Survival of the temperate actinophage φC31 and Streptomyces lividans in soil and the effects of competition and selection on lysogens

Abstract

Lysogenic infections were demonstrated m microcosms of sterde soil Inoculated with Streptomyces hvtdans and the thC31 derwatwe, KC301, in free state or via lysogemzed hosts Intermittent SOil mixing caused liberation of KC301 due to lysis of germinating lysogemzed and uninfected spores The presence of lysogentzed hosts ensured that KC301 was maintained at a constant density The lysogen S hwdans TK24 (KC301) achieved a population density lower than that of tts non-lysogemzed counterpart. Thiostrepton in the sod did not select for the thlostrepton resistance gene of KC301 The long-term survwal tn sod of a temperate actmophage was demonstrated.

Phage-host interactions in soil

“…The results of Pantastico-Caldas et al [39] suggested that the presence of the virulent Bacillus subtilis phage, SP10C, in soil resulted in a decrease in the host population level by one order of magnitude. The lytic action of the temperate actinophage KC301 appeared to have no numerical impact on streptomycete populations in sterile and nonsterile soil [40][41][42]. Where the infection efficiency of KC301 was sufficiently high to retard vegetative growth of Streptomyces lividans in sterile soil, sporulation compensated for the reduction in propagule numbers (Fig.…”

“…Lysogenic conversion can also confer pathogenicity, for example the prophage of lysogenic Corynebacterium diptheriae strains encodes the toxins enabling establishment of bacterial infection in hosts [7]. Engineered phages containing antibiotic and heavy metal resistance determinants [40,41,[44][45][46] may be advantageous to lysogenic hosts in selective environments [42].…”

“…In natural environments, the rates of prophage induction are usually very low [42,47] probably resulting in a negligible impact on host populations. This and the large amounts of lysozyme released at prophage induction [47] means that reversion to the lytic cycle by prophages constitutes a potential 'weapon' for lysogenic popula-tions, whereby released lysozyme would attack bacteria sensitive to both the phage and lysozyme in a particular niche and provide additional resources to the lysogens in the form of liberated nutrients.…”

“…Lysogenic conversion as shown by lysogenic infections of inoculated hosts in soil by temperate phages containing genetic markers [40][41][42]45,46] is likely to be a far more frequent occurrence in soil in comparison to transduction. This is because all of the daughter progeny of a lysing cell will contain the genetic information to be expressed by the prophages of subsequent lysogenic infections.…”

“…Growth of hosts is shown by increases in total (n) and spore (in) counts. Temperate (*) and virulent (o) phages were detected 24 h after initial wetting of soil(Marsh and Wellington, 1993. Unpublished data),…”