Occurrence of Resistance to Antibiotics,UV-B,and Arsenic in Bacteria Isolated from Extreme Environments in High-Altitude (Above 4400 m) Andean Wetlands

High-altitude Andean wetlands are pristine environments with extreme conditions such as high UV radiation, high heavy metal content (mainly arsenic), high salinity, and oligotrophy. In this paper, the UV-B resistance and tolerance to arsenic of phylogenetically characterized bacteria (Actinobacteria [six isolates], Firmicutes [four isolates], and γ-Proteobacteria [three isolates]) isolated from Laguna Vilama (4400-m altitude) and Laguna Azul (4560 m) were determined. In addition, given that multiple antibiotic resistances were also determined, a relationship between antibiotic resistances as a consequence of mutagenic ability or in relation to metal resistance is proposed. High UV-B resistances were found, since after 30 min (0.7 KJ m⁻²) and 60 min (1.4 KJ m⁻²) of irradiation, most of the studied bacteria did not show a decreased survival; what is more, many of them had an improved survival with the increased doses. Augmentations in mutagenesis rates were observed after UV-B irradiation in only 4 of the 13 tested isolates. Arsenite tolerance was also established in 8 of the 13 tested strains: Staphylococcus saprophyticus A3 and Micrococcus sp. A7, which were able to grow in media containing up to 10 mM As(III). Finally, predominance of antibiotic resistances (azithromycin, erythromycin, clarithromycin, roxithromycin, streptomycin, chloramphenicol, gentamycin, kanamycin, tetracycline, and ampicillin) was found, in all the isolated strains from both wetlands, with unexpectedly high minimal inhibitory concentrations (MICs; >2 mg mL⁻¹) for macrolides. These results demonstrate that in extreme environments like high-altitude wetlands there is a correlation of multiresistances to UV-B radiation and arsenic, and that antibiotic resistances are also widespread in these pristine environments, where antibiotic selective pressure is supposed to be absent.     

Soluble polyamines in Salix myrsinifolia and S. myrsinites × S. myrsinifolia plantlets exposed to increased UV-B irradiation and decreased watering

Hybridisation between certain willow species is a common feature leading to novel genotypes varying in growth rate and stress tolerance. The objective of this 4-week study was to investigate the effects of decreased watering, enhanced ultraviolet-B irradiation (UV-B_BE, 280–315 nm, 7.2 kJ m⁻² day⁻¹) and combined decreased watering and enhanced UV-B irradiation on di- and polyamines in the leaves of Salix myrsinifolia and its hybrid with S. myrsinites. Control plantlets were well-watered and exposed to ambient UV-B irradiation (UV-B_BE, 3.6 kJ m⁻² day⁻¹). HPLC analyses showed that the constitutive concentrations of soluble di- and polyamines varied markedly between S. myrsinifolia and its hybrids. The degree of responses to treatments also varied: in S. myrsinifolia, concentrations of free putrescine were clearly increased by reduced watering, while in the hybrid willow, change in putrescine was less pronounced and not significant. Results also showed that the increase in putrescine in S. myrsinifolia by reduced watering was mitigated by concurrent enhancement of UV-B irradiation. There were no direct UV-B effects on the soluble polyamines.     

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.     

Ethylene evolution and ABA and polyamine contents in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> during UV-B stress

Changes in plant growth, membrane integrity, ethylene evolution, ABA content, and the content of free polyamines were examined in 14-day-old Arabidopsis thaliana (L.) Heynh., strain Columbia (Col-0) plants after a single UV-B irradiation with low (3 kJ/m²), moderate (6–9 kJ/m²), high (18 kJ/m²), and lethal (27 kJ/m²) doses. The UV-B treatment caused dose-dependent suppression of plant growth. One hour after irradiation, the membrane damage was evident from the increased leakage of electrolytes. The low-dose and moderate-dose irradiation caused a transient increase in evolution of ethylene and in the content of putrescine (spermidine and spermine precursor) with the peaks of these parameters attained at 5 and 24 h, respectively. The high-and lethaldose irradiation induced a smaller rise in ethylene evolution, with a slight trend to its decrease, especially, after the exposure to the lethal dose. The high and lethal doses of UV-B suppressed putrescine accumulation, depleted spermidine and spermine pools, and caused severe injuries and plant death. During the first day after irradiation, the ABA content increased in proportion to the irradiation dose. On the second day, the accumulation of ABA was observed in plants irradiated with moderate doses. The accumulation was arrested after a high-dose irradiation and was diminished by 45% after a lethal dose treatment. The results provide evidence for the involvement of ethylene, ABA, and polyamines in plant responses induced by UV-B irradiation.     

Photosynthesis performance in sweet almond [<Emphasis Type="Italic">Prunus dulcis</Emphasis> (Mill) D. Webb] exposed to supplemental UV-B radiation

Due to anthropogenic influences, solar UV-B irradiance at the earth’s surface is increasing. To determine the effects of enhanced UV-B radiation on photosynthetic characteristics of Prunus dulcis, two-year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-B_c), 4.42 (UV-B₁), 7.32 (UV-B₂) and 9.36 (UV-B₃) kJ m⁻² d⁻¹. Effects of UV-B stress on a range of chlorophyll (Chl) fluorescence parameters (FPs), Chl contents and photosynthetic gas-exchange parameters were investigated. UV-B stress promoted an increase in minimal fluorescence of dark-adapted state (F₀) and F₀/F_m, and a decrease in variable fluorescence (F_v, F_v/F_m, F_v/F₀ and F₀/F_m) due to its adverse effects on photosystem II (PSII) activity. No significant change was observed for maximal fluorescence of dark-adapted state (F_m). Enhanced UV-B radiation caused a significant inhibition of net photosynthetic rate (P _N) at UV-B₂ and UV-B₃ levels and this was accompanied by a reduction in stomatal conductance (g _s) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increased UV-B stress. In general, adverse UV-B effects became significant at the highest tested radiation dose 9.36 kJ m⁻² d⁻¹. The most sensitive indicators for UV-B stress were F_v/F₀, Chl a content and P _N. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis.     

Studies on the effects of UV-B radiation on phytoplankton of sub-antarctic lakes and ponds

Summary Experiments were performed to determine the effects of UV-B (ultraviolet, 280–320 nm) radiation on motility and growth of phytoplankton from lakes and ponds in South Georgia. After 4 h of solar radiation and 4h artificial radiation (UV-B_BE 11.6 kJ m^-2 day^-1, UV-B lamps) the swimming velocity of Cryptomonas sp. decreased. The growth rate of Botryococcus, Lyngbya sp. and Stauraslrum sp. did not show any significant variations between the different light conditions. The UV-B component was reduced by filtering solar radiation through glass bottles und cellulose acetate. Cloudy days had only 30% of the radiation of clear days in both the PAR (photosynthetic active radiation) and UV-B regions. The ponds contained large amounts of humic substances, which are responsible for the absorbance in the UV region.     

Low doses of ultraviolet-B or ultraviolet-C radiation affect phytohormones in young pea plants

Pea (Pisum sativum L., cv. Scinado) seedlings were exposed to low doses of ultraviolet-B (UV-B; 4.4 and 13.3 kJ m⁻² d⁻¹) or UV-C (0.1 and 0.3 kJ m⁻² d⁻¹) radiation for 14 d. Aminocyclopropane carboxylic acid (ACC), indoleacetic acid (IAA) and abscisic acid (ABA) contents were quantified by gas chromatography coupled to mass spectrometry (GC-MS). The accumulation of ACC upon irradiation was dose-dependent. ABA content was reduced and IAA content increased upon UV-C treatment whereas the UV-B doses used did not cause significant changes in ABA and IAA contents.     

Ambient levels of UV-B in Hawaii combined with nutrient deficiency decrease photosynthesis in near-isogenic maize lines varying in leaf flavonoids: Flavonoids decrease photoinhibition in plants exposed to UV-B

Near-isogenic lines of maize varying in their genes for flavonoid biosynthesis were utilized to examine the effects of foliar flavonoids and nutrient deficiency on maximum net photosynthetic rate (P _N) and chlorophyll (Chl) fluorescence (F_v/F_m) in response to ultraviolet-B (UV-B) radiation. Plants with deficient (30 to 70 % lower N, K, Mn, Fe, and Zn) and sufficient nutrients were exposed to four irradiation regimes: (1) no UV-B with solar photosynthetically active radiation (PAR), (2) two day shift to ambient artificial UV-B, 8.2–9.5 kJ m⁻² d⁻¹ (21–25 mmol m⁻² d⁻¹); (3) continuous ambient artificial UV-B; (4) continuous solar UV-B in Hawaii 12–18 kJ m⁻² d⁻¹ (32–47 mmol m⁻² d⁻¹). The natural ratio of UVB: PAR (0.25–0.40) was maintained in the UV-B treatments. In the adequately fertilized plants, lines b and lc had higher contents of flavonoids and anthocyanins than did lines hi27 and dta. UV-B induced the accumulation of foliar flavonoids in lines hi27 and b, but not in the low flavonoid line dta or in the high flavonoid line lc. In plants grown on deficient relative to adequate nutrients, flavonoid and anthocyanin contents decreased by 30–40 and 40–50 %, respectively, and Chl a and Chl b contents decreased by 30 and 70 %, respectively. The UV-B treatments did not significantly affect P _N and F_v/F_m in plants grown on sufficient nutrients, except in the low flavonoid lines dta and hi27 in which P _N and F_v/F_m decreased by ∼15 %. P _N, F_v/F_m, and stomatal conductance decreased markedly (20–30 %) in all lines exposed to UV-B when grown on low nutrients. The decrease in F_v/F_m was 10 % less in higher flavonoid lines b and lc. The photosynthetic apparatus of maize readily tolerated ambient UV-B in the tropics when plants were adequately fertilized. In contrast, ambient UV-B combined with nutrient deficiency significantly reduced photosynthesis in this C₄ plant. Nutrient deficiency increased the susceptibility of maize to UV-B-induced photoinhibition in part by decreasing the contents of photoprotective compounds.     

Responses of Tradescantia stamen hairs and pollen to UV-B irradiation

Clones 02 and 4430 of Tradescantia were tested in field, greenhouse and controlled environment chambers as monitors for the potentially hazardous UV-B irradiation increase that could result from stratospheric ozone decrease. In addition to about 16 hr of solar emissions at about 2100 micro-einsteins·m⁻²·s⁻¹ (400–700 nm) and 15 hr at about 1800 micro-einsteins·m⁻²·s⁻¹ in the field and greenhouse, respectively, plants were given 7 hr of supplemental UV-B irradiation per day for 27 days. After the first 7 days of UV-B irradiation exposure, cumulative data were recorded for 20 days. Cuttings of Tradescantia plants in controlled-environment, exposed to 16 hr of simulated solar emission of about 800 micro-einsteins·m⁻²·s⁻¹ (400–700 nm), were also exposed to 10 hr of supplemental UV-B irradiation per day for 1 or 2 days. All plants were checked for somatic aberrations (color changes in the flower petals and stamen hairs), number of hairs per stamen, and cells per hair. Pollen germination and pollen tube growth were noted after a 90-min UV-B irradiation period.Somatic aberrations occurred infrequently in the petals and were judged unreliable criteria for use in monitoring enhanced UV-B irradiation environments. The number of aberrant events within stamen hairs, however, was significantly increased by the UV-B irradiation treatments. while pollen germination and pollen tube growth were significantly reduced. These data indicate that color changes in stamen hairs and pollen viability are useful criteria for monitoring UV-B irradiation changes.     

Consequences of depletion of stratospheric ozone for terrestrial Antarctic ecosystems: the response of Deschampsia antarctica to enhanced UV-B radiation in a controlled environment

Mini UV lamps were installed over antarctic plants at Léonie Island, Antarctic peninsula, and shoot length measurements of Deschampsia antarctica were performed during the austral summer January–February 1999.We studied the response of the antarctic hairgrass, Deschampsia antarctica to enhanced UV-B. In a climate room experiment we exposed tillers of Deschampsia antarctica, collected at Léonie Island, Antarctic peninsula, to ambient and enhanced levels of UV-B radiation. In this climate room experiment with 0, 2.5 and 5 kJ m^–2 day^–1 UV-B_BE treatments we observed that length growth of shoots at 2.5 and 5 kJ m^–2 day^–1 UV-B_BE was markedly reduced compared to 0 kJ m^–2 day^–1 UV-B_BE. In addition, there was an increased number of shoots and increased leaf thickness with enhanced UV-B. The Relative Growth Rate (RGR) was not affected by UV-B, possibly because reduced shoot length growth by enhanced UV-B was compensated by increased tillering. Light response curves of net leaf photosynthesis of plants exposed to 5 kJ m^–2 day^–1 UV-B_BE did not differ from those exposed to 0 kJ m^–2 day^–1 UV-B_BE. The content of UV-B absorbing compounds of plants exposed to increasing UV-B did not significantly change.Mini UV-B lamp systems were installed in the field, to expose the terrestrial antarctic vegetation at Léonie Island to enhanced solar UV-B. In that study, the increment of shoot length of tagged plants of Deschampsia antarctica during the January-February 1999 at Léonie Island, was recorded and compared to shoot length growth under controlled conditions.The consequences of enhanced UV-B radiation as a result of ozone depletion for the terrestrial antarctic ecosytems are discussed.     

Effect of ABA on the UV-B-Induced Ethylene Evolution by the etr and ctr Mutants of Arabidopsis thaliana

The responses of 14-day-old Arabidopsis thaliana (L.) Heynh. plants to UV-B irradiation (280–320 nm) and ABA treatment were investigated. Wild-type plants as well as ethylene-insensitive etr1-1 and ctr1-1 mutants were used. Theetr1-1 mutant considerably differed from the ctr1-1 one in the fresh weight production after UV-B treatment (29.5 kJ/m²). The irradiated etr1-1 plants fell well behind the nonirradiated ones during the first two days after stress, but by the 8th day, their weight attained 70% of control plant weight. In contrast, Ctr1-1 mutant weight comprised 70% of control level after two days of stress but, by the 8th day, it was only 56% of the weight of control plants. In wild-type and ctr1-1 plants, ABA, in the 8 × 10^–6 to 2 × 10^–4 M concentration range, increased the difference between the weights of nonirradiated and irradiated plants, but in etr1-1 plants, ABA decreased this difference. The etr1-1, ctr1-1, and wild-type plants were very similar in the dynamics of ethylene evolution after UV-B treatment (7.4 kJ/m²). In wild-type, etr1-1, and ctr1-1 plants, ABA, in a concentration-dependent manner, inhibited UV-B-induced ethylene evolution to the same extent. The results obtained show that ABA exerted an opposite effect on UV-B-dependent growth in the plants with active (wild type and ctr1-1) and blocked (etr1-1) ethylene signal pathway, whereas the inhibition of ethylene synthesis by ABA was not related to ethylene signal transmission.     

THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE) REQUIRES MARINE BACTERIA FOR GROWTH1

Interactions with the bacterial community are increasingly considered to have a significant influence on marine phytoplankton populations. Here we used a simplified dinoflagellate‐bacterium experimental culture model to conclusively demonstrate that the toxic dinoflagellate Gymnodinium catenatum H. W. Graham requires growth‐stimulatory marine bacteria for postgermination survival and growth, from the point of resting cyst germination through to vegetative growth at bloom concentrations (10³ cells · mL^?1). Cysts of G. catenatum were germinated and grown in unibacterial coculture with antibiotic‐resistant or antibiotic‐sensitive Marinobacter sp. DG879 or Brachybacterium sp., and with mixtures of these two bacteria. Addition of antibiotics to cultures grown with antibiotic‐sensitive strains of bacteria resulted in death of the dinoflagellate culture, whereas cultures grown with antibiotic‐resistant bacteria survived antibiotic addition and continued to grow beyond the 21 d experiment. Removal of either bacterial type from mixed‐bacterial dinoflagellate cultures (using an antibiotic) resulted in cessation of dinoflagellate growth until bacterial concentration recovered to preaddition concentrations, suggesting that the bacterial growth factors are used for dinoflagellate growth or are labile. Examination of published reports of axenic dinoflagellate culture indicate that a requirement for bacteria is not universal among dinoflagellates, but rather that species may vary in their relative reliance on, and relationship with, the bacterial community. The experimental model approach described here solves a number of inherent and logical problems plaguing studies of algal‐bacterium interactions and provides a flexible and tractable tool that can be extended to examine bacterial interactions with other phytoplankton species.     

Effects of UV-B radiation on a charophycean alga,Chara aspera

The charophycean algal species Chara aspera was exposed for 73 days to three levels of UV-B radiation (weighted according to Caldwell's generalized plant action spectrum): 1.9 kJ m^–2 day^–1 (`no UV-B'), 6.4 KJ m<sup>–2</sup> day<sup>–1</sup> (ambient) and 10.5 kJ m<sup>–2</sup> day<sup>–1</sup> (enhanced UV-B), the latter level simulating 30% ozone reduction in The Netherlands.Charophycean algae are mainly freshwater organisms and are thought to be the algae most closely related to higher land plants. Therefore we expected that responses of charophycean algae to UV-B radiation might be more related to those observed in the higher land plants than those of other `lower' algal groups.Under elevated UV-B radiation algal length was reduced. There was no induction of UV absorbing compounds under enhanced UV-B. This might relate to a sensitive response to UV-B radiation. The charophycean algae show similar adaptations to UV-B radiation as terrestrial plants, while not having UV-screens as occur in many angiosperms. Vegetative reproduction (bulbils) increased in the presence of UV-B radiation, while generative reproduction (antheridia and oogonia) decreased.     

Effect of Enhanced UV-B Radiation on Polyamine Content and Membrane Permeability in Cucumber Leaves

Cucumber plants (Cucumis sativus L., cv. Jingchun 3) were grown in a greenhouse under PAR illumination of 400–600 mol/(m² s) at 30/15°C (day/night) temperature. Two enhanced biologically effective UV-B radiation levels per day were applied: 8.82 kJ/m² (T₁) and 12.6 kJ/m² (T₂). Cucumber seedlings were irradiated 7 h per day for 25 days under T₁ and T₂. A comparative study of growth, membrane permeability, and polyamine content in cucumber leaves under T₁ and T₂ treatments was conducted. UV-B radiation resulted in the dose-dependent decrease in leaf area, dry weight of foliage, and plant height. The T₁ and T₂ treatments caused an increase in the contents of putrescine, spermine, and spermidine. However, the total polyamine content declined slightly when electrolyte leakage increased dramatically on the 18th day of treatment, especially after T₂ treatment. It can be concluded that polyamine accumulation in the cucumber leaves is an adaptive mechanism to the stress caused by UV-B radiation.     

Interactive effects of UV-B irradiation and triadimefon on nodulation and nitrogen metabolism in Vigna radiata plants

Supply of aqueous solution of triadimefon (20 mg dm⁻³) to unstressed green gram plants increased the contents of soluble proteins, amino acids, nitrate and nitrite, and the activity of nitrate reductase in the leaves and nitrate reductase in nodules. The nitrogenase activity in nodules and roots was also increased. Number and fresh mass of nodules and their nitrate and nitrite contents were also higher than those of the controls. In contrast, the UV-B stress (12.2 kJ m⁻² d⁻¹) suppressed nodulation and nitrogen metabolism in leaves and roots compared to plants under natural UV-B (10 kJ m⁻² d⁻¹). Triadimefon-treated plants did not show such severe inhibitions after exposure to elevated UV-B. Thus triadimefon increased their tolerance to UV-B stress.     

Hydrocaffeic and p-coumaric acids,natural phenolic compounds,inhibit UV-B damage in WKD human conjunctival cells in vitro and rabbit eye in vivo

This paper studied the effect on UV-B ocular damage of 10µm hydrocaffeic acid (HCAF) alone and as a mixture (MIX) (5µm HCAF+5µm p-coumaric acid). Since ocular UV-B damage is mediated by reactive oxygen species, the aim was to test if HCAF and MIX could reduce oxidation damage in human conjunctival cells (WKD) in vitro and in cornea and sclera of rabbits in vivo. After UVB irradiation (44 J/m²) of WKD cells, 8-oxodG levels in DNA were markedly increased and this effect was attenuated by HCAF and MIX. Rabbit eyes were treated by application of HCAF and MIX drops before UV-B exposure (79 J/m²). Corneal and scleral DNA oxidation damage, xanthine-oxidase (XO) activity and malondialdehyde levels (MDA) in corneal tissue and prostaglandin E₂ (PGE₂) in the aqueous humour were reduced by HCAF alone and in combination with p-coumaric acid, showing their potential as a topical treatment against UV-B damage.     

EFFECTS OF ULTRAVIOLET-B RADIATION ON FUNGAL DISEASE DEVELOPMENT IN CUCUMIS SATIVUS

Three cucumber (Cucumis sativus L.) cultivars were exposed to a daily dose of 11.6 kJ m^-2biologically effective ultraviolet-B (UV-B_Be) radiation in an unshaded greenhouse before and/ or after infection by Colletotrichum lagenarium (Pass.) Ell. and Halst. or Cladosporium cucumerinum Ell. and Arth. and analyzed for disease development. Two of these cultivars, Poinsette and Calypso Hybrid, were disease resistant, while the third cultivar, Straight-8, was disease susceptible. Preinfectional treatment of 1 to 7 days with UV-B_BE in Straight-8 led to greater severity of both diseases. Postinfectional UV treatment did not lead to increased disease severity caused by C. lagenarium, while preinfectional UV treatment in both Straight-8 and Poinsette substantially increased disease severity. Although resistant cultivars Poinsette and Calypso Hybrid showed increased anthracnose disease severity when exposed to UV-B, this effect was apparent only on the cotyledons. Both higher spore concentration and exposure to UV-B radiation resulted in greater disease severity. Of the cucumber cultivars tested for UV-B sensitivity, growth in Poinsette was most sensitive and Calypso Hybrid was least sensitive. These preliminary results indicate that the effects of UV-B radiation on disease development in cucumber vary depending on cultivar, timing and duration of UV-B exposure, inoculation level, and plant age.     

Marine Bacterial Isolates Display Diverse Responses to UV-B Radiation

The molecular and biological consequences of UV-B radiation were investigated by studying five species of marine bacteria and one enteric bacterium. Laboratory cultures were exposed to an artificial UV-B source and subjected to various post-UV irradiation treatments. Significant differences in survival subsequent to UV-B radiation were observed among the isolates, as measured by culturable counts. UV-B-induced DNA photodamage was investigated by using a highly specific radioimmunoassay to measure cyclobutane pyrimidine dimers (CPDs). The CPDs determined following UV-B exposure were comparable for all of the organisms except Sphingomonas sp. strain RB2256, a facultatively oligotrophic ultramicrobacterium. This organism exhibited little DNA damage and a high level of UV-B resistance. Physiological conditioning by growth phase and starvation did not change the UV-B sensitivity of marine bacteria. The rates of photoreactivation following exposure to UV-B were investigated by using different light sources (UV-A and cool white light). The rates of photoreactivation were greatest during UV-A exposure, although diverse responses were observed. The differences in sensitivity to UV-B radiation between strains were reduced after photoreactivation. The survival and CPD data obtained for Vibrio natriegens when we used two UV-B exposure periods interrupted by a repair period (photoreactivation plus dark repair) suggested that photoadaptation could occur. Our results revealed that there are wide variations in marine bacteria in their responses to UV radiation and subsequent repair strategies, suggesting that UV-B radiation may affect the microbial community structure in surface water.     

Culturable Airborne Bacteria in Outdoor Environments in Beijing,China

Airborne bacteria are important biological components of bioaerosol and play an important role in ecosystem. Bacteria at a high concentration in the atmosphere can result in biological air pollution and all kinds of diseases. In this study, a systematical survey on the culturable airborne bacteria was carried out for 1 year at three sites in Beijing urban area. Results showed that concentrations of culturable bacteria ranged from 71 colony forming units (CFU)/m³ to 22,100 CFU/m³, and the mean was 2,217 CFU/m³. Bacterial concentrations at the human activity-enriched site (RCEES) and the highly trafficked site (XZM) were virtually the same point. They were significantly higher than those at the greener site (BBG). Significant variation in bacterial concentrations in different seasons was observed at RCEES and XZM with higher concentrations in summer and autumn. In a single day, significantly lower concentrations were detected at 13:00 hours through all sampling sites. In this study, 165 species in 47 genera of culturable bacteria were identified. Micrococcus was one of the most dominant bacterial groups and contributed to approximately 20∼30% of the total bacterial concentration, followed by Staphylococcus, Bacillus, Corynebacterium, and Pseudomonas. The bacterial species with a high concentration percentage included Micrococcus luteus and Micrococcus roseus.     

In assessing biological UV-B effects,natural fluctuations of solar radiation should be taken into account

Daily and weekly fluctuations of PAR, UV-A, and UV-B have been continuously monitored for 5 months in Ancient Korinthos, Greece (37°58 N, 23°0 E) using a calibrated instrument based on 3 sharp band sensors. Daily dose ranged between 521–12 006 kJ m^-2 for PAR; 52–1, 239 kJ m^-2 for UV-A; and 0.66–22.5 kJ m² for UV-B. Weekly dose ranged between 16 778-81 788 kJ m^-2 for PAR; 1 406–8 517 kJ m^-2 for UV-A; and 18–151 kJ m^-2 for UV-B. UV-B/PAR and UV-A/PAR ratio distribution, however, does not follow closely PAR fluctuations. Generally, the UV-B/PAR and UV-A/PAR ratios were high in bright light conditions (2.1×10^-3, 118×10^-3) and low in darker weeks (0.9×10^-3, 63×10^-3. The UV-B/UV-A ratio exhibits smaller fluctuations with season (20x1×10^-3, 12×10^-3). Attention is drawn to the effects of sudden changes in ambient radiation and to the ratios of UV-B, UV-A, and PAR.