Isolation and characterization of lytic phages fromBacterioides ruminicola ssbrevis

Characterization of two lytic bacteriophages, infecting Streptococcus bovis/equinus complex (SBSEC) from Korean ruminant

Streptococcus bovis/equinus complex (SBSEC) is one of the most important lactic acid-producing rumen bacteria causing subacute ruminal acidosis. Despite the significance of the ruminal bacteria, lytic bacteriophages (phages) capable of infecting SBSEC in the rumen have been rarely characterized. Hence, we describe the biological and genomic characteristics of two lytic phages (designated as vB_SbRt-pBovineB21 and vB_SbRt-pBovineS21) infecting various SBSEC species, including the newly reported S. ruminicola. The isolated SBSEC phages were morphologically similar to Podoviridae and could infect other genera of lactic acid-producing bacteria, including Lactococcus and Lactobacillus. Additionally, they showed high thermal- and pH-stability, and those characteristics induce strong adaptation to the ruminal environment, such as the low pH found in subacute ruminal acidosis. Genome-based phylogeny revealed that both phages were related to Streptococcus phage C1 in the Fischettivirus. However, they had a lower nucleotide similarity and distinct genomic arrangements than phage C1. The phage bacteriolytic activity was evaluated using S. ruminicola, and the phages efficiently inhibited planktonic bacterial growth. Moreover, both phages could prevent bacterial biofilms of various SBSEC strains and other lactic acid-producing bacteria in vitro. Thus, the newly isolated two SBSEC phages were classified as new Fischettivirus members and could be considered as potential biocontrol agents against ruminal SBSEC bacteria and their biofilms.

Bacteriophages as Fecal Pollution Indicators

Bacteriophages are promising tools for the detection of fecal pollution in different environments, and particularly for viral pathogen risk assessment. Having similar morphological and biological characteristics, bacteriophages mimic the fate and transport of enteric viruses. Enteric bacteriophages, especially phages infecting Escherichia coli (coliphages), have been proposed as alternatives or complements to fecal indicator bacteria. Here, we provide a general overview of the potential use of enteric bacteriophages as fecal and viral indicators in different environments, as well as the available methods for their detection and enumeration, and the regulations for their application.

Bacteriophage-mediated extracellular DNA release is important for the structural stability of aerobic granular sludge

The aim of this study was to investigate the microbial characteristics and the structural role of exDNA in different size AGSs. Metagenomic results showed that exDNA has a significantly lower GC content, ~46.0%, than the ~65.0% GC of intracellular DNA (inDNA). Taxonomic predictions showed most of the reads from the exDNA that could be taxonomically assigned were from members of the phyla Bacteroidetes (55.0-64.2% of the total exDNA reads). Assigned inDNA reads were mainly from Proteobacteria (50.9-57.8%) or Actinobacteria (18.0-28.0%). Reads mapping showed that exDNA read depths were similar across all predicted open reading frames from assembled genomes that were assigned as Bacteroidetes which is consistent with cell lysis as a source of exDNA. Enrichment of CRISPR-CAS proteins in exDNA reads and CRISPR spacers in Bacteroidetes associated draft genomes suggested that bacteriophage infection may be an important cause of lysis of these cells. A critical role for this exDNA was found using DNase I digestion experiments which showed that the exDNA was vital for the structural stability of relatively small sized AGS but not for the larger sized AGS. The characteristics of exDNA in AGSs revealed in this work provide a new perspective on AGS components and structural stability.

Rumen Virus Populations: Technological Advances Enhancing Current Understanding

The rumen contains a multi-kingdom, commensal microbiome, including protozoa, bacteria, archaea, fungi and viruses, which enables ruminant herbivores to ferment and utilize plant feedstuffs that would be otherwise indigestible. Within the rumen, virus populations are diverse and highly abundant, often out-numbering the microbial populations that they both predate on and co-exist with. To date the research effort devoted to understanding rumen-associated viral populations has been considerably less than that given to the other microbial populations, yet their contribution to maintaining microbial population balance, intra-ruminal microbial lysis, fiber breakdown, nutrient cycling and genetic transfer may be highly significant. This review follows the technological advances which have contributed to our current understanding of rumen viruses and drawing on knowledge from other environmental and animal-associated microbiomes, describes the known and potential roles and impacts viruses have on rumen function and speculates on the future directions of rumen viral research.

Toward Understanding Phage:Host Interactions in the Rumen; Complete Genome Sequences of Lytic Phages Infecting Rumen Bacteria

The rumen is known to harbor dense populations of bacteriophages (phages) predicted to be capable of infecting a diverse range of rumen bacteria. While bacterial genome sequencing projects are revealing the presence of phages which can integrate their DNA into the genome of their host to form stable, lysogenic associations, little is known of the genetics of phages which utilize lytic replication. These phages infect and replicate within the host, culminating in host lysis, and the release of progeny phage particles. While lytic phages for rumen bacteria have been previously isolated, their genomes have remained largely uncharacterized. Here we report the first complete genome sequences of lytic phage isolates specifically infecting three genera of rumen bacteria: Bacteroides, Ruminococcus, and Streptococcus. All phages were classified within the viral order Caudovirales and include two phage morphotypes, representative of the Siphoviridae and Podoviridae families. The phage genomes displayed modular organization and conserved viral genes were identified which enabled further classification and determination of closest phage relatives. Co-examination of bacterial host genomes led to the identification of several genes responsible for modulating phage:host interactions, including CRISPR/Cas elements and restriction-modification phage defense systems. These findings provide new genetic information and insights into how lytic phages may interact with bacteria of the rumen microbiome.

Indicators of Waterborne Viruses

Enteric viruses excreted by humans and animals may reach water resources and cause large outbreaks. Drinking water is one of the essential global life elements for humanity. However, some of our resources are contaminated with viruses and indicators for continuous monitoring have been developed. The classical ones are coliforms and fecal coliforms that are still the iron standard for water indicator monitoring (see Chap. 10.1007/978-94-017-9499-2_34). In the last decades, bacteriophages have been suggested as potential indicators of enteric viruses and many studies showed their potential as such mainly due to their comparable resistance to water processes such as disinfection. In this chapter, the indicator role of bacteriophages in water is critically reviewed and discussed.

Bacteriophages infecting Bacteroides as a marker for microbial source tracking

Bacteriophages infecting certain strains of Bacteroides are amid the numerous procedures proposed for tracking the source of faecal pollution. These bacteriophages fulfil reasonably well most of the requirements identified as appropriate for a suitable marker of faecal sources. Thus, different host strains are available that detect bacteriophages preferably in water contaminated with faecal wastes corresponding to different animal species. For phages found preferably in human faecal wastes, which are the ones that have been more extensively studied, the amounts of phages found in waters contaminated with human fecal samples is reasonably high; these amounts are invariable through the time; their resistance to natural and anthropogenic stressors is comparable to that of other relatively resistant indicator of faecal pollution such us coliphages; the abundance ratios of somatic coliphages and bacteriophages infecting Bacteroides thetaiotaomicron GA17 are unvarying in recent and aged contamination; and standardised detection methods exist. These methods are easy, cost effective and provide data susceptible of numerical analysis. In contrast, there are some uncertainties regarding their geographical stability, and consequently suitable hosts need to be isolated for different geographical areas. However, a feasible method has been described to isolate suitable hosts in a given geographical area. In summary, phages infecting Bacteroides are a marker of faecal sources that in our opinion merits being included in the "toolbox" for microbial source tracking. However, further research is still needed in order to make clear some uncertainties regarding some of their characteristics and behaviour, to compare their suitability to the one of emerging methods such us targeting Bacteroidetes by qPCR assays; or settling molecular methods for their determination.

Bacteriophages that infect the cellulolytic ruminal bacterium Ruminococcus albus AR67

AIM

To isolate bacterial viruses that infect the ruminal cellulolytic bacterium Ruminococcus albus.

METHODS

Four phages infecting R. albus AR67 were isolated under anaerobic conditions using the soft-agar overlay technique. The phages were characterized on morphology, solvent stability, nucleic acid type and digestion characteristics. Two phages, phiRa02 and phiRa04 comprised icosahedral virions with linear double-stranded DNA and appeared to belong to the family Podoviridae [corrected] The other two phages are most likely filamentous phages with circular single-stranded DNA of the family Inoviridae.

SIGNIFICANCE OF THE STUDY

Viruses of the family Inoviridae [corrected] have not previously been isolated from rumen bacteria. The phages isolated in this study are the first phages shown to infect the cellulolytic bacteria of the rumen. This suggests that the cellulolytic populations of the rumen are subject to lytic events that may impact on the ability of these bacteria to degrade plant fibre and on the nutrition of the animal.

Systematics and evolution of ruminal species of the genus Prevotella

Bacterial species of the genus Prevotella represent a numerically dominant microbial population in the rumen of cattle. They belong to the phylogenetic division Cytophaga-Flexibacter-Bacteroides (CFB) which is a large group of ecologically diverse bacteria with only a few shared traits. The phylogenetic descent from a common ancestor seems to be unquestionable, however, as judged from the small subunit ribosomal RNA analysis. Only 4 ruminal Prevotella species have been described to date, even though the sequence analysis of directly retrieved 16S rRNA genes indicates a large genetic diversity within this group of rumen bacteria. The closest relatives of ruminal Prevotella spp. are not surprisingly other species of the genus Prevotella, typically inhabiting the gastrointestinal tract, oral cavity and genital areas of other animals and man. The previous phylogenetic analysis showed that species of the genus Prevotella can be split into two groups or superclusters, the "ruminal" and the "non-ruminal prevotellas". One of 4 currently described ruminal Prevotella spp., i.e. P. albensis, has been placed outside the supercluster containing ruminal Prevotella spp. and within the supercluster containing the non-ruminal Prevotella spp. However, the number of available small subunit rRNA sequences from this species represents only a fraction of all known ruminal Prevotella sequences.

The bacteriophages of ruminal prevotellas

Rumen bacteriophage-lyzed bacterial strains of the genus Prevotella were isolated and preliminarily characterized. The strain TCl-1 the species P. bryantii was the only prevotella strain successfully infected with filter sterilized rumen fluid from a black-and-white Holstein cow. Two types of plaques were observed, both rather small and turbid. Preliminary electron microscopy observation showed that several morphologically different bacteriophages were present in these plaques. The plaque eluates were further used for the infection of other prevotella strains. The plaques produced by the bacteriophages were observed with two strains, i.e. P. bryantii B(1)4 and P. brevis GA33. The bacteriophages from both strains were examined by transmission electron microscopy and several morphologically different bacteriophages were observed, among others also a large virion with an icosahedral head with the diameter of approximately 120 nm. The bacteriophage was identified in plaques of bacterial cells of the strain GA33 and has an approximately 800 nm long helical tail, which places it among the largest ruminal bacteriophages described to date. Other bacteriophages from the same indicator strain as well as from P. bryantii B(1)4 strain were smaller and tail structures were not observed in all of them.

Detection of phages infecting Bacteroides fragilis HSP40 using a specific DNA probe

Nine bacteriophage isolates of Bacteroides fragilis, obtained from urban sewage and pig faeces samples using four different host strains (HSP40, RYC4023, RYC2056 and RYC3318), were compared on the basis of morphology, host range, DNA restriction patterns, DNA hybridisation and protein composition. All the phages are siphovirus and, as judged from cleavage by restriction endonucleases, their genome is composed of double-stranded DNA of similar size ( approximately 51-kb). Host range analysis differentiated two types of phages: (1) phages that clearly infect B. fragilis strains HSP40 (B40-2, B23-1, B23-2, B23-3 and B23-4, of which B40-8 is the phage type); and (2) the group of bacteriophages that were not infectious for HSP40 (B56-1, B56-2 and B18-1). Similarity in DNA restriction patterns and protein characteristics was found in the HSP40 infectious phages. Anti-B40-8 serum recognised only the proteins of the phages of this type. Although all phages showed similar major protein sizes, minor specific bands were detected. Bacteriophages B56-1, B56-2 and B18-1 showed heterogeneity in their DNA restriction profiles although some degree of DNA-DNA homology between all genomes was observed. Southern blot analysis with phage B40-8 DNA based probes identified a 1.5-kb DNA region homologous for all HSP40 phage isolates, but absent in the genome of the other phage isolates that did not infect this bacterial strain. The homologous region was used as a specific probe to specifically detect B. fragilis HSP40 phages.

Do ruminal bacteria exchange genetic material?

This paper discusses the reasons and current evidence for gene transfer between ruminal bacteria and other bacteria in the environment, possible routes for genetic exchange, and candidate genes. Gene transfer between ruminal bacteria has been demonstrated in vitro; however, success has been only minimal in obtaining plasmids and other self-transmissible genetic material from ruminal bacteria. The application of molecular biology techniques with ruminal microorganisms should permit the opportunity for an in vivo assessment of gene transfer. Studies that could provide pertinent information for ruminal microbiologists and dairy nutritionists are outlined.

Isolation and characterization of a temperate bacteriophage from a ruminal acetogen

Nine acetogenic bacterial cultures recently isolated from the bovine rumen were tested for phage susceptibility by plaque formation. Both clear plaques and plaques with turbid centers were occasionally seen, but could not be used repeatedly to lyse pure cultures of acetogens, suggesting the possibility of a temperate phage. Five of the nine acetogenic isolates showed a response to mitomycin C induction. Acetogenic isolate H3HH was chosen for further study because it produced the greatest lysogenic response to mitomycin C. The bacteriophage was induced with mitomycin C, examined by transmission electron microscopy, and shown to have a hexagonal head (diameter, 59 eta m), a long flexible tail (192 eta m), and a flat collar (diameter, 31 eta m). The bacteriophage was classified within Bradley's group B. Bacteriophage DNA was determined to contain 36.2 kilobases of linear double-stranded DNA.