Affiliation:
1. Pharmaceutical Sciences Division, University of Wisconsin—Madison, Madison, Wisconsin, USA
2. Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, Virginia, USA
3. Department of Biology, Randolph-Macon College, Ashland, Virginia, USA
Abstract
ABSTRACT
The uncultured bacterial symbiont “
Candidatus
Endobugula sertula” is known to produce cytotoxic compounds called bryostatins, which protect the larvae of its host,
Bugula neritina
. The symbiont has never been successfully cultured, and it was thought that its genome might be significantly reduced. Here, we took a shotgun metagenomics and metatranscriptomics approach to assemble and characterize the genome of “
Ca
. Endobugula sertula.” We found that it had specific metabolic deficiencies in the biosynthesis of certain amino acids but few other signs of genome degradation, such as small size, abundant pseudogenes, and low coding density. We also identified homologs to genes associated with insect pathogenesis in other gammaproteobacteria, and these genes may be involved in host-symbiont interactions and vertical transmission. Metatranscriptomics revealed that these genes were highly expressed in a reproductive host, along with
bry
genes for the biosynthesis of bryostatins. We identified two new putative
bry
genes fragmented from the main
bry
operon, accounting for previously missing enzymatic functions in the pathway. We also determined that a gene previously assigned to the pathway,
bryS
, is not expressed in reproductive tissue, suggesting that it is not involved in the production of bryostatins. Our findings suggest that “
Ca
. Endobugula sertula” may be able to live outside the host if its metabolic deficiencies are alleviated by medium components, which is consistent with recent findings that it may be possible for “
Ca
. Endobugula sertula” to be transmitted horizontally.
IMPORTANCE
The bryostatins are potent protein kinase C activators that have been evaluated in clinical trials for a number of indications, including cancer and Alzheimer's disease. There is, therefore, considerable interest in securing a renewable supply of these compounds, which is currently only possible through aquaculture of
Bugula neritina
and total chemical synthesis. However, these approaches are labor-intensive and low-yielding and thus preclude the use of bryostatins as a viable therapeutic agent. Our genome assembly and transcriptome analysis for “
Ca
. Endobugula sertula” shed light on the metabolism of this symbiont, potentially aiding isolation and culturing efforts. Our identification of additional
bry
genes may also facilitate efforts to express the complete pathway heterologously.
Funder
Division of Intramural Research, National Institute of Allergy and Infectious Diseases
American Foundation for Pharmaceutical Education
Thomas F. and Kate Miller Jeffress Memorial Trust
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
41 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献