Seasonal Population Dynamics and Interactions of Competing Bacteriophages and Their Host in the Rhizosphere

Ashelford, Kevin E.; Norris, S. J.; Fry, John C.; Bailey, Mark; Day, Martin J.

doi:10.1128/aem.66.10.4193-4199.2000

Cited by 87 publications

(61 citation statements)

References 24 publications

(19 reference statements)

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“…Viable counts were carried out as described previously (1,4), and so they are only briefly described here. Heterotrophic bacteria were enumerated on tryptone soy broth agar (TSBA), and viable counts of Serratia-like and S. quinivorans CP6-like bacteria (likely CP6 phage hosts) were made on Serratia selective medium (SSM).…”

Section: Methodsmentioning

confidence: 99%

Elevated Abundance of Bacteriophage Infecting Bacteria in Soil

Ashelford

Day

Fry

2003

Appl Environ Microbiol

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237

166

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Here we report the first direct counts of soil bacteriophage and show that substantial populations of these viruses exist in soil (grand mean ‫؍‬ 1.5 ؋ 10 7 g ؊1 ), at least 350-fold more than the highest numbers estimated from traditional viable plaque counts. Adding pure cultures of a Serratia phage to soil showed that the direct counting methods with electron microscopy developed here underestimated the added phage populations by at least eightfold. So, assuming natural phages were similarly underestimated, virus numbers in soil averaged 1.5 ؋ 10 8 g ؊1 , which is equivalent to 4% of the total population of bacteria. This high abundance was to some extent confirmed by hybridizing colonies grown on Serratia and Pseudomonas selective media with cocktails of phage infecting these bacteria. This showed that 8.9 and 3.9%, respectively, hybridized with colonies from the two media and confirmed the presence of phage DNA sequences in the cultivable fraction of the natural population. Thus, soil phage, like their aquatic counterparts, are likely to be important in controlling bacterial populations and mediating gene transfer in soil.Direct counts made with electron and epifluorescence microscopy have shown bacteriophage to be abundant in water from marine (5, 6, 16) and freshwater (18) habitats. They occur at densities of up to 2.5 ϫ 10 8 ml Ϫ1 and are an average of 10-fold more abundant than their bacterial hosts. Fewer direct counts have been done on sediments, and results have been more variable. Numbers of bacterial viruses in sediment are higher than in water, and counts of up to 2 ϫ 10 9 ml Ϫ1 have been recorded (11). However, bacterial counts are also higher, and in some cases, bacteriophage in sediments are more abundant than bacteria (11, 13) and sometimes less abundant (10).Although it is difficult to grow bacteriophage from soil without enrichment (31), some viable counts have been reported (1,7,8,21,22,26,27). These range from 0 to 4 ϫ 10 4 g Ϫ1 and have been determined from a wide variety of host bacteria. To date, no direct counts of bacterial viruses in this environment have been reported, so in this study we developed methods for counting the total numbers of bacteriophage in soil. We chose to count soil viruses by using transmission electron microscopy (TEM), as a direct observation of phage morphology would allow us to be confident of counting bacterial viruses. We believed that epifluorescence counting would be problematic because there are so many fine particles in soil that interact nonspecifically with most of the DNA stains used for direct virus counts in water and sediment. (greater bitter cress) and bulk soil from molehills. Suspensions were made from soil and rhizosphere samples (1 g [wet weight]) by homogenization in 10 ml of water with 5-mm-diameter glass beads first by vortex mixing for 1 min and then by shaking for 10 min on an orbital shaker. All values are expressed as wet weights, and the average water content of the soil used was 56.2% (coefficient of variation, 29.3%). Before TEM cou...

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Section: Methodsmentioning

confidence: 99%

Elevated Abundance of Bacteriophage Infecting Bacteria in Soil

Ashelford

Day

Fry

2003

Appl Environ Microbiol

Self Cite

237

166

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“…It has been postulated that approximately 10 30 bacteriophages are present in the biosphere (Ashelford et al, 2000). Despite this rich reservoir of phages present in the environment, very few (about 300) have been characterized (Casjens, 2008).…”

Section: Introductionmentioning

confidence: 99%

Characterization of Siphoviridae phage Z and studying its efficacy against multidrug-resistant Klebsiella pneumoniae planktonic cells and biofilm

Jamal

Hussain

Das

et al. 2015

Journal of Medical Microbiology

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Biofilm has many serious consequences for public health and is a major virulence factor contributing to the chronicity of infections. The aim of the current study was to isolate and characterize a bacteriophage that inhibits multidrug-resistant Klebsiella pneumonia (M) in planktonic form as well as biofilm. This phage, designated bacteriophage Z, was isolated from wastewater. Its adsorption rate to its host bacterium was significantly enhanced by MgCl 2 and CaCl 2 . It has a wide range of pH and heat stability. From its one-step growth, latent time and burst size were determined to be 24 min and about 320 virions per cell, respectively. As analysed by transmission electron microscopy, phage Z had an icosahedral head of width 76±10 nm, length 92±14 nm and icosahedron side 38 nm, and a non-contractile tail 200±15 nm long and 14-29 nm wide. It belongs to the family Siphoviridae in the order Caudovirales. Six structural proteins ranging from 18 to 65 kDa in size were revealed by SDS-PAGE. The genome was found to comprise double-stranded DNA with an approximate size of 36 kb. Bacteria were grown in suspension and as biofilms to compare the susceptibility of both phenotypes to the phage lytic action. Phage Z was effective in reducing biofilm biomass after 24 and 48 h, showing more than twofold and threefold reduction, respectively. Biofilm cells and stationary-phase planktonic bacteria were killed at a lower rate than exponential-phase planktonic bacteria.

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“…Compared to these marine paradigms, however, our understanding of the ecological significance of viruses in soils is extremely limited. Thus far, studies of soil phage ecology have focused on population dynamics of cultivable soil phages and their hosts (6,7,44). While these model systems have provided valuable insights into phage-host interactions in soils, culture-independent detection and analyses will be critical in obtaining a more complete understanding of the ecological impacts of viruses in soils.…”

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confidence: 99%

Abundance and Diversity of Viruses in Six Delaware Soils

Williamson

Radosevich

Wommack

2005

Appl Environ Microbiol

258

199

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The importance of viruses in marine microbial ecology has been established over the past decade. Specifically, viruses influence bacterial abundance and community composition through lysis and alter bacterial genetic diversity through transduction and lysogenic conversion. By contrast, the abundance and distribution of viruses in soils are almost completely unknown. This study describes the abundance and diversity of autochthonous viruses in six Delaware soils: two agricultural soils, two coastal plain forest soils, and two piedmont forest soils. Viral abundance was measured using epifluorescence microscopy, while viral diversity was assessed from morphological data obtained through transmission electron microscopy. Extracted soil virus communities were dominated by bacteriophages that demonstrated a wide range of capsid diameters (20 nm to 160 nm) and morphologies, including filamentous forms and phages with elongated capsids. The reciprocal Simpson's index suggests that forest soils harbor more diverse assemblages of viruses, particularly in terms of morphological distribution. Repeated extractions of virus-like particles (VLPs) from soils indicated that the initial round of extraction removes approximately 70% of extractable viruses. Higher VLP abundances were observed in forest soils (1.31 ؋ 10 9 to 4.17 ؋ 10 9 g ؊1 dry weight) than in agricultural soils (8.7 ؋ 10 8 to 1.1 ؋ 10 9 g ؊1 dry weight). Soil VLP abundance was significantly correlated to moisture content (r ‫؍‬ 0.988) but not to soil texture. Land use (agricultural or forested) was significantly correlated to both bacterial (r ‫؍‬ 0.885) and viral (r ‫؍‬ 0.812) abundances, as were soil organic matter and water content. Thus, land use is a significant factor influencing viral abundance and diversity in soils.

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Seasonal Population Dynamics and Interactions of Competing Bacteriophages and Their Host in the Rhizosphere

Cited by 87 publications

References 24 publications

Elevated Abundance of Bacteriophage Infecting Bacteria in Soil

Elevated Abundance of Bacteriophage Infecting Bacteria in Soil

Characterization of Siphoviridae phage Z and studying its efficacy against multidrug-resistant Klebsiella pneumoniae planktonic cells and biofilm

Abundance and Diversity of Viruses in Six Delaware Soils

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