Isolation and characterization of a sponge-associated actinomycete that produces manzamines

Abstract

Two Indonesian sponges, Acanthostrongylophora sp. Sponge 35 and Sponge 52, containing manzamine A were collected off the coast of Manado, Indonesia. Manzamines are a family of marine alkaloids that exhibit a complex molecular architecture and possess bioactivities including antitumour, antimicrobial, antiparasitic and insecticidal activities. Manzamines have been found in 17 different species of sponges with wide geographical distribution which has led to speculation that they may be produced by a microbial symbiont rather than by the sponges themselves. The sponges' microbial communities were investigated using 16S rRNA gene analysis and a rational culture-based microbiology approach in which specific bacterial groups were targeted. The molecular analysis of these microbial communities revealed that they were complex and diverse. Microbiological analyses were conducted on Acanthostrongylophora sp. with a particular emphasis on the isolation of actinomycetes because of the high number of actinomycete sequences in this sponge 16S rRNA gene clone library and their excellent track record as bioactive compound producers. One of the isolated actinomycetes, Micromonospora sp. strain M42, produces manzamine A and 8-hydroxy-manzamine, compounds initially detected in the sponge. A detailed analysis of Micromonospora sp. strain M42 showed that it grew on a wide range of salt concentrations with an optimal growth at 0-1% NaCl. Cultures of Micromonospora sp. strain M42 consistently produced manzamine A with a maximum yield of 1 mg/l. The genome size of Micromonospora sp. strain M42 was estimated at 6.7 Mb by pulsed field gel electrophoresis. The biosynthetic gene pathway encoding manzamine A was investigated using both biochemistry and molecular methods yet it remains elusive. Micromonospora sp. strain M42 underwent UV mutagenesis leading to isolation of mutants with yield of manzamine A improved by 3.5 fold. One of the mutants produces manzamine B, the putative biosynthetic precursor of manzamine A. A fosmid library of Micromonospora sp. strain M42 was constructed and low-pass genome sequencing gave insights into the strain's genome and revealed a high number of genes devoted to the production of secondary metabolites including polyketides and non-ribosomal peptides. The isolation of Micromonospora sp. strain M42 greatly improves the chances of manzamines becoming a drug class for treatment of malaria.