A study of some facultatively thermophilic soil viruses

Abstract

1) Results of some pilot studies on the ecology of thermophilic phage in soil are reported.

2) The possible use of phage as a monitor for the activity of spore-forming bacteria in soil has been assessed.

3) It has been shown that the optimal temperature for the growth of "thermophilic" phage in soil is 45°C (or 37°) and not 55°. This fact, in conjunction with other data, suggests that most phage parasitic upon B. stearothermophilus are biochemically adapted to mesophily in soil rather than thermophily. It is suggested that all thermophilic viruses isolated for soil bacteria represent merely a mutant minority of a population of particles widely distributed with respect to heat tolerance.

4) 4 facultatively thermophilic viruses have been isolated for B. stearothermophilus T16.

5) The biological properties of 2 of these phages, D-S and D-6, have been determined.

6) The growth and lytic ability of phages D-S and D-6 have been compared at a mesophilic and thermophilic temperature.

7) The thermostability of phage D-S in broth and in dilute and strong salt solution has been determined. From this data some inferences concerning the nature of thermo-phily can be drawn.

8) The morphology of phage D-5 has been elucidated from an electron microscopic study

9) The problem of the origin of the genetic code is discussed in the light of known data.

10) It is postulated that ancient codes contained only 2 bases and coded for only a few amino acids.

11) It is suggested that the 2 primordial bases may have been U and I. Features of the code and its evolution are examined in terms of this theory.

12) Evidence for amino acid - polynucleotide interaction is reviewed.

13) Some selective advantages of circular DNA are described in terms of selected contemporary genomes.

14) It is postulated that DNA circularity played an obligatory role in the extension of gene data throughout evolution. The significance of repeat base sequences in eucaryote DNA is assessed in terms of this theory.

15) The role of viruses as gene vectors is discussed. It is postulated that the genomes of viruses and cellular species are in constant interaction and that this exchange of gene data has been not merely advantageous but necessary for the evolutionary process.