Biology Reference
In-Depth Information
Pseudomonad
by using a cosmid library constructed from metagenomic DNA.
94
In addition,
Banik and coworkers
95
identified two new biosynthetic gene clusters associated with the
biosynthesis of teicoplanin and vancomycin-like glycopeptide antibiotics after they screened
a soil DNA cosmid library using the sequence-based method. One of these glycopeptide
pathways contains three sulfotransferases, which is a class of tailoring enzymes that has rarely
been found within glycopeptide biosynthesis clusters. By using the eDNA-derived
sulfotransferases, seven new anionic glycopeptide congeners
87
were generated in vitro.
METAGENOMICS APPROACH TOWARDS THE DISCOVERY OF
NATURAL PRODUCTS FROM THE SEA
Whereas the bacterial world represents a rich source of bioactive natural products in the
soil, marine organisms provide an untapped reservoir for undiscovered, bioactive natural
products as well. However, traditional chemical approaches to discover new valuable
bioactive compounds are not effective because the vast majority of marine natural products
have extreme chemical variability.
84
In contrast, metagenomic methods enabled the
discovery of new natural products. For example, the sequence-based metagenomic library
screening method was used to successfully clone a gene cluster encoding the biosynthesis of
pederin-related onnamide from symbionts associated with field collected
Demospongiae
sponges.
96
Similarly, the gene cluster encoding the biosynthesis of the antitumor agent
psymberin was identified from a sponge
bacteria association.
97
Later an enhanced
antitumor compound derived from pederin was identified by using a recombinant
O
-
methyltransferase, PedO, from the pederin biosynthesis gene cluster to methylate
mycalamide A.
98
Cyanobactins are an important example of novel bioactive compounds discovered from
the sea using metagenomics. One example is from cyanobacterial symbionts associated
with marine
Demospongiae
sponges. Schmidt and coworkers
99
identified several
patellamide biosynthetic genes and a related cluster in an important cyanobacterium,
Trichodesmium erythraeum
IMS101, which was confirmed by heterologous expression of the
whole pathway in
E. coli
. A large family of cytotoxic cyclic peptides exemplified by the
patellamides was isolated from ascidians harboring the obligate cyanobacterial symbionts
Prochloron
spp. Later, the Schmidt group reported the PCR amplification of 30 genes
encoding novel patellamide-like precursor peptides from uncultured
Prochloron
spp.
symbionts living in consortia with marine sponges.
100,101
The discovery of new
patellamide-like precursor peptides demonstrates the power of comparative analysis of
closely related symbiotic pathways to direct the biological synthesis of new molecules and
aids in generating additional members of the important cyclic peptide families. In
addition, an assembly line responsible for the biosynthesis of diverse cyanobactins was
reported.
102
By comparing five new cyanobactin biosynthetic clusters, the prenylated
antitumor preclinical candidate trunkamide was produced in
E. coli
using genetic
engineering.
192
COMBINATORIAL APPROACHES FOR NOVEL DRUG GENERATION
In the past few decades, more than 20 000 chemically diverse and biologically active
compounds have been discovered from microbial sources by traditional screening efforts.
103
The successful cloning of the first antibiotic biosynthetic gene cluster
104
prompted
researchers to investigate whether recombinant bacteria containing one or more genes
from different organisms that make biosynthetically related metabolites could produce
novel ones. The resulting combinatorial biosynthesis method, which was developed
independently by Houghten and Geysen in the 1980s, allows interchanging of secondary
metabolism genes between antibiotic-producing microorganisms to generate a large
library of pathways for high-throughput screening.
