Inducible UV repair potential of Pseudomonas aeruginosa PAO

Growth conditions influence UVB sensitivity and oxidative damage in an estuarine bacterial isolate

The dose-dependent variation of oxidative cellular damage imposed by UVB exposure in a representative estuarine bacterial strain, Pseudomonas sp. NT5I1.2B, was studied at different growth phases (mid-exponential, late-exponential, and stationary), growth temperatures (15 °C and 25 °C) and growth media (nutrient-rich Tryptic Soy Broth [TSB] and nutrient-poor M9). Survival and markers of oxidative damage (lipid peroxidation, protein carbonylation, DNA strand breakage, and DNA-protein cross-links) were monitored during exposure to increasing UVB doses (0-60 kJ m(-2)). Oxidative damage did not follow a clear linear dose-dependent pattern, particularly at high UVB doses (>10 kJ m(-2)), suggesting a dynamic interaction between damage induction and repair during irradiation and/or saturation of oxidative damage. Survival of stationary phase cells generally exceeded that of exponential phase cells by up to 33.5 times; the latter displayed enhanced levels of DNA-protein cross-links (up to 15.6-fold) and protein carbonylation (up to 6.0-fold). Survival of mid-exponential phase cells was generally higher at 15 °C than at 25 °C (up to 6.6-fold), which was accompanied by lower levels of DNA strand breaks (up to 4000-fold), suggesting a temperature effect on reactive oxygen species (ROS) generation and/or ROS interaction with cellular targets. Survival under medium-high UVB doses (>10 kJ m(-2)) was generally higher (up to 5.4-fold) in cells grown in TSB than in M9. These results highlight the influence of growth conditions preceding irradiation on the extent of oxidative damage induced by UVB exposure in bacteria.

General and inducible hypermutation facilitate parallel adaptation in Pseudomonas aeruginosa despite divergent mutation spectra

The successful growth of hypermutator strains of bacteria contradicts a clear preference for lower mutation rates observed in the microbial world. Whether by general DNA repair deficiency or the inducible action of low-fidelity DNA polymerases, the evolutionary strategies of bacteria include methods of hypermutation. Although both raise mutation rate, general and inducible hypermutation operate through distinct molecular mechanisms and therefore likely impart unique adaptive consequences. Here we compare the influence of general and inducible hypermutation on adaptation in the model organism Pseudomonas aeruginosa PAO1 through experimental evolution. We observed divergent spectra of single base substitutions derived from general and inducible hypermutation by sequencing rpoB in spontaneous rifampicin-resistant (Rif(R)) mutants. Likewise, the pattern of mutation in a draft genome sequence of a derived inducible hypermutator isolate differed from those of general hypermutators reported in the literature. However, following experimental evolution, populations of both mutator types exhibited comparable improvements in fitness across varied conditions that differed from the highly specific adaptation of nonmutators. Our results suggest that despite their unique mutation spectra, general and inducible hypermutation can analogously influence the ecology and adaptation of bacteria, significantly shaping pathogenic populations where hypermutation has been most widely observed.

Streptomyces sp. JS520 produces exceptionally high quantities of undecylprodigiosin with antibacterial, antioxidative, and UV-protective properties

A Gram-positive, red-pigment-producing bacterial strain, designated JS520 was isolated from the pristine sediment from the cave on mountain Miroc in Serbia. Strain was confirmed to belong to Streptomyces genus based on phenotypic and genetic analysis. Streptomyces sp. JS520 has the ability to produce exceptionally high amounts of deep red pigment into both solid and liquid media. Liquid chromatography and mass spectroscopy of the purified pigments revealed the major component to be undecylprodigiosin (93 %) with minor component being oxidatively cyclized derivative. The pigment production was affected by medium composition, temperature, pH, and the aeration rate. By medium optimization, yields of undecylprodigiosin of 138 mg l(-1) were achieved, what is the highest level of undecylprodigiosin production reported for the members of Gram-positive Streptomyces genus. Purified pigment had antimicrobial properties against bacterial Bacillus and Micrococcus species (50 μg ml(-1)) and against Candida albicans species (100-200 μg ml(-1) range). The ability to affect auto-oxidation of the linoleic acid was demonstrated for the purified undecylprodigiosin, suggesting antioxidative properties of this pigment. Multiple ecophysiological roles of the pigment were revealed by comparing cultures grown under pigment-producing and pigment-nonproducing conditions. Cells grown under undecylprodigiosin-producing conditions could tolerate presence of hydrogen peroxide exhibiting three times smaller zones of inhibition at 100 mM H(2)O(2). Undecylprodigiosin-producing cells were also less susceptible to tetracycline, kanamycin, chloramphenicol, and 8-hydroxyquinoline. While the growth of the cells not producing pigment was completely inhibited by 15 min of exposure to ultraviolet light (254 nm), cells producing undecylprodigiosin and cells supplied with purified pigment in vitro showed survival rates at 22 and 8 %, respectively.

Contrasting effects of ultraviolet radiation on the growth efficiency of freshwater bacteria

In this study, we tested the hypothesis that the growth efficiency of freshwater bacteria is differentially affected by ultraviolet radiation (UVR, 280-400 nm) as mediated through changes in their production and respiration rates. Five bacterial strains affiliated to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Actinobacteria were isolated from different freshwater habitats and exposed in the laboratory to photosynthetically active radiation (PAR) and PAR + UVR, or kept in the dark for 4 h. Afterward, bacterial carbon production and respiration were assessed by measuring leucine incorporation and oxygen consumption rates, respectively. Ultraviolet radiation decreased significantly the bacterial production of Acidovorax sp., Pseudomonas sp. and Actinobacterium MHWTa3, and the respiration rate of Acidovorax sp. and Acinetobacter lwoffii. Measurements of respiration of a natural bacterial community collected from the same lake where A. lwoffii was isolated resulted in significantly higher rates after exposure to PAR + UVR than in the dark. In the presence of UVR, bacterial growth efficiency significantly decreased in Acidovorax sp., Pseudomonas sp., and Actinobacterium MHWTa3, but it increased in A. lwoffii or it remained unchanged in Sphingomonas sp. Our results indicate that although the outcome was strain-specific, UVR has the potential to alter the efficiency by which dissolved organic matter is transformed into bacterial biomass and thus to affect the biogeochemical carbon cycle.

Characterization of melanin-overproducing transposon mutants of Pseudomonas putida F6

Two melanin-overproducing Pseudomonas putida F6 mutants were generated using transposon (Tn5) mutagenesis. Mutants were disrupted in a transcriptional regulator (TR) and a homogentisate 1,2-dioxygenase (HDO) gene. Colonies of mutant F6-TR overproduced a black pigment on solid medium. The same mutant (F6-TR) had a 3.7-fold higher tyrosinase activity compared with the wild-type strain when induced with ferulic acid. However in tyrosine uptake assays whole cells of the mutant strain F6-TR consumed eight times less tyrosine compared with the wild-type strain. Mutant F6-HDO produced a diffusible red pigment into the growth medium. Pigment production by mutant F6-HDO is sixfold higher than the wild-type strain. The biomass yield of mutant F6-HDO grown on tyrosine as the sole source of carbon and energy was 1.2-fold lower than the wild-type strain. While the growth of the wild-type strain was completely inhibited by 5 min of exposure to UV light (254 nm) both mutant strains showed survival rates >30%. Mutant F6-HDO was able to tolerate higher concentrations of hydrogen peroxide (H(2)O(2)) exhibiting 1.5 times smaller zones of inhibition at 10 mM H(2)O(2) compared with mutant F6-TR and the wild-type strain. The pigments produced by all strains were purified and confirmed to be melanins.

Diverse responses to UV-B radiation and repair mechanisms of bacteria isolated from high-altitude aquatic environments

Acinetobacter johnsonii A2 isolated from the natural community of Laguna Azul (Andean Mountains at 4,560 m above sea level), Serratia marcescens MF42, Pseudomonas sp. strain MF8 isolated from the planktonic community, and Cytophaga sp. strain MF7 isolated from the benthic community from Laguna Pozuelos (Andean Puna at 3,600 m above sea level) were subjected to UV-B (3,931 J m-2) irradiation. In addition, a marine Pseudomonas putida strain, 2IDINH, and a second Acinetobacter johnsonii strain, ATCC 17909, were used as external controls. Resistance to UV-B and kinetic rates of light-dependent (UV-A [315 to 400 nm] and cool white light [400 to 700 nm]) and -independent reactivation following exposure were determined by measuring the survival (expressed as CFU) and accumulation of cyclobutane pyrimidine dimers (CPD). Significant differences in survival after UV-B irradiation were observed: Acinetobacter johnsonii A2, 48%; Acinetobacter johnsonii ATCC 17909, 20%; Pseudomonas sp. strain MF8, 40%; marine Pseudomonas putida strain 2IDINH, 12%; Cytophaga sp. strain MF7, 20%; and Serratia marcescens, 21%. Most bacteria exhibited little DNA damage (between 40 and 80 CPD/Mb), except for the benthic isolate Cytophaga sp. strain MF7 (400 CPD/Mb) and Acinetobacter johnsonii ATCC 17909 (160 CPD/Mb). The recovery strategies through dark and light repair were different in all strains. The most efficient in recovering were both Acinetobacter johnsonii A2 and Cytophaga sp. strain MF7; Serratia marcescens MF42 showed intermediate recovery, and in both Pseudomonas strains, recovery was essentially zero. The UV-B responses and recovery abilities of the different bacteria were consistent with the irradiation levels in their native environment.

A DNA polymerase V homologue encoded by TOL plasmid pWW0 confers evolutionary fitness on Pseudomonas putida under conditions of environmental stress

Plasmids in conjunction with other mobile elements such as transposons are major players in the genetic adaptation of bacteria in response to changes in environment. Here we show that a large catabolic TOL plasmid, pWW0, from Pseudomonas putida carries genes (rulAB genes) encoding an error-prone DNA polymerase Pol V homologue which increase the survival of bacteria under conditions of accumulation of DNA damage. A study of population dynamics in stationary phase revealed that the presence of pWW0-derived rulAB genes in the bacterial genome allows the expression of a strong growth advantage in stationary phase (GASP) phenotype of P. putida. When rulAB-carrying cells from an 8-day-old culture were mixed with Pol V-negative cells from a 1-day-old culture, cells derived from the aged culture out-competed cells from the nonaged culture and overtook the whole culture. At the same time, bacteria from an aged culture lacking the rulAB genes were only partially able to out-compete cells from a fresh overnight culture of the parental P. putida strain. Thus, in addition to conferring resistance to DNA damage, the plasmid-encoded Pol V genes significantly increase the evolutionary fitness of bacteria during prolonged nutritional starvation of a P. putida population. The results of our study indicate that RecA is involved in the control of expression of the pWW0-encoded Pol V.

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.

Inhibition of bacterial attachment by pulsed Nd:YAG laser irradiations: an in vitro study using marine biofilm-forming bacterium Pseudoalteromonas carrageenovora

The effect of low mean power laser irradiations with short pulse duration from an Nd:YAG (neodymium-doped yttrium aluminium garnet) laser on a marine biofilm-forming bacterium, Pseudoalteromonas carrageenovora, was investigated in the laboratory. Laser-irradiated bacteria were tested for their ability to attach on nontoxic titanium nitride (TiN) coupons with nonirradiated bacteria as the reference. Two durations of irradiation were tested, 10 and 15 min. Bacterial attachment was monitored after 20 min, 40 min, and 1 h of irradiation. The average laser fluence used for this study was 0.1 J/cm(2). The area of attachment of the irradiated bacteria was significantly less than the reference for both durations of irradiation. The growth of irradiated bacteria showed a longer lag phase than the nonirradiated sample, mainly due to mortality in the former. The bacterial mortality observed was 23.4 +/- 0.71 and 48.6 +/- 6.5% for 10- and 15-min irradiations, respectively. Thus, the results show that low-power pulsed laser irradiations resulted in a significant bacterial mortality and a reduced bacterial attachment on nontoxic hard surfaces.

Influence of infected cell growth state on bacteriophage reactivation levels

Reactivation of UV-C-inactivated Pseudomonas aeruginosa bacteriophages D3C3, F116, G101, and UNL-1 was quantified in host cells infected during the exponential phase, during the stationary phase, and after starvation (1 day, 1 and 5 weeks) under conditions designed to detect dark repair and photoreactivation. Our experiments revealed that while the photoreactivation capacity of stationary-phase or starved cells remained about the same as that of exponential-phase cells, in some cases their capacity to support dark repair of UV-inactivated bacteriophages increased over 10-fold. This enhanced reactivation capacity was correlated with the ca. 30-fold-greater UV-C resistance of P. aeruginosa host cells that were in the stationary phase or exposed to starvation conditions prior to irradiation. The dark repair capacity of P. aeruginosa cells that were infected while they were starved for prolonged periods depended on the bacteriophage examined. For bacteriophage D3C3 this dark repair capacity declined with prolonged starvation, while for bacteriophage G101 the dark repair capacity continued to increase when cells were starved for 24 h or 1 week prior to infection. For G101, the reactivation potentials were 16-, 18-, 10-, and 3-fold at starvation intervals of 1 day, 1 week, 5 weeks, and 1. 5 years, respectively. Exclusive use of exponential-phase cells to quantify bacteriophage reactivation should detect only a fraction of the true phage reactivation potential.

Regulation of the rulAB mutagenic DNA repair operon of Pseudomonas syringae by UV-B (290 to 320 nanometers) radiation and analysis of rulAB-mediated mutability in vitro and in planta

The effects of the rulAB operon of Pseudomonas syringae on mutagenic DNA repair and the transcriptional regulation of rulAB following irradiation with UV-B wavelengths were determined. For a rulB::Km insertional mutant constructed in P. syringae pv. syringae B86-17, sensitivity to UV-B irradiation increased and UV mutability decreased by 12- to 14-fold. rulAB-induced UV mutability was also tracked in phyllosphere populations of B86-17 for up to 5 days following plant inoculation. UV mutability to rifampin resistance (Rif(r)) was detected at all sampling points at levels which were significantly greater than in nonirradiated controls. In P. aeruginosa PAO1, the cloned rulAB determinant on pJJK17 conferred a 30-fold increase in survival and a 200-fold increase in mutability following a UV-B dose of 1,900 J m(-2). In comparative studies using defined genetic constructs, we determined that rulAB restored mutability to the Escherichia coli umuDC deletion mutant RW120 at a level between those of its homologs mucAB and umuDC. Analyses using a rulAB::inaZ transcriptional fusion in Pseudomonas fluorescens Pf5 showed that rulAB was rapidly induced after UV-B irradiation, with expression levels peaking at 4 h. At the highest UV-B dose administered, transcriptional activity of the rulAB promoter was elevated as much as 261-fold compared to that of a nonirradiated control. The importance of rulAB for survival of P. syringae in its phyllosphere habitat, coupled with its wide distribution among a broad range of P. syringae genotypes, suggests that this determinant would be appropriate for continued investigations into the ecological ramifications of mutagenic DNA repair.

Temperature-responsive genetic loci in the plant pathogen Pseudomonas syringae pv. glycinea

Plant-pathogenic bacteria may sense variations in environmental factors, such as temperature, to adapt to plant-associated habitats during pathogenesis or epiphytic growth. The bacterial blight pathogen of soybean, Pseudomonas syringae pv. glycinea PG4180, preferentially produces the phytotoxin coronatine at 18 degrees C and infects the host plant under conditions of low temperature and high humidity. A miniTn5-based promoterless glucuronidase (uidA) reporter gene was used to identify genetic loci of PG4180 preferentially expressed at 18 or 28 degrees C. Out of 7500 transposon mutants, 61 showed thermoregulated uidA expression as determined by a three-step screening procedure. Two-thirds of these mutants showed an increased reporter gene expression at 18 degrees C whilst the remainder exhibited higher uidA expression at 28 degrees C. MiniTn5-uidA insertion loci from these mutants were subcloned and their nucleotide sequences were determined. Several of the mutants induced at 18 degrees C contained the miniTn5-uidA insertion within the 32.8 kb coronatine biosynthetic gene cluster. Among the other mutants with increased uidA expression at 18 degrees C, insertions were found in genes encoding formaldehyde dehydrogenase, short-chain dehydrogenase and mannuronan C-5-epimerase, in a plasmid-borne replication protein, and in the hrpT locus, involved in pathogenicity of P. syringae. Among the mutants induced at 28 degrees C, insertions disrupted loci with similarities to a repressor of conjugal plasmid transfer, UV resistance determinants, an isoflavanoid-degrading enzyme, a HU-like DNA-binding protein, two additional regulatory proteins, a homologue of bacterial adhesins, transport proteins, LPS synthesis enzymes and two proteases. Genetic loci from 13 mutants did not show significant similarities to any database entries. Results of plant inoculations showed that three of the mutants tested were inhibited in symptom development and in planta multiplication rates. Temperature-shift experiments suggested that all of the identified loci showed a rather slow induction of expression upon change of temperature.

The effects of ultraviolet radiation on the moderate halophileHalomonas elongataand the extreme halophileHalobacterium salinarum

Both the moderately halophilic bacterium, Halomonas elongata, and the extremely halophilic archaea, Halobacterium salinarum, can be found in hypersaline environments (e.g., salterns). On complex media, H. elongata grows over a salt range of 0.05-5.2 M, whereas, H. salinarum multiplies over a salt range of 2.5-5.2 M. The purpose of this study was to illustrate the effect that solar (UV-A and UV-B) and germicidal radiation (UV-C) had on the growth patterns of these bacteria at varied salt concentrations. Halomonas elongata grown on a complex medium at 0.05, 1.37, and 4.3 M NaC1 was found to be more sensitive to UV-A and UV-B radiation, as the salt concentration of the medium increased. Halobacterium salinarum grown on a complex medium at 3.0 and 4.3 M NaC1 did not show a significant drop in viability after 39.3 kJ·m-2of UV-A and UV-B exposure. When exposed to UV-C, H. elongata exhibited substantially more sensitivity than H. salinarum. In H. elongata, differential sensitivity to UV-C was observed. At 0.05 M NaCl, H. elongata was less sensitive to UV-C than at 1.37 and 4.3 M NaCl. Both bacteria showed some photoreactivation when incubated under visible light following both UV-A, UV-B, and UV-C exposure. Mutagenesis following UV-C exposure was demonstrated by both organisms.

Characterization of Pseudomonas aeruginosa bacteriophage UNL-1, a bacterial virus with a novel UV-A-inducible DNA damage reactivation phenotype

UNL-1, a lytic virus of Pseudomonas aeruginosa, was observed to express a novel inducible DNA damage reactivation activity in UV-A-irradiated P. aeruginosa host cells. The expression of bacteriophage reactivation was quantified in hosts exposed to either UV-C or UV-A radiation. While reactivation of UV-C-damaged UNL-1 was not inducible in UV-C-irradiated host cells, an approximately 13-fold induction was observed in UV-A-irradiated host cells. When host cells were exposed to sunlight, reactivation of damaged UNL-1 virus increased eightfold. The UV-A induction of UNL-1 DNA damage reactivation was supported in hosts lacking recA gene function. This report is the first description of a recA-independent, UV-inducible virus DNA damage repair system. Our findings suggest that a combination of both host and virus DNA repair processes contribute to the persistence and sustained replication of some bacterial viruses in aquatic environments.

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.

Functional analysis of the Pseudomonas syringae rulAB determinant in tolerance to ultraviolet B (290-320 nm) radiation and distribution of rulAB among P. syringae pathovars

The effect of the plasmid-encoded rulAB (resistance to ultraviolet radiation) determinant on responses of Pseudomonas syringae to ultraviolet-B (UV-B) radiation and the distribution of rulAB among pathovars of P. syringae were determined. The cloned rulAB determinant and the native rulAB+ plasmid pPSR1 both conferred approximately a 10-fold increase in survival on P. syringae pv. syringae FF5 following increasing doses of UV-B radiation. rulAB+ P. syringae strains also maintained significantly larger epiphytic populations on leaf surfaces irradiated with UV-B. rulAB-insertional mutants, constructed in two native rulAB+ strains, were from 10- to 100-fold more sensitive to UV-B radiation. The UV tolerance phenotype and the rulAB genes were widely distributed among P. syringae pathovars isolated from varied plant hosts throughout the world and within a broad range of genotypic backgrounds of P. syringae pv. syringae. With one exception, the rulAB determinant was harboured on pPT23A-like plasmids; these replicons are indigenous residents of the species P. syringae and also tend to encode determinants of importance in host-pathogen interactions.

Prevalence of broad-host-range lytic bacteriophages of Sphaerotilus natans, Escherichia coli, and Pseudomonas aeruginosa

Two bacteriophage collections were examined with regard to their ability to form plaques on multiple bacterial host species. Nine of 10 phages studied were found to be broad-host-range bacteriophages. These phages fell into two groups. Group 1, the SN series, was isolated from sewage treatment plant samples with Sphaerotilus natans ATCC 13338 as a host. The DNAs of these bacteriophages contained modified bases and were insensitive to cleavage by type I and II restriction endonucleases. The efficiency of plating of these bacteriophages was changed only slightly on the alternate host. Group 2, the BHR series, was isolated by a two-host enrichment protocol. These bacteriophages were sensitive to restriction, and their efficiency of plating was dramatically reduced on the alternate host. Our results suggest that a multiple-host enrichment protocol may be more effective for the isolation of broad-host-range bacteriophages by avoiding the selection bias inherent in single-host methods. At least two of the broad-host-range bacteriophages mediated generalized transduction. We suggest that broad-host-range bacteriophages play a key role in phage ecology and gene transfer in nature.

Bacteriophage infection and multiplication occur in Pseudomonas aeruginosa starved for 5 years

Bacteriophages specific for Pseudomonas aeruginosa and Escherichia coli were examined for their ability to multiply in stationary phase hosts. Four out of five bacteriophages tested, including E. coli bacteriophage T7M, were able to multiply in stationary phase hosts. The bacteriophage ACQ had a mean burst size of approximately 1000 in exponential phase P. aeruginosa hosts and 102 in starved hosts, with corresponding latent periods that increased from 65 to 210 min. The bacteriophage UT1 had a mean burst size of approximately 211 in exponential phase P. aeruginosa hosts and 11 in starved hosts, with latent periods that increased from a mean of 90 min in exponential phase hosts to 165 min in starved hosts. Bacteriophage multiplication occurred whether or not the hosts had entered stationary phase, either because the cultures had been incubated for 24 h or were starved. Significantly, bacteriophage multiplication occurred in P. aeruginosa, which had been starved for periods of 24 h, several weeks, or 5 years. Only one P. aeruginosa virus, BLB, was found to be incapable of multiplication in stationary phase hosts. These results reveal that starvation does not offer bacterial hosts refuge from bacteriophage infection and suggest that bacteriophages will be responsible for significant bacterial mortality in most natural ecosystems.

Chlorella virus PBCV-1 encodes a homolog of the bacteriophage T4 UV damage repair gene denV

The bacteriophage T4 denV gene encodes a well-characterized DNA repair enzyme involved in pyrimidine photodimer excision. We have discovered the first homologs of the denV gene in chlorella viruses, which are common in fresh water. This gene functions in vivo and also when cloned in Escherichia coli. Photodamaged virus DNA can also be photoreactivated by the host chlorella. Since the chlorella viruses are continually exposed to solar radiation in their native environments, two separate DNA repair systems, one that functions in the dark and one that functions in the light, significantly enhance their survival.

Resistance to ultraviolet light in Pseudomonas syringae: sequence and functional analysis of the plasmid-encoded rulAB genes

The indigenous plasmids, pPSR1 and pPSR5, were each shown to confer resistance to ultraviolet light (UV) in Pseudomonas syringae (Ps) pv. syringae FF5. The UV-resistance (UVR) determinant was subcloned from a cosmid library of pPSR1, and sequence analysis revealed the presence of two ORFs, designated rulAB which are homologous to the Escherichia coli umuDC mutagenic DNA repair systems and other plasmid-encoded UVR operons. Amino acid (aa) alignments indicated that RulAB are most closely related to the RumAB proteins from plasmid R391, sharing 40.5% and 48.6% aa identity with RumA and RumB, respectively. UV sensitivity assays with the cloned rulAB genes indicated that the expression of UVR in Ps required a functional recA gene.

The uvrB gene of Pseudomonas aeruginosa is not DNA damage inducible

The uvrB gene of Pseudomonas aeruginosa has been isolated from a genomic library by complementation of an Escherichia coli uvrB mutant. The complete nucleotide sequence of P. aeruginosa uvrB consists of 2,013 bp, encoding a polypeptide of 670 amino acids. A P. aeruginosa SOS consensus region, which functions as a binding site for the LexA repressor molecule, is not present in the upstream region of the uvrB gene isolated. By transcriptional fusions with a reporter gene, it has been demonstrated that, contrary to what happens with the homologous gene of E. coli, the P. aeruginosa uvrB gene is not DNA damage inducible. Nevertheless, the UvrB protein must be functional in P. aeruginosa cells because a uvrB-defective mutant is extremely sensitive to UV radiation.

Increased mutagenesis mediated by cloned plasmid CAM-OCT genes: potential for expanding substrate ranges of Pseudomonas spp

Twenty-five kilobases of Pseudomonas plasmid CAM-OCT DNA encoding a DNA repair gene(s) was cloned into the broad-host-range vector pVK100. The presence of the cloned genes increased the isolation frequency of Pseudomonas putida derivatives capable of using ethyl lactate or 3-methyl-3-buten-1-ol as their carbon source 15- and 8-fold, respectively, after UV irradiation. Ethyl lactate-utilizing strains expressed a novel intracellular hydrolase.

Lethal effect induced in Pseudomonas aeruginosa Exposed to Ultraviolet-A radiation

Ultraviolet-A (365 nm, 120 kJ/m2/h) exposure caused cell death in Pseudomonas aeruginosa at doses at which Escherichia coli cell viability was not affected. We have not found that UVA induced growth delay or any other sublethal effect. Irradiated suspensions of P. aeruginosa showed a marked reduction in membrane-bound succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) activities. Succinate-driven respiration and several nutrient transport systems were also inhibited. Whereas SDH and LDH activities were independent of the irradiation conditions, cell viability, respiration and transport systems were protected when irradiation was performed in an N2 atmosphere. A similar protective effect was observed when cells were grown in media containing glycerol or when preirradiation bacterial growth was carried out at 30 degrees C (instead of 37 degrees C). Results suggest that UVA induces a differential damaging effect on several biochemical functions of P. aeruginosa. The UVA- induced photodamage may fall into two categories: indirect damage mediated by oxygen (cell killing and inhibition of respiration and transport systems) and direct damage to SDH and LDH (apparently not oxygen dependent). These enzymes and leucine transport appear not to be involved in the lethal effect described herein because they were altered despite viability-preserving conditions

recA-dependence of the response of Pseudomonas aeruginosa to UVA and UVB irradiation

The responses of the autochthonous soil and aquatic organism, Pseudomonas aeruginosa to UV radiation wavelengths (UVA, 320-400 nm, and UVB, 280-320 nm) has been investigated in this study. P. aeruginosa recA mutants were found to be more sensitive to both UVA and UVB radiation than were their isogenic RecA+ parents. Introduction of a low-copy-number plasmid containing the cloned wild-type P. aeruginosa recA gene restored UVA and UVB resistance to recA mutants. The concentration of RecA protein increased twofold 120 min after exposure to either UVA or UVB radiation, suggesting induction of expression of the recA gene by these wavelengths. In this study, we found that a functional RecA protein is required for activation of D3 prophage in lysogenic cells following exposure to UVB radiation. Prophage were not induced by exposure of their hosts to UVA radiation. Induction of damage-inducible (din) genes in response to UVA or UVB irradiation was also shown to be RecA dependent. These data indicate that the recA gene plays a role in the response of P. aeruginosa to exposure to wavelengths of UV radiation found in the solar spectrum.

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.