Characterization and optimization of antifungal production in Streptomyces sp. RMIT01 from the Australian mangrove rhizosphere

Background Mangroves are dynamic coastal ecosystems that provide a rich habitat for diverse microorganisms. Streptomyces strain RMIT01 was isolated from the rhizosphere of the mangrove Avicennia marina located in Jawbone Sanctuary, Williamstown, Victoria, Australia. This study aimed to characterize RMIT01’s genomic and biochemical traits, optimize its antifungal production, and explore its biosynthetic gene clusters to predict potential antifungal compounds. Methods The RMIT01 strain was characterized using International Streptomyces Project (ISP) media series to observe morphological traits over a 21-day period, comparing results with standard species and colour charts. Micromorphological features were examined through light and scanning electron microscopy. Growth tolerance was assessed across various temperatures, pH levels, and NaCl concentrations in ISP2 medium, along with testing carbon and nitrogen source utilisation using standard kits. Whole genome sequencing was conducted using the Illumina platform, and AntiSMASH 8.0 was employed to predict secondary metabolite biosynthetic gene clusters, aiding in the identification of potential antimicrobial compounds. Results The strain exhibited morphological and biochemical characteristics consistent with the genus Streptomyces possessing a Gram-positive cell wall and square shaped spores. Genomic analysis revealed a size of 7,609,141 bp and a Guanine and Cytosine (GC) content of 72%. The average nucleotide identity between strain RMIT01 and the closest related species- Streptomyces sindenensis JCM 4164 T , Streptomyces parvus JCM 4069 T , and Streptomyces YPW6 - were 92.19%, 92.45%, and 98.22%, respectively. Given the 95% cutoff for species delineation, RMIT01 is likely to represent a new species, as Streptomyces YPW6 has not yet been officially described or named. RMIT01 demonstrated antifungal properties against Candida albicans . Antifungal optimization experiments showed that incubation of RMIT01 in starch casein medium with Sigma TM sea salt at 25 °C for 6 days under aerobic conditions yielded a maximum inhibition zone diameter of 20.9 mm. The RMIT01 genome harbours unique biosynthetic gene clusters for bafilomycin B1; thiazostatin, watasemycins, and 2-hydroxyphenylthiazoline; enantiopyochelin and isopyochelin; tylactone; inthomycin; desulfoclethramycin/clethramycin; and niphimycin, several showing low similarity to known biosynthetic gene clusters. Conclusions These findings highlight the significant potential of Streptomyces sp. RMIT01 as a source of antifungal agents, emphasizing the importance of exploring mangrove ecosystems for biotechnological applications.