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Anaeramoebae is a recently described phylum of anaerobic, marine amoebae, and amoeboflagellates belonging to the Metamonada supergroup. So far, six species have been described based on light microscopic morphology and sequences of the SSU rRNA gene. Here we present three new strains of Anaeramoeba with a description of their morphology, ultrastructure, and phylogenetic position based on the analysis of SSU rRNA gene sequences. Two of the strains represent a new species, Anaeramoeba pumila sp. nov., that has the smallest cells of all known Anaeramoeba species, and one that represents a species from the newly recognized Anaeramoeba flamelloides complex. Anaeramoebae are known to have a syntrophic relationship with prokaryotes. Our strains display two novel, remarkable types of symbioses, previously unknown from Anaeramoebae. [ABSTRACT FROM AUTHOR]

Green hydrogen, produced during microalgal photosynthesis, is regarded as one of the most promising sustainable energy sources. It utilizes sunlight and water, which are essentially unlimited, and its combustion results in only water as a waste product. In microalgal hydrogen energy production systems, the sensitivity of hydrogenase to O2 poses a significant challenge, limiting sustained photosynthetic H2 production in microalgae. Additionally, efficient photosynthetic H2 production in anaerobic microalgal cells is hindered by impaired electron source (photosystem II) and electron loss through the Calvin‐Benson cycle, cyclic electron transfer around photosystem I, and O2 photoreduction, which are identified as the other key challenges. Over the past eight decades, considerable progress has been made in addressing these challenges and regulating electron transfer to achieve sustainable and efficient photosynthetic H2 production in microalgae. In this review, we discuss a range of regulatory methods for achieving sustainable and efficient photosynthetic H2 production in microalgae. Emphasizing the significant progress made over the past eight decades, we also address current challenges and propose potential future solutions. [ABSTRACT FROM AUTHOR]

BACKGROUND: The present study aimed to determine the optimal conditions for making wines by the carbonic maceration (CM) method. In this test, we attempted to identify the causes of the higher volatile acidity of some wines vinified by this method. Accordingly, we measured the development and speed of intracellular fermentation inside the whole grapes under different vinification conditions. RESULTS: An active fermentation of the must in the tanks produced by inoculation with active dry yeasts was more efficient for the process than the addition of exogenous carbon dioxide (CO2). In addition, in CM vinification, the moment of devatting had a great influence on the content of acetaldehyde and acetic acid in the whole grapes. CONCLUSION: Yeast inoculation in the tanks and control of the devatting time are technological tools that could play an important role in the characteristics of the wines produced by carbonic maceration, especially with respect to acetic acid content. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

We describe a collection of aquatic and wetland habitats in an inland landscape, and their occurrence within a terrestrial matrix, as a "freshwater ecosystem mosaic" (FEM). Aquatic and wetland habitats in any FEM can vary widely, from permanently ponded lakes, to ephemerally ponded wetlands, to groundwater‐fed springs, to flowing rivers and streams. The terrestrial matrix can also vary, including in its influence on flows of energy, materials, and organisms among ecosystems. Biota occurring in a specific region are adapted to the unique opportunities and challenges presented by spatial and temporal patterns of habitat types inherent to each FEM. To persist in any given landscape, most species move to recolonize habitats and maintain mixtures of genetic materials. Species also connect habitats through time if they possess needed morphological, physiological, or behavioral traits to persist in a habitat through periods of unfavorable environmental conditions. By examining key spatial and temporal patterns underlying FEMs, and species‐specific adaptations to these patterns, a better understanding of the structural and functional connectivity of a landscape can be obtained. Fully including aquatic, wetland, and terrestrial habitats in FEMs facilitates adoption of the next generation of individual‐based models that integrate the principles of population, community, and ecosystem ecology. Research Impact Statement: Fully including aquatic, wetland, and terrestrial habitats facilitates adoption of next‐generation, individual‐based, models that integrate principles of population, community, and ecosystem ecology. [ABSTRACT FROM AUTHOR]

BACKGROUND Lactic acid bacteria inocula have been developed over the years to improve the aerobic stability of silages. The aims of the study were to evaluate the effect of various conservation periods and the use of Lactobacillus hilgardii inoculum on aerobic stability, fermentative profile and microbial population of corn and sorghum silages. Trials were carried out on two corns and one sorghum crops. The crops were untreated or treated with L. buchneri (LB, application rate 300 000 cfu g−1 FM), L. hilgardii (LH, application rate 300 000 cfu g−1 FM) and a combination (LB + LH, application rate 150 000 cfu g−1 FM each). Silos were opened after 15, 30, 100 and 250 days of conservation, and the silages were analysed for fermentative profile, microbial count and aerobic stability. RESULTS: During conservation, the inocula influenced the fermentation profile. The use of LH increased the aerobic stability at 15 and 30 days in one out of three trials, while after 100 and 250 days, the presence of LB alone or with LH led to greater stability. In all the trials, the acetic acid content increased, the yeast count decreased and the aerobic stability increased during the conservation period. CONCLUSIONS: This study has shown that a long period in complete anaerobiosis reduced yeast count and improved aerobic stability in all silages. The addition of LB was confirmed to be a good option for increasing aerobic stability of silages, whereas the effect of LH alone or in combination with LB on aerobic stability was not consistent between trials. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Osm1, a soluble fumarate reductase from Saccharomyces cerevisiae, is localized in both the mitochondria and the endoplasmic reticulum (ER). OSM1 genetically interacts with ERO1, which encodes an essential ER oxidoreductase for disulfide‐bond formation under anaerobic conditions. However, the detailed enzymatic mechanisms involved in this interaction and the cellular roles of Osm1 are not fully understood. In this study, monomeric and stable recombinant Osm1 was successfully prepared for structural study. During purification, it was realized that the majority of recombinant Osm1 expressed in Escherichia coli lacked the flavin adenosine dinucleotide (FAD) cofactor. However, exogenously introduced FAD could be incorporated into recombinant Osm1, generating stable and homogenous holo Osm1. Moreover, after removing a flexible fragment by limited proteolysis, holo Osm1 formed isotropic crystals that retained catalytic activity. X‐ray diffraction data were successfully collected from the Osm1 crystals to a resolution of 1.75 Å. Osm1, a soluble fumarate reductase from Saccharomyces cerevisiae, was purified and crystallized. The crystals were found to belong to space group P21, with unit‐cell parameters a = 43.88, b = 109.32, c = 49.93 Å, β = 112.25°. Crystals were obtained at 293 K and diffracted to a resolution of 1.75 Å. [ABSTRACT FROM AUTHOR]

We report the discovery of a new genus of heterolobosean flagellates, Dactylomonas gen. nov., with two species, D. venusta sp. nov. and D. crassa sp. nov. Phylogenetic analysis of the SSU rRNA gene showed that Dactylomonas is closely related to the amoeba Selenaion, the deepest‐branching lineage of Tetramitia. Dactylomonads possess two flagella, and ultrastructural studies revealed an unexpected organization of the flagellar apparatus, which resembled Pharyngomonada (the second lineage of Heterolobosea) instead of Tetramitia: basal bodies were orthogonal to each other and a putative root R1 was present in the mastigont. On the other hand, Dactylomonas displayed several features uncommon in Heterolobosea: a microtubular corset, a distinctive rostrum supported by the main part of the right microtubular root, a finger‐like projection on the proximal part of the recurrent flagellum, and absence of a ventral groove. In addition, Dactylomonas is anaerobic and seems to have lost mitochondrial cristae. Dactylomonas and Selenaion are accommodated in the family Selenaionidae fam. nov. and order Selenionida ord. nov. The taxonomy of Tetramitia is partially revised, and the family Neovahlkampfiidae fam. nov. is established. [ABSTRACT FROM AUTHOR]

In Euglena gracilis, wax ester fermentation produces ATP during anaerobiosis. Here, we report that anaerobic wax ester production is suppressed when the mitochondrial electron transport chain complex I is inhibited by rotenone, whereas it is increased by the uncoupler carbonyl cyanide m‐chlorophenylhydrazone (CCCP). The ADP/ATP ratio in anaerobic cells is elevated by treatment with either rotenone or CCCP. Gene silencing experiments indicate that acyl‐CoA dehydrogenase, electron transfer flavoprotein (ETF), and rhodoquinone (RQ) participate in wax ester production. These results suggest that fatty acids are synthesized in mitochondria by the reversal of β‐oxidation, where trans‐2‐enoyl‐CoA is reduced mainly by acyl‐CoA dehydrogenase using the electrons provided by NADH via the electron transport chain complex I, RQ, and ETF, and that ATP production is highly supported by anaerobic respiration utilizing trans‐2‐enoyl‐CoA as a terminal electron acceptor. [ABSTRACT FROM AUTHOR]

In Bradyrhizobium diazoefficiens, maximal expression of the nitrous oxide reductase gene ( nosZ) requires oxygen limitation and the presence of a nitrogen oxide. The putative transcription antiterminator NasT is a positive regulator of nosZ; but in the absence of nitrate, NasT is counteracted by the nitrate sensor NasS. Here, we examined the NasT-mediated mechanism of nosRZDFYLX gene cluster expression. We mapped two transcription start sites of nosR and identified two potential hairpins, H1 and H2, within the 5′-leader of nosR transcripts. Electrophoretic mobility shift assay showed that NasT specifically bound the nosR-leader RNA and deletion of H1 abolished such binding. Under aerobic nitrate-deficient conditions, deletion of H1 or H2 increased the level of nosRZD transcripts. Under denitrifying conditions (anaerobiosis with nitrate supply), the level of nosRZD transcripts was severely impaired in the nasT mutant; in the nasT background, deletions of either hairpin led to increased level of nosRZD transcripts. In contrast to nosRZD coding region, nosR-leader transcript level was not affected by nasS or nasT mutations under aerobic or denitrifying conditions respectively. These results suggest that the two-hairpin RNA structure acts for transcription termination upstream of nosR and the binding of NasT to H1 facilitates read-through transcription to induce nos expression. [ABSTRACT FROM AUTHOR]

The article presents community recommendations on terminology and procedures used in flooding and low oxygen stress research. This include flooding, anaerobiosis, anaerobic metabolism, anoxia, hypoxia, hyperoxia/superoxia, stress conditions and scoring survival. It also discusses the challenge of monitoring oxygen levels in plants.

The article offers information about geomycology, which can be defined as the roles and importance of fungi in processes of relevance to geology and geomicrobiology. Several topics being highlighted include the cycling of major elements, the links between organic and inorganic components of geomicrobial processes, and chemolithotorphy and anaerobiosis in prokaryotes.

Seagrasses grow submerged in aerated seawater but often in low O2 sediments. Elevated temperatures and low O2 are stress factors., Internal aeration was measured in two tropical seagrasses, Thalassia hemprichii and Enhalus acoroides, growing with extreme tides and diel temperature amplitudes. Temperature effects on net photosynthesis ( PN) and dark respiration ( RD) of leaves were evaluated., Daytime low tide was characterized by high pO2 (54 kPa), pH (8.8) and temperature (38°C) in shallow pools. As PN was maximum at 33°C (9.1 and 7.2 μmol O2 m−2 s−1 in T. hemprichii and E. acoroides, respectively), the high temperatures and reduced CO2 would have diminished PN, whereas RD increased (Q10 of 2.0-2.7) above that at 33°C (0.45 and 0.33 μmol O2 m−2 s−1, respectively). During night-time low tides, O2 declined resulting in shoot base anoxia in both species, but incoming water containing c. 20 kPa O2 relieved the anoxia. Shoots exposed to 40°C for 4 h showed recovery of PN and RD, whereas 45°C resulted in leaf damage., These seagrasses are 'living near the edge', tolerant of current diel O2 and temperature extremes, but if temperatures rise both species may be threatened in this habitat. [ABSTRACT FROM AUTHOR]

Changes in the redox state of iron (Fe) can be coupled to the biogeochemical cycling of carbon (C), nitrogen, and phosphorus, and thus regulate soil C, ecosystem nutrient availability, and greenhouse gas production. However, its importance broadly in non-flooded upland terrestrial ecosystems is unknown. We measured Fe reduction in soil samples from an annual grassland, a drained peatland, and a humid tropical forest. We incubated soil slurries in an anoxic glovebox for 5.5 days and added sodium acetate daily at rates up to 0.4 mg C·(g soil)-1·d-1. Soil moisture, poorly crystalline Fe oxide concentrations, and Fe(II) concentrations differed among study sites in the following order: annual grassland, drained peatland, tropical forest (P, 0.001 for all characteristics). All of the soil samples demonstrated high Fe reduction potential with maximum rates over the course of the incubation averaging 1706 ± 66, 6, 2016 ± 12, and 2973 ± 115 μg Fe·(g soil)-1·d-1 (mean ± SE) for the tropical forest, annual grassland, and drained peatland, respectively. Our results suggest that upland soils from diverse ecosystems have the potential to exhibit high short-term rates of Fe reduction that may play an important role in driving soil biogeochemical processes during periods of anaerobiosis. [ABSTRACT FROM AUTHOR]

In anaerobiosis, the microalga Chlamydomonas reinhardtii is able to produce H2 gas. Electrons mainly derive from mobilization of internal reserves or from water through biophotolysis. However, the exact mechanisms triggering this process are still unclear. Our hypothesis was that, once a proper redox state has been achieved, H2 production is eventually observed., To avoid nutrient depletion, which would result in enhanced fermentative pathways, we aimed to induce long-lasting H2 production solely through a photosynthesis : respiration equilibrium. Thus, growing cells were incubated in Tris Acetate Phosphate (TAP) medium under low light and high chlorophyll content., After a 250-h acclimation phase, a 350-h H2 production phase was observed. The light-to-H2 conversion efficiency was comparable to that given in some reports operating under sulphur starvation. Electron sources were found to be water, through biophotolysis, and proteins, particularly through photofermentation. Nonetheless, a substantial contribution from acetate could not be ruled out. In addition, photosystem II ( PSII) inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea ( DCMU) showed that it actively contributed to maintaining a redox balance during cell acclimation., In appropriate conditions, PSII may represent the major source of reducing power to feed the H2 evolution process, by inducing and maintaining an ideal excess of reducing power. [ABSTRACT FROM AUTHOR]

The origin and early evolution of animals marks an important event in life's history. This event is historically associated with an important variable in Earth history - oxygen. One view has it that an increase in oceanic oxygen levels at the end of the Neoproterozoic Era (roughly 600 million years ago) allowed animals to become large and leave fossils. How important was oxygen for the process of early animal evolution? New data show that some modern sponges can survive for several weeks at low oxygen levels. Many groups of animals have mechanisms to cope with low oxygen or anoxia, and very often, mitochondria - organelles usually associated with oxygen - are involved in anaerobic energy metabolism in animals. It is a good time to refresh our memory about the anaerobic capacities of mitochondria in modern animals and how that might relate to the ecology of early metazoans. [ABSTRACT FROM AUTHOR]

Ethylene is known to play an essential role in mediating hypoxic responses in plants. Here, we show that in addition to regulating hypoxic responses, ethylene also regulates cellular responses in the reoxygenation stage after anoxic treatment in Arabidopsis. We found that expression of several ethylene biosynthetic genes and ethylene-responsive factors, including ERF1 and ERF2, was induced during reoxygenation. Compared with the wild type, two ethylene-insensitive mutants ( ein2-5 and ein3eil1) were more sensitive to reoxygenation and displayed damaged phenotypes during reoxygenation. To characterize the role of ethylene, we applied microarray analysis to Col-0, ein2-5 and ein3eil1 under reoxygenation conditions. Our results showed that gene transcripts involved in reactive oxygen species ( ROS) detoxification, dehydration response and metabolic processes were regulated during reoxygenation. Moreover, ethylene signalling may participate in regulating these responses and maintaining the homeostasis of different phytohormones. Our work presents evidence that ethylene has distinct functions in recovery after anoxia and provides insight into the reoxygenation signalling network. [ABSTRACT FROM AUTHOR]

Dynamic flux balance analysis was utilized to simulate the metabolic behaviour of initially fully respirative and respirofermentative steady-state cultures of Saccharomyces cerevisiae during sudden oxygen depletion. The hybrid model for the dynamic flux balance analysis included a stoichiometric genome-scale metabolic model as a static part and dynamic equations for the uptake of glucose and the cessation of respirative metabolism. The yeast consensus genome-scale metabolic model [Herrgård MJ et al. (2008) Nat Biotechnol 26, 1155-1160; Dobson PD et al. (2010) BMC Syst Biol 4, 145] was refined with respect to oxygen-dependent energy metabolism and further modified to reflect S. cerevisiae anabolism in the absence of oxygen. Dynamic flux balance analysis captured well the essential features of the dynamic metabolic behaviour of S. cerevisiae during adaptation to anaerobiosis. Modelling and simulation enabled the identification of short time-scale flux distribution dynamics under the transition to anaerobic metabolism, during which the specific growth rate was reduced, as well as longer time-scale process dynamics when the specific growth rate recovered. Expression of the metabolic genes was set into the context of the identified dynamics. Metabolic gene expression responses associated with the specific growth rate and with the cessation of respirative metabolism were distinguished. [ABSTRACT FROM AUTHOR]

• Pondweed (Potamogeton distinctus) turions can elongate in the absence of O2. Alcoholic fermentation serves to produce energy for anoxic elongation via the breakdown of starch stored in cells. However, the mechanism of cell growth during anoxic elongation is not fully understood. • Changes in pH, H+ equivalent and lactate content of the incubation medium were measured during anoxic elongation. The effects of fusicoccin (FC), indole-3- acetic acid (IAA), vanadate, erythrosine B and K+ channel blockers on anoxic elongation were examined. Cytoplasmic pH and vacuolar pH were measured by 31P nuclear magnetic resonance (NMR) spectroscopy. • Acidification of the incubation medium occurred during anoxic elongation. The contribution of CO2 and lactic acid was not sufficient to explain the acidification. FC and IAA enhanced the elongation of stem segments. Vanadate and erythrosine B inhibited anoxic elongation. Acid growth of notched segments was observed. The activity of plasma membrane H+-ATPase extracted from pondweed turions was increased slightly in anoxic conditions, but that from pea epicotyls sensitive to anoxic conditions was decreased by incubation in anoxic conditions. Both the cytoplasmic pH and vacuolar pH of pondweed turion cells chased by 32P NMR spectroscopy were stabilized during a short period < 3 h after anoxic conditions.• We propose that the enhancement of H+ extrusion by anoxic conditions induces acidification in the apoplast and may contribute to the stabilization of pH in the cytoplasm. [ABSTRACT FROM AUTHOR]

• To adapt to waterlogging in soil, some gramineous plants, such as maize (Zea mays), form lysigenous aerenchyma in the root cortex. Ethylene, which is accumulated during waterlogging, promotes aerenchyma formation. However, the molecular mechanism of aerenchyma formation is not understood. • The aim of this study was to identify aerenchyma formation-associated genes expressed in maize roots as a basis for understanding the molecular mechanism of aerenchyma formation. Maize plants were grown under waterlogged conditions, with or without pretreatment with an ethylene perception inhibitor 1-methylcyclopropene (1-MCP), or under aerobic conditions. Cortical cells were isolated by lasermicrodissection and their mRNA levels were examined with a microarray. • The microarray analysis revealed 575 genes in the cortical cells, whose expression was either up-regulated or down-regulated under waterlogged conditions and whose induction or repression was suppressed by pretreatment with 1-MCP. • The differentially expressed genes included genes related to the generation orscavenging of reactive oxygen species, Ca2+ signaling, and cell wall loosening and degradation. The results of this study should lead to a better understanding of the mechanism of root lysigenous aerenchyma formation. [ABSTRACT FROM AUTHOR]

In this article the authors discuss several studies related to plants and flooding stress, which are published in the 2011 issue of the journal "New Phytologist." They say that flooding is a compound stress consists of changes inside the plant cells caused by the flood water surrounding the plant. They cite the study of D. Vashisht and colleagues on natural variation in flooding tolerance of Arabidopsis thaliana. They also mention a study on acclimation and genetic diversity in flooding.

Flooding, a natural cause of anaerobiosis, is often accompanied by high CO concentrations in the flood water. Plants need to respond to these environmental conditions. Strong anaerobic reporter gene activity in tobacco ( Nicotiana tabacum) controlled by the glycolytic glyceraldehyde-3-phosphate dehydrogenase ( GapC4) promoter from maize ( Zea mays) depends on the presence of CO and light. To identify factors required for CO regulated gene expression, promoter deletions fused to the β-glucuronidase reporter gene were studied in transgenic tobacco. Deletion of a 40 bp fragment directly upstream of the TATA box leads to increased anaerobic reporter gene activity both, in the presence and absence of CO. This deletion does not affect light specific anaerobic expression. A positive correlation between increasing CO concentrations and gene activity is observed. Electrophoretic mobility shift experiments indicate that tobacco nuclear extracts harbour proteins that bind to part of the 40 bp fragment. Database assisted as well as experimental analysis reveal a role for AP2/EREBP transcription factors for conferring the high CO specificity to the GapC4 promoter in tobacco leaves. This work highlights the importance for plants to respond to high environmental CO concentrations under anaerobic conditions. [ABSTRACT FROM AUTHOR]

This work was devoted to separate acetate role in creating anaerobiosis from that of sulfur deprivation. Chlamydomonas reinhardtii grown in TAP (Tris-acetate-phosphate) medium was resuspended in sulfur-replete or -deprived medium in sealed or nonsealed cultures. Sulfur deprivation was substantial for starch accumulation and hydrogen evolution; however, acetate induced anaerobiosis in the presence or absence of sulfur in only sealed cultures . In nonsealed cultures, Chlamydomonas did not lose its photosynthetic activity; however, it was arrested in anoxia with no photosynthetic activity as long as the culture was sealed. The sealed cultures resumed photosynthesis upon unsealing overnight unless the cells died by anoxia at late stage of the experiment. These results indicate that the enhanced oxygen consumption for the enormous acetate respiration and inhibition of the external oxygen supply in sealed cultures of Chlamydomonas are the main reasons for the steady anaerobic conditions. Although acetate was substantial for creating anaerobiosis in Chlamydomonas, sulfur deprivation alone could create anaerobiosis in Spirulina platensis grown autotrophically. Hydrogen evolution and glycogen accumulation were induced under such conditions. Severely reduced phycocyanin, chlorophyll and photosynthesis, while respiration had increased, induced anaerobiosis in Spirulina. This study reports for the first time anaerobiosis under autotrophic conditions in a cyanobacterium. [ABSTRACT FROM AUTHOR]

The spreading of vinasse on soils may favor not only anoxia but also mineral alterations and metal mobilization. Our aims were to record the geochemical changes occurring in a ferralsol subjected to vinasse input and anaerobiosis, and to check for soil resilience after a return to aerobic conditions. Soil slurries were therefore incubated under successive 7 d of aerobic, 0 to 28 d of anaerobic, and 28 d of aerobic conditions, vinasse being supplied at one of three levels when anaerobiosis began. At several dates, the slurry solution was characterized (pH and organic and mineral compounds) and Mn and Fe oxidation states in solids were assessed. Before incubations, about 20% ofthe Fe in solids was already reduced, whereas almost all Mn was found as Mn(IV). During the first aerobic period, mobilized metals included Pb, Zn, Ni, Cu, and Cr. After vinasse input during the first 14 d of anaerobiosis, the principal biotransformations were fermentation and true acetogenesis; Fe and Mn were mobilized during this period (up to 4.05 and 6.2 mmol L-1, respectively), and most Mn and an unknown but small fraction of Fe in solids were reduced. During the subsequent 14 d of anaerobiosis, only acetoclastic methanogenesis was observed. The return to aerobic conditions led to rapid oxidative immobilization of Fe, desorption of exchangeable Fe(II), and the partial immobilization of other metals (Ca, Mg, K, Na, Mn, Pb, and Ni). Manganese was not oxidized, and there was no return to the initial conditions for Fe and Mn in solids. [ABSTRACT FROM AUTHOR]

The phage shock protein (Psp) system found in enterobacteria is induced in response to impaired inner membrane integrity (where the Psp response is thought to help maintain the proton motive force of the cell) and is implicated in the virulence of pathogens such as Yersinia and Salmonella. We provided evidence that the two-component ArcAB system was involved in induction of the Psp response in Escherichia coli and now report that role of ArcAB is conditional. ArcAB, predominantly through the action of ArcA regulated genes, but also via a direct ArcB–Psp interaction, is required to propagate the protein IV (pIV)-dependent psp-inducing signal(s) during microaerobiosis, but not during aerobiosis or anaerobiosis. We show that ArcB directly interacts with the PspB, possibly by means of the PspB leucine zipper motif, thereby allowing cross-communication between the two systems. In addition we demonstrate that the pIV-dependent induction of psp expression in anaerobiosis is independent of PspBC, establishing that PspA and PspF can function as a minimal Psp system responsive to inner membrane stress. [ABSTRACT FROM AUTHOR]

Bacteria have evolved different systems to tightly control both cytosolic and envelope copper concentration to fulfil their requirements and at the same time, avoid copper toxicity. We have previously demonstrated that, as in Escherichia coli, the Salmonella cue system protects the cytosol from copper excess. On the other hand, and even though Salmonella lacks the CusCFBA periplasmic copper efflux system, it can support higher copper concentrations than E. coli under anaerobic conditions. Here we show that the Salmonella cue regulon is also responsible for the control of copper toxicity in anaerobiosis. We establish that resistance in this condition requires a novel CueR-controlled gene named cueP. A Δ cueP mutant is highly susceptible to copper in the absence of oxygen, but shows a faint phenotype in aerobic conditions unless other copper-resistance genes are also deleted, resembling the E. coli CusCFBA behaviour. Species that contain a cueP homologue under CueR regulation have no functional CusR/CusS-dependent Cus-coding operon. Conversely, species that carry a CusR/CusS-regulated cus operon have no cueP homologues. Even more, we show that the CueR-controlled cueP expression increases copper resistance of a Δ cus E. coli. We posit that CueP can functionally replace the Cus complex for periplasmic copper resistance, in particular under anaerobic conditions. [ABSTRACT FROM AUTHOR]

Abstract: We have found the transcript of one of at least six ferredoxin encoding genes of the green alga Chlamydomonas reinhardtii, FDX5, strongly accumulating in anaerobiosis, indicating a vital role of the encoded protein in the anaerobic metabolism of the cells. According to absorption and electron paramagnetic resonance spectroscopy, Fdx5 is a plant-type [2Fe2S]-ferredoxin with a redox potential similar to that of the ferredoxin PetF. However, although Fdx5 seems to be located in the chloroplast, it is not able to photoreduce nicotinamide adenine dinucleotide phosphate (NADP+) via ferredoxin-NADP-reductase, nor to be an electron donor to the plastidic [FeFe]-hydrogenase HydA1. Thus, Fdx5 seems to have a special role in a yet to be identified anaerobic pathway. [Copyright &y& Elsevier]

For decades altitude training has been used by endurance athletes and coaches to enhance sea-level performance. Whether altitude training does, in fact, enhance sea level performance and, if so, by what means has been the subject of a number of investigations. Data produced principally by Levine and Stray-Gundersen have shown that living for 4 weeks at 2500 m, while performing the more intense training sessions near sea level will provide an average improvement in sea level endurance performance (duration of competition: 7–20 min) of approximately 1.5%, ranging from no improvement to 6% improvement. This benefit lasts for at least 3 weeks on return to sea level. Two mechanisms have been shown to be associated with improvement in performance. One is an increase in red cell mass (∼8%) that results in an improved maximal oxygen uptake (∼5%). That must be combined with maintenance of training velocities and oxygen flux to realize the improvement in subsequent sea level performance. We find no evidence of changes in running economy or markers of anaerobic energy utilization. Our results have been obtained in runners ranging from collegiate to elite. Wehrlin et al. have recently confirmed these results in elite orienteers. While there are no specific studies addressing the use of living high, training low in football players, it is likely that an improvement in maximal oxygen uptake, all other factors equal, would enhance football performance. This benefit must be weighed against the time away (4 weeks) from home and competition necessary to gain these benefits. [ABSTRACT FROM AUTHOR]

With the use of technologically constructed hypoxic environments (TCHE) in soccer as our case, we propose four check points from which to evaluate new performance-enhancing technologies in sport. These are (I) Is the technology beneficial, (II) Is it safe, (III) Can fairness be assured, and (IV) Is the technology in line with the spirit of or rationale for sport? The use of TCHE is ambiguous. On the one hand, in situations with grave inequalities between teams due to lack of acclimatization of one team, TCHE can be an efficient means to even the playing field and out of concern for athlete welfare and health. On the other hand, if used as a pure performance-enhancing means to enhance the oxygen-carrying capacity of the blood independent of altitude, it belongs to a category of expert-assisted performance enhancement that may challenge athletic autonomy and the responsibility for one's own performance and, hence, the spirit of sport. [ABSTRACT FROM AUTHOR]

Heterotermes tenuis is a native termite of large negative impact on the Brazilian economy. Many studies have focused on optimizing the baiting method for termite control by improving its use and its efficacy. In order to maximize termite bait consumption, this study aimed to select nutrient solutions which are able to enhance termite feeding. The effects of some sugars and urea on feeding preference of the subterranean termite H. tenuis were determined by double choice feeding tests, and the consumption was evaluated by variation in dry mass of filter paper after 28 days of termite feeding. Most of the solutions tested did not significantly influence feeding of H. tenuis. Termites fed preferentially on filter paper treated with 0.03 g/ml trehalose and 0.015 g/ml urea solutions. The data indicate that trehalose and urea solutions are phagostimulants to H. tenuis, and their future use in bait matrices may increase consumption of baits and improve this control technique. [ABSTRACT FROM AUTHOR]

Lactobacillus rhamnosus R0011 was inoculated in an apple–pear–raspberry juice blend at 4.5 × 109 CFU/250 mL portion, and viability was followed during storage in conditions simulating consumer use. Study parameters were age of the juice (2 or 4 wk), sampling size (one to three 250-mL portions), incubation temperature (between 2 and 7 °C), and atmosphere (aerobic compared with anaerobic). Dependent variables were pH, dissolved oxygen (DO) level, and viable count. The DO level in the unopened PETE commercial bottles decreased from 10% to 3% over a 5-wk storage period at 7 °C. In shaken and opened bottles, DO increased to 15% during the 1st week of storage, irrespective of sampling size. However, agitation of bottles having more that 250 mL of headspace initially increased DO readings to 30% of maximum, but the DO level subsequently dropped to 15% during the 1-wk storage period between samplings. The presence of L. rhamnosus R0011 did not affect the DO data. The pH varied between 3.6 and 3.9, and was not influenced by L. rhamnosus R0011. However, the pH increased on average by 0.1 unit following multiple agitations and samplings. When the juices remained unopened in the PETE bottles, the viable population gradually dropped by 75% over 5 wk of storage at 7 °C, while in opened bottles reduction were only between 20% and 40%. Viability losses under anaerobic conditions were twice as high at 7 °C than at 4 °C. Data show that consumers can expect good viability of L. rhamnosus R0011 over a few weeks of storage in a refrigerator, even if the bottles have been opened and cells are exposed to oxygen. [ABSTRACT FROM AUTHOR]

There are two distinctly different pathways for the catabolism ofl-rhamnose in microorganisms. One pathway with phosphorylated intermediates was described in bacteria; here the enzymes and the corresponding gene sequences are known. The other pathway has no phosphorylated intermediates and has only been described in eukaryotic microorganisms. For this pathway, the enzyme activities have been described but not the corresponding gene sequences. The first enzyme in this catabolic pathway is the NAD-utilizingl-rhamnose 1-dehydrogenase. The enzyme was purified from the yeast Pichia stipitis, and the mass of its tryptic peptides was determined using MALDI-TOF MS. This enabled the identification of the corresponding gene, RHA1. It codes for a protein with 258 amino acids belonging to the protein family of short-chain alcohol dehydrogenases. The ORF was expressed in Saccharomyces cerevisiae. As the gene contained a CUG codon that codes for serine in P. stipitis but for leucine in S. cerevisiae, this codon has changed so that the same amino acid was expressed in S. cerevisiae. The heterologous protein showed the highest activity and affinity withl-rhamnose and a lower activity and affinity withl-mannose andl-lyxose. The enzyme was specific for NAD. A northern blot analysis revealed that transcription in P. stipitis is induced during growth onl-rhamnose but not on other carbon sources. [ABSTRACT FROM AUTHOR]

Objectives: To determine whether episodes of haemoglobin oxygen (SpO2) desaturation in full-term infants restrained in car seats can be reduced by a simple foam plastic infant car seat insert designed to push the body forward, with space for the protuberant occiput to lie behind the spine, and so reduce flexion of the infant's head on the trunk. Methods: Eighteen healthy full-term babies were evaluated while restrained in an infant car safety seat with, and without, the foam insert. Infants were monitored in each position for 30 min with continuous polygraphic recording of respiratory and heart rate, nasal airflow and SpO2. Results: Placement of the insert in the car seat was associated with a significant reduction in the rate of apneas with a fall in SpO2 >5% (median, interquartile range: 4.4 (0, 10.6) vs. 9.2 (5.4, 15.2) events per hour, p = 0.03). The one clinically severe episode of apnea, with a fall in SpO2 of more than 30%, occurred in the car seat without the insert. Conclusions: A car seat insert that allows the newborn's head to lie in a neutral position during sleep may reduce the frequency of mild episodes of reduced SpO2 in some full-term newborn babies. [ABSTRACT FROM AUTHOR]

The actinomycete Streptomyces coelicolor is an obligate aerobe that is found in soil and aqueous habitats. The levels of oxygen in these environments can vary considerably, which raises the question of how these bacteria survive during periods of anaerobiosis. Although S. coelicolor cannot grow in the complete absence of oxygen, we demonstrate here that it is capable of microaerobic growth and maintaining viability through several weeks of strict anaerobiosis. Both resting and germinated spores are able to survive abrupt exposure to anaerobiosis, which contrasts the situation with Mycobacterium species where gradual oxygen depletion is required to establish a latent state in which the bacterium is able to survive extended periods of anaerobiosis. Growth of S. coelicolor resumes immediately upon re-introduction of oxygen. Taken together these findings indicate that survival is not restricted to spores and suggest that the bacterium has evolved a mechanism to maintain viability and a membrane potential in the hyphal state. Furthermore, although we demonstrate that several members of the genus also survive long periods of anaerobic stress, one species, Streptomyces avermitilis, does not have this capacity and might represent a naturally occurring variant that is unable to adopt this survival strategy. [ABSTRACT FROM AUTHOR]

In the absence of oxygen, Escherichia coli can use alternative exogenous electron acceptors, including trimethylamine oxide (TMAO), to generate energy. In this study, we showed that in contrast to the other anaerobic respiratory systems, the TMAO reductase (Tor) system was expressed during both aerobiosis and anaerobiosis. By using a torA–lacZ fusion and quantitative reverse transcription polymerase chain reaction, we established that the torCAD operon encoding the Tor system was induced in the presence of TMAO mainly during exponential phase, and that optimal induction required a certain level of DNA supercoiling. We also showed that the presence of oxygen prevented neither the biogenesis of the Tor system nor the reduction of TMAO. The physiological role of TMAO reduction during aerobiosis has not been yet established, but our experiments suggest that alkaline TMA production could enhance the growth conditions by increasing the pH of the culture. [ABSTRACT FROM AUTHOR]

The effect of oxygen and anaerobiosis on the redox properties of Cyt b559 was investigated in PSII preparations from spinach with different degree of disintegration of the donor side. Comparative studies were performed on intact PSII membranes and PSII membranes that were deprived of the 18-kDa peripheral subunit (0.25 NaCl washed), the 18- and 24-kDa peripheral subunits (1 M NaCl washed), the 18-, 24- and 33-kDa peripheral subunits (1.2 M CaCl2 washed), Cl depleted and after complete depletion of the Mn cluster (Tris washed). In active PSII centers, about 75% of Cyt b559 was found in the high-potential form and the rest in the intermediate potential form. With decomposition of the donor side, the intermediate potential form started to dominate, reaching more than 90% after Tris treatment. The oxygen-dependent conversion of the intermediate potential form of Cyt b559 into the low-potential and high-potential forms was only observed after treatments that directly affect the Mn cluster. In PSII membranes, deprived of all three extrinsic subunits (CaCl2 treatment), 21% of the intermediate potential form was converted into the low-potential form and 14% into the high-potential form by the removal of oxygen. In Tris-washed PSII membranes, completely lacking the Mn cluster, this conversion amounted to 60 and 33%, respectively. In intact PSII membranes, the oxygen-dependent conversion did not occur. The possible physiological role of this oxygen-dependent behavior of the Cyt b559 redox forms during the assembly/photoactivation cycle of PSII is discussed. [ABSTRACT FROM AUTHOR]

1. River metabolism was measured over an annual cycle at three sites distributed along a 1000 km length of the lowland Murray River, Australia. 2. Whole system metabolism was measured using water column changes in dissolved oxygen concentrations while planktonic and benthic metabolism were partitioned using light-dark bottles and benthic chambers. 3. Annual gross primary production (GPP) ranged from 775 to 1126 g O2 m−2 year−1 which in comparison with rivers of similar physical characteristics is moderately productive. 4. Community respiration (CR) ranged from 872 to 1284 g O2 m−2 year−1 so that annual net ecosystem production (NEP) was near zero, suggesting photosynthesis and respiration were balanced and that allochthonous organic carbon played a minor role in fuelling metabolism. 5. Planktonic rates of gross photosynthesis and respiration were similar to those of the total channel, indicating that plankton were responsible for much of the observed metabolism. 6. Respiration rates correlated with phytoplankton standing crop (estimated as the sum of GPP plus the chlorophyll concentration in carbon units), yielding a specific respiration rate of −1.1 g O2 g C−1 day−1. The respiration rate was equivalent to 19% of the maximum rate of phytoplankton photosynthesis, which is typical of diatoms. 7. The daily GPP per unit phytoplankton biomass correlated with the mean irradiance of the water column giving a constant carbon specific photon fixation rate of 0.35 gO2 g Chl a−1 day−1 per μmole photons m−2 s−1 (ca. 0.08 per mole photons m−2 on a carbon basis) indicating that light availability determined daily primary production. 8. Annual phytoplankton net production (NP) estimates at two sites indicated 25 and 36 g C m−2 year−1 were available to support riverine food webs, equivalent to 6% and 11% of annual GPP. 9. Metabolised organic carbon was predominantly derived from phytoplankton and was fully utilised, suggesting that food-web production was restricted by the energy supply. [ABSTRACT FROM AUTHOR]

1. Reduced metabolic rate among cave organisms compared with surface species has long been suggested as an adaptation to food shortage in cave environments. However, comparisons of metabolic rates between species have not often included closely related surface and cave species. By measuring metabolic rate across three seasons and over a range of body sizes, we examined the hypothesis that the routine metabolic rate of Gammarus acherondytes, a federally listed stygobitic amphipod, is lower than that of the closely related stygophilic Gammarus troglophilus. To determine if human activities increased the supply of organic matter to caves, we also examined the relationship between residential development and bacterial contamination in water wells. 2. For G. acherondytes, the slope of the overall relationship between oxygen consumption and body dry mass did not differ from zero and did not vary seasonally, whereas for G. troglophilus it was positive and higher in summer than in winter and spring. These results provide insights into a potential novel metabolic adaptation among stygobites. Higher metabolic rate in young G. acherondytes would allow efficient use of typically transient energy sources and a low metabolic rate at larger body sizes would increase survival through periods of food scarcity. 3. The number of wells with faecal coliform contamination was weakly but positively correlated with the number of residential building permits, indicating that surface land-use changes probably increase the availability of energy in groundwater systems inhabited by G. acherondytes. This may give stygophilic animals, with higher metabolic rates, a competitive advantage in the caves, thus reducing the abundance of stygobites such as G. acherondytes. [ABSTRACT FROM AUTHOR]

During the first billion years of life on the Earth, the environment was anaerobic. Iron and sulphur were plentiful, and they were recruited in the formation of iron-sulphur (Fe-S) clusters within ancient proteins. These clusters provided many enzymes with the ability to transfer electrons; to others they offered a cationic feature that tightly bound oxyanionic and nitrogenous metabolites. Still others acquired a crystallizing surface around which polypeptide could fold to establish a three-dimensional structure. However, the subsequent oxygenation of the Earth's atmosphere by photosynthetic organisms created a threat to cluster-dependent proteins that still has not been fully resolved. By oxidizing environmental iron, oxygen limits its bioavailability, requiring that organisms employ complex schemes with which to satisfy their iron requirement. More directly, oxygen species convert exposed Fe-S clusters to unstable forms that quickly decompose. Some microbes responded to this dilemma by retreating to anaerobic habitats. Others abandoned the use of low-potential electron-transfer pathways, which rely upon the least stable cluster enzymes, and developed antioxidant strategies to protect the remainder. These adjustments were only partially successful: largely because of their reliance upon Fe-S clusters, aerobes remain vulnerable to iron restriction and oxidative stress, features that higher organisms exploit in defending themselves against bacterial pathogens. Thus, the history of Fe-S clusters is an unusual one that has profoundly shaped contemporary microbial ecology. [ABSTRACT FROM AUTHOR]

Glutathione S-transferases (GSTs) play critical roles in detoxification, response to oxidative stress, regeneration of S-thiolated proteins, and catalysis of reactions in nondetoxification metabolic pathways. Liver GSTs were purified from the anoxia-tolerant turtle, Trachemys scripta elegans. Purification separated a homodimeric (subunit relative molecular mass =34 kDa) and a heterodimeric (subunit relative molecular mass = 32.6 and 36.8 kDa) form of GST. The enzymes were purified 23–69-fold and 156–174-fold for homodimeric and heterodimeric GSTs, respectively. Kinetic data gathered using a variety of substrates and inhibitors suggested that both homodimeric and heterodimeric GSTs were of the α class although they showed significant differences in substrate affinities and responses to inhibitors. For example, homodimeric GST showed activity with known α class substrates, cumene hydroperoxide and p-nitrobenzylchloride, whereas heterodimeric GST showed no activity with cumene hydroperoxide. The specific activity of liver GSTs with chlorodinitrobenzene (CDNB) as the substrate was reduced by 2.6- and 8.7-fold for homodimeric and heterodimeric GSTs isolated from liver of anoxic turtles as compared with aerobic controls, suggesting an anoxia-responsive stable modification of the protein that may alter its function during natural anaerobiosis. [ABSTRACT FROM AUTHOR]

Shewanella oneidensisstrain MR-1 is well known for its respiratory versatility, yet little is understood about how it regulates genes involved in anaerobic respiration. The Arc two-component system plays an important role in this process inEscherichia coli; therefore, we determined its function inS. oneidensis.arcAfromS. oneidensiscomplements anE. coli arcAmutant, but the Arc regulon inS. oneidensisconstitutes a different suite of genes. For example, one of the strongest ArcA-regulated gene clusters inE. coli,sdh, is not regulated by the Arc system inS. oneidensis, and thecydlocus, which is induced by ArcA inE. coliunder microaerobic conditions, is repressed by ArcA inS. oneidensisunder anaerobic conditions.One locus that we identified as being potentially regulated by ArcA inS. oneidensiscontains genes predicted to encode subunits of a dimethyl sulphoxide (DMSO) reductase. We demonstrate that these genes encode a functional DMSO reductase, and that anarcAmutant cannot fully induce their expression and is defective in growing on DMSO under anaerobic conditions. WhileS. oneidensislacks a highly conserved full-length ArcB homologue, ArcA is partially activated by a small protein homologous to the histidine phosphotransfer domain of ArcB fromE. coli, HptA. This protein alone is unable to compensate for the lack ofarcBinE. coli, indicating that another protein is required in addition to HptA to activate ArcA inS. oneidensis. [ABSTRACT FROM AUTHOR]

The tiger beetle, Phaeoxantha klugii Chaudoir, survives the annual inundation period in Central Amazonian floodplains as a third-instar larvae submerged in the soil at approximately 29°C for up to 3.5 months. Previous studies showed an exceptional anoxia resistance in these larvae and this study investigates whether they perform anaerobiosis. Larvae collected in the field were exposed to a pure nitrogen atmosphere for 0-9 days in the laboratory. The content of lactate, alanine, free sugars and glycogen is analysed in surviving larvae. Lactate and alanine contents rise during anoxia from around 1.5 and 7 to 6-14 and 15-22 µmol g-1 fresh mass, respectively, providing evidence for anaerobic metabolism. Both compounds show a steep increase during the first 12 h and a tendency to rise further with increasing duration of anoxic conditions, indicating a significant metabolic depression within the first day. Content of free sugars and glycogen varies greatly between individuals and ranges from 0.08-2.5 and 0.05-2.9 mg g-1 fresh mass, respectively. Whether glycogen is used as metabolic substrate for anaerobiosis could not be verified. The findings for free sugars indicate that larvae apparently maintain the ability to regulate the level of glucose and/or trehalose even after 9 days of anoxia. [ABSTRACT FROM AUTHOR]

A small anaerobically induced tomato transcription factor was isolated from a subtractive library. This factor, designated ABZ1 (anaerobic basic leucine zipper), is anaerobically induced in fruits, leaves and roots and encodes a nuclear localized protein. ABZ1 shares close structural and sequence homology with the S-family of small basic leucine zipper (bZIP) transcription factors that are implicated in stress response. Nuclear localization of ABZ1 is mediated by the basic region and occurs under normoxic conditions. ABZ1 binds to G-box-like target sites as a dimer. Binding can be abolished by heterodimerization with a truncated protein retaining the leucine zipper but lacking the DNA binding domain. The protein binds in a sequence specific manner to the CaMV 35S promoter which is down regulated when ABZ1 is coexpressed. This correlates with the anaerobic down regulation of the 35S promoter in tomato and tobacco. These results may suggest that small bZIP proteins are involved in the negative regulation of gene expression under anaerobic conditions. [ABSTRACT FROM AUTHOR]

The activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10−6 mol g−1 fresh weight s−1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1-week exposure to either dissolved oxygen at air-saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot-to-root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of 14C-labelled photo-assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high 14C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning. [ABSTRACT FROM AUTHOR]

1. Ten Arctic species of Collembola and two species of cryptostigmatic mites survived anoxia at 5 °C over periods ranging from 1 to 36 days. 2. Highly active, surface-dwelling collembolans such as Isotoma anglicana, Isotoma tschernovi, and Sminthurides malmgreni were the most susceptible to anoxia. Mites and Collembola living deeper in the soil or in wet habitats, such as Camisia anomia and Hypogastrura viatica, were most tolerant. Tolerance, however, appears more closely linked to taxonomic relatedness than to ecological groupings per se, although the two may coincide. 3. Implications for life-history strategies, including metabolic cold adaptation in its broadest sense, are discussed. [ABSTRACT FROM AUTHOR]

Three soft rot erwinias, Erwinia carotovora ssp. carotovora , E. carotovora ssp. atroseptica and E. chrysanthemi are associated with potatoes causing tuber soft rot and blackleg (stem rot). Latent infection of tubers and stems is widespread. As opportunistic pathogens, the bacteria tend to cause disease when potato resistance is impaired. Pathogenesis or disease development in potato tubers and stems is discussed in terms of the interaction between pathogen, host and environment, microbial competition and recent findings on the molecular basis of pathogenicity. Emphasis is placed on the role of free water and anaerobiosis in weakening tuber resistance and in providing nutrient for erwinias to multiply. Blackleg symptoms are expressed when erwinias predominate in rotting mother tubers, invade the stems and multiply in xylem vessels under favourable weather conditions. Soft rot erwinias tend to out-compete other bacteria in tuber rots because of their ability to produce larger quantities of a wider range of cell wall-degrading enzymes. However, despite extensive studies on their induction, regulation and secretion, little is known about the precise role of the different enzymes in pathogenesis. The putative role of quorum-sensing regulation of these enzymes in disease development is evaluated. The role certain pathogenicity-related characters, including motility, adhesion, siderophores, detoxifying systems and the hrp gene complex, common to most bacteria including symbionts and saprophytes, could play in latent and active infections is also discussed. [ABSTRACT FROM AUTHOR]

1. Elevated oxygen consumption during recovery is the majority of total metabolic costs associated with short vigorous activity, thus any assessment of total costs associated with such activity should also examine the excess postexercise oxygen consumption (EPOC). This study examined EPOC and total metabolic costs in Dipsosaurus (N = 8; 75 ± 3 g) over a variety of submaximal intensities: 50%, 100% and 400% of the maximum aerobic speed (MAS = 0.27 m s[sup -1]; the speed at which ...[sub O[sub 2]max] is elicited). Activity duration was also varied (15, 60 and 300 s) over these intensities. 2. Total costs increased significantly with both activity intensity and duration. EPOC increased significantly with activity intensity. EPOC increased significantly with activity duration at higher intensities, but not the lowest intensity of 50% MAS. 3. These recovery costs constitute amounts of energy large enough to have an impact on energy budget analyses. The metabolic cost of an individual bout of activity and subsequent recovery was as high as 5% of the predicted daily energy expenditure, an increase of 5-8 × estimates that do not incorporate recovery. 4. To compare the relative economy of different activity regimens, the cost of activity (C[sub act]; ml O[sub 2] g[sup -1] km[sup -1]), was calculated as total costs, including EPOC, per unit distance travelled. C[sub act] was independent of activity intensity over these ranges, but was inversely related to activity duration. 5. From these data, the most economical strategy to travel a certain distance would utilize a low-intensity and extended duration, as seen in regular activities such as foraging. High-intensity activities, such as escape, prey capture or mating behaviours, are thus predicted to be less economical. These should only be observed where metabolic costs would be considered secondary to the more proximal needs of the animal. [ABSTRACT FROM AUTHOR]

Chlamydomonas reinhardtii , a unicellular green alga, contains a hydrogenase enzyme, which is induced by anaerobic adaptation of the cells. Using the suppression subtractive hybridization (SSH) approach, the differential expression of genes under anaerobiosis was analyzed. A␣PCR fragment with similarity to the genes of bacterial Fe-hydrogenases was isolated and used to screen an anaerobic cDNA expression library of C. reinhardtii . The cDNA sequence of hydA contains a 1494-bp ORF encoding a protein with an apparent molecular mass of 53.1 kDa. The transcription of the hydrogenase gene is very rapidly induced during anaerobic adaptation of the cells. The deduced amino-acid sequence corresponds to␣two␣polypeptide sequences determined by sequence analysis of the isolated native protein. The Fe-hydrogenase contains a short transit peptide of 56 amino acids, which routes the hydrogenase to the chloroplast stroma. The isolated protein belongs to a new class of Fe-hydrogenases. All four cysteine residues and 12 other␣amino acids, which are strictly conserved in the active site (H-cluster) of Fe-hydrogenases, have been identified. The N-terminus of the C. reinhardtii protein is markedly truncated compared to other nonalgal Fe-hydrogenases. Further conserved cysteines that coordinate additional Fe–S-cluster in other Fe-hydrogenases are missing. Ferredoxin PetF, the natural electron donor, links the hydrogenase from C. reinhardtii to the photosynthetic electron transport chain. The hydrogenase enables the survival of the green algae under anaerobic conditions by transferring the electrons from reducing equivalents to the enzyme. [ABSTRACT FROM AUTHOR]

The molecular basis of obligate anaerobiosis is not well established. Bacteroides thetaiotaomicron is an opportunistic pathogen that cannot grow in fully aerobic habitats. Because microbial niches reflect features of energy-producing strategies, we suspected that aeration would interfere with its central metabolism. In anaerobic medium, this bacterium fermented carbohydrates to a mixture of succinate, propionate and acetate. When cultures were exposed to air, the formation of succinate and propionate ceased abruptly. In vitro analysis demonstrated that the fumarase of the succinate–propionate pathway contains an iron–sulphur cluster that is sensitive to superoxide. In vivo, fumarase activity fell to < 5% when cells were aerated; virtually all activity was recovered after extracts were chemically treated to rebuild iron–sulphur clusters. Aeration minimally affected the remainder of this pathway. However, aeration reduced pyruvate:ferredoxin oxidoreductase (PFOR), the first enzyme in the acetate fermentation branch, to 3% of its anaerobic activity. This cluster-containing enzyme was damaged in vitro by molecular oxygen but not by superoxide. Thus, aerobic growth is precluded by the vulnerability of these iron–sulphur cluster enzymes to oxidation. Importantly, both enzymes were maintained in a stable, inactive form for long periods in aerobic cells; they were then rapidly repaired when the bacterium was returned to anaerobic medium. This result explains how this pathogen can easily recover from occasional exposure to oxygen. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae PAU genes constitute the largest multigene family in yeast, with 23 members located mainly in subtelomeric regions. The role and regulation of these genes were previously unknown. We detected PAU gene expression during alcoholic fermentation. An analysis of PAU gene regulation using PAU–lacZ fusions and Northern analyses revealed that they were regulated by anaerobiosis. PAU genes display, however, different abilities to be induced by anaerobiosis and this appears to be related to their chromosomal localization; two subtelomeric copies are more weakly inducible than an interstitial one. We show that PAU genes are negatively regulated by oxygen and repressed by haem. Examination of PAU gene expression in rox1Δ and tup1Δ strains indicates that PAU repression by oxygen is mediated by an unknown, haem-dependent pathway, which does not involve the Rox1p anaerobic repressor but requires Tup1p. Given the size of the gene family, PAU genes could be expected to be important during yeast life and some of them probably help the yeast to cope with anaerobiosis. [ABSTRACT FROM AUTHOR]

ABSTRACTA new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy–pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark–light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology. [ABSTRACT FROM AUTHOR]