(2) were seen in other frames as distinct, after tumbling generated permuted genome. The reason is that non-permutation has been a change in orientation (not shown) and (3) were revealed for the previously found36 to cause laboratory propagation-generated view in Figure 4 via asymmetry of the lower two spots; asymmetry selection for retention of DNA length and, therefore, selection can also be generated by limited time resolution during motion. for retention of genes non-essential in the laboratory. That is to Seven of the eight spots (packaged DNAs) are at a distance from say, genome non-permutation has an anti-deletion activity that the cell surface consistent with attachment of a bacteriophage does not exist when the genome is permuted. particle via the tail tip or tail fibers. These considerations suggest that bacteriophages with non- The uppermost spot at the lower left, on the other hand, permuted genomes be preferred when selecting bacteriophages appeared to be attached to the cell surface at a distance too for managing bacteria, assuming that the “environment function small to be tail tip-to-cell surface attachment. This condition was only” genes, such as those observed here, are present. In addition, maintained during tumbling, although this resolution-limited long-genome bacteriophages should be preferred, because they spot was slightly separated from the surface in one orientation. are likely to have more “environment function only” genes than We conclude that bacteriophage 0305w8-36 is selected to bacteriophages with shorter genomes. Managing of bacteria is adsorb to its host by the tip of its tail, but that alternative essentially never done in laboratory conditions and is, therefore, patterns of adsorption can occur. We further conclude that the likely to be assisted by these genes. observed tail tip-tail tip dimerization (Fig. 3B and C) inhibits Biofilms. The laboratory propagation-based isolation of a initiation of infection by 0305w8-36. The significance of this reduced aggregation mutant suggests that, like presence of the latter conclusion is discussed in the next section. DNA translocation operon, the occurrence of propagation- Parenthetically, we note that seven of the bacteriophages of associated extensive aggregation4 has a selective advantage in the ©adsorb Figure 4 du2ring had adsorbed m0icrosc1opy. to the T2hisbacteLriophaagepanrticle host cell before the microscopy wdasnoet03s05w8-36 wild that it Bisparitof does not othe have frsamewcork in the laboratory. oifa ebiofilm The n(baccteriopehage possibility exists . began. But, the bacteriophage at the upper right appeared to that the selective advantage specific to the wild occurs while observed before stable adsorption and appeared to have diffused as biofilm component hypothesis), as suggested by thin sections into focus while it was attaching. Thus, we did not obtain infor- of human dental plaque (Introduction). Possible alternative mation about the events that occurred before stable attachment. selective advantages of aggregation include protection against This limitation exists, in general, unless the thermal motion of environmental damage, even in the absence of a biofilm. of solution so that thDepartiocles are tnracked obeforteand dduringisforbtacterriopihagbesin ubiofiltms. eDuri.ng biofilm formation, the bacteriophage particles is restricted to a thin enough zone The following previous observations suggest additional roles adsorption. recombination-dependent genomic DNA rearrangement is a mechanism for bacterial phase variation, i.e., for epigenetically Discussion changing the state of bacteria37 in a relatively short time period.38 The rearrangement is sometimes among DNA segments from one Genes for both bacteriophage-encoded DNA translocation and bacterial cell. But, it also is sometimes between the genome other functions non-essential in the laboratory. We have found of a cell and an externally derived DNA molecule, such as a that (1) a DNA translocation operon is in the bacteriophage plasmid, a transposon or a viral genome, as found for the 0305w8-36 genome and (2) this DNA translocation operon does filamentous Pseudomonas aeruginosa bacteriophage Pf4.39 A more not provide any selective advantage in the laboratory, the latter comprehensive review has been presented and theory has been as judged by the absence of a significant effect of deleting this developed to describe the distribution of bacterial states induced operon on either I or D. To our knowledge, a DNA translocation by DNA translocation, followed by recombination.40 Thus, the operon has not been previously documented for other character- DNA translocation operon of 0305w8-36 has potentially been ized bacteriophages, although at least bacteriophage SPO1 has a selected, in part, for promoting biofilm formation-associated similar operon, based on the analysis in Table 2 and Figure 2. bacterial phase variation. For the following reason, we conclude that DNA transloca- The possibility also exists that the genomes of aggregating, tion does have a function in the wild. A previous study8 has biofilm-forming bacteriophages are among the DNA molecules shown that no 0305w8-36 genes have characteristics that suggest translocated from cell-to-cell. These bacteriophages might even disuse-derived deterioration. The projected functionality of all propagate in a biofilm by DNA translocation, without the classical 0305w8-36 genes leads to the following conclusion. All laboratory bacteriophage particle. Propagation of this type is made efficient propagation generated/selected deletions are likely to compromise by the contact to each other of host cells. This concept of propagation in the environment. propagation-by-translocation is foreshadowed by theory that This conclusion is potentially significant for the use of defines a virus via its intracellular state, rather than its extra- bacteriophages to manage bacteria, because similar laboratory cellular state41,42 and that also sometimes postulates the evolution propagation-generated deletions will occur, although more of viruses from cells via parasitism that results in loss of func- slowly, even in the absence of selection for stability to elevated tions.42 Thus, the bacteriophage as biofilm component hypothesis temperature. For any given procedure of propagation, laboratory leads to the prediction that aggregating, biofilm-forming bacterio- propagation-generated deletions are expected to occur more phages in general and 0305w8-36 in particular have DNA trans- rapidly when the bacteriophage has (unlike 0305w8-36) a location operons that do not provide the advantage in the www.landesbioscience.com Bacteriophage 31