Research progress on the RIG project (winter 2011): Chromobacterium sensu latto as
a potential biological control agent for Phytophthora root rot and the fairy ring fungus
Thanatophytum crocorum
Principal investigator: Scott Soby, Biomedical Sciences, Phone: 623-572-3858; Email:
ssobyx@midwestern.edu.
Research progress
Funding approved in the winter of 2011 has been used to address the specific aims
outlined in the proposal dated January 11, 2011. This project began in August 2010, and
has yielded rapid and significant results, which will be presented at an international
meeting in August, and is the foundation of at least two manuscripts currently in
preparation. The specific research goals were: (1) define the taxonomy of violaceinproducing isolates; (2) confirm and quantify the biological activity of [1] and [2] on
Phytophthora cinnamomi mycelial growth, zoospore germination; and on Arabidopsis
seedlings to determine plant toxicity, and (3) determine the chemical structures of
unknown MWU300 pigments.
(1) The violacein-producing isolates are Chromobacterium violaceum. The 16S
ribosomal genes from the isolates were cloned, sequenced, and compared with the
NCBI database. The cranberry isolate is unusual in that it has two copies of the
16S gene which are highly related. It is notable that the NCBI database
annotations for these genes in other isolates do not stipulate that there are two
genes. It is thus highly likely that nucleotide sequence accessions currently in the
database are corrupted by direct sequencing of PCR amplicons, which would give
a hybrid sequence, if the tropical isolates have more than one copy. No mention of
multiple 16S sequences appears in the C. violaceum literature. A second note is
that the cranberry isolates of C. violaceum do not utilize citrate as a carbon
source. There is one mention in the literature of some Brazilian Amazon isolates
that also fail to use citrate. It is likely that the genus Chromobacterium is in need
of revision, which may be the subject of a future manuscript (but other things are
more important to address at the present).
(2) Confirming studies have been performed on the biological activity of [1] and [2]
on Phytophthora cinnamomi mycelial growth, and additional experiments have
been conducted on a number of ascomycete fungi isolated from roots and
phyllosphere of diseased cranberry plants. Interestingly, only Thanatophytum
crocorum, the root pathogen, was inhibited by [1] and [2]. Several other fungi,
which together form the fruit rot complex, actually increased mycelial growth on
these compounds, indicating that these fungi may use [1] and [2] as a carbon
and/or nitrogen source, or by recycling the compound to recover tryptophan. An
experiment is planned for late June to answer this question. Arabidopsis culture
has been ongoing in the lab to bulk up the number of seeds required to do the
germination and root toxicity experiments. These should be accomplished over
the summer.
(3) Nothing further has been done on the unknown pigments. This project is
dependent on a major contribution by Robert Bates, an emeritus professor at the
University of Arizona. It is a lower-priority project for both of us, interesting as
the result might be.