An alternative interpretation for tailing in survival curves for bacteria exposed to germicidal radiation.

It has been proposed that transient and reversible phenotypic changes could modify the response of bacteria to germicidal radiation, eventually leading to tailing in the survival curves. If this were the case, changes in susceptibility to radiation would reflect variations in gene expression and should only occur in cells in which gene expression is active. To obtain experimental evidence supporting the involvement of phenotypic changes in the origin of tailing, we studied changes in the susceptibility to radiation of cells able to survive high fluences, using split irradiations. Stationary phase cells of Enterobacter cloacae and Deinococcus radiodurans, in which gene expression is active, and spores of Bacillus subtilis, which are dormant cells without active gene expression, were used as microbial models. While cells of E. cloacae and D. radiodurans became susceptible after surviving exposures to high fluences, tolerant spores exhibited unchanged response to radiation. The results can be interpreted assuming that noise in gene expression modifies bacterial susceptibility to radiation, and tailing is the result of intrinsic phenomena of bacterial physiology rather than a technical artifact. For either theoretical or practical purposes, deviations from simple exponential decay kinetics should be considered in estimations of the effects of germicidal radiation at high fluences.

Protective Effects of Halite to Vacuum and Vacuum-Ultraviolet Radiation: A Potential Scenario During a Young Sun Superflare.

Halite (NaCl mineral) has exhibited the potential to preserve microorganisms for millions of years on Earth. This mineral was also identified on Mars and in meteorites. In this study, we investigated the potential of halite crystals to protect microbial life-forms on the surface of an airless body (e.g., meteorite), for instance, during a lithopanspermia process (interplanetary travel step) in the early Solar System. To investigate the effect of the radiation of the young Sun on microorganisms, we performed extensive simulation experiments by employing a synchrotron facility. We focused on two exposure conditions: vacuum (low Earth orbit, 10-4 Pa) and vacuum-ultraviolet (VUV) radiation (range 57.6-124 nm, flux 7.14 W/m2), with the latter representing an extreme scenario with high VUV fluxes comparable to the amount of radiation of a stellar superflare from the young Sun. The stellar VUV parameters were estimated by using the very well-studied solar analog of the young Sun, κ1 Cet. To evaluate the protective effects of halite, we entrapped a halophilic archaeon (Haloferax volcanii) and a non-halophilic bacterium (Deinococcus radiodurans) in laboratory-grown halite. Control groups were cells entrapped in salt crystals (mixtures of different salts and NaCl) and non-trapped (naked) cells, respectively. All groups were exposed either to vacuum alone or to vacuum plus VUV. Our results demonstrate that halite can serve as protection against vacuum and VUV radiation, regardless of the type of microorganism. In addition, we found that the protection is higher than provided by crystals obtained from mixtures of salts. This extends the protective effects of halite documented in previous studies and reinforces the possibility to consider the crystals of this mineral as potential preservation structures in airless bodies or as vehicles for the interplanetary transfer of microorganisms.

An electrochemical sensing approach for scouting microbial chemolithotrophic metabolisms.

The present study was aimed to test an electrochemical sensing approach for the detection of an active chemolithotrophic metabolism (and therefore the presence of chemolithotrophic microorganisms) by using the corrosion of pyrite by Acidithiobacillus ferrooxidans as a model. Different electrochemical techniques were combined with adhesion studies and scanning electron microscopy (SEM). The experiments were performed in presence or absence of A. ferrooxidans and without or with ferrous iron in the culture medium (0 and 0.5 g L-1, respectively). Electrochemical parameters were in agreement with voltammetric studies and SEM showing that it is possible to distinguish between an abiotically-induced corrosion process (AIC) and a microbiologically-induced corrosion process (MIC). The results show that our approach not only allows the detection of chemolithotrophic activity of A. ferrooxidans but also can characterize the corrosion process. This may have different kind of applications, from those related to biomining to life searching missions in other planetary bodies.

In Situ Search for Extraterrestrial Life: A Microbial Fuel Cell-Based Sensor for the Detection of Photosynthetic Metabolism.

Microbial fuel cells (MFCs) are bioelectrochemical systems (BES) capable of harvesting electrons from redox reactions involved in metabolism. In a previous work, we used chemoorganoheterotrophic microorganisms from the three domains of life-Bacteria, Archaea, and Eukarya-to demonstrate that these BES could be applied to the in situ detection of extraterrestrial life. Since metabolism can be considered a common signature of life "as we know it," we extended in this study the ability to use MFCs as sensors for photolithoautotrophic metabolisms. To achieve this goal, two different photosynthetic microorganisms were used: the microalgae Parachlorella kessleri and the cyanobacterium Nostoc sp. MFCs were loaded with nonsterilized samples, sterilized samples, or sterilized culture medium of both microorganisms. Electric potential measurements were recorded for each group in single experiments or in continuum during light-dark cycles, and power and current densities were calculated. Our results indicate that the highest power and current density values were achieved when metabolically active microorganisms were present in the anode of the MFC. Moreover, when continuous measurements were performed during light-dark cycles, it was possible to see a positive response to light. Therefore, these BES could be used not only to detect chemoorganoheterotrophic metabolisms but also photolithoautotrophic metabolisms, in particular those involving oxygenic photosynthesis. Additionally, the positive response to light when using these BES could be employed to distinguish photosynthetic from nonphotosynthetic microorganisms in a sample.

A new P. putida instrumental toxicity bioassay.

Here, we present a new toxicity bioassay (CO2-TOX), able to detect toxic or inhibitory compounds in water samples, based on the quantification of Pseudomonas putida KT2440 CO2 production. The metabolically produced CO2 was measured continuously and directly in the liquid assay media, with a potentiometric gas electrode. The optimization studies were performed using as a model toxicant 3,5-DCP (3,5-dichlorophenol); later, heavy metals (Pb(2+), Cu(2+), or Zn(2+)) and a metalloid (As(5+)) were assayed. The response to toxics was evident after 15 min of incubation and at relatively low concentrations (e.g., 1.1 mg/L of 3,5-DCP), showing that the CO2-TOX bioassay is fast and sensitive. The EC50 values obtained were 4.93, 0.12, 6.05, 32.17, and 37.81 mg/L for 3,5-DCP, Cu(2+), Zn(2+), As(5+), and Pb(2+), respectively, at neutral pH. Additionally, the effect of the pH of the sample and the use of lyophilized bacteria were also analyzed showing that the bioassay can be implemented in different conditions. Moreover, highly turbid samples and samples with very low oxygen levels were measured successfully with the new instrumental bioassay described here. Finally, simulated samples containing 3,5-DCP or a heavy metal mixture were tested using the proposed bioassay and a standard ISO bioassay, showing that our test is more sensible to the phenol but less sensible to the metal mixtures. Therefore, we propose CO2-TOX as a rapid, sensitive, low-cost, and robust instrumental bioassay that could perform as an industrial wastewater-process monitor among other applications.

Analytical applications of microbial fuel cells. Part I: Biochemical oxygen demand.

Microbial fuel cells (MFCs) are bio-electrochemical devices, where usually the anode (but sometimes the cathode, or both) contains microorganisms able to generate and sustain an electrochemical gradient which is used typically to generate electrical power. In the more studied set-up, the anode contains heterotrophic bacteria in anaerobic conditions, capable to oxidize organic molecules releasing protons and electrons, as well as other by-products. Released protons could reach the cathode (through a membrane or not) whereas electrons travel across an external circuit originating an easily measurable direct current flow. MFCs have been proposed fundamentally as electric power producing devices or more recently as hydrogen producing devices. Here we will review the still incipient development of analytical uses of MFCs or related devices or set-ups, in the light of a non-restrictive MFC definition, as promising tools to asset water quality or other measurable parameters. An introduction to biological based analytical methods, including bioassays and biosensors, as well as MFCs design and operating principles, will also be included. Besides, the use of MFCs as biochemical oxygen demand sensors (perhaps the main analytical application of MFCs) is discussed. In a companion review (Part 2), other new analytical applications are reviewed used for toxicity sensors, metabolic sensors, life detectors, and other proposed applications.

Analytical applications of microbial fuel cells. Part II: Toxicity, microbial activity and quantification, single analyte detection and other uses.

Microbial fuel cells were rediscovered twenty years ago and now are a very active research area. The reasons behind this new activity are the relatively recent discovery of electrogenic or electroactive bacteria and the vision of two important practical applications, as wastewater treatment coupled with clean energy production and power supply systems for isolated low-power sensor devices. Although some analytical applications of MFCs were proposed earlier (as biochemical oxygen demand sensing) only lately a myriad of new uses of this technology are being presented by research groups around the world, which combine both biological-microbiological and electroanalytical expertises. This is the second part of a review of MFC applications in the area of analytical sciences. In Part I a general introduction to biological-based analytical methods including bioassays, biosensors, MFCs design, operating principles, as well as, perhaps the main and earlier presented application, the use as a BOD sensor was reviewed. In Part II, other proposed uses are presented and discussed. As other microbially based analytical systems, MFCs are satisfactory systems to measure and integrate complex parameters that are difficult or impossible to measure otherwise, such as water toxicity (where the toxic effect to aquatic organisms needed to be integrated). We explore here the methods proposed to measure toxicity, microbial metabolism, and, being of special interest to space exploration, life sensors. Also, some methods with higher specificity, proposed to detect a single analyte, are presented. Different possibilities to increase selectivity and sensitivity, by using molecular biology or other modern techniques are also discussed here.

Comparative survival analysis of Deinococcus radiodurans and the haloarchaea Natrialba magadii and Haloferax volcanii exposed to vacuum ultraviolet irradiation.

The haloarchaea Natrialba magadii and Haloferax volcanii, as well as the radiation-resistant bacterium Deinococcus radiodurans, were exposed to vacuum UV (VUV) radiation at the Brazilian Synchrotron Light Laboratory. Cell monolayers (containing 10(5) to 10(6) cells per sample) were prepared over polycarbonate filters and irradiated under high vacuum (10(-5) Pa) with polychromatic synchrotron radiation. N. magadii was remarkably resistant to high vacuum with a survival fraction of (3.77±0.76)×10(-2), which was larger than that of D. radiodurans (1.13±0.23)×10(-2). The survival fraction of the haloarchaea H. volcanii, of (3.60±1.80)×10(-4), was much smaller. Radiation resistance profiles were similar between the haloarchaea and D. radiodurans for fluences up to 150 J m(-2). For fluences larger than 150 J m(-2), there was a significant decrease in the survival of haloarchaea, and in particular H. volcanii did not survive. Survival for D. radiodurans was 1% after exposure to the higher VUV fluence (1350 J m(-2)), while N. magadii had a survival lower than 0.1%. Such survival fractions are discussed regarding the possibility of interplanetary transfer of viable microorganisms and the possible existence of microbial life in extraterrestrial salty environments such as the planet Mars and Jupiter's moon Europa. This is the first work to report survival of haloarchaea under simulated interplanetary conditions.

Archaea-based microbial fuel cell operating at high ionic strength conditions.

In this work, two archaea microorganisms (Haloferax volcanii and Natrialba magadii) used as biocatalyst at a microbial fuel cell (MFC) anode were evaluated. Both archaea are able to grow at high salt concentrations. By increasing the media conductivity, the internal resistance was diminished, improving the MFC's performance. Without any added redox mediator, maximum power (P (max)) and current at P (max) were 11.87/4.57/0.12 µW cm(-2) and 49.67/22.03/0.59 µA cm(-2) for H. volcanii, N. magadii and E. coli, respectively. When neutral red was used as the redox mediator, P (max) was 50.98 and 5.39 µW cm(-2) for H. volcanii and N. magadii, respectively. In this paper, an archaea MFC is described and compared with other MFC systems; the high salt concentration assayed here, comparable with that used in Pt-catalyzed alkaline hydrogen fuel cells, will open new options when MFC scaling up is the objective necessary for practical applications.

Male and female reproductive toxicity induced by sub-chronic ethanol exposure in CF-1 mice.

Since genetic damage induced by ethanol exposure is controversial and incomplete and because germ and somatic cells constitute bioindicators for monitoring reproductive toxicity and genotoxic actions of ethanol consumption, the purpose of the present investigation was to evaluate morphological sperm, oocyte alterations and parental genotoxic effects after sub-chronic ethanol intake in the CF-1 outbred mouse strain. Ethanol 10% was administered to CF-1 adult male (treated males, TM) and female (treated females, TF) mice for 27 days, whereas water was given to controls from both sexes too (CM and CF). Post-treatment micronucleus frequency (MN-PCE/1,000/mouse) and gamete morphology were evaluated. To test whether change of female reproductive status results in maternal genotoxicity, CF-1 females received ethanol 10% (exposed group, periconceptionally treated females (PTF)) or water (control group, pregnant control females (PCF)) in drinking water for 17 days previous and up to 10 days of gestation. TM had a high percentage of abnormal spermatozoa vs CM (p < 0.001) and elevated parthenogenetic activated oocyte frequency appeared in TF vs CF (p < 0.001). Sub-chronic ethanol ingestion induced increased MN frequency in TM and TF (p < 0.01). In PTF, where blood alcohol concentrations were between 19-28 mg/dl, very significantly increased MN frequency was found vs PCF (p < 0.01), whereas MN values were similar to TF. These results show that sub-chronic alcohol ingestion in CF-1 mice produces sperm head dysmorphogenesis and oocyte nuclear anomalies, suggesting that morphological abnormalities in germ cells are probably related to parental genotoxicity after ethanol consumption.

Microbial fuel cells applied to the metabolically based detection of extraterrestrial life.

Since the 1970s, when the Viking spacecrafts carried out experiments to detect microbial metabolism on the surface of Mars, the search for nonspecific methods to detect life in situ has been one of the goals of astrobiology. It is usually required that a methodology detect life independently from its composition or form and that the chosen biological signature point to a feature common to all living systems, such as the presence of metabolism. In this paper, we evaluate the use of microbial fuel cells (MFCs) for the detection of microbial life in situ. MFCs are electrochemical devices originally developed as power electrical sources and can be described as fuel cells in which the anode is submerged in a medium that contains microorganisms. These microorganisms, as part of their metabolic process, oxidize organic material, releasing electrons that contribute to the electric current, which is therefore proportional to metabolic and other redox processes. We show that power and current density values measured in MFCs that use microorganism cultures or soil samples in the anode are much larger than those obtained with a medium free of microorganisms or sterilized soil samples, respectively. In particular, we found that this is true for extremophiles, which have been proposed as potential inhabitants of extraterrestrial environments. Therefore, our results show that MFCs have the potential to be used for in situ detection of microbial life.

The bone marrow micronucleus test and metronidazole genotoxicity in different strains of mice (Mus musculus)

The mouse (Mus musculus) bone marrow micronucleus test was carried out using 24 outbred National Institutes of Health (NIH) mice, 24 inbred Swiss Webster (CFW) mice and 20 inbred Bagg albino/color locus Jackson (BALB/cJ) mice. The mice in the experimental group (n = 32) were injected intraperitoneally with 133 mg kg-1 of metronidazole parenteral solution and the control group consisted of mice (n = 36) which had not been injected with metronidazole. There was no significant difference (p > 0.05) between the sexes regarding the micronucleus frequency in either the experimental or the control group. When the Mn frequencies of the three strains were compared, the results for the CFW and BALB/cJ strains did not differ statistically (p > 0.05) for either the experimental or control groups but there were significant (p < 0.05) differences between the CFW and NIH strains and the NIH and BALB/cJ strains for the experimental and control groups, with the NIH strain always showing the highest micronucleus frequency. Our results also show that metronidazole was possible genotoxic agent because it produced a significant increase (p < 0.05) in the micronucleus frequency of the experimental group as compared to the control group for all the three mouse strains tested.