DNA-repair potential of Halomonas spp. from the Salt Plains Microbial Observatory of Oklahoma

The Great Salt Plains (GSP), an unvegetated, barren salt flat that is part of the Salt Plains National Wildlife Refuge near Cherokee, Oklahoma, is the site of the Salt Plains Microbial Observatory. At the GSP the briny remains of an ancient sea rise to the surface, evaporate under dry conditions, and leave crusts of white salt. Adaptation to this environment requires development of coping mechanisms providing tolerance to desiccating conditions due to the high salinity, extreme temperatures, alkaline pH, unrelenting exposure to solar UV radiation, and prevailing winds. Several lines of evidence suggest that the same DNA repair mechanisms that are usually associated with UV light or chemically induced DNA damage are also important in protecting microbes from desiccation. Because little is known about the DNA repair capacity of microorganisms from hypersaline terrestrial environments, we explored the DNA repair capacity of microbial isolates from the GSP. We used survival following exposure to UV light as a convenient tool to assess DNA repair capacity. Two species of Halomonas (H. salina and H. venusta) that have been isolated repeatedly from the GSP were chosen for analysis. The survival profiles were compared to those of Escherichia coli, Pseudomonas aeruginosa, and Halomonas spp. from aquatic saline environments. Survival of GSP organisms exceeded that of the freshwater organism P. aeruginosa, although they survived no better than E. coli. The GSP isolates were much more resistance to killing by UV than were the aquatic species of Halomonas reported in the literature [Martin et al. (2000) Can J Microbiol 46:180-187]. Unlike E. coli, the GSP isolates did not appear to have an inducible, error-prone repair mechanism. However, they demonstrated high levels of spontaneous mutation.

Environmental bacteriophage-host interactions: factors contribution to natural transduction

Over the past two decades the potential for the exchange of bacterial genes in natural environments through transduction (bacteriophage-mediated gene transfer) has been well established. Studies carried out by various laboratories throughout the world have demonstrated that both chromosomal and plasmid DNA can be successfully transduced in natural environments ranging from sewer plants to rivers and lakes. Transduction has been shown to take place in the gills of oysters and the kidneys of mice. Model studies have demonstrated the ability of transduction to maintain genetic material in bacterial gene pools that would otherwise be lost because of negative fitness. Thus, transduction may affect the course of bacterial evolution. Identification of natural transduction has led to the investigation of the dynamics of bacteriophage host interactions in natural aquatic environments and to the exploration of various environmental factors that affect virus-host interactions. Two important environmental factors which affect virus-host interactions are the metabolic state of the host and the exposure of the host to DNA-damaging stresses such as solar UV light. Recent researches on these two areas of virus-host relationships are reviewed.

Genetic diversity among Arthrobacter species collected across a heterogeneous series of terrestrial deep-subsurface sediments as determined on the basis of 16S rRNA and recA gene sequences

This study was undertaken in an effort to understand how the population structure of bacteria within terrestrial deep-subsurface environments correlates with the physical and chemical structure of their environment. Phylogenetic analysis was performed on strains of Arthrobacter that were collected from various depths, which included a number of different sedimentary units from the Yakima Barricade borehole at the U.S. Department of Energy's Hanford site, Washington, in August 1992. At the same time that bacteria were isolated, detailed information on the physical, chemical, and microbiological characteristics of the sediments was collected. Phylogenetic trees were prepared from the 39 deep-subsurface Arthrobacter isolates (as well as 17 related type strains) based on 16S rRNA and recA gene sequences. Analyses based on each gene independently were in general agreement. These analyses showed that, for all but one of the strata (sedimentary layers characterized by their own unifying lithologic composition), the deep-subsurface isolates from the same stratum are largely monophyletic. Notably, the layers for which this is true were composed of impermeable sediments. This suggests that the populations within each of these strata have remained isolated under constant, uniform conditions, which have selected for a particular dominant genotype in each stratum. Conversely, the few strains isolated from a gravel-rich layer appeared along several lineages. This suggests that the higher-permeability gravel decreases the degree of isolation of this population (through greater groundwater flow), creating fluctuations in environmental conditions or allowing migration, such that a dominant population has not been established. No correlation was seen between the relationship of the strains and any particular chemical or physical characteristics of the sediments. Thus, this work suggests that within sedimentary deep-subsurface environments, permeability of the deposits plays a major role in determining the genetic structure of resident bacterial populations.

Response of a Pseudomonas aeruginosa biofilm community to DNA-damaging chemical agents

Pseudomonas aeruginosa strain RM4440 carries a plasmid-borne fusion of the P. aeruginosa recA gene promoter to a promoterless lux operon from Vibrio fisheri. We tested the response of RM4440 in a biofilm to exposure to a 1-h pulse of each of 17 chemicals known to be toxic to bacteria and other organisms. The induction of light produced from the recA-lux fusion present in RM4440 proved to be sensitive and specific for DNA-damaging chemicals when included in a biofilm environment. This study demonstrates the potential usefulness of this construct for in situ investigation of bacterial communities.

Study of the response of a biofilm bacterial community to UV radiation

We have developed a bioluminescent whole-cell biosensor that can be incorporated into biofilm ecosystems. RM4440 is a Pseudomonas aeruginosa FRD1 derivative that carries a plasmid-based recA-luxCDABE fusion. We immobilized RM4440 in an alginate matrix to simulate a biofilm, and we studied its response to UV radiation damage. The biofilm showed a protective property by physical shielding against UV C, UV B, and UV A. Absorption of UV light by the alginate matrix translated into a higher survival rate than observed with planktonic cells at similar input fluences. UV A was shown to be effectively blocked by the biofilm matrix and to have no detectable effects on cells contained in the biofilm. However, in the presence of photosensitizers (i.e., psoralen), UV A was effective in inducing light production and cell death. RM4440 has proved to be a useful tool to study microbial communities in a noninvasive manner.

A Pseudomonas aeruginosa biosensor responds to exposure to ultraviolet radiation

We fused the Pseudomonas aeruginosa recA promoter to a promoterless Vibrio fisheri lux operon. This recA-lux fusion (pMOE15) was introduced into wild-type P. aeruginosa strain FRD1 and recA expression was monitored by measuring 490-nm light production. The RM4440 strain responded to increasing doses of ultraviolet radiation by an increase in its bioluminescence. RM4440 has the potential to be useful as a biosensor for the presence of DNA-damaging agents in the environment.

Ecomycins, unique antimycotics from Pseudomonas viridiflava

A novel family of peptide antimycotics, termed ecomycins, is described from Pseudomonas viridiflava, a plant-associated bacterium. Ecomycins B and C have molecular masses of 1153 and 1181. They contain equimolar amounts of a beta hydroxyaspartic acid, homoserine, threonine, serine, alanine, glycine and one unknown amino acid. Fatty acids were detectable after hydrolysis, methylation and gas chromatography and mass spectroscopy. The ecomycins have significant bioactivities against a wide range of human and plant pathogenic fungi. The minimum inhibitory concentration values for ecomycin B were 4.0 micrograms ml-1 against Cryptococcus neoformans and 31 micrograms ml-1 against Candida albicans. Pseudomonas viridiflava also produces what appears to be syringotoxin, an antifungal lipopeptide previously described from Ps. syringae.

Construction of a recA mutant of Burkholderia (formerly Pseudomonas), cepacia

A recA mutant was constructed of a soil isolate of Burkholderia cepacia, strain ATCC 17616. Prior to mutagenesis, the recA gene was cloned from this strain by its ability to complement the methyl methanesulfonate sensitivity of an Escherichia coli recA mutant. Sequence analysis of the strain showed high sequence similarity (94% nucleic acid and 99% amino acid identity) with the recA gene previously cloned from a clinical isolate of B. cepacia, strain JN25. The subcloned recA gene from B. cepacia ATCC 17616 restored UV resistance and recombination proficiency to recA mutants of E. coli and Pseudomonas aeruginosa, as well as restoring the ability of D3 prophages to be induced to lytic growth from a RecA- strain of P. aeruginosa. The recA mutant of B. cepacia ATCC 17616 was constructed by lambda-mediated Tn5 mutagenesis of the cloned recA gene in E. coli, followed by replacement of the Tn5-interrupted gene for the wild-type allele in the chromosome of B. cepacia by marker exchange. The RecA- phenotype of the mutant was demonstrated by the loss of UV resistance as compared to the parental strain. Southern hybridization analysis of chromosomal DNA from the mutant indicated the presence of Tn5 in the recA gene, and the location of the Tn5 insertion in the recA allele was identified by nucleotide sequence analysis. A test using the recA mutant to see if acquired resistance to D-serine toxicity in B. cepacia might be a result of RecA-mediated activities proved negative; nevertheless, RecA activity potentially contributes to the overall genomic plasticity of B. cepacia and a recA mutant will be useful in bioengineering of this species.

Characterization of a Vascular Wilt of Erythroxylum coca Caused by Fusarium oxysporum f. sp. erythroxyli Forma Specialis Nova

A new forma specialis of Fusarium oxysporum (F. oxysporum f. sp. erythroxyli) pathogenic to Erythroxylum coca and E. novogranatense is described. The pathogen was isolated from the vascular tissue of diseased plants from an Erythroxylum plantation in Hawaii. This pathogen causes vascular wilt symptoms and death in both E. coca and E. novogranatense plants as soon as 7 weeks after soil infestation. The pathogenicity of seven isolates from the affected field was determined in field and growth-chamber studies. Genetic variation was not detected among the seven Hawaiian isolates, using arbitrarily primed polymerase chain reaction. The seven isolates could be differentiated from a strain isolated from a diseased E. coca plant from South America. All Hawaiian isolates and the South American isolate belonged to a single vegetative compatibility group.

Nurse call systems: impact on nursing performance

Outcries for health care reform and more cost-effective patient care have motivated many organizations to examine routine unit activities. The article reports a study that used a descriptive design to examine nursing utilization of and satisfaction with nurse call systems in two large metropolitan hospitals. Findings revealed that nurse call system features such as the ability of unit secretaries to receive and screen patient calls reduced unnecessary nurse interruptions, saved actual nursing time, and enabled some nurses to begin preparing to meet patients, needs before entering their rooms. Problems with the nurse call system identified from the data were the sound quality of the transmission, inability to locate the nurse, inability to prioritize and confirm calls, and inability to speak directly to patients and staff.

A Continuous Culture Model To Examine Factors That Affect Transduction among Pseudomonas aeruginosa Strains in Freshwater Environments

Transduction among Pseudomonas aeruginosa strains was observed in continuous cultures operated under environmentally relevant generation times, cell densities, and phage-to-bacterium ratios, suggesting its importance as a natural mechanism of gene transfer. Transduction was quantified by the transfer of the Tra(sup-) Mob(sup-) plasmid Rms149 from a plasmid-bearing strain to an F116 lysogen that served as both the recipient and source of transducing phages. In control experiments in which transduction was prevented, there was a reduction in the phenotype of the mock transductant over time. However, in experiments in which transduction was permitted, the proportion of transductants in the population increased over time. These data suggest that transduction can maintain a phenotype for an extended period of time in a population from which it would otherwise be lost. Changes in the numbers of transductants were analyzed by a two-part mathematical model, which consisted of terms for the selection of the transductant's phenotype and for the formation of new transductants. Transduction rates ranged from 10(sup-9) to 10(sup-6) per total viable cell count per ml per generation and increased with both the recipient concentration and the phage-to-bacterium ratio. These observations indicate an increased opportunity for transduction to occur when the interacting components are in greater abundance.

Effects of Suspended Particulates on the Frequency of Transduction among Pseudomonas aeruginosa in a Freshwater Environment

Transduction has been shown to play a significant role in the transfer of plasmid and chromosomal DNA in aquatic ecosystems. Such ecosystems contain a multitude of environmental factors, any one of which may influence the transduction process. It was the purpose of this study to show how one of these factors, particulate matter, affects the frequency of transduction. In situ transduction rates were measured in lake water microcosms containing either high or low concentrations of particulate matter. The microcosms were incubated in a freshwater lake in central Oklahoma. Transduction frequencies were found to be enhanced as much as 100-fold in the presence of particulates. Our results suggest that aggregations of bacteriophages and bacterial cells are stimulated by the presence of these suspended particulates. This aggregation increases the probability of progeny phages and transducing particles finding and infecting new host cells. Consequently, both phage production and transduction frequencies increase in the presence of particulate matter.

Transduction of a freshwater microbial community by a new Pseudomonas aeruginosa generalized transducing phage, UT1

A pseudolysogenic, generalized transducing bacteriophage, UT1, isolated from a natural freshwater habitat, is capable of mediating the transfer of both chromosomal and plasmid DNA between strains of Pseudomonas aeruginosa. Several chromosomal alleles from three different P. aeruginosa strains were found to transduce at frequencies from 10(-8) to 10(-10) transductants per PFU at multiplicities of infection (MOI) between 0.1 and 1. Transduction frequencies of certain alleles increased up to 1000-fold as MOIs were decreased to 0.01. UT1 is also capable of transducing plasmid DNA to indigenous populations of microorganisms in natural lake-water environments. Data obtained in this study suggest that environmentally endemic bacteriophages such as UT1 are formidable transducers of naturally occurring microbial communities. It should be possible to develop model systems to test transduction in freshwater environments using components derived exclusively from these environments.

Evidence for phage-mediated gene transfer among Pseudomonas aeruginosa strains on the phylloplane

As the use of genetically engineered microorganisms for agricultural tasks becomes more frequent, the ability of bacteria to exchange genetic material in the agricultural setting must be assessed. Transduction (bacterial virus-mediated horizontal gene transfer) is a potentially important mechanism of gene transfer in natural environments. This study investigated the potential of plant leaves to act as surfaces on which transduction can take place among microorganisms. Pseudomonas aeruginosa and its generalized transducing bacteriophage F116 were used as a model system. The application of P. aeruginosa lysogens of F116 to plant leaves resulted in genetic exchange among donor and recipient organisms resident on the same plant. Transduction was also observed when these bacterial strains were inoculated onto adjacent plants and contact was made possible through high-density planting.

IncN plasmids mediate UV resistance and error-prone repair in Pseudomonas aeruginosa PAO

While it seems likely that the ability to induce the expression of recA-controlled genes is nearly universal among the eubacteria, the expression of plasmid-borne ultraviolet (UV-resistance and mutagenesis genes seems to be species-dependent in a complex fashion. Some plasmids encoding UV-resistance and mutagenesis functions only express these phenotypes in a select number of bacterial species. Several UV-resistance plasmids that express these functions in Escherichia coli are either unstable or simply do not express the UV-resistance-mutagenesis phenotype in Pseudomonas aeruginosa. In order to clarify the role of these plasmids in microbial ecology, we have undertaken a study of the ability of the well-characterized UV-resistance IncN plasmids pKM101 and R46 to express the UV-resistance phenotype in P. aeruginosa. In addition, we have examined the IncP plasmids RP4 and R68.45, observed to confer a UV-resistant phenotype upon Myxococcus xanthus, for the ability to express this phenotype in P. aeruginosa. Our experiments reveal that while pKM101 and R46 transfer to P. aeruginosa at a very low frequency, these plasmids, once transferred, are maintained and clearly support the expression of the UV-resistance and mutagenesis phenotype observed in E. coli. Studies of plasmids R68.45 and RP4 in P. aeruginosa revealed that they do not express UV-resistance functions in this species. UV-resistance plasmids may play an important role in the natural ecology of bacterial habitats exposed to solar radiation or to various DNA-damaging natural and man-made chemicals.

Application of DNA probes to analysis of bacteriophage distribution patterns in the environment

Radiolabeled bacteriophage DNA probes have been used in this study to determine the distribution of Pseudomonas aeruginosa-infecting bacteriophages in natural samples of lake water, sediment, soil, and sewage. The sensitivity of detection of bacteriophage with the DNA probes was between 10(3) and 10(4) PFU and 10(6) to 10(7) CFU of lysogenized bacteria detectable with a homologous phage DNA probe. Analyses of environmental samples suggest that up to 40% of P. aeruginosa in natural ecosystems contain DNA sequences homologous to phage genomes. By using different bacteriophage DNA probes, the diversity of the bacteriophage population in sewage was estimated to be higher than that in other natural samples. The indication that transducing phages and prophages are widely distributed in the Pseudomonas populations investigated has considerable implications for the frequency of natural gene transfer by transduction and of lysogenic conversion of host bacteria in natural ecosystems.

Characterization of stress-responsive behavior in Pseudomonas aeruginosa PAO: isolation of Tn3-lacZYA fusions with novel damage-inducible (din) promoters

Although the pervasive soil and water microorganism Pseudomonas aeruginosa demonstrates heightened sensitivity to UV radiation, this species possesses a recA gene that, based on structural and functional properties, could mediate a DNA damage-responsive regulon similar to the SOS regulon of Escherichia coli. To determine whether P. aeruginosa encodes such stress-inducible genes, the response of P. aeruginosa to DNA-damaging agents including far-UV radiation (UVC) and the quinolone antimicrobial agent norfloxacin was investigated by monitoring the expression of fusions linking P. aeruginosa promoters to a beta-galactosidase reporter gene. These fusions were obtained by Tn3-HoHoI insertional mutagenesis of a P. aeruginosa genomic library. Eight different damage-inducible (din) gene fusions were isolated which lack homology to the P. aeruginosa recA gene. Expression of the three gene fusions studied, dinA::lacZYA, dinB::lacZYA, and dinC::lacZYA, increased following UVC and quinolone exposure but not following heat shock. Similar to E. coli SOS genes, the din genes were induced to different extents and with dissimilar kinetics following UVC irradiation.

Localization of alg, opr, phn, pho, 4.5S RNA, 6S RNA, tox, trp, and xcp genes, rrn operons, and the chromosomal origin on the physical genome map of Pseudomonas aeruginosa PAO

The genes encoding the rrn operons, the 4.5S and 6S RNAs, elements of protein secretion, and outer membrane proteins F and I, and regulatory as well as structural genes for exotoxin A, alkaline phosphatase, and alginate and tryptophan biosynthesis, were assigned on the SpeI/DpnI macrorestriction map of the Pseudomonas aeruginosa PAO chromosome. The zero point of the map was relocated to the chromosomal origin of replication.

Imipenem resistance in pseudomonas aeruginosa PAO: mapping of the OprD2 gene

Carbapenem antibiotics have been shown to penetrate the outer membrane of Pseudomonas aeruginosa through a unique porin protein, OprD2. We mapped the OprD2 gene by conjugation using plasmid FP2 and by transduction using phage F116L. This gene maps between 71 and 75 min on the PAO1 chromosome.

Inducible UV repair potential of Pseudomonas aeruginosa PAO

Pseudomonas aeruginosa PAO lacks UV-inducible Weigle reactivation and Weigle mutagenesis of UV-damaged bacteriophages. This lack of UV-inducible, error-prone DNA repair appears to be due to the absence of efficiently expressed umuDC-like genes in this species. When the P. aeruginosa recA gene is introduced into a recA(Def) mutant of Escherichia coli K12, the P. aeruginosa recA gene product is capable of mediating UV-induced mutagenesis, indicating that it could participate in a recA-lexA-like regulatory network and function in inducible DNA repair pathways if such existed in P. aeruginosa. The presence of the IncP9, UV-resistance plasmid R2 in RecA+ strains of P. aeruginosa PAO allows UV-inducible, mutagenic DNA repair of UV-irradiated bacteriophages. R2 also greatly stimulates the ability of UV radiation to induce mutagenesis of the bacterial chromosome. When R2 is introduced into P. aeruginosa strains containing either the recA908 or recA102 mutation, plasmid-mediated UV resistance and Weigle reactivation are not observed. These observations suggest that the increased protection afforded to P. aeruginosa by R2 is derived from a RecA-mediated, DNA-damage-inducible, error-prone DNA repair system which complements the lack of a chromosomally encoded umuDC-like operon.

Dynamic interactions ofPseudomonas aeruginosa and bacteriophages in lake water

The persistence and interaction between newly isolated strains ofPseudomonas aeruginosa and resident bacteriophages indigenous to a freshwater environment was monitored over 45 days in lake water microcosms. The interaction between susceptible and resistant bacteria with pure phage (UT1) particles or a mixed phage population (M1) was investigated by following temporal changes in host density, phage-to-bacteria ratio (PBR), and the appearance of apparent prophage carriers within the host population. Decay rates of the phage (UT1) ranged from 0.054 hour(-1) in natural water to 0.027 hour(-1) in filtered lake water. About 45% of sensitive bacteria incubated with phase UT1 were pseudolysogenic within 12 hours of incubation in natural lake water. This process was delayed until 72 hours in the steile lake water control, suggesting that host-phage interaction is promoted in the presence of a viable natural microbial community. Phage UT1 appeared to stabilize the density of host bacteria in lake water at a level of 10(4) colony-forming units (cfu) ml(-1). Bacterial coexistence with the mixed phage (M1) population resulted in an oscillating equilibrium with the PBR stabilizing at about 3. The presence of extraneous homoimmune phages appeared to be detrimental to the stability of the pseudolysogens, which were maintained at a lower population density than prophage-free cells in lake water containing the mixed phage (M1) population.

Molecular cloning of rat precursor cathepsin H and the expression of five lysosomal cathepsins in normal tissues and in a rat carcinosarcoma

1. A rat cathepsin H cDNA was isolated from a rat liver cDNA library with synthetic oligonucleotide probes. 2. DNA sequence analysis indicated that it codes for rat preprocathepsin H. 3. Using this clone together with the cDNA for cathepsins B, D, L and S as probes, the expression of five major lysosomal proteinases was investigated in ten different normal rat tissues and in a rat carcinoma. 4. The common feature of their expression is that the five cathepsins have relatively high mRNA levels in lung and kidney, suggesting that they all play important roles in organs engaged in active protein metabolism. 5. In other tissues, the concentrations of the five cathepsin mRNAs are significantly different. This may indicate that their expressions are differentially regulated and that they may have specialized functions in specific tissues. 6. The cathepsin B mRNA level is at least 2.5-fold higher in the rat W256-carcinoma than in any of the normal rat tissues surveyed. 7. In contrast, the mRNA levels for the other four cathepsins show no comparable elevations. 8. This finding is consistent with previous observations reporting a correlation between cathepsins B expression and malignant tumors.

Transduction of linked chromosomal genes between Pseudomonas aeruginosa strains during incubation in situ in a freshwater habitat

Both transduction of single chromosomal loci and cotransduction of closely linked loci were observed between lysogenic and nonlysogenic strains of Pseudomonas aeruginosa in a freshwater habitat. Transductants were recovered at frequencies of 10(-6) to 10(-5) transductants per CFU. Transductants of lysogenized strains were recovered 10- to 100-fold more frequently than were transductants of nonlysogenic parents. Lysogens are thus capable of introducing phages which mediate generalized transduction into the natural microbial community and serving as recipients of transduced DNA. It would appear that lysogeny has the potential of increasing the size and flexibility of the gene pool available to natural populations of bacteria. The ability to generate and select new genetic combinations through phage-mediated exchange can be significant in the face of a continually changing environment and may contribute to the apparent fitness of the lysogenic state in natural ecosystems.

Conjugal transfer of R68.45 and FP5 between Pseudomonas aeruginosa strains in a freshwater environment

Recent concern over the release of genetically engineered organisms has resulted in a need for information about the potential for gene transfer in the environment. In this study, the conjugal transfer in Pseudomonas aeruginosa of the plasmids R68.45 and FP5 was demonstrated in the freshwater environment of Fort Loudoun Resevoir, Knoxville, Tenn. When genetically well defined plasmid donor and recipient strains were introduced into test chambers suspended in Fort Loudoun Lake, transfer of both plasmids was observed. Conjugation occurred in both the presence and absence of the natural microbial community. The number of transconjugants recovered was lower when the natural community was present. Transfer of the broad-host-range plasmid R68.45 to organisms other than the introduced recipient was not observed in these chambers but was observed in laboratory simulations when an organism isolated from lakewater was used as the recipient strain. Although the plasmids transferred in laboratory studies were genetically and physically stable, a significant number of transconjugants recovered from the field trials contained deletions and other genetic rearrangements, suggesting that factors which increase gene instability are operating in the environment. The potential for conjugal transfer of genetic material must be considered in evaluating the release of any genetically engineered microorganism into a freshwater environment.

Expression of the recA gene of Pseudomonas aeruginosa PAO is inducible by DNA-damaging agents

Western (immunoblot) analysis using Escherichia coli anti-RecA antiserum revealed that expression of the RecA protein of Pseudomonas aeruginosa PAO is induced upon exposure of the bacterium to UV irradiation or norfloxacin, a quinolone related to nalidixic acid.

Molecular characterization of Pseudomonas aeruginosa bacteriophages: identification and characterization of the novel virus B86

We have characterized a new phage, B86, of Pseudomonas aeruginosa isolated from nature. It is a temperate, uv-inducible, generalized transducing phage. To determine the relatedness of this phage to other characterized P. aeruginosa phages, DNA homology studies were carried out. P. aeruginosa phages have previously been grouped by immunological cross-reactivity. Our studies confirm this classification by demonstrating that phages of different class share little or no DNA homology. Based on homology studies as well as cross-immunity to superinfection, B86 is related to other class B phages and is most homologous with phage B39. The virion morphology of these two phages is quite different, however, as are the restriction enzyme digestion patterns of their genomes with several restriction enzymes. Wild-type B86 is subject to the host-controlled restriction-modification systems of P. aeruginosa PAO and PAT. Virulent mutants of this phage are not restricted by these same restriction-modification systems.

Characterization of the Pseudomonas aeruginosa recA gene: the Les- phenotype

The Les- phenotype (lysogeny establishment deficient) is a pleiotropic effect of the lesB908 mutation of Pseudomonas aeruginosa PAO. lesB908-containing strains are also (i) deficient in general recombination, (ii) sensitive to UV irradiation, and (iii) deficient in UV-stimulated induction of prophages. The P. aeruginosa recA-containing plasmid pKML3001 complemented each of these pleiotropic characteristics of the lesB908 mutation, supporting the hypothesis that lesB908 is an allele of the P. aeruginosa recA gene. The phenotypic effects of the lesB908 mutation may be best explained by the hypothesis that the lesB908 gene product is altered in such a way that it has lost synaptase activity but possesses intrinsic protease activity in the absence of DNA damage. The Les- phenotype is a result of the rapid destruction of newly synthesized phage repressor, resulting in lytic growth of the infecting virus. This hypothesis is consistent with the observations that increasing the number of copies of the phage repressor gene by increasing the multiplicity of infection (i.e., average number of phage genomes per cell) or by introducing the cloned phage repressor gene into a lesB908 mutant will also suppress the Les- phenotype in a phage-specific fashion.

Cloning and characterization of the c1 repressor of Pseudomonas aeruginosa bacteriophage D3: a functional analog of phage lambda cI protein

We cloned the gene (c1) which encodes the repressor of vegetative function of Pseudomonas aeruginosa bacteriophage D3. The cloned gene was shown to inhibit plating of D3 and the induction of D3 lysogens by UV irradiation. The efficiency of plating and prophage induction of the heteroimmune P. aeruginosa phage F116L were not affected by the presence of the cloned c1 gene of D3. When the D3 DNA fragment containing c1 was subcloned into pBR322 and introduced into Escherichia coli, it was shown to specifically inhibit the plating of phage lambda and the induction of the lambda prophage by mitomycin C. The plating of lambda imm434 phage was not affected. Analysis in minicells indicated that these effects correspond to the presence of a plasmid-encoded protein of 36,000 molecular weight. These data suggest the possibility that coliphage lambda and the P. aeruginosa phage D3 evolved from a common ancestor. The conservation of the functional similarities of their repressors may have occurred because of the advantage to these temperate phages of capitalizing on the potential of the evolutionarily conserved RecA protein to monitor the level of damage to the host genome.

Potential for transduction of plasmids in a natural freshwater environment: effect of plasmid donor concentration and a natural microbial community on transduction in Pseudomonas aeruginosa

Transduction of Pseudomonas aeruginosa plasmid Rms149 by the generalized transducing bacteriophage phi DS1 was shown to occur during a 9-day incubation of environmental test chambers in a freshwater reservoir. Plasmid DNA was transferred from a nonlysogenic plasmid donor to a phi DS1 lysogen of P. aeruginosa that served both as the source of the transducing phage and as the recipient of the plasmid DNA. When the concentration of donors introduced into the chambers was varied while the recipient concentration in each chamber was at a level equivalent to natural concentrations of P. aeruginosa, the concentration of plasmid-containing donor cells introduced was shown to affect the frequency of transduction significantly. Transduction was observed both in the absence and in the presence of the natural microbial community. The presence of the natural community resulted in a rapid decrease in the numbers of the introduced donors and recipients and a decrease in the number of transductants recovered. These results demonstrate the potential for naturally occurring transduction in aquatic environments and indicate that donor load may be an important parameter in assessing this potential.

Characterization of the Pseudomonas aeruginosa recA analog and its protein product: rec-102 is a mutant allele of the P. aeruginosa PAO recA gene

We cloned a 2.3-kilobase-pair fragment of the Pseudomonas aeruginosa PAO chromosome which is capable of complementing recA mutations of Escherichia coli. The recA-complementing activity was further localized to a 1.5-kilobase-pair PvuII-HindIII fragment. Southern blot analysis under conditions of high stringency indicated that DNA sequence homology is shared by the E. coli recA gene and the P. aeruginosa recA analog. The cloned recA analog was shown to restore resistance to methyl methanesulfonate, nitrofurantoin, and UV irradiation to E. coli recA mutants. Upon introduction of the cloned P. aeruginosa gene, these mutants regained recombination proficiency in HfrH-mediated conjugation and the ability to induce lambda prophages and SOS functions (din gene transcription) after exposure to DNA-damaging agents. Lambda prophage carrying a cI ind mutation was not inducible, suggesting that the mechanism of induction of these SOS functions by the P. aeruginosa RecA analog is similar to that by the activated E. coli RecA protein. The product of the recA analog was identified in minicells as a protein of approximately 47,000 daltons. Western blot analysis using anti-E. coli RecA antibody demonstrated that this protein is antigenically cross-reactive with the E. coli recA protein. The recA-containing fragment was cloned into the broad-host-range vector pCP13 and introduced into Rec- strains of P. aeruginosa containing the rec-102 allele. The plasmid was shown to restore recombination proficiency in FP5-mediated conjugations and to restore resistance to UV irradiation and methyl methanesulfonate to these Rec- mutants. It was shown that a wild-type allele of rec-102 is necessary for UV-mediated induction of D3 and F116 prophages. The cloned recA analog restored the UV inducibility of these prophages in rec-102 mutants. These data indicate that rec-102 is a mutant allele of the P. aeruginosa recA gene and suggest that there has been considerable conservation of the recA gene in the evolution of the gram-negative bacteria.

Specialized transduction of Pseudomonas aeruginosa PAO by bacteriophage D3

D3, a temperate bacteriophage of Pseudomonas aeruginosa PAO, was found to specifically transduce the alleles met-49 and met-117. Induction of established lysogens with UV light was necessary for the production of transducing lysates. Transduced cells were immune to superinfection by phage D3 and could give rise to high-frequency transducing lysates. Cotransduction of these two alleles could not be demonstrated. met-117 was mapped to 26 min on the PAO genetic map. Complementation studies using the generalized transducing phage F116L indicated that met-49 is an allele of met-9011 which maps at 55 min. The integrated D3 prophage was shown to be coinherited with met-117 and with met-49.

Effects of norfloxacin on DNA metabolism in Pseudomonas aeruginosa

Norfloxacin is a quinolone (pyridonecarboxylic acid derivative) effective against Pseudomonas aeruginosa infections. We studied the effects of this drug on DNA metabolism in P. aeruginosa. Norfloxacin inhibits DNA replication immediately on its addition to a logarithmically growing culture of P. aeruginosa. It inhibits the ability of P. aeruginosa DNA gyrase to supercoil relaxed, closed circular DNA in vitro. At intermediate concentrations of the drug, inhibition of DNA replication in vivo is followed by secondary (recovery) synthesis. Both recovery synthesis and the bactericidal effects of norfloxacin are dependent on continued protein synthesis, suggesting that these are inducible functions. Neither norfloxacin nor nalidixic acid induces Weigle-reactivation (inducible DNA repair) or mutagenesis in P. aeruginosa.

Unilateral eyelid, conjunctival, and choroidal tumours as initial presentation of diffuse large-cell lymphoma

Simultaneous ipsilateral eyelid, conjunctival, and choroidal tumours developed in an otherwise healthy man. Biopsy of the eyelid mass led to the diagnosis of large-cell lymphoma. Further examination revealed systemic lymphoma. Although the ocular and adnexal lesions responded to systemic chemotherapy, additional skin tumours later developed. Large-cell lymphoma (also called reticulum cell sarcoma and histiocytic lymphoma) is becoming increasingly recognised for its ophthalmic manifestations. The clinical signs, diagnostic investigations, and treatment of this disease are discussed.

Mucoid conversion by phages of Pseudomonas aeruginosa strains from patients with cystic fibrosis

A total of 21 of 22 independent isolates of cystic fibrosis-associated Pseudomonas aeruginosa were found to be lysogenic for DNA-containing, complex capsid viruses. Several of the phages demonstrated the ability to select mucoid cells from populations of nonmucoid bacteria. Conversion to mucoid growth was more frequently achieved when phages were isolated from mucoid as opposed to nonmucoid cystic fibrosis-associated strains.

Identification of Pseudomonas plasmids able to suppress the lysogeny-establishment-deficiency (Les-) phenotype

A suppressor of the mutations which inhibit the establishment of lysogeny in Pseudomonas aeruginosa has been found to be encoded by P. aeruginosa plasmids of four separate incompatibility groups. The wide distribution of this phenotype (designated Sly for suppressor of lysogeny establishment deficiency) indicates that these plasmids are able to enhance or replace host functions involved in the stable establishment of extrachromosomal DNA.

DNA gyrase (Topoisomerase II) from Pseudomonas aeruginosa

DNA gyrase (Topoisomerase II) has been purified from Pseudomonas aeruginosa strain PAO. This enzyme is inhibited by novobiocin and nalidixic acid. DNA gyrase from P. aeruginosa is resistant to a much higher level of nalidixic acid than is Escherichia coli DNA gyrase. This increased level of resistance may explain, at least in part, the higher levels of natural resistance exhibited by P. aeruginosa toward nalidixic acid.

Selection of nonmucoid derivatives of mucoid Pseudomonas aeruginosa is strongly influenced by the level of iron in the culture medium

We investigated the effects of cations on the stability in culture of mucoid strains pf Pseudomonas aeruginosa isolated from patients with cystic fibrosis by studying their effects on the selection of nonmucoid derivatives which arise by spontaneous mutation in cultures of mucoid organisms. Calcium ion concentrations in the range 0.55 to 1.85 mM had no effect on the growth or stability of the mucoid cultures. Higher levels (5.0 mM) inhibited the growth of both mucoid and nonmucoid cells. Likewise, magnesium ion in concentrations of 0.3 to 3.0 mM had no effect. The concentration of iron (either Fe2+ or Fe3+) had a profound effect on the selection of nonmucoid mutants in unshaken cultures of mucoid organisms. In medium containing 0.01 mM iron, nonmucoid mutants rapidly accumulated to a greater than 100-fold-higher frequency than the mucoid forms. Rates of accumulation of nonmucoid derivatives were lower in media containing lower concentrations of iron. The possible role of iron in the selection of nonmucoid cells from a population of mucoid P. aeruginosa is discussed.

Motility as a selective force in the reversion of cystic fibrosis-associated mucoid Pseudomonas aeruginosa to the nonmucoid phenotype in culture

Motility acted as a strong positive selection for nonmucoid Pseudomonas aeruginosa in unshaken cultures. Consistent with this finding, electron microscopic examination of mucoid and nonmucoid revertant strains indicated that the mucoid cells were nonflagellated whereas the nonmucoid revertants were flagellated.

Peptidase activity in the inner membrane of Pseudomonas aeruginosa

The location of peptidase activity within the cell envelope structure of Pseudomonas aeruginosa has been studied. Inner and outer membrane fractions were separated on the basis of buoyant density using two consecutive sucrose steps gradients and identified on the basis of known components. The inner membrane was shown to contain peptidase activity while the outer membrane contained none. These data support the hypothesis that P. aeruginosa transports intact peptides.

PaeExo IX: a unique deoxyribonuclease from Pseudomonas aeruginosa active in the presence of EDTA

A new deoxyribonuclease, PaeExo IX, has been purified to electrophoretic homogeneity from extracts of Pseudomonas aeruginosa strain PAO. This enzyme, which is active in the presence of EDTA, is equally efficient in hydrolyzing native and heart-denatured DNA to acid-s-luble products. The enzyme is partially or totally inhibited by the presence of several divalent cations. The active protein has a molecular weight of 1.6 +/- 0.1 x 10(5) and is composed of two nonidentical polypeptides with molecular weights of 78,000 and 69,000.

Evaluation of Myrothecium verrucaria as a nutrient source for ruminants

The soil saprophytic fungus Myrothecium verrucaria was cultivated from glucose, starch, or xylan as the carbon source, and the biomass was compared with three selected feedstuffs. Fungal biomass was analyzed for nitrogen, protein, lipid, water soluble fraction, hemicellulose, cellulose, lignin, and residual ash, and the in vitro dry matter disappearance was determined. The chemical composition of M. verrucaria varied with substrate. In nitrogen content, the fungal biomass was more similar to alfalfa hay than to milo stalks or wheat straw. Content of water soluble fraction of fungal biomass was between those of alfalfa hay and milo stalks; content of hemicellulose was between those of milo stalks and wheat straw. The fungal fractions identified as cellulose and lignin varied widely with substrate. The fungal biomass was less digestible than alfalfa hay but more digestible than milo stalks or wheat straw. There may be potential uses of this organism in upgrading nutritive value of low-quality forages.

NgoII, a restriction endonuclease from Neisseria gonorrhoeae

EndoR . NgoII, a class II restriction endonuclease isolated from Neisseria gonorrhoeae, was purified to electrophoretic homogeneity. We were able to separate it from another restriction endonuclease of N. gonorrhoeae, NgoI, by phosphocellulose chromatography. NgoII is an isoschizomer of HaeIII, a restriction endonuclease of Haemophilus aegyptius, and was found to recognize the deoxyribonucleic acid nucleotide base sequence GGCC. NgoII was able to digest phage lambda deoxyribonucleic acid over a wide pH range, with optimal activity at pH 8.5. The enzyme has an absolute requirement for Mg2+; maximal enzyme activity was observed at 1 mM Mg2+. The active enzyme has a molecular weight of 65,000 and appears to be composed of six subunits of identical molecular weight (11,000). No methylase activity could be detected in the purified enzyme preparation.

Frequency of F116-mediated transduction of Pseudomonas aeruginosa in a freshwater environment

Transduction of Pseudomonas aeruginosa streptomycin resistance by a generalized transducing phage, F116, was shown to occur during a 10-day incubation in a flow-through environmental test chamber suspended in a freshwater reservoir. Mean F116 transduction frequencies ranged from 1.4 X 10(-5) to 8.3 X 10(-2) transductants per recipient during the in situ incubation. These transduction frequencies were comparable to transduction frequencies determined in preliminary laboratory transduction experiments. The results demonstrate the potential for naturally occurring transduction in aquatic environments and concurrent environmental and ecological ramifications.