[Source: Proceedings of the National Academy of Sciences of the United States of America, full page: (LINK). Abstract, edited.]
Niche adaptation limits bacteriophage predation of Vibrio cholerae in a nutrient-poor aquatic environment
Cecilia A. Silva-Valenzuela and Andrew Camilli
PNAS published ahead of print January 11, 2019 / DOI: https://doi.org/10.1073/pnas.1810138116
Edited by Lucia B. Rothman-Denes, The University of Chicago, Chicago, IL, and approved December 11, 2018 (received for review June 13, 2018)
Virulent phages can reduce populations of bacteria and help shape bacterial evolution. Here, we used three virulent phages to understand their equilibrium with V. cholerae in nutrient-limiting aquatic microcosms. It has been proposed that phages quench cholera outbreaks, but no direct evidence of phage predation in aquatic environments had been established. Here, we show that different phages possess varied abilities to infect in certain niches or stages of the host bacterial life cycle. Unveiling the phage/bacterial interactions in their natural setting is important to the understanding of cholera outbreaks and could be ultimately used to help develop a method for outbreak prediction and/or control.
Vibrio cholerae, the causative agent of cholera, has reservoirs in fresh and brackish water where it interacts with virulent bacteriophages. Phages are the most abundant biological entity on earth and coevolve with bacteria. It was reported that concentrations of phage and V. cholerae inversely correlate in aquatic reservoirs and in the human small intestine, and therefore that phages may quench cholera outbreaks. Although there is strong evidence for phage predation in cholera patients, evidence is lacking for phage predation of V. choleraein aquatic environments. Here, we used three virulent phages, ICP1, ICP2, and ICP3, commonly shed by cholera patients in Bangladesh, as models to understand the predation dynamics in microcosms simulating aquatic environments. None of the phages were capable of predation in fresh water, and only ICP1 was able to prey on V. cholerae in estuarine water due to a requirement for salt. We conclude that ICP2 and ICP3 are better adapted for predation in a nutrient rich environment. Our results point to the evolution of niche-specific predation by V. cholerae-specific virulent phages, which complicates their use in predicting or monitoring cholera outbreaks as well as their potential use in reducing aquatic reservoirs of V. cholerae in endemic areas.
Vibrio cholerae – cholera – bacteriophage – aquatic reservoir – environment
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Author contributions: C.A.S.-V. and A.C. designed research; C.A.S.-V. and A.C. performed research; C.A.S.-V. contributed new reagents/analytic tools; C.A.S.-V. and A.C. analyzed data; and C.A.S.-V. and A.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1810138116/-/DCSupplemental.
Published under the PNAS license.
Keywords: Vibrio cholerae; Cholera; Bacteriophages.