Derepressed plasmids of incompatibility group I1 determine two different morphological forms of pilus

IncI₁ plasmids R144drd3 and R64drd11 determined thick, probably rigid pili in addition to the well-known thinner I₁ pili. Electron microscopy revealed that the thick I₁ pili often had large knobs at one end and were pointed at the other. They did not appear to act as receptors for any I-specific bacteriophages.     

Pathogenicity of Nocardia caviae,N. asteroides and N. brasiliensis

The pathogenicity ofNocardia caviae, N. asteroides andN. brasiliensis has been tested for white mice, guinea pigs and rabbits and chorio-allantoic membrane of the developing chick embryo. Altogether, 14 strains belonging to the 3Nocardia species originating from soil, human and animal sources in India or abroad were tested. All of them proved pathogenic though the degree of virulence varied from strain to strain. Incorporation of hog gastric mucin in the inoculum enhanced the virulence of all the 3Nocardia species for white mice.N. caviae strains were uniformly more virulent than those ofN. asteroides andN. brasiliensis.In the white mice inoculated intraperitoneally, a greater dissemination of the disease was apparent withN. caviae than withN. asteroides. Of the 6 strains ofN. caviae tested, 5 disseminated to the lung, 3 to the heart and 2 to the brain. InN. asteroides dissemination of the disease to the brain was observed with 2 of its 3 strains.N. brasiliensis showed no dissemination.N. caviae was found to be equally virulent for white mice, guinea pigs and rabbits. On the other hand,N. asteroides andN. brasiliensis were more virulent for white mice than for guinea pigs and rabbits. The lesions caused byN. caviae in mice, guinea pigs and rabbits persisted up to 4 weeks. In strong contrast to this the lesions due toN. asteroides andN. brasiliensis found in the guinea pigs and rabbits showed a strong tendency towards spontaneous clearance.Histologically, the lesions caused byN. caviae, N. asteroides andN. brasiliensis in mice, guinea pigs and rabbits were in the form of abscesses which showed an acute or chronic reaction. In the case ofN. caviae these abscesses showed both granules and freely dispersed cocco-bacillary bodies or filaments. As forN. asteroides it occurred in the form of cocco-bacillary bodies or filaments whereasN. brasiliensis consistently produced granules in the lesions.The lesions caused by the 3Nocardia species on the chorio-allantoic membrane of the developing chick embryo were in the form of abscesses which contained cocco-bacillary bodies and branching filaments but no granules.This forms a part of the thesis submitted by P.V.K. for Ph. D. degree, of the University of Delhi.     

Seasonal N uptake and N2fixation by common and adzuki bean at various spacings

The adzuki bean (Vigna angularis (Wild.) Ohwi and Ohashi) and common bean (Phaseolus vulgaris L.) have a high physiological demand for N. A 2-year field study was conducted to investigate the seasonal change of available soil N and symbiotic N₂ fixation usage. The beans were seeded at two densities, 22.2 plants m^–2 with a row spacing of 0.3 m and 11.1 plants m^–2 with a row spacing of 0.6 m. The amount of fixed N₂ in the shoot was calculated using the ¹⁵N natural abundance method. The common bean demonstrated low N₂ fixation and the ability to accumulate high levels of soil N. Soil nitrate under the common bean was continually absorbed. The adzuki bean, on the other hand, had a remarkable peak of N accumulation in the early reproductive stage. This was mainly due to N₂ fixation, though the soil nitrate level was high. Narrowing the plant row spacing increased the dry matter yield of both species, but the origin of the increased N differed between the species. For the first 77 DAP in 1999 (73 DAP in 2000) the N increase for both beans was due to both soil and atmospheric N₂. At harvest, though, the increase of N in common bean was mainly due to soil N, while that in adzuki bean was mainly due to atmospheric N₂. It can be concluded that the low symbiotic N₂ fixation ability of common bean was due to its high soil N uptake ability and constant N accumulation, which enabled an efficient soil N absorption. Adzuki bean absorbed N mainly for a short period and depended more on symbiotically fixed N₂ and, in contrast to common bean, left a high level of NO₃-N remaining in the soil after cropping.     

The binding of Pseudomonas aeruginosa pili to glycosphingolipids is a tip-associated event involving the C-terminal region of the structural pilin subunit

Pili are one of the adhesins of Pseudomonas aeruginosa that mediate adherence to epithelial cell-surface receptors. The pili of P. aeruginosa strains PAK and PAO were examined and found to bind gangliotetraosyl ceramide (asialo-GM₁) and, to a lesser extend, ll³N-acetylneuraminosylgangliotetraosyl ceramide (GM₁) in solid-phase binding assays. Asialo-GM₁, but not GM₁, inhibited both PAK and PAK pili binding to immobilized asialo-GM₁ on the microtitre plate. PAO pili competitively inhibited PAK pili binding to asialo-GM₁, suggesting the presence of a structurally similar receptor-binding domain in both pilus types. The interaction between asialo-GM₁ and pili occurs at the pilus tip as asialo-GM₁ coated colloidal gold only decorates the tip of purified pili. Three sets of evidence suggest that the C-terminal disulphide-bonded region of the Pseudomonas pilin is exposed at the tip of the pilus: (i) immunocytochemical studies indicate that P. aeruginosa pili have a basal-tip structural differentiation where the monoclonal antibody (mAb) PK3B recognizes an antigenic epitope displayed only on the basal ends of pili (produced by shearing) while the mAb PK99H, whose antigenic epitope resides in residues 134–140 (Wong et al., 1992), binds only to the tip of PAK pili; (ii) synthetic peptides, PAK(128–144)^ox-OH and PAO(128–144)^ox-OH, which correspond to the C-terminal disulphide-bonded region of Pseudomonas pilin are able to bind to asialo-GM₁ and inhibit the binding of pili to the glycolipid; (iii) PK99H was shown to block PAK pilus binding to asialo-GM₁ Monoclonal antibody PK3B had no effect on PAK pili binding to asialo-GM₁ Thus, the adherence of the Pseudomonas pilus to glycosphingolipid receptors is a tip-associated phenomenon Involving a tip-exposed C-terminal region of the pilin structural subunit.     

Polymorphism of the X-chromosome,Y-chromosome and autosomes in the Australian hopping mice,Notomys alexis,N. cervinus and N. fuscus (Rodentia,Muridae)

All three species of Notomys so far studied possess a diploid number of 48. Many elements in the karyotype of N. alexis are polymorphic due to variation in heterochromatin, but the variation is most marked in autosomal pair 1, which occurs in at least four forms, the X-chromosome, which occurs in three forms, and the Y-chromosome which occurs in many forms. N. cervinus is unique in the genus in possessing an entirely biarmed karyotype due mainly to the addition of heterochromatic short arms. The X-chromosome of N. cervinus occurs in three forms and the Y-chromosome in two forms. The karyotype of N. fuscus is mainly telocentric although two autosomal pairs are polymorphic due to pericentric inversions. The X- and Y-chromosomes both occur in two forms in N. fuscus. Chromosome measurements and C-banding show that most of the variation in the size and morphology of the sex-pair both within and between species is due to variation in constitutive heterochromatin.     

Pilus-facilitated adherence of Neisseria meningitidis to human epithelial and endothelial cells: modulation of adherence phenotype occurs concurrently with changes in primary amino acid sequence and the glycosylation status of pilin

Adherence of capsulate Neisseria meningitidis to endothelial and epithelial cells is facilitated in variants that express pili. Whereas piliated variants of N. meningitidis strain C311 adhered to endothelial cells in large numbers (<150 bacteria/cell), derivatives containing specific mutations that disrupt pilE encoding the pilin subunit were both non-piliated and failed to adhere to endothelial cells (<1 bacterium/ cell). In addition, meningococcal pili recognized human endothelial and epithelial cells but not cells originating from other animals. Variants of strain C311 were obtained that expressed pilins of reduced apparent M_r and exhibited a marked increase in adherence to epithelial cells. Structural analysis of pilins from two hyper-adherent variants and the parent strain were carried out by DNA sequencing of their pilE genes. Deduced molecular weights of pilins were considerably tower compared with their apparent M_r values on SDS-PAGE. Hyper-adherent pilins shared unique changes in sequence including substitution of Asn-113 for Asp-113 and changes from Asn-Asp-Thr-Asp to Thr-Asp-Ala-Lys at residues 127-130 in mature pilin. Asn residues 113 and 127 of‘parental’pilin both form part of the typical eukaryotic N-glycosylation motif Asn-X-Ser/Thr and could potentially be glycosylated post-translationally. The presence of carbohydrate on pilin was demonstrated and when pilins were deglycosylated, their migration on SDS-PAGE increased, supporting the notion that variable glycosylation accounts for discrepancies in apparent and deduced molecular weights. Functionally distinct pilins produced by two fully piliated variants of a second strain (MC58) differed only in that the putative glycosylation motif Asn-60-Asn-61-Thr-62 in an adherent variant was replaced with Asp-60-Asn-61-Ser-62 in a non-adherent variant. Fully adherent backswitchers obtained from the non-adherent variant always regained Asn-60 but retained Ser-62. We propose, therefore, that functional variations in N. meningitidis pili may be modulated in large part by primary amino acid sequence changes that ablate or create N-linked glycosylation sites on the pilin subunit.     

The Nanomechanical Properties of Lactococcus lactis Pili Are Conditioned by the Polymerized Backbone Pilin

Pili produced by Lactococcus lactis subsp. lactis are putative linear structures consisting of repetitive subunits of the major pilin PilB that forms the backbone, pilin PilA situated at the distal end of the pilus, and an anchoring pilin PilC that tethers the pilus to the peptidoglycan. We determined the nanomechanical properties of pili using optical-tweezers force spectroscopy. Single pili were exposed to optical forces that yielded force-versus-extension spectra fitted using the Worm-Like Chain model. Native pili subjected to a force of 0–200 pN exhibit an inextensible, but highly flexible ultrastructure, reflected by their short persistence length. We tested a panel of derived strains to understand the functional role of the different pilins. First, we found that both the major pilin PilB and sortase C organize the backbone into a full-length organelle and dictate the nanomechanical properties of the pili. Second, we found that both PilA tip pilin and PilC anchoring pilin were not essential for the nanomechanical properties of pili. However, PilC maintains the pilus on the bacterial surface and may play a crucial role in the adhesion- and biofilm-forming properties of L. lactis.     

Some Properties of the Pili of Corynebacterium renale

Some properties of the pili of the gram-positive bacteria Corynebacterium renale were described. A relationship was found between the morphological features of pili and the types of C. renale. Strains of types I and III usually possessed a small number of pili, whereas those of type II possessed numerous pili. Thick and long bundles of pili characteristic of C. renale were frequently observable in type II strains. Piliation of C. renale was stable under various cultural conditions. No ability to agglutinate red blood cells was demonstrated by piliated strains of C. renale. Pili were isolated from the cells of C. renale and studied serologically by immunodiffusion. The pili of a type II strain were serologically identical with the pili of another type II strain but not with those of the strains belonging to types I and III. The pili were serologically distinct from the cell wall. The pili were broken into short pieces by boiling, but their antigenicity was increased after boiling.     

N and P Cycling in Tanzanian Humid Savanna: Influence of Herbivores, Fire, and N2-Fixation

Availabilities of nitrogen (N) and phosphorus (P) have a strong influence on plant growth and the species composition of savannas, but it is not clear how these availabilities depend on factors such as fire, N₂-fixation, and activities of wild herbivores and cattle. We quantified soil N and P availabilities in various ways (extractable pools, mineralization, resin adsorption) along vegetation gradients within a recently abandoned cattle ranch and a former game reserve in Tanzania (both areas now part of the Saadani National Park). We also assessed annual N and P balances to evaluate how long-term availabilities of N and P are affected by large herbivores, symbiotic N₂-fixation, and fire. The results show that cattle ranching led to a spatial re-distribution of nutrients, with the local accumulation of P being stronger and more persistent than that of N. In the former game reserve, intensively grazed patches of short grass tended to have elevated soil N and P availabilities; however, because quantities of nutrients removed through grazing exceeded returns in dung and urine, the nutrient balances of these patches were negative. In dense Acacia stands, N₂-fixation increased N availability and caused a net annual N input. Fire was the major cause for nutrient losses from tallgrass savanna, and estimated N inputs from the atmosphere and symbiotic N₂-fixation were insufficient to compensate for these losses. Our results call into question the common assumption that N budgets in annually burned savanna are balanced; rather, these ecosystems are a mosaic of patches with both N enrichment and impoverishment, which vary according to the vegetation type.     

Antigenic variation of pilin regulates adhesion of Neisseria meningitidis to human epithelial cells

Pili have been shown to play an essential role in the adhesion of Neisseria meningitidis to epithelial cells. However, among piliated strains, both inter- and intrastrain variability exist with respect to their degree of adhesion to epithelial cells in vitro (Virji et al., 1992). This suggests that factors other than the presence of pili per se are involved in this process. The N. meningitidis pilin subunit undergoes extensive antigenic variation. Piliated low- and high-adhesive derivatives of the same N. meningitidis strain were selected and the nucleotide sequence of the pilin gene expressed in each was determined. The highly adhesive derivatives had the same pilin sequence. The alleles encoding the pilin subunit of the low-adhesive derivatives were completely different from the one found in the high-adhesive isolates. Using polyclonal antibodies raised against one hyperadhesive variant, it was confirmed that the low-adhesive piliated derivatives expressed pilin variants antigenically different from the highly adhesive strains. The role of antigenic variation in the adhesive process of N. meningitidis was confirmed by performing allelic exchanges of the pilE locus between low-and high-adhesive isolates. Antigenic variation has been considered a means by which virulent bacteria evade the host immune system. This work provides genetic proof that a bacterial pathogen, N. meningitidis, can use antigenic variation to modulate their degree of virulence.     

Studies on the availability of Azolla N and urea N for rice growth using 15N

Field experiments (20 m² plots) were conducted to compare Azolla and urea as N sources for rice (Oryza sativa L.) in both the wet and dry seasons. Parallel microplot (1 m²) experiments were conducted using ¹⁵N. A total of approximately 60 kg N ha^-1 was applied as urea, Azolla, or urea plus Azolla. Urea or Azolla applied with equal applications of 30 kg N ha^-1 at transplanting (T) and at maximum tillering (MT) were equally effective for increasing rice grain yields in both seasons. Urea at 30 kg N ha^-1 at T and Azolla 30 kg N ha^-1 at MT was also equally effective. Urea applied by the locally recommended best split (40 kg at T and 20 kg at MT) gave a higher yield in the wet season, but an equal yield in the dry season. The average yield increase was 23% in the wet season, and 95% in the dry season. The proportion of the N taken up by the rice plants which was derived from urea (%NdfU) or Azolla (%NdfAz) was essentially identical for the treatments receiving the same N split. Recovery of ¹⁵N in the grain plus straw was also very similar. Positive yield responses to residual N were observed in the succeeding rice crop following both the wet and dry seasons, but the increases were not always statistically significant. Recovery of residual ¹⁵N ranged from 5.5 to 8.9% for both crops in succeeding seasons. Residual recovery from the urea applications was significantly higher than from Azolla in the crop succeeding the dry season crop. Azolla was equally effective as urea as an N source for rice production on a per kg N basis.     

Pili of a Vibrio cholerae O139

The pili of a strain of Vibrio cholerae O139 were purified and characterized. They were morphologically, electrophoretically and immunologically indistinguishable from the pili with 16 kDa subunit protein of V. cholerae O1. All 22 strains of V. cholerae O139 examined possessed the pili. The pili were different in hemagglutination inhibition pattern from V. cholerae O1 16K pili.     

Ultrastructure of Spermatozoa of the Yellow-rumped Elephant Shrew Rhynchocyon chrysopygus (Mammalia: Macroscelidea) and the Phylogeny of Elephant Shrews

The spermatozoa of the yellow-rumped elephant shrew Rhynchocyon chrysopygus have a spatulate head, tapering to a rounded proximal end with a marked narrowing at the equatorial segment. There is a short pointed subacrosome and about 24 gyres of mitochondria were found in the midpiece. The coarse fibres surrounding the axonome show enlargement of numbers 1, 5, 6 and 9. The spermatozoa of all genera of elephant shrews have now been described allowing comparisons among them. R. chrysopygus has the shortest spermatozoon and the fewest number of gyres. The pointed subacrosome is considered an ancestral feature and is shared with Macroscelides. The enlargement of coarse fibres 1, 5, 6 and 9 is found in several groups including members of the archonta and paenungulates, both postulated as being related to elephant shrews.     

Unfolding and refolding properties of S pili on extraintestinal pathogenic Escherichia coli

S pili are members of the chaperone-usher-pathway-assembled pili family that are predominantly associated with neonatal meningitis (S_II) and believed to play a role in ascending urinary tract infections (S_I). We used force-measuring optical tweezers to characterize the intrinsic biomechanical properties and kinetics of S_II and S_I pili. Under steady-state conditions, a sequential unfolding of the layers in the helix-like rod occurred at somewhat different forces, 26 pN for S_II pili and 21 pN for S_I pili, and there was an apparent difference in the kinetics, 1.3 and 8.8 Hz. Tests with bacteria defective in a newly recognized sfa gene (sfaX _II) indicated that absence of the sfaX _II gene weakens the interactions of the fimbrium slightly and decreases the kinetics. Data of S_I are compared with those of previously assessed pili primary associated with urinary tract infections, the P and type 1 pili. S pili have weaker layer-to-layer bonds than both P and type 1 pili, 21, 28 and 30 pN, respectively. In addition, the S pili kinetics are ~10 times faster than the kinetics of P pili and ~550 times faster than the kinetics of type 1 pili. Our results also show that the biomechanical properties of pili expressed ectopically from a plasmid in a laboratory strain (HB101) and pili expressed from the chromosome of a clinical isolate (IHE3034) are identical. Moreover, we demonstrate that it is possible to distinguish, by analyzing force-extension data, the different types of pili expressed by an individual cell of a clinical bacterial isolate.     

Physiological responses of two moss species to the combined stress of water deficit and elevated N deposition (II): Carbon and nitrogen metabolism

Nitrogen (N) deposition levels and frequencies of extreme drought events are increasing globally. In efforts to improve understanding of plants' responses to associated stresses, we have investigated responses of mosses to drought under elevated nitrogen conditions. More specifically, we exposed Pogonatum cirratum subsp. fuscatum and Hypnum plumaeforme to various nitrate (KNO₃) or ammonium (NH₄Cl) treatments, with and without water deficit stress and monitored indices related to carbon (C) and N metabolism both immediately after the stress and after a short recovery period. The results show that N application stimulated both C and N assimilation activities, including ribulose‐1,5‐bisphosphate carboxylase, glutamine synthetase/glutamate synthase (GS/GOGAT), and glutamate dehydrogenase (GDH) activities, while water deficit inhibited C and N assimilation. The mosses could resist stress caused by excess N and water deficit by increasing their photorespiration activity and proline (Pro) contents. However, N supply increased their sensitivity to water stress, causing sharper reductions in C and N assimilation rates, and further increases in photorespiration and Pro contents, indicating more serious oxidative or osmotic stress in the mosses. In addition, there were interspecific differences in N assimilation pathways, as the GS/GOGAT and GDH pathways were the preferentially used ammonium assimilation pathways in P. cirratum and H. plumaeforme when stressed, respectively. After rehydration, both mosses exhibited overcompensation effects for most C and N assimilation activities, but when supplied with N, the activities were generally restored to previous levels (or less), indicating that N supply reduced their ability to recover from water deficit stress. In conclusion, mosses can tolerate a certain degree of water deficit stress and possess some resilience to environmental fluctuations, but elevated N deposition reduces their tolerance and ability to recover.     

Expression of hemagglutination is dependent on environmental factors and bacterial concentration ofEscherichia coli andKlebsiella pneumoniae

Hemagglutination of human type A and guinea pig erythrocytes showed that both mannose-sensitive and mannose-resistant adhesive mechanisms (pili) were detectable in broth cultures ofEscherichia coli while only a mannose-sensitive mechanism (type 1 pili) was noted withKlebsiella pneumoniae. The degree of hemagglutination was shown to be related to differences in erythrocytes, bacterial concentration, and growth media constituents.Escherichia coli grown in human urine produced both types of hemagglutinins, whileK. pneumoniae cultured in urine continued to express only a mannose-sensitive hemagglutinin.     

Evaluation of the availability ofAzolla-N and urea-N to rice using15N

Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha^–1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two¹⁵N methods. In the first,Azolla caroliniana (Willd.) was labelled with¹⁵N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha^–1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of¹⁵N-urea was applied separately or in combination with either 250 or 330 kg N ha^–1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha^–1 to 430 kg N ha^–1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using¹⁵N-labelledAzolla, this method is preferable to the¹⁵N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at –20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla.     

Identification and characterization of pilG, a highly conserved pilus-assembly gene in pathogenic Neisseria

Expression of type IV pili appears to be a requisite determinant of infectivity for the strict human pathogens Neisseria gonorrhoeae and Neisseria meningitidis. The assembly of these colonization factors is a complex process. This report describes a new pilus-assembly gene, pilG, that immediately precedes the gonococcal (Gc) pilD gene encoding the pre-pilin leader peptidase. The nucleotide sequence of this region revealed a single complete open reading frame whose derived polypeptide displayed significant identities to the pilus-assembty protein PilC of Pseudomonas aeruginosa and other polytopic integral cytoplasmic membrane constituents involved in protein export and competence. A unique polypeptide of M_r 38kDa corresponding to the gene product was identified. A highly related gene and flanking sequences were cloned from a group E polysaccharide-producing strain of N. meningitidis (Mc). The results indicate that the pilG genes and genetic organization at these loci in Gc and Me are extremely conserved. Hybridization studies strongly suggest that pilG-related genes exist in commensal Neisseria species and other species known to express type IV pili. Defined genetic lesions were created by using insertional and transposon mutagenesis and moved into the Gc and Me chromosomes by allelic replacement. Chromosomal pilG insertion mutants were devoid of pili and displayed dramatically reduced competence for transformation. These findings could not be ascribed to pilin-gene alterations or to polarity exerted on pilD expression. The results indicated that PilG exerts its own independent role in neisserial pilus biogenesis.     

Natural abundance of 15N in actinorhizal plants and nodules

Substantial enrichment of some plant parts in ¹⁵N relative to the rest of the plant is unusual, but is found in the nitrogen-fixing nodules of many legumes. A range of actinorhizal plants was surveyed to determine whether the nodules of any of them are also substantially enriched in ¹⁵N. The nonlegume Parasponia, nodulated by a rhizobium, was also included. Four of the actinorhizal genera and Parasponia were grown in N-free culture, and three actinorhizal genera were collected from the field. Nodules of Parasponia, Casuarina and Alnus were¹⁵N enriched relative to other plant parts, but only Parasponia approached the degree of enrichment found in some legume nodules. The nodules of Datisca, Myrica, Elaeagnus, Shepherdia, and Coriaria were depleted in ¹⁵N. Thus many actinorhizal nodules are depleted in ¹⁵N compared to other plant parts and enrichment is modest when it does occur. Whole plant ¹⁵N content (¹⁵N) in four actinorhizal plants and Parasponia showed a relatively narrow range of –1.41 to –1.90. Hence regardless of the degree of nodule enrichment or depletion, whole plant ¹⁵N content appears to vary little in plants grown in N-free culture.     

Adsorption of bacteriophages specific for Pseudomonas aeruginosa R factors RP1 and R1822

Short, thick pili were found by electron microscopy on bacteria carrying the P group drug resistance plasmids RP1 and R1822. The R1822-specific phage PRR1 was seen to adsorb to the bases of the pili. Three RP1-specific phages, one filamentous (Pf3), and two with very thick capsids (PR3, PR4), were seen to attach all around the surface of $\text{P. aeruginosa}$ cells, and were thought to be somatic, since pilus phages appear to be strictly polar on this species. PR3 and PR4 also lysed a strain of $\text{E. coli}$ containing an N group plasmid, suggesting a relationship between the N and P group plasmids.