Induction of unique tandem-base change mutations in bacterial spores exposed to extreme dryness

Synergistic Interactions among Vacuum, Solar Heating, and UV Irradiation Enhance the Lethality of Interplanetary Space

A Planetary Atmospheric Chamber (PAC) was used to create simulations of interplanetary conditions to test the spore survival of three Bacillus spp. exposed to interacting conditions of vacuum (VAC), simulated solar heating (HEAT), and simulated solar ultraviolet irradiation (UV). Synergism was observed among the experimental factors for all three Bacillus spp. tested that suggested the increased lethality of HEAT and UV when concomitantly exposed to VAC. The most aggressive biocidal effects were observed for assays with VAC + HEAT + UV conditions run simultaneously over short time-steps. The results were used to predict the accumulation of extremely rapid Sterility Assurance Levels (SALs; def., -12 logs of bioburden reduction) measured in a few minutes to a few hours for external surfaces of interplanetary spacecraft. Furthermore, the results were extrapolated to predict that approx. 1 × 104 SAL exposures might be accumulated for external surfaces on the Europa Clipper spacecraft during a 3.5-year transit time between Venus (0.7 AU) and Mars (1.5 AU) during a series of Venus-Earth-Earth gravity assists (VEEGA trajectory) to Jovian space. The results are applicable to external spacecraft surfaces exposed to direct solar heating and UV irradiation during transits though the inner solar system.

New Thoughts on an Old Topic: Secrets of Bacterial Spore Resistance Slowly Being Revealed

The quest for bacterial survival is exemplified by spores formed by some Firmicutes members. They turn up everywhere one looks, and their ubiquity reflects adaptations to the stresses bacteria face. Spores are impactful in public health, food safety, and biowarfare. Heat resistance is the hallmark of spores and is countered principally by a mineralized gel-like protoplast, termed the spore core, with reduced water which minimizes macromolecular movement/denaturation/aggregation. Dry heat, however, introduces mutations into spore DNA. Spores have countermeasures to extreme conditions that are multifactorial, but the fact that spore DNA is in a crystalline-like nucleoid in the spore core, likely due to DNA saturation with small acid-soluble spore proteins (SASPs), suggests that reduced macromolecular motion is also critical in spore dry heat resistance. SASPs are also central in the radiation resistance characteristic of spores, where the contributions of four spore features-SASP; Ca2+, with pyridine-2,6-dicarboxylic acid (CaDPA); photoproduct lyase; and low water content-minimize DNA damage. Notably, the spore environment steers UV photochemistry toward a product that germinated spores can repair without significant mutagenesis. This resistance extends to chemicals and macromolecules that could damage spores. Macromolecules are excluded by the spore coat which impedes the passage of moieties of ≥10 kDa. Additionally, damaging chemicals may be degraded or neutralized by coat enzymes/proteins. However, the principal protective mechanism here is the inner membrane, a compressed structure lacking lipid fluidity and presenting a barrier to the diffusion of chemicals into the spore core; SASP saturation of DNA also protects against genotoxic chemicals. Spores are also resistant to other stresses, including high pressure and abrasion. Regardless, overarching mechanisms associated with resistance seem to revolve around reduced molecular motion, a fine balance between rigidity and flexibility, and perhaps efficient repair.

Proteomic and Metabolomic Profiling of Deinococcus radiodurans Recovering After Exposure to Simulated Low Earth Orbit Vacuum Conditions

The polyextremophile, gram-positive bacterium Deinococcus radiodurans can withstand harsh conditions of real and simulated outer space environment, e.g., UV and ionizing radiation. A long-term space exposure of D. radiodurans has been performed in Low Earth Orbit (LEO) in frames of the Tanpopo orbital mission aiming to investigate the possibility of interplanetary life transfer. Space vacuum (10^-4–10^-7 Pa) is a harmful factor, which induces dehydration and affects microbial integrity, severely damaging cellular components: lipids, carbohydrates, proteins, and nucleic acids. However, the molecular strategies by which microorganisms protect their integrity on molecular and cellular levels against vacuum damage are not yet understood. In a simulation experiment, we exposed dried D. radiodurans cells to vacuum (10^-4–10^-7 Pa), which resembles vacuum pressure present outside the International Space Station in LEO. After 90 days of high vacuum exposure, survival of D. radiodurans cells was 2.5-fold lower compared to control cells. To trigger molecular repair mechanisms, vacuum exposed cells of D. radiodurans were recovered in complex medium for 3 and 6 h. The combined approach of analyzing primary metabolites and proteins revealed important molecular activities during early recovery after vacuum exposure. In total, 1939 proteins covering 63% of D. radiodurans annotated protein sequences were detected. Proteases, tRNA ligases, reactive oxygen species (ROS) scavenging proteins, nucleic acid repair proteins, TCA cycle proteins, and S-layer proteins are highly abundant after vacuum exposure. The overall abundance of amino acids and TCA cycle intermediates is reduced during the recovery phase of D. radiodurans as they are needed as carbon source. Furthermore, vacuum exposure induces an upregulation of Type III histidine kinases, which trigger the expression of S-layer related proteins. Along with the highly abundant transcriptional regulator of FNR/CRP family, specific histidine kinases might be involved in the regulation of vacuum stress response. After repair processes are finished, D. radiodurans switches off the connected repair machinery and focuses on proliferation. Combined comparative analysis of alterations in the proteome and metabolome helps to identify molecular key players in the stress response of D. radiodurans, thus elucidating the mechanisms behind its extraordinary regenerative abilities and enabling this microorganism to withstand vacuum stress.

Experimental studies addressing the longevity of Bacillus subtilis spores - The first data from a 500-year experiment

The ability to form endospores allows certain Gram-positive bacteria (e.g. Bacillus subtilis) to challenge the limits of microbial resistance and survival. Thus, B. subtilis is able to tolerate many environmental extremes by transitioning into a dormant state as spores, allowing survival under otherwise unfavorable conditions. Despite thorough study of spore resistance to external stresses, precisely how long B. subtilis spores can lie dormant while remaining viable, a period that potentially far exceeds the human lifespan; is not known although convincing examples of long term spore survival have been recorded. In this study, we report the first data from a 500-year microbial experiment, which started in 2014 and will finish in 2514. A set of vials containing a defined concentration of desiccated B. subtilis spores is opened and tested for viability every two years for the first 24 years and then every 25 years until experiment completion. Desiccated baseline spore samples were also exposed to environmental stresses, including X-rays, 254 nm UV-C, 10% H₂O₂, dry heat (120°C) and wet heat (100°C) to investigate how desiccated spores respond to harsh environmental conditions after long periods of storage. Data from the first 2 years of storage show no significant decrease in spore viability. Additionally, spores of B. subtilis were subjected to various short-term storage experiments, revealing that space-like vacuum and high NaCl concentration negatively affected spore viability.

Proteometabolomic response of Deinococcus radiodurans exposed to UVC and vacuum conditions: Initial studies prior to the Tanpopo space mission

The multiple extremes resistant bacterium Deinococcus radiodurans is able to withstand harsh conditions of simulated outer space environment. The Tanpopo orbital mission performs a long-term space exposure of D. radiodurans aiming to investigate the possibility of interplanetary transfer of life. The revealing of molecular machinery responsible for survivability of D. radiodurans in the outer space environment can improve our understanding of underlying stress response mechanisms. In this paper, we have evaluated the molecular response of D. radiodurans after the exposure to space-related conditions of UVC irradiation and vacuum. Notably, scanning electron microscopy investigations showed that neither morphology nor cellular integrity of irradiated cells was affected, while integrated proteomic and metabolomic analysis revealed numerous molecular alterations in metabolic and stress response pathways. Several molecular key mechanisms of D. radiodurans, including the tricarboxylic acid cycle, the DNA damage response systems, ROS scavenging systems and transcriptional regulators responded in order to cope with the stressful situation caused by UVC irradiation under vacuum conditions. These results reveal the effectiveness of the integrative proteometabolomic approach as a tool in molecular analysis of microbial stress response caused by space-related factors.

Bacillus subtilis RecA and its accessory factors, RecF, RecO, RecR and RecX, are required for spore resistance to DNA double-strand break

Bacillus subtilis RecA is important for spore resistance to DNA damage, even though spores contain a single non-replicating genome. We report that inactivation of RecA or its accessory factors, RecF, RecO, RecR and RecX, drastically reduce survival of mature dormant spores to ultrahigh vacuum desiccation and ionizing radiation that induce single strand (ss) DNA nicks and double-strand breaks (DSBs). The presence of non-cleavable LexA renders spores less sensitive to DSBs, and spores impaired in DSB recognition or end-processing show sensitivities to X-rays similar to wild-type. In vitro RecA cannot compete with SsbA for nucleation onto ssDNA in the presence of ATP. RecO is sufficient, at least in vitro, to overcome SsbA inhibition and stimulate RecA polymerization on SsbA-coated ssDNA. In the presence of SsbA, RecA slightly affects DNA replication in vitro, but addition of RecO facilitates RecA-mediated inhibition of DNA synthesis. We propose that repairing of the DNA lesions generates a replication stress to germinating spores, and the RecA·ssDNA filament might act by preventing potentially dangerous forms of DNA repair occurring during replication. RecA might stabilize a stalled fork or prevent or promote dissolution of reversed forks rather than its cleavage that should require end-processing.

Mutagenesis in bacterial spores exposed to space and simulated martian conditions: data from the EXPOSE-E spaceflight experiment PROTECT

As part of the PROTECT experiment of the EXPOSE-E mission on board the International Space Station (ISS), the mutagenic efficiency of space was studied in spores of Bacillus subtilis 168. After 1.5 years' exposure to selected parameters of outer space or simulated martian conditions, the rates of induced mutations to rifampicin resistance (Rif(R)) and sporulation deficiency (Spo(-)) were quantified. In all flight samples, both mutations, Rif(R) and Spo(-), were induced and their rates increased by several orders of magnitude. Extraterrestrial solar UV radiation (>110 nm) as well as simulated martian UV radiation (>200 nm) led to the most pronounced increase (up to nearly 4 orders of magnitude); however, mutations were also induced in flight samples shielded from insolation, which were exposed to the same conditions except solar irradiation. Nucleotide sequencing located the Rif(R) mutations in the rpoB gene encoding the β-subunit of RNA polymerase. Mutations isolated from flight and parallel mission ground reference (MGR) samples were exclusively localized to Cluster I. The 21 Rif(R) mutations isolated from the flight experiment showed all a C to T transition and were all localized to one hotspot: H482Y. In mutants isolated from the MGR, the spectrum was wider with predicted amino acid changes at residues Q469K/L/R, H482D/P/R/Y, and S487L. The data show the unique mutagenic power of space and martian surface conditions as a consequence of DNA injuries induced by solar UV radiation and space vacuum or the low pressure of Mars.

Astrobiological aspects of the mutagenesis of cosmic radiation on bacterial spores

Based on their unique resistance to various space parameters, Bacillus endospores are one of the model systems used for astrobiological studies. In this study, spores of B. subtilis were used to study the effects of galactic cosmic radiation (GCR) on spore survival and induced mutagenesis. In interplanetary space, outside Earth's protective magnetic field, spore-containing rocks would be exposed to bombardment by high-energy charged particle radiation from galactic sources and from the Sun, which consists of photons (X-rays, gamma rays), protons, electrons, and heavy, high-energy charged (HZE) particles. B. subtilis spores were irradiated with X-rays and accelerated heavy ions (helium, carbon, silicon and iron) in the linear energy transfer (LET) range of 2-200 keV/mum. Spore survival and the rate of the induced mutations to rifampicin resistance (Rif(R)) depended on the LET of the applied species of ions and radiation, whereas the exposure to high-energy charged particles, for example, iron ions, led to a low level of spore survival and increased frequency of mutation to Rif(R) compared to low-energy charged particles and X-rays. Twenty-one Rif(R) mutant spores were isolated from X-ray and heavy ion-irradiated samples. Nucleotide sequencing located the Rif(R) mutations in the rpoB gene encoding the beta-subunit of RNA polymerase. Most mutations were primarily found in Cluster I and were predicted to result in amino acid changes at residues Q469L, A478V, and H482P/Y. Four previously undescribed alleles in B. subtilis rpoB were isolated: L467P, R484P, and A488P in Cluster I and H507R in the spacer between Clusters I and II. The spectrum of Rif(R) mutations arising from spores exposed to components of GCR is distinctly different from those of spores exposed to simulated space vacuum and martian conditions.

Space microbiology

The responses of microorganisms (viruses, bacterial cells, bacterial and fungal spores, and lichens) to selected factors of space (microgravity, galactic cosmic radiation, solar UV radiation, and space vacuum) were determined in space and laboratory simulation experiments. In general, microorganisms tend to thrive in the space flight environment in terms of enhanced growth parameters and a demonstrated ability to proliferate in the presence of normally inhibitory levels of antibiotics. The mechanisms responsible for the observed biological responses, however, are not yet fully understood. A hypothesized interaction of microgravity with radiation-induced DNA repair processes was experimentally refuted. The survival of microorganisms in outer space was investigated to tackle questions on the upper boundary of the biosphere and on the likelihood of interplanetary transport of microorganisms. It was found that extraterrestrial solar UV radiation was the most deleterious factor of space. Among all organisms tested, only lichens (Rhizocarpon geographicum and Xanthoria elegans) maintained full viability after 2 weeks in outer space, whereas all other test systems were inactivated by orders of magnitude. Using optical filters and spores of Bacillus subtilis as a biological UV dosimeter, it was found that the current ozone layer reduces the biological effectiveness of solar UV by 3 orders of magnitude. If shielded against solar UV, spores of B. subtilis were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite powder (artificial meteorites). The data support the likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis.

Exposure of DNA and Bacillus subtilis spores to simulated martian environments: use of quantitative PCR (qPCR) to measure inactivation rates of DNA to function as a template molecule

Several NASA and ESA missions are planned for the next decade to investigate the possibility of present or past life on Mars. Evidence of extraterrestrial life will likely rely on the detection of biomolecules, which highlights the importance of preventing forward contamination not only with viable microorganisms but also with biomolecules that could compromise the validity of life-detection experiments. The designation of DNA as a high-priority biosignature makes it necessary to evaluate its persistence in extraterrestrial environments and the effects of those conditions on its biological activity. We exposed DNA deposited on spacecraft-qualified aluminum coupons to a simulated martian environment for periods ranging from 1 minute to 1 hour and measured its ability to function as a template for replication in a quantitative polymerase chain reaction (qPCR) assay. We found that inactivation of naked DNA or DNA extracted from exposed spores of Bacillus subtilis followed a multiphasic UV-dose response and that a fraction of DNA molecules retained functionality after 60 minutes of exposure to simulated full-spectrum solar radiation in martian atmospheric conditions. The results indicate that forward-contaminant DNA could persist for considerable periods of time at the martian surface.

Exogenous Endophthalmitis in Pediatric Age Group

PURPOSE

To identify the microbiological spectrum and visual outcome of exogenous infectious endophthalmitis in the pediatric age group.

METHODS

We reviewed the medical records of all children 14 years and younger with culture-positive endophthalmitis treated at King Khaled Eye Specialist Hospital and King Abdulaziz University Hospital between January 1, 1980, and December 31, 2004.

RESULTS

Forty-nine children were identified. There were 32 males and 17 females with a mean age of 5.7 +/- 2.8 years (range 1-13 years). Thirty-five (71.4 %) cases occurred after penetrating open globe injuries and the remaining 14 (28.6%) followed ocular surgery. Primary vitrectomy was performed on 29 (59.2%) eyes. The mean follow-up was 28.4 +/- 28.4 months (range 1.2-98.5 months). A single species was isolated in 42 (85.7%) eyes, and multiple organisms in seven (14.3%) with a total of 56 infecting organisms. The most common isolates were Streptococcus species and coagulase-negative Staphylococci comprising 44.6% and 21.4% of the isolates, respectively. Final visual acuity was 20/200 or better in 15 (34.1%), counting fingers in 8 (18.2%), light perception to hand motions in 8 (18.2%), no light perception in 13 (29.5%) eyes, including 3 that have been enucleated or eviscerated, and not available in 5 patients. None of the children who had nonvirulent organisms had a final visual acuity of no light perception compared with 39.4% of children who had virulent organisms (p = 0.011). Visual outcome of counting fingers was attained in 26% of children who were treated with primary vitrectomy compared with 5.9% of children treated with antibiotics alone on presentation (p = 0.0484). Visual outcome was no light perception in 18.5% of children who underwent primary vitrectomy compared with 47.1% of children treated with antibiotics alone.

CONCLUSIONS

The most common organisms identified were Streptococcus species and coagulase-negative Staphylococci. Culture of a nonvirulent organism, and treatment with primary vitrectomy were associated with better visual outcomes. Visual outcomes were generally poor.

Ancient micronauts: interplanetary transport of microbes by cosmic impacts

Recent developments in microbiology, geophysics and planetary sciences raise the possibility that the planets in our solar system might not be biologically isolated. Hence, the possibility of lithopanspermia (the interplanetary transport of microbial passengers inside rocks) is presently being re-evaluated, with implications for the origin and evolution of life on Earth and within our solar system. Here, I summarize our current understanding of the physics of impacts, space transport of meteorites, and the potentiality of microorganisms to undergo and survive interplanetary transfer.

Isolation of rpoB mutations causing rifampicin resistance in Bacillus subtilis spores exposed to simulated Martian surface conditions

ABSTRACT Bacterial spores are considered prime candidates for Earth-to-Mars transport by natural processes and human spaceflight activities. Previous studies have shown that exposure of Bacillus subtilis spores to ultrahigh vacuum (UHV) characteristic of space both increased the spontaneous mutation rate and altered the spectrum of mutation in various marker genes; but, to date, mutagenesis studies have not been performed on spores exposed to milder low pressures encountered in the martian environment. Mutations to rifampicin-resistance (Rif(R)) were isolated in B. subtilis spores exposed to simulated martian atmosphere (99.9% CO(2), 710 Pa) for 21 days in a Mars Simulation Chamber (MSC) and compared to parallel Earth controls. Exposure in the MSC reduced spore viability by approximately 67% compared to Earth controls, but this decrease was not statistically significant (P = 0.3321). The frequency of mutation to Rif(R) was also not significantly increased in the MSC compared to Earth-exposed spores (P = 0.479). Forty-two and 51 Rif(R) mutant spores were isolated from the MSC- and Earth-exposed controls, respectively. Nucleotide sequencing located the Rif(R) mutations in the rpoB gene encoding the beta subunit of RNA polymerase at residue V135F of the N-cluster and at residues Q469K/L, H482D/P/R/Y, and S487L in Cluster I. No mutations were found in rpoB Clusters II or III. Two new alleles, Q469L and H482D, previously unreported in B. subtilis rpoB, were isolated from spores exposed in the MSC; otherwise, only slight differences were observed in the spectra of spontaneous Rif(R) mutations from spores exposed to Earth vs. the MSC. However, both spectra are distinctly different from Rif(R) mutations previously reported arising from B. subtilis spores exposed to simulated space vacuum.

Microbiologic spectrum and visual outcome of posttraumatic endophthalmitis

PURPOSE

To identify the microbiologic spectrum and visual outcome of infectious endophthalmitis after open globe injuries.

METHODS

We reviewed the medical records of all patients with culture-positive endophthalmitis after open globe injuries who were treated at King Khaled Eye Specialist Hospital and King Abdulaziz University Hospital (Riyadh, Saudi Arabia) between January 1, 1993, and December 31, 2003.

RESULTS

Sixty-seven patients were identified. There were 55 males and 12 females (mean age +/- SD, 23.3 +/- 18.3 years; range, 2-65 years). The mean follow-up +/- SD was 18.8 +/- 23.9 months (range, 1-120 months). Twenty-nine eyes (43%) had intraocular foreign bodies (IOFBs). A single species was isolated from 59 eyes, and multiple organisms were isolated from 8 eyes (total number of infecting organisms, 78). The most common isolates were coagulase-negative staphylococci and Streptococcus species (26.9% of isolates each). Gram-negative organisms and fungi comprised 12.8% and 3.8% of isolates, respectively. Staphylococcus epidermidis comprised 37.1% of isolates in the group with IOFBs and 16.3% of isolates in the group without IOFBs (P = 0.0358). Streptococcus species comprised 41.8% of isolates in the group without IOFBs and 8.6% of isolates in the group with IOFBs (P = 0.0024). Final visual acuity was 20/200 or better in 30 eyes (47.6%). Visual acuity of 20/200 or better at presentation (P = 0.0474) and time from injury to presentation to our institutes of <1 day (P = 0.0348) were significantly associated with better visual acuity outcome. Final visual acuity of 20/200 or better was achieved in 61.9% of patients infected with nonvirulent organisms compared with 40.5% of patients infected with virulent organisms.

CONCLUSIONS

The most common organisms identified were coagulase-negative staphylococci and Streptococcus species. Clinical features associated with better visual acuity outcomes included better presenting visual acuity, early presentation to our institutes, and isolation of a nonvirulent organism. Posttraumatic endophthalmitis is associated with a poor visual prognosis.

Role of DNA repair by nonhomologous-end joining in Bacillus subtilis spore resistance to extreme dryness, mono- and polychromatic UV, and ionizing radiation

The role of DNA repair by nonhomologous-end joining (NHEJ) in spore resistance to UV, ionizing radiation, and ultrahigh vacuum was studied in wild-type and DNA repair mutants (recA, splB, ykoU, ykoV, and ykoU ykoV mutants) of Bacillus subtilis. NHEJ-defective spores with mutations in ykoU, ykoV, and ykoU ykoV were significantly more sensitive to UV, ionizing radiation, and ultrahigh vacuum than wild-type spores, indicating that NHEJ provides an important pathway during spore germination for repair of DNA double-strand breaks.

Bacillus subtilis spores on artificial meteorites survive hypervelocity atmospheric entry: implications for Lithopanspermia

An important but untested aspect of the lithopanspermia hypothesis is that microbes situated on or within meteorites could survive hypervelocity entry from space through Earth's atmosphere. The use of high-altitude sounding rockets to test this notion was explored. Granite samples permeated with spores of Bacillus subtilis strain WN511 were attached to the exterior telemetry module of a sounding rocket and launched from White Sands Missile Range, New Mexico into space, reaching maximum atmospheric entry velocity of 1.2 km/s. Maximum recorded temperature during the flight was measured at 145 degrees C. The surfaces of the post-flight granite samples were swabbed and tested for recovery and survival of WN511 spores, using genetic markers and the unique DNA fingerprint of WN511 as recovery criteria. Spore survivors were isolated at high frequency, ranging from 1.2% to 4.4% compared with ground controls, from all surfaces except the forward-facing surface. Sporulation-defective mutants were noted among the spaceflight survivors at high frequency (4%). These experiments constitute the first report of spore survival to hypervelocity atmospheric transit, and indicate that sounding rocket flights can be used to model the high-speed atmospheric entry of bacteria-laden artificial meteorites.

Base-change mutations induced by various treatments of Bacillus subtilis spores with and without DNA protective small, acid-soluble spore proteins

Previous work has shown that spores of wild-type Bacillus subtilis are more resistant to killing by dry and wet heat, low vacuum lyophilization and hydrogen peroxide than are spores lacking the majority of their DNA protective alpha/beta-type small, acid-soluble spore proteins (SASP) (termed alpha(-)beta(-) spores). These four treatments kill alpha(-)beta(-) spores in large part by DNA damage with accompanying mutagenesis, but only dry heat kills wild-type spores by DNA damage and mutagenesis. DNA sequence analysis of nalidixic acid-resistant (nal(r)) mutants generated by these treatments has now shown that the nal(r) mutations are base changes in the gyrA gene that encodes one subunit of DNA gyrase. Analysis of the DNA sequence of the gyrA gene in a large number of nal(r) mutants also indicates that: (1) base changes induced by hydrogen peroxide and wet heat in alpha(-)beta(-) spores are similar to those in spontaneous nal(r) mutants with only a few notable differences; (2) base changes induced by dry heat in wild-type spores and low vacuum lyophilization of alpha(-)beta(-) spores are similar, and include a high level of a tandem base change seen previously only in spores treated with very high vacuum and (3) base changes induced by lyophilization and dry heat are very different from those in spontaneous mutants in wild-type and alpha(-)beta(-) spores, which exhibit only one significant difference. While the initial DNA damage generated in spores by dry heat, lyophilization or high vacuum is almost certainly different than that generated by hydrogen peroxide or wet heat, the precise nature of the DNA damage remains to be determined.

UV photochemistry of DNA in vitro and in Bacillus subtilis spores at earth-ambient and low atmospheric pressure: implications for spore survival on other planets or moons in the solar system

Two major parameters influencing the survival of Bacillus subtilis spores in space and on bodies within the Solar System are UV radiation and vacuum, both of which induce inactivating damage to DNA. To date, however, spore survival and DNA photochemistry have been explored only at the extremes of Earth-normal atmospheric pressure (101.3 kPa) and at simulated space vacuum (10(-3)-10(-6) Pa). In this study, wild-type spores, mutant spores lacking alpha/beta-type small, acid-soluble spore proteins (SASP), naked DNA, and complexes between SASP SspC and DNA were exposed simultaneously to UV (254 nm) at intermediate pressure (1-2 Pa), and the UV photoproducts cis,syn-thymine-thymine cyclobutane dimer (c,sTT), trans,syn-thymine-thymine cyclobutane dimer (t,sTT), and "spore photoproduct" (SP) were quantified. At 101.3 kPa, UV-treated wild-type spores accumulated only SP, but spores treated with UV radiation at 1-2 Pa exhibited a spectrum of DNA damage similar to that of spores treated at 10(-6) Pa, with accumulation of SP, c,sTT, and t,sTT. The presence or absence of alpha/beta-type SASP in spores was partly responsible for the shift observed between levels of SP and c,sTT, but not t,sTT. The changes observed in spore DNA photochemistry at 1-2 Pa in vivo were not reproduced by irradiation of naked DNA or SspC:DNA complexes in vitro, suggesting that factors other than SASP are involved in spore DNA photochemistry at low pressure.

Survival of microorganisms in space protected by meteorite material: results of the experiment 'EXOBIOLOGIE' of the PERSEUS mission

During the early evolution of life on Earth, before the formation of a protective ozone layer in the atmosphere, high intensities of solar UV radiation of short wavelengths could reach the surface of the Earth. Today the full spectrum of solar UV radiation is only experienced in space, where other important space parameters influence survival and genetic stability additionally, like vacuum, cosmic radiation, temperature extremes, microgravity. To reach a better understanding of the processes leading to the origin, evolution and distribution of life we have performed space experiments with microorganisms. The ability of resistant life forms like bacterial spores to survive high doses of extraterrestrial solar UV alone or in combination with other space parameters, e.g. vacuum, was investigated. Extraterrestrial solar UV was found to have a thousand times higher biological effectiveness than UV radiation filtered by stratospheric ozone concentrations found today on Earth. The protective effects of anorganic substances like artificial or real meteorites were determined on the MIR station. In the experiment EXOBIOLOGIE of the French PERSEUS mission (1999) it was found that very thin layers of anorganic material did not protect spores against the deleterious effects of energy-rich UV radiation in space to the expected amount, but that layers of UV radiation inactivated spores serve as a UV-shield by themselves, so that a hypothetical interplanetary transfer of life by the transport of microorganisms inside rocks through the solar system cannot be excluded, but requires the shielding of a substantial mass of anorganic substances.

Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments

Endospores of Bacillus spp., especially Bacillus subtilis, have served as experimental models for exploring the molecular mechanisms underlying the incredible longevity of spores and their resistance to environmental insults. In this review we summarize the molecular laboratory model of spore resistance mechanisms and attempt to use the model as a basis for exploration of the resistance of spores to environmental extremes both on Earth and during postulated interplanetary transfer through space as a result of natural impact processes.

Sunlight mutagenesis: changes in mutational specificity during the irradiation of phage M13mp2

We reported previously that the mutations in phage M13mp2, a single-stranded DNA phage, induced by sunlight exposure are predominated by G-to-C transversions. We have now made an unexpected observation that an exposure to sunlight for a short period of time results in induction mainly of C-to-T transitions while a longer exposure results in the induction of G-to-C transversions. This peculiar phenomenon suggests that DNA damage formed by initial sunlight exposure can be transformed during an elongated exposure. 7, 8-Dihydro-8-oxoguanine (8-oxoG) in DNA might be involved in the shift of the mutational specificity, as 8-oxoG was formed in the phage DNA upon the sunlight exposure. We also compared the mutagenic activity of UVB irradiation with that of sunlight exposure. The results demonstrate that the genotoxic properties of sunlight and UVB in phage M13mp2 mutagenesis are different. The shift in the mutational specificity associated with the dose of the sunlight may call for general cautions in the studies of agent-induced mutagenesis.

Post-traumatic endophthalmitis: causative organisms and visual outcome

PURPOSE

Post-traumatic endophthalmitis makes up a distinct subset of intraocular infections. The purpose of the present study was to identify the causative organisms and record the visual outcome after infectious endophthalmitis in eyes with penetrating trauma.

METHODS

We reviewed 18 consecutive cases of culture-positive endophthalmitis that developed after penetrating ocular trauma. All cases were treated with pars plana vitrectomy and intravenous and intraocular antibiotics.

RESULTS

The 15 males and 3 females ranged in age from 4 to 43 years (mean 25.1 +/- 11 years). Nine (50%) had intraocular foreign bodies. A single species was isolated in 16 cases, and multiple organisms in two. Staphylococcus epidermidis and gram-negative organisms were the most frequent and were cultured either alone or in association with other organisms in respectively five (27.7%) and four cases (22.2%). Clostridium perfringens was isolated in three cases (16.6%). Bacillus was not found as a cause of endophthalmitis. Final visual acuity was better than 20/400 in eight cases (44%). In five cases (27.7%), the eye was saved but visual acuity was counting fingers. Two eyes (11%) had no light perception. The remaining three eyes (16.6%) were enucleated or eviscerated. Clostridium perfringens was isolated from two eyes and Aspergillus niger from one. Postoperative retinal detachment developed in four eyes, which were successfully operated.

CONCLUSIONS

Organisms isolated in this series were similar to those in previous reports of post-traumatic endophthalmitis from other parts of the world, except that the frequency of Clostridium perfringens isolation was high and no Bacillus species were cultured. In view of its devastating outcome, post-traumatic endophthalmitis must be treated promptly with vitrectomy and intravitreal antibiotics.