Isolation and characterization of a temperate bacteriophage from a ruminal acetogen

Methanogen genomics to discover targets for methane mitigation technologies and options for alternative H2 utilisation in the rumen

Reducing ruminant methane emissions is an important objective for ensuring the sustainability of ruminant-based agriculture. Methane is formed in the rumen by methanogens (part of the domain Archaea), mainly from H2 and CO2. Methanogens from a wide range of habitats are being genome-sequenced to gain a better understanding of their biology and, in particular, to identify targets for inhibition technologies for gut-associated methanogens. Genome comparisons are identifying common genes that define a methanogen, while gene differences are providing an insight into adaptations that allow methanogen survival and persistence under different environmental conditions. Within the rumen microbial food web, methanogens perform the beneficial task of removing H2, which allows reduced cofactors to be reoxidised and recycled, thereby enhancing the breakdown and fermentation of plant material. Therefore, rumen methane mitigation strategies need to consider alternative routes of H2 utilisation in the absence (or decreased levels) of methanogenesis to maintain rumen function. Two main alternatives are possible: enhancing rumen microorganisms that carry out reductive acetogenesis (combining CO2 and H2 to form acetate) or promotion of organisms that consume reducing equivalents during the conversion of metabolic intermediates (malate, fumarate and crotonate) into propionate and butyrate. A better understanding of the role and scale of methane oxidation in the rumen may also lead to future options for methane mitigation.

Lack of surface receptors not restriction-modification system determines F4 phage resistance in Streptococcus bovis II/1

The resistance of Streptococcus bovis strain II/1, the producer of SbvI restriction endonuclease, to F4 phage infection was demonstrated by the double-agar-layer method. Despite the presence of restriction endonuclease SbvI which can cleave F4 phage DNA to numerous fragments in vitro, the evidence that adsorption inhibition is the most important defence mechanism in phage resistance of S. bovis II/1 strain was obtained by adhesion experiments in vivo. Electron microscopy of phage-host mixtures showed many phage particles on the bacterial surface of phage-sensitive S. bovis 47/3 control strain in comparison with no phage particles seen on S. bovis II/1 (phage-resistant) strain surface.

The role of ciliate protozoa in the lysis of methanogenic archaea in rumen fluid

Predation by ciliate protozoa can account for 90% of the eubacterial protein turnover in the rumen. However, little is known about the factors affecting the lysis of archaea in rumen fluid. Bacterial lysis was followed from the release of acid-soluble 14C from 14C leucine-labelled bacteria. The rumen methanogen Methanobrevibacter MF1 was broken down more rapidly than other non-ruminal archaea in rumen fluid withdrawn from sheep harbouring either a mixed protozoa population or monofaunated with Polyplastron multivesiculatum or Entodinium spp. The removal of protozoa from the rumen fluid had little effect on the breakdown of Methanobrevibacter, while lysis of the non-methanogenic ruminal bacterium Selenomonas ruminantium decreased by over 70%. Substantial lysis of Methanobrevibacter occurred in cell-free rumen fluid and this effect could be abolished by autoclaving. In view of the high number of bacteriophages in rumen fluid and susceptibility of ruminal bacteria to phage-induced lysis it is tempting to suggest that phages have a role in the lysis of archaea in rumen fluid.