The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

Many studies on phage biology are based on isolation methods that may inadvertently select for narrow-host-range phages. Consequently, broad-host-range phages, whose ecological significance is largely unexplored, are consistently overlooked. To enhance research on such polyvalent phages, we developed two sequential multihost isolation methods and tested both culturedependent and culture-independent phage libraries for broad infectivity. Lytic phages isolated from activated sludge were capable of interspecies or even interorder infectivity without a significant reduction in the efficiency of plating (0.45 to 1.15). Two polyvalent phages (PX1 of the Podoviridae family and PEf1 of the Siphoviridae family) were characterized in terms of adsorption rate (3.54 ؋ 10 ؊10 to 8.53 ؋ 10 ؊10 ml/min), latent time (40 to 55 min), and burst size (45 to 99 PFU/cell), using different hosts. These phages were enriched with a nonpathogenic host (Pseudomonas putida F1 or Escherichia coli K-12) and subsequently used to infect model problematic bacteria. By using a multiplicity of infection of 10 in bacterial challenge tests, >60% lethality was observed for Pseudomonas aeruginosa relative to uninfected controls. The corresponding lethality for Pseudomonas syringae was ϳ50%. Overall, this work suggests that polyvalent phages may be readily isolated from the environment by using different sequential hosts, and this approach should facilitate the study of their ecological significance as well as enable novel applications.T he total bacteriophage (phage) population on Earth is estimated at 10 31 or more, making phages by far the most abundant biological entities on the planet (1, 2). As such, phages exert a significant influence over global biogeochemical cycles (3, 4) and are important drivers of bacterial diversity (5). Considering their ecological importance and value as a potential genetic resource, increasing our fundamental understanding of phage biology may facilitate the development of novel applications. However, research on phage diversity and ecology may be inadvertently limited by the use of biased isolation techniques that preferentially select for narrow-host-range phages (6, 7), while-broad hostrange phages are consistently overlooked.The classic approach to isolate and study phages is typically performed with high-density, nutrient-rich batch monocultures grown under planktonic conditions and most often results in the isolation of narrow-host-range phages (8)(9)(10).Previous studies have demonstrated the existence of polyvalent phages, among which the temperate phages P1 and Mu are the most studied (11, 12). However, their broad-host-range properties were discovered accidently, and few studies have explored methods for isolating and enriching polyvalent phages. Jensen et al. developed a multiple-host enrichment method to identify phages capable of interclass infectivity (13), and Bielke et al. used a sequential isolation method to isolate phages with intergenus infectivity (14). However, these phage isolation methods have...