Affiliation:
1. Agro-Biotechnology Research Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
2. Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, Tokyo, Japan
3. Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Hyogo, Japan
Abstract
ABSTRACT
To elucidate why plasmid-borne catabolic ability differs among host bacteria, we assessed the expression dynamics of the P
ant
promoter on the carbazole-degradative conjugative plasmid pCAR1 in
Pseudomonas putida
KT2440(pCAR1) (hereafter, KTPC) and
Pseudomonas resinovorans
CA10. The P
ant
promoter regulates the transcription of both the
car
and
ant
operons, which are responsible for converting carbazole into anthranilate and anthranilate into catechol, respectively. In the presence of anthranilate, transcription of the P
ant
promoter is induced by the AraC/XylS family regulator AntR, encoded on pCAR1. A reporter cassette containing the P
ant
promoter followed by
gfp
was inserted into the chromosomes of KTPC and CA10. After adding anthranilate, GFP expression in the population of CA10 showed an unimodal distribution, whereas a small population with low GFP fluorescence intensity appeared for KTPC. CA10 has a gene,
antR
CA
, that encodes an iso-functional homolog of AntR on its chromosome. When
antR
CA
was disrupted, a small population with low GFP fluorescence intensity appeared. In contrast, overexpression of pCAR1-encoded AntR in KTPC resulted in unimodal expression under the P
ant
promoter. These results suggest that the expression of pCAR1-encoded AntR is insufficient to ameliorate the stochastic expression of the P
ant
promoter. Raman spectra of single cells collected using deuterium-labeled carbazole showed that the C–D Raman signal exhibited greater variability for KTPC than CA10. These results indicate that heterogeneity at the transcriptional level of the P
ant
promoter due to insufficient AntR availability causes fluctuations in the pCAR1-borne carbazole-degrading capacity of host bacterial cells.
IMPORTANCE
Horizontally acquired genes increase the competitiveness of host bacteria under selective conditions, although unregulated expression of foreign genes may impose fitness costs. The “appropriate” host for a plasmid is empirically known to maximize the expression of plasmid-borne traits. In the case of pCAR1-harboring
Pseudomonas
strains,
P. resinovorans
CA10 exhibits strong carbazole-degrading capacity, whereas
P. putida
KT2440 harboring pCAR1 exhibits low degradation capacity. Our results suggest that a chromosomally encoded transcription factor affects transcriptional and metabolic fluctuations in host cells, resulting in different carbazole-degrading capacities as a population. This study may provide a clue for determining appropriate hosts for a plasmid and for regulating the expression of plasmid-borne traits, such as the degradation of xenobiotics and antibiotic resistance.
Funder
MEXT | Japan Science and Technology Agency
MEXT | Japan Society for the Promotion of Science
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology