A new aminoglycoside antibiotic, sannamycin C and its 4-N-glycyl derivative

Isolation, phylogenetic analysis and anti-infective activity screening of marine sponge-associated actinomycetes

Terrestrial actinomycetes are noteworthy producers of a multitude of antibiotics, however the marine representatives are much less studied in this regard. In this study, 90 actinomycetes were isolated from 11 different species of marine sponges that had been collected from offshore Ras Mohamed (Egypt) and from Rovinj (Croatia). Phylogenetic characterization of the isolates based on 16S rRNA gene sequencing supported their assignment to 18 different actinomycete genera representing seven different suborders. Fourteen putatively novel species were identified based on sequence similarity values below 98.2% to other strains in the NCBI database. A putative new genus related to Rubrobacter was isolated on M1 agar that had been amended with sponge extract, thus highlighting the need for innovative cultivation protocols. Testing for anti-infective activities was performed against clinically relevant, Gram-positive (Enterococcus faecalis, Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria, fungi (Candida albicans) and human parasites (Leishmania major, Trypanosoma brucei). Bioactivities against these pathogens were documented for 10 actinomycete isolates. These results show a high diversity of actinomycetes associated with marine sponges as well as highlight their potential to produce anti-infective agents.

Comparison of fortimicins with other aminoglycosides and effects on bacterial ribosome and protein synthesis

Fortimicins are bicyclic aminoglycoside antibiotics that contain a fortamine moiety instead of the deoxystreptamine found in other aminoglysides. Fortimicin A had a bactericidal effect on Escherichia coli and Staphylococcus epidermidis and was found to inhibit protein synthesis in vivo. In vitro, fortimicin A inhibited polyuridylic acid-directed phenylalanine polymerization and induced misreading, as shown by leucine incorporation. In contrast, fortimicin B had no effect on either polymerization or misreading. In assays programmed with natural mRNA, only a weak polymerization inhibition effect was observed with fortimicin A, whereas a strong stimulation was seen in the presence of fortimicin B. Both fortimicins A and B inhibited dissociation of 70S ribosomes into their subunits and neither was able to displace [3H]dihydrostreptomycin, [3H]tobramycin, or [3H]gentamicin from their respective binding sites on the 70S particle.