i> due to its potential to produce antibiotics. Three <i>Streptomyces</i> strains (7NS1, 7NS2 and 7NS3) were isolated from <i>P. acuta</i>, and the antimicrobial activity of the crude extracts were tested against a selection of Gram-positive and Gram-negative bacteria and fungi. 7NS3 showed the strongest activity against Gram-positive bacteria and, thus, was selected for genome sequencing and a phylogenomic analysis. 7NS3 represents a novel <i>Streptomyces</i> species, which was deposited as <i>Streptomyces</i> sp. DSM 110735 at the Leibniz Institute-German Collection of Microorganisms and Cell Cultures (DSMZ). Bioassay-guided high-performance liquid chromatography (HPLC) and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS) analyses of crude extract fractions resulted in the detection of four compounds, one of which matched the compound characteristics of emycin A, an angucycline-like aromatic polyketide. Genome mining studies based on the whole-genome sequence of 7NS3 resulted in the identification of a gene cluster potentially coding for emycin A biosynthesis. Our study demonstrates that freshwater snails like <i>P. acuta</i> can represent promising reservoirs for the isolation of new antibiotic-producing actinobacterial species.