Interactions between a genetically marked Pseudomonas fluorescens strain and bacteriophage ΦR2f in soil: Effects of nutrients, alginate encapsulation, and the wheat rhizosphere

Abstract

The introduction of bacteriophages could potentially be used as a control method to limit the population size of engineered bacteria that have been introduced into soil. Hence, the ability of a species-specific phage, ΦR2f, to infect and lyse its host, a Pseudomonas fluorescens R2f transposon Tn5 derivative, in soil, was studied. Control experiments in liquid media revealed that productive lysis of host cells by phage ϕR2f occurred when cells were freely suspended, whereas cells present in alginate beads resisted lysis. The presence of nutrients enhanced the degree of lysis as well as the production of phage progeny, both with the suspended cells and with cells escaped from the alginate beads. Experiments in which host cells and phage ΦR2f were introduced into two soils of different texture revealed that host cells were primarily lysed in the presence of added nutrients, and phage reached highest titres in these nutrient-amended soils. Encapsulation of the host cells in alginate beads inhibited lysis by the phage in soil. Populations of free host cells introduced into soil that colonized the rhizosphere of wheat were not substantially lysed by phage ΦR2f. However, P. fluorescens R2f populations colonizing the rhizosphere after introduction in alginate beads were reduced in size by a factor of 1,000. Cells migrating from the alginate beads towards the roots may have been in a state of enhanced metabolic activity, allowing for phage ΦR2f infection and cell lysis.

A composite bacteriophage alters colonization by an intestinal commensal bacterium

“…Nutrient availability is known to influence prophage induction and lytic replication (23)(24)(25). E. faecalis V583 responds to enhanced amino acid availability in culture by inducing ϕV1/7, suggesting that amino acid availability acts as an important environmental cue governing E. faecalis prophage induction.…”

New Approaches for Bioaugmentation as a Remediation Technology

“…Additionally, bacteriophages may be useful for containment of GEMs. Smit et al 216 added P. fluorescens R2f encapsulated in alginate to soil along with phage R2f. The phage did not impact bacterial numbers in the alginate, but it decreased the number of P. fluorescens R2f that developed outside of the alginate matrix by a factor of up to 10…”

Encapsulation of plant growth‐promoting bacteria in alginate beads enriched with humic acid

“…Moreover, alginate beads are capable of entrapping sufficient number of bacteria (Fenice et al, 2000;Zohar-Perez et al, 2002). The use of encapsulated cells for environmental applications has several advantages over free cell formulations namely, protection from biotic stresses (Smit et al, 1996) and abiotic stresses such as the inhibitory effect of toxic compounds (Cassidy et al, 1997), enhanced survival and improved physiological activity (Weir et al, 1995), supply of encapsulated nutritional additives (Trevors et al, 1993), increased cell densities and preferential cell growth in various internal aerobic and anaerobic zones of encapsulating gel. The encapsulation technologies face the trade-off among several major considerations such as, mechanical stability, controlled release, environmentally responsive, biodegradable, and cost-effectiveness.…”