Low Substrate Availability Research Articles

Future European biogas: Animal manure, straw and grass potentials for a sustainable European biogas production

Biogas is expected to play an important role in reaching the future energy policy targets of the European Union (EU). The sustainability of biogas substrates has however been recently critically discussed due to the increasing shares of agricultural land used for energy crop production.The aim of this study was to project and map the biomass and biogas energy potential from a selection of potentially sustainable agricultural residues, which have been documented to improve in biogas yields when co-digested in biogas production, for the EU28 in year 2030. The investigated types of residual biomasses were animal manure, straw by-products from cereal production, and excess grass from rotational and permanent grasslands and meadows. The biogas energy potential from the investigated biomass was projected to range from 1.2·103 to 2.3·103 PJ y−1 in year 2030 in the EU28, depending on the biomass availability. Alone the biogas energy potential projected in the scenario representing low substrate availability corresponds to a doubling of the European biogas production in 2015. The results shows that sustainable alternatives to the use of maize are present in all the member states of the EU28 to an extent that is sufficient to ensure a continuous progressive development of the European biogas sector.

Drought tolerance in two oil palm hybrids as related to adjustments in carbon metabolism and vegetative growth

Drought tolerance was examined in two oil palm hybrids (BRS Manicore and BRS C 2501) grown in large pots and subjected to long-term drought (57 days) and rehydration. Regardless of hybrids, predawn water potential (Ψ pd), net photosynthesis rates, and stomatal conductance decreased similarly upon drought imposition, but the absolute values of these variables were lower in BRS C 2501 than in BRS Manicore. Overall, drought-induced decreases in activities of key enzymes associated with carbon metabolism, including Rubisco, ADP-glucose pyrophosphorylase, and sucrose-phosphate synthase, were stronger in BRS C 2501 than in BRS Manicore. Our data suggest that synthesis of starch (and possibly sucrose) was fundamentally limited by a lower substrate availability rather than by enzymatic constraints, particularly until day 34 after suspending watering. Drought stress provoked similar decreases in biomass accumulation in either hybrid; however, BRS Manicore plants displayed higher total leaf area and root length coupled with greater relative decreases in dry matter of above-ground parts than of roots as compared to BRS C 2501, thereby leading to an increased root-to-above ground ratio in the former. Upon resuming irrigation, the slow recovery of Ψ pd preceded the recovery of stomatal conductance and photosynthesis irrespective of hybrid. BRS Manicore was better able to recover enzyme activities and carbohydrate status than BRS C 2501. In conclusion, both hybrids could tolerate (or survive) the severe drought conditions, but, overall, BRS Manicore plants were better able to adjust its physiological, morphological, and biochemical traits to cope with drought than did BRS C 2501.

Natural and Induced Mitochondrial Phosphate Carrier Loss: DIFFERENTIAL DEPENDENCE OF MITOCHONDRIAL METABOLISM AND DYNAMICS AND CELL SURVIVAL ON THE EXTENT OF DEPLETION

The relevance of mitochondrial phosphate carrier (PiC), encoded by SLC25A3, in bioenergetics is well accepted. However, little is known about the mechanisms mediating the cellular impairments induced by pathological SLC25A3 variants. To this end, we investigated the pathogenicity of a novel compound heterozygous mutation in SLC25A3. First, each variant was modeled in yeast, revealing that substituting GSSAS for QIP within the fifth matrix loop is incompatible with survival on non-fermentable substrate, whereas the L200W variant is functionally neutral. Next, using skin fibroblasts from an individual expressing these variants and HeLa cells with varying degrees of PiC depletion, PiC loss of ∼60% was still compatible with uncompromised maximal oxidative phosphorylation (oxphos), whereas lower maximal oxphos was evident at ∼85% PiC depletion. Furthermore, intact mutant fibroblasts displayed suppressed mitochondrial bioenergetics consistent with a lower substrate availability rather than phosphate limitation. This was accompanied by slowed proliferation in glucose-replete medium; however, proliferation ceased when only mitochondrial substrate was provided. Both mutant fibroblasts and HeLa cells with 60% PiC loss showed a less interconnected mitochondrial network and a mitochondrial fusion defect that is not explained by altered abundance of OPA1 or MFN1/2 or relative amount of different OPA1 forms. Altogether these results indicate that PiC depletion may need to be profound (>85%) to substantially affect maximal oxphos and that pathogenesis associated with PiC depletion or loss of function may be independent of phosphate limitation when ATP requirements are not high.

Increasing Levels of Dietary Hempseed Products Leads to Differential Responses in the Fatty Acid Profiles of Egg Yolk, Liver and Plasma of Laying Hens.

The limited efficiency with which dietary alpha-linolenic acid (ALA) is converted by hens into docosahexaenoic acid (DHA) for egg deposition is not clearly understood. In this study, dietary ALA levels were increased via the inclusion of hempseed (HS) and hempseed oil (HO) in hen diets, with the goal of assessing the effects on the fatty acid (FA) profiles of total lipids and lipid classes in yolk, liver and plasma. Forty-eight hens were individually caged and fed one of six diets containing either HS:10, 20 or 30, HO:4.5 or 9.0 (%, diet) or a control (containing corn oil), providing a range (0.1-1.28%, diet) of ALA. Fatty acid methyl esters of total lipids and lipid classes, including phosphatidyl choline (PtdCho) and ethanolamine (PtdEtn) in yolk, plasma and liver were then determined. Levels of n-3 FAs in both total lipids and lipid classes increased in all tissues. ALA and eicosapentaenoic acid (EPA) increased linearly, while docosapentaenoic acid and DHA increased quadratically. The FA profiles of yolk closely reflected levels in both plasma and liver. While ALA was highly concentrated in the triacylglycerol, it was low but equally distributed between PtdCho and PtdEtn in all tissues; however, the net accumulation was lower (P<0.0001) in liver compared to yolk and plasma. Levels of EPA and ALA in yolk-PtdEtn were linearly (P<0.0001; R (2)=0.93) associated, and reflected those in liver-PtdEtn (P<0.0001; R (2)=0.90). In the liver, a strong inverse correlation (P<0.0001; r=-0.94) between PL-DHA and ALA-to-EPA ratio in PtdEtn supports theories of low substrate availability, possibly limiting the conversion of ALA into DHA for egg enrichment.

Long-term fertilization effects on active ammonia oxidizers in an acidic upland soil in China

The effects of long-term fertilization of acidic soils on ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and its ecological implications remain poorly understood. We chose an acidic upland soil site under long-term (27-year) fertilization to investigate ammonia oxidizer communities under four different regimes: mineral N fertilizer (N), mineral NPK fertilizer (NPK), organic manure (OM) and an unfertilized control (CK). Soil net nitrification rates were significantly higher in OM soils than in CK, N or NPK soils. Quantitative analysis of the distribution of amoA genes by DNA-based stable isotope probing revealed that AOA dominate in CK, N and NPK soils, while AOB dominate in OM soils. Denaturing gradient gel electrophoresis and clone library analyses of amoA genes revealed that Group 1.1a-associated AOA (also referred to as Nitrosotalea) were the most dominant active AOA population (>92%), while Nitrosospira Cluster 3 and Cluster 9 were predominant among active AOB communities. The functional diversity of active ammonia oxidizers in acidic soils is affected by long-term fertilization practices, and the responses of active ammonia oxidizers to mineral fertilizer and organic manure are clearly different. Our results provide strong evidence that AOA are more highly adapted to growth at low pH and low substrate availability than AOB, and they suggest that the niche differentiation and metabolic diversity of ammonia oxidizers in acidic soils are more complex than previously thought.

P80 - Organizing principles underlying microorganism's growth-robustness trade-off

Growth Robustness Reciprocity (GRR) is an intriguing microbial manifestation: the impairment of microorganism’s growth enhances their ability to resist acute stresses, and vice-versa. This is caused by regulatory interactions that determine higher expression of protection mechanisms in response to low growth rates. But because such regulatory mechanisms are species-specific, GRR must result from convergent evolution. Why does natural selection favor such an outcome? We used mathematical models of optimal cellular resource allocation to identify the general principles underlying GRR. Non-linear optimization allowed to predict allocation patterns of biosynthetic resources (ribosomes devoted to the synthesis of each cell component) that maximize growth. These models predict the down-regulation of stress defenses under high substrate availabilities and low stress levels. Under these conditions, stress tolerance ensues from growth-related damage dilution: the higher the substrate availability, the fastest the dilution of damaged proteins by newly synthesized proteins, the lower the accumulation of damaged components into the cell. In turn, under low substrate availability growth is too slow for effective damage dilution, and the expression of the defenses up to some optimal level then increases growth. As a consequence, slow-growing cells are pre-adapted to withstand acute stresses. Therefore, the observed negative correlation between growth and stress tolerance can be explained as a consequence of optimal resource allocation for maximal growth.We acknowledge fellowship SFRH/BPD/90065/2012 and grants PEst-C/SAU/LA0001/2013-2014 and FCOMP-01-0124-FEDER-020978 financed by FEDER through the “Programa Operacional Factores de Competitividade, COMPETE” and by national funds through “FCT, Fundação para a Ciência e a Tecnologia” (project PTDC/QUI-BIQ/119657/2010).

Disturbances, Their Interactions, and Cumulative Effects on Carbon and Charcoal Stocks in a Forested Ecosystem

Disturbances have a strong role in the carbon balance of many ecosystems, and the cycle of vegetation growth, disturbance, and recovery is very important in determining the net carbon balance of terrestrial biomes. Compound disturbances are phenomena of growing concern which can impact ecosystems in novel ways, altering disturbance intensity, severity, and recovery trajectories. This research focuses on carbon stocks in a compound disturbance environment, with special attention on black carbon (charcoal), a potential source of long-term carbon sequestration. We report on a well-studied compound disturbance event (wind, logging, and severe fire) in a Colorado, USA subalpine forest that was extensively surveyed for impacts on carbon, black carbon, and regeneration. All major pools were considered, including organic and mineral soil (10 cm depth), and contrasted with neighboring undisturbed forests as a reference. The disturbances had an additive effect on carbon loss, with increasing numbers of disturbances resulting in progressively decreasing carbon/black carbon stocks. This resulted from lower substrate availability and higher fire intensity. Surprisingly, there was no significant difference between reference and burned plots in terms of total black carbon. It appears that high-intensity fires do not significantly increase net black carbon in these forests (over the entire fire-return interval), with additional disturbances potentially resulting in a net loss. Disturbances, and their interactions, will have long-lasting legacies for carbon and black carbon.

Steady sucrose degradation is a prerequisite for tolerance to root hypoxia.

We investigated the role of glycolysis and sucrolysis in the difference in tolerance to root hypoxia between two Myrtaceae tree species, Melaleuca cajuputi (which shows superior tolerance to root hypoxia) and Eucalyptus camaldulensis (which does not). Analysis of the adenylate energy charge (AEC) in roots subjected to a 4-day hypoxic treatment (HT) in hydroponic culture revealed that the interspecies difference in tolerance corresponds to the ability to maintain energy status under root hypoxia: AEC was reduced by HT in E. camaldulensis, but not in M. cajuputi. The energy status in HT roots of E. camaldulensis was restored by feeding of glucose (Glc) but not sucrose (Suc). These data provide evidence that low substrate availability for glycolysis resulting from an impairment of sucrolysis suppresses ATP production under hypoxic conditions in this species. Measurements of the rates of O2 consumption and CO2 production in roots indicated that E. camaldulensis, but not M. cajuputi, failed to activate fermentation in HT roots. These results cannot be attributed to enzymatic dysfunction, because no inhibition of main glycolytic and fermentative enzymes was observed in both species, and Glc feeding had a beneficial effect on AEC of HT roots of E. camaldulensis. The impairment of sucrolysis was demonstrated by inhibited soluble acid invertase activity in HT roots of E. camaldulensis. In contrast, there was no inhibition in all sucrolytic enzymes tested in HT roots of M. cajuputi, suggesting that steady Suc degradation is essential for maintaining high energy status under root hypoxia. We conclude that root sucrolysis is one of the essential factors that determines the extent of tolerance to root hypoxia.

Effects of climatic and soil properties on cellulose decomposition rates in temperate and tropical forests

Cellulose decomposition experiments were conducted under field conditions to analyze the effects of climatic and soil properties on rates of organic matter decomposition in temperate and tropical forests. The mass loss rates of cellulose filter papers buried in the soil surface were measured to estimate the respiratory C fluxes caused by cellulose decomposition and mean residence time (MRT) of cellulose. The rates of cellulose decomposition increased with soil temperature, except for during the dry season, while rate constants of decomposition (normalized for temperature) decreased with decreasing pH because of lower cellulase activity. The estimated MRTs of soil cellulosic carbohydrates varied from 81 to 495 days for the temperate forests and from 31 to 61 days for the tropical forests. As a major organic substrate, the C fluxes from cellulose decomposition can account for a substantial fraction of heterotrophic (basal) soil respiration. However, the respiratory C fluxes can be limited by the low substrate availability and low pH in tropical soils, despite high microbial activity. The rate-regulating factors of cellulose decomposition, i.e., temperature, soil pH, and substrate availability, can accordingly influence the rates of heterotrophic soil respiration.

The seasonal pattern of soil microbial community structure in mesic low arctic tundra

Soil microorganisms are critical to carbon and nutrient fluxes in terrestrial ecosystems. Understanding the annual pattern of soil microbial community structure and how it corresponds to soil nutrient availability and plant production is a fundamental first step towards being able to predict impacts of environmental change on ecosystem functioning. We investigated the composition, structure and nutrient stoichiometry of the soil microbial community in mesic arctic tundra on 9 sample dates in 6 months from winter to fall using phospholipid fatty acid analysis (PLFA), quantitative polymerase chain reaction (qPCR), epifluorescent microscopy and chloroform-fumigation–extraction (CFE). PLFA analysis indicates that the winter microbial community was fungal-dominated, cold-adapted and associated with high C, N and P in the soil solution and microbial biomass. The microscopy data suggest that both bacteria and fungi were active and growing in soils between −5 °C and 0 °C. A significant shift occurred in the PLFA data, qPCR patterns, microscopy and microbial biogeochemistry after the thaw period, resulting in a distinct community that persisted through our spring, summer and fall sample dates, despite large changes in plant productivity. This shift was characterised by increasing relative abundances of certain bacteria (especially Gram +ves) as well as a decline in fungal biomass, and corresponded with decreasing C, N and P in the soil solution. The summer period of low substrate availability (plant–microbe competition) was associated with microbial indicators of nutritional stress. Overall, our results indicate that tundra microbial communities are clearly differentiated according to the changes in soil nutrient status and environmental conditions that occur between winter and post-thaw, and that those changes reflect functionally important adaptations to those conditions.

Ceramide metabolism in mouse tissue

Ceramides with different N-acyl chains can act as second messengers in various signaling pathways. They are involved in cell processes such as apoptosis, differentiation and inflammation. Ceramide synthases (CerS) are key enzymes in the biosynthesis of ceramides and dihydroceramides. Six isoenzymes (CerS1–6) catalyze the N-acylation of the sphingoid bases, albeit with strictly acyl-Coenzyme A (CoA) chain length specificity. We analyzed the mRNA expression, the protein expression, the specific activity of the CerS, and acyl-CoA, dihydroceramide and ceramide levels in different tissues by LC–MS/MS. Our data indicate that each tissue express a distinct composition of CerS, whereby the CerS mRNA expression levels do not correlate with the respective protein expression levels in the tissues. Furthermore, we found a highly significant negative correlation between the protein expression level of CerS6 and the C16:0-acyl-CoA amounts as well as between the protein expression of CerS2 and C24:0-acyl-CoA amounts. These data indicate that in mouse tissues low substrate availability is compensated by higher CerS protein expression level and vice versa. Apart from the expression level and the specific activity of the CerS, other enzymes of the sphingolipid pathway also influence the composition of ceramides with distinct chain lengths in each cell. Acyl-CoA availability seems to be less important for ceramide composition and might be compensated for by CerS expression/activity.

English

The aim of this study is to study the effects of water deficit on physiologic parameters related to yield in two wheat cultivars (Triticum aestivum&nbsp;L.), Marvdasht and Zagros (sensitive and tolerant to terminal season drought, respectively) grown in pots under well watered and water-stressed starting from anthesis to maturity. Water stress resulted in a marked increase in leaf proline content of the drought-tolerant that led to alleviate the deleterious effect of water stress whereas, a slightly increment at the end of grain development observed in drought sensitive cv. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive. The results indicate that grain filling processes under water restriction are limited by low substrate availability and reduced synthesis capacity of the sink. Hence, the main physiological factor associated with yield stability of Zagros under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf. The higher assimilate in Zagros grains under drought could also be related to drought resistance. These results raise the possibility that water stress-induced elevated levels of proline in Zagros contribute to reduced harmful stress during grain filling. &nbsp; Key words:&nbsp;Assimilate, flag leaves, grain yield, proline, soluble proteins, wheat (Triticum aestivum&nbsp;L.).

Abstract 234: Plasma Renin-Independent Generation of Angiotensin II and its Role in the Supine Hypertension of Autonomic Failure

At least 50% of primary autonomic failure [AF] patients exhibit supine hypertension, despite profound impairments in sympathetic activity. Plasma renin activity is often undetectable in AF suggesting renin mechanisms are not involved in the hypertension. However, since aldosterone levels are preserved we examined the status and contribution of the renin-angiotensin [Ang] system in AF. Supine plasma Ang peptide levels were measured in hypertensive AF patients [AF-HT, n=18], normotensive patients [AF-NT, n=11] and matched healthy subjects [n=10]. Despite suppressed renin activity, total renin concentration was intact in AF [16 ± 5 AF-HT vs 11 ± 4 AF-NT vs 7 ± 1 pg/mL healthy; p=0.29] and plasma prorenin was selectively elevated in hypertensive patients [2.0 ± 0.5 AF-HT vs 0.7 ± 0.1 AF-NT vs 0.6 ± 0.1 ng/mL healthy; p &lt; 0.05]. While levels of Ang I were similar among groups, Ang II was paradoxically elevated [39 ± 4 AF-HT vs 42 ± 6 AF-NT vs 27 ± 4 pg/mL healthy; p&lt;0.05] in AF. In contrast, Ang-(1-7) was suppressed in AF patients [7 ± 1 AF-HT vs 4 ± 1 AF-NT vs 22 ± 6 pg/mL healthy; p&lt;0.05]. Plasma aldosterone was preserved in AF and did not correlate with Ang II levels, suggesting Ang II-independent regulation. The Ang II AT 1 receptor antagonist losartan [50mg, PO] significantly reduced supine systolic blood pressure [25 ± 15 mmHg at 6 hrs after administration; p&lt;0.05] in 9 AF-HT patients, indicating that elevated Ang II contributes to hypertension in AF. These findings suggest an imbalance in Ang II and Ang-(1-7) activity in AF independent of hypertensive status, which may reflect differences in ACE and ACE2 enzyme activity. The source of Ang II in these patients, in the absence of plasma renin activity, is still under investigation. The loss of renin activity is not due to reduced renin content, but may result from low substrate availability or defective enzyme activation. Regardless, Ang II appears to contribute to the supine hypertension of AF. Further, prorenin levels are elevated in hypertensive patients which could provide a stimulus for Ang II generation and actions. Collectively, these patients offer a unique model to study cardiovascular regulation and Ang II production in the absence of autonomic and traditional renin influences.

Effect of post-anthesis water deficit on yield and some physiological parameters on two wheat cultivars

This work investigates the effects of water deficit on physiologic parameters related to yield in two wheat cultivars (Triticum aestivum L.), Marvdasht and Zagros (sensitive and tolerant to terminal season drought, respectively) grown in pots under well watered and water-stressed starting from anthesis until maturity. All physiological parameters were affected by drought stress. Results showed that, water deficits enhanced the senescence by accelerating loss of leaf chlorophyll and soluble proteins and the loss was more in Marvdasht than Zagros. The net CO2 assimilation rate (PN) in flag leaves during water deficit display a strict correlation with the drought sensitivity of the genotypes and showed an early reduction in Marvdasht. Water stress resulted in a marked increase in leaf proline content of the drought-tolerant that led to alleviate the deleterious effect of water stress whereas, a slightly increment at the end of grain development observed in drought sensitive cv. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive. The results indicate that grain filling processes under water restriction are limited by low substrate availability and reduced synthesis capacity of the sink. These results raise the possibility that water stress-induced elevated levels of proline in Zagros contribute to reduce harmful of stress during grain filling. Key words: Chlorophyll, flag leaves, grain yield, proline, soluble proteins, wheat (Triticum aestivum L.).

Relationship between abscisic acid (ABA) concentration and some physiological traits in two wheat cultivars differing in post-anthesis drought-resistance

This work investigated the effects of endogenous abscisic acid (ABA) and physiologic parameters related to yield in two wheat cultivars (Triticum aestivum L.), Marvdasht and Zagros (sensitive and tolerant to terminal season drought, respectively) grown in pots under well watered and water-stressed starting from anthesis until maturity. All physiological parameters were affected by drought stress. Results show that water deficits enhanced the senescence by accelerating loss of leaf chlorophyll and soluble proteins and the loss was more in Marvdasht than Zagros. The net CO 2 assimilation rate (PN) in flag leaves during water deficit displayed a strict correlation with the drought sensitivity of the genotypes and showed an early reduction in Marvdasht. Water stress resulted in a marked increase just in the ABA content of the drought-sensitive that led to reduced transport of sucrose into the grains and lowered the starch synthesis ability of grains, whereas, sucrose uptake and conversion by grains was stimulated by low ABA concentrations in Zagros. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive. The results indicate that grain filling processes under water restriction are limited by low substrate availability and reduced synthesis capacity of the sink. These results raised the possibility that water stress-induced elevated levels of endogenous ABA contribute to reduced grain growth. Key words : Abscisic acid, chlorophyll, flag leaves, grain yield, soluble proteins, soluble sugar, starch, wheat (Triticum aestivum L.).

Repeated exposure to severely limited sleep results in distinctive and persistent physiological imbalances in rats.

Chronic sleep disruption in laboratory rats leads to increased energy expenditure, connective tissue abnormalities, and increased weights of major organs relative to body weight. Here we report on expanded findings and the extent to which abnormalities become long-lasting, potentially permanent changes to health status after apparent recuperation from chronic sleep disruption. Rats were exposed 6 times to long periods of disrupted sleep or control conditions during 10 weeks to produce adaptations and then were permitted nearly 4 months of undisturbed sleep. Measurements were made in tissues from these groups and in preserved tissue from the experimental and control groups of an antecedent study that lacked a lengthy recuperation period. Cycles of sleep restriction resulted in energy deficiency marked by a progressive course of hyperphagia and major (15%) weight loss. Analyses of tissue composition in chronically sleep-restricted rats indicated that protein and lipid amounts in internal organs were largely spared, while adipose tissue depots appeared depleted. This suggests high metabolic demands may have preserved the size of the vital organs relative to expectations of severe energy deficiency alone. Low plasma corticosterone and leptin concentrations appear to reflect low substrate availability and diminished adiposity. After nearly 4 months of recuperation, sleep-restricted rats were consuming 20% more food and 35% more water than did comparison control rats, despite normalized weight, normalized adipocytes, and elevated plasma leptin concentrations. Plasma cholesterol levels in recuperated sleep-restricted rats were diminished relative to those of controls. The chronically increased intake of nutriments and water, along with altered negative feedback regulation and substrate use, indicate that internal processes are modified long after a severe period of prolonged and insufficient sleep has ended.

Transcriptomic analysis of Clostridium thermocellumATCC 27405 cellulose fermentation

BackgroundThe ability of Clostridium thermocellum ATCC 27405 wild-type strain to hydrolyze cellulose and ferment the degradation products directly to ethanol and other metabolic byproducts makes it an attractive candidate for consolidated bioprocessing of cellulosic biomass to biofuels. In this study, whole-genome microarrays were used to investigate the expression of C. thermocellum mRNA during growth on crystalline cellulose in controlled replicate batch fermentations.ResultsA time-series analysis of gene expression revealed changes in transcript levels of ~40% of genes (~1300 out of 3198 ORFs encoded in the genome) during transition from early-exponential to late-stationary phase. K-means clustering of genes with statistically significant changes in transcript levels identified six distinct clusters of temporal expression. Broadly, genes involved in energy production, translation, glycolysis and amino acid, nucleotide and coenzyme metabolism displayed a decreasing trend in gene expression as cells entered stationary phase. In comparison, genes involved in cell structure and motility, chemotaxis, signal transduction and transcription showed an increasing trend in gene expression. Hierarchical clustering of cellulosome-related genes highlighted temporal changes in composition of this multi-enzyme complex during batch growth on crystalline cellulose, with increased expression of several genes encoding hydrolytic enzymes involved in degradation of non-cellulosic substrates in stationary phase.ConclusionsOverall, the results suggest that under low substrate availability, growth slows due to decreased metabolic potential and C. thermocellum alters its gene expression to (i) modulate the composition of cellulosomes that are released into the environment with an increased proportion of enzymes than can efficiently degrade plant polysaccharides other than cellulose, (ii) enhance signal transduction and chemotaxis mechanisms perhaps to sense the oligosaccharide hydrolysis products, and nutrient gradients generated through the action of cell-free cellulosomes and, (iii) increase cellular motility for potentially orienting the cells' movement towards positive environmental signals leading to nutrient sources. Such a coordinated cellular strategy would increase its chances of survival in natural ecosystems where feast and famine conditions are frequently encountered.

Temperature sensitivity of soil organic matter decomposition in boreal soils

The temperature sensitivity of decomposition of different soil organic matter (SOM) fractions was studied with laboratory incubations using C and C isotopes to differentiate between SOM of different age. The quality of SOM and the functionality and composition of microbial communities in soils formed under different climatic conditions were also studied. Transferring of organic layers from a colder to a warmer climate was used to assess how changing climate, litter input and soil biology will affect soil respiration and its temperature sensitivity. Together, these studies gave a consistent picture on how warming climate will affect the decomposition of different SOM fractions in Finnish forest soils: the most labile C was least temperature sensitive, indicating that it is utilized irrespective of temperature. The decomposition of intermediate C, with mean residence times from some years to decades, was found to be highly temperature sensitive. Even older, centennially cycling C was again less temperature sensitive, indicating that different stabilizing mechanisms were limiting its decomposition even at higher temperatures. Because the highly temperature sensitive, decadally cycling C, forms a major part of SOM stock in the organic layers of the studied forest soils, these results mean that these soils could lose more carbon during the coming years and decades than estimated earlier. SOM decomposition in boreal forest soils is likely to increase more in response to climate warming, compared to temperate or tropical soils, also because the Q10 is temperature dependent. In the northern soils the warming will occur at a lower temperature range, where Q10 is higher, and a similar increase in temperature causes a higher relative increase in respiration rates. The Q10 at low temperatures was found to be inversely related to SOM quality. At higher temperatures respiration was increasingly limited by low substrate availability.

Understanding the physiology of Lactobacillus plantarum at zero growth

Situations of extremely low substrate availability, resulting in slow growth, are common in natural environments. To mimic these conditions, Lactobacillus plantarum was grown in a carbon-limited retentostat with complete biomass retention. The physiology of extremely slow-growing L. plantarum--as studied by genome-scale modeling and transcriptomics--was fundamentally different from that of stationary-phase cells. Stress resistance mechanisms were not massively induced during transition to extremely slow growth. The energy-generating metabolism was remarkably stable and remained largely based on the conversion of glucose to lactate. The combination of metabolic and transcriptomic analyses revealed behaviors involved in interactions with the environment, more particularly with plants: production of plant hormones or precursors thereof, and preparedness for the utilization of plant-derived substrates. Accordingly, the production of compounds interfering with plant root development was demonstrated in slow-growing L. plantarum. Thus, conditions of slow growth and limited substrate availability seem to trigger a plant environment-like response, even in the absence of plant-derived material, suggesting that this might constitute an intrinsic behavior in L. plantarum.

Enhanced hydrogenotrophic sulfate reduction using Desulfovibrio vulgaris Hildenborough cells permeabilized with ethanol

BACKGROUND: Low substrate (H2) availability restricts microbial sulfate reduction when H2 is used as an electron donor. In order to enhance hydrogenotrophic sulfate conversion, Desulfovibrio vulgaris Hildenborough (DvH) cells permeabilized with ethanol were used as whole-cell biocatalysts. RESULTS: Cell growth was retarded after permeabilization. The maximum ethanol percentage for the recovery of cell proliferation was 15% (v/v) when permeabilization process duration was 30 min at 4 °C. Cells treated with 10% ethanol achieved 1.7-fold measurable hydrogenase activity compared with the control, while hydrogenase activity decreased remarkably with further increase in ethanol percentage. The 10% ethanol-treated cells were also shown to have the highest metabolic activity, 2.31-fold higher than the control. The accelerated metabolic activity was resulted from the enhancement of accessibility to substrate and product efflux due to increased permeability of the cell envelope when 10–15% ethanol was used High ethanol percentages caused cytoplasm leakage and interruption of the electron transfer chain and consequently loss of metabolic activity. CONCLUSION: The utilization of DvH cells permeabilized by 10–15% ethanol solutions with both cell viability and ability to reproduce being maintained promoted hydrogenotrophic sulfate reduction. These preliminary data may contribute to an enhancement of the bioprocess in sulfidogenic reactors. Copyright © 2009 Society of Chemical Industry