Low-moisture Environments Research Articles

Distribution of Myxomycetes on coarse woody debris of <i>Pinus densiflora</i> at different decay stages in secondary forests of western Japan

The relationship between myxomycete species and the decay stage of wood of Pinus densiflora coarse woody debris was investigated in warm temperate secondary forests of western Japan. The number of species and species diversity of the myxomycete community reached the maximum on moderately decayed wood. The 25 dominant species recorded from 8 or more samples of the total 1530 samples were arranged in order of the succession index corresponding to the stage of decay. Species on slightly decayed hard pine wood were characterized by Stemonitis splendens, Enerthenema papillatum, and Physarum viride, whereas species of Cribrariaceae were found on brittle decayed soft wood increasing abundance according to the decay stages. Most of the species occurred where there was sufficient moisture preserved in the environment of the decaying wood, although S. splendens specifically emerged in low-moisture environments. Because the myxomycete species had preference to different decay stages of wood, it appears that they change sequentially during myxomycete community succession on dead pine wood according to the progression of decay.

Heat and acid tolerance of Listeria monocytogenes after exposure to single and multiple sublethal stresses

The majority of published studies on the adaptive heat or acid tolerance response of Listeria monocytogenes have been performed with a single strain exposed to a single adaptation treatment; however, in food ecosystems, microorganisms commonly exist as multi-species communities and encounter multiple stresses, which may result in “stress hardening”. Therefore, the present study evaluated the adaptive responses to heat (52, 57 and 63 °C) or lactic acid (pH 3.5) of a 10-strain composite of L. monocytogenes meat and human isolates at stationary phase, following exposure to combinations of osmotic (10% NaCl), acidic (pH 5.0 with HCl) and thermal (T; 46 °C) stresses, sequentially or simultaneously within 1.5 h, in tryptic soy broth with 0.6% yeast extract (TSBYE). All treatments induced adaptive responses on L. monocytogenes at 57 °C, while no such cross-protection was observed at 52 and 63 °C. Survivor curves at 57 °C appeared convex with profound shoulders determined by a Weibull model. The highest thermotolerance was observed after combined exposure to acid and heat shock (pH–T), followed by exposure to osmotic shock, and by the combination of osmotic with heat shock (NaCl–T). Regarding acid tolerance, prior exposure to low pH, pH–T, or a combination of NaCl, pH and T resulted in a marked increase of resistance to pH 3.5, showing concave inactivation curves with tails at higher levels of survivors (log 10 CFU ml −1) than the control cultures. The sequence of exposure to sublethal stresses did not affect the thermotolerance of L. monocytogenes, whereas simultaneous exposure to most multiple stresses (e.g., NaCl–pH–T, NaCl–T and NaCl–pH) resulted in higher survivors of L. monocytogenes at pH 3.5 than exposure to the same stresses sequentially. The results indicate that combinations and sequences of sublethal hurdles may affect L. monocytogenes acid and heat tolerance, especially in acidic environments with mild heating or in low moisture environments.

In Situ Freeze-Capturing of Fracture Water using Cryogenic Coring

Current methods do not allow for sampling of in situ water from unsaturated fractures in low-moisture environments. A novel cryogenic coring technique based on the method developed by Simon and Cooper (1996) is used to collect in situ water in unsaturated fractures. This method uses liquid nitrogen as the drilling fluid, which can freeze the fracture water in place while coring. Laboratory experiments are conducted to demonstrate that water in an unsaturated fracture can be frozen and collected using cryogenic coring.

SURVIVAL DIFFERENCES OF THE TWO MALE MORPHS IN THE DWARF SPIDER OEDOTHORAX GIBBOSUS BLACKWALL, 1841 (ERIGONINAE, LINYPHIIDAE, ARANEAE)

Oedothorax gibbosus is a rare dwarf spider species in Flanders bound to oligo- and mesotrophic alder carrs. This dwarf spider is characterised by the appearance of a male dimorphism; there is a gibbosus male morph with a hunch on the last third of the carapace, anterior to which is a hairy groove, and a tuberosus morph without these features. Earlier studies have already indicated some differences between both male morphs. According to VANACKER et al. (2001) the juvenile phase (the period between the emergence of the spiders and the last moult) of the gibbosus morph is significantly longer than the juvenile phase of the tuberosus morph, and this is presumably necessary for the production of the hunch and the hairy groove. This hairy groove probably secretes a fluid that is important for the gustatoric courtship behaviour and gibbosus would therefore have a reproductive advantage (HEINEMANN & UHL, 2000). In this paper we report another interesting difference between both morphs. To examine if the male morphs also differ in survival, some survival experiments, in normal food and moisture conditions and in two extreme conditions, namely in foodless and low moisture environments, were set up. The gibbosus male is significantly more susceptible to foodless conditions than the tuberosus male, and also in normal conditions tuberosus lives significantly longer than gibbosus. This is demonstrated by means of survival curves. In low moisture conditions, however, we could not prove that survival rate differs between both male morphs. The higher survival rate of tuberosus is a possible explanation for the morph ratio in favour of tuberosus in the studied field population.

Poly(ethylene glycol) interactions with alumina and silica powders determined via DRIFT

Diffuse reflection infrared spectroscopy (DRIFT) is used to determine interfacial interactions between poly(ethylene glycol) (PEG), alumina and silica powders. The interactions are created by grafting in high temperature and low moisture environments due to preferential adsorption between PEG and water. Under these grafting conditions, a shoulder appears on the C–O–C stretching band of the DRIFT spectrum. This is found to occur when PEG is in the presence of a hydrogen donor such as surface hydroxyls on alumina and silica. The shoulder is reported as an interaction band due to hydrogen bonding between the PEG etheric oxygen and the surface hydroxyls of alumina and silica. Specific band positions are measured when the PEG chain is interacting with alumina (1090 cm−1), silica (1080 cm−1), or water (1085 cm−1).

Effect of Environmental and Substrate Factors on Survival and Growth of Helicobacter pylori

The effect of temperature (4 to 42°C), NaCl concentration (0.5 to 7.5%), NaNO2 concentration (0 to 400 μg/ml), water activity (aw level of 0.6 to 0.995), pH (3.5 to 7.3) and urea (8 mM) on the survival and growth of Helicobacter pylori in a nutrient-rich laboratory culture medium was investigated. Under microaerobic conditions (5% O2, 10% CO2, and 85% N2), the organism grew well in brain heart infusion broth supplemented with 7% horse serum and antibiotics (BHI-HS-TVA) in a temperature range of 30 to 37°C with agitation. H. pylori (initial population of ca. 5 × 103 CFU/ml) survived for 14 days at 4°C, for 2 days at 25°C, and for less than 1 day at 40 and 42°C. The optimal NaCl concentration for growth of H. pylori was 0.5 to 1.0%; 2.0% NaCl inhibited growth. Up to 400 μg of NaNO2 per ml did not prevent growth. The minimum aw (adjusted with glycerol) and pH (acidified with HCl) for growth of H. pylori was 0.98 and 4.5, respectively. The addition of urea to broth greatly enhanced the growth of H. pylori at both pH 4.5 and 5.5. Although H. pylori did not grow at pH 3.5, the presence of urea in broth enhanced its survival. Considering the apparent fastidious conditions for growth of H. pylori in BHI-HS-TVA broth, H. pylori is unlikely to grow well, if at all, in most foods. The bacterium may, however, survive for extended periods of time in low acid-high moisture environments under refrigerated storage.

Microbial abundance and activities in relation to water potential in the vadose zones of arid and semiarid sites

Numbers and activities of microorganisms were measured in the vadose zones of three arid and semiarid areas of the western United States, and the influence of water availability was determined. These low-moisture environments have vadose zones that are commonly hundreds of meters thick. The specific sampling locations chosen were on or near U.S. Department of Energy facilities: the Nevada Test Site (NTS), the Idaho National Engineering Laboratory (INEL), and the Hanford Site (HS) in southcentral Washington State. Most of the sampling locations were uncontaminated, but geologically representative of nearby locations with storage and/or leakage of waste compounds in the vadose zone. Lithologies of samples included volcanic tuff, basalt, glaciofluvial and fluvial sediments, and paleosols (buried soils). Samples were collected aseptically, either by drilling bore-holes (INEL and HS), or by excavation within tunnels (NTS) and outcrop faces (paleosols near the HS). Total numbers of microorganisms were counted using direct microscopy, and numbers of culturable microorganisms were determined using plate-count methods. Desiccation-tolerant microorganisms were quantified by plate counts performed after 24 h desiccation of the samples. Mineralization of (14)C-labeled glucose and acetate was quantified in samples at their ambient moisture contents, in dried samples, and in moistened samples, to test the hypothesis that water limits microbial activities in vadose zones. Total numbers of microorganisms ranged from log 4.5 to 7.1 cells g(-1) dry wt. Culturable counts ranged from log <2 to 6.7 CFU g(-1) dry wt, with the highest densities occurring in paleosol (buried soil) samples. Culturable cells appeared to be desiccation-tolerant in nearly all samples that had detectable viable heterotrophs. Water limited mineralization in some, but not all samples, suggesting that an inorganic nutrient or other factor may limit microbial activities in some vadose zone environments.

Free-Radical Formation during Storage of Freeze-dried Serratia marcescens

BACTERIA which have survived freeze-drying retain the capacity to regenerate colonies after prolonged storage under vacuum, in contrast to their rapid loss of this capacity when stored in air. The question of whether bacteria stored under such conditions are dormant or whether some metabolic activity continues to maintain the bacilli in a living state is of fundamental importance to a further understanding of the physiology of life in low-moisture environments. Heckly1 has reviewed many of the problems associated with freeze-drying. Results of preliminary work on freeze-dried cells had indicated a slow gaseous uptake when the material was stored in dry air and a greater uptake if stored under moistened air. Because the results were not reproducible, other techniques were examined, specifically that of electron paramagnetic resonance, in the hope of finding an indirect measurement of respiration. The fundamental theory and practice of electron paramagnetic resonance has been reviewed by Ingram2, while a review of biological applications of the phenomenon has been given by Sands3.