Chitinolytic enzymes produced by ovine rumen bacteria

Two strains of clostridia, isolated from the rumen fluid of sheep as potential antagonists toward anaerobic fungi showed a complete array of chitinolytic enzymes. Enzyme tests in cultures demonstrated endochitinase, exochitinase,N-acetylglucosaminidase, chitosanase and chitin deacetylase activities mainly in the extracellular fractions. In all samples, the highest was the activity of exochitinase (600–1100 nmol mL⁻¹ h⁻¹); the activity of endochitinase (280–500 nmol mL⁻¹ h⁻¹) was also significant. Chitinases were stimulated in the presence of reducing compounds and no dependence on cations was observed. In both strains different isoforms of chitinases of molar mass 36–96 kDa were detected. The chitinases from our isolates lyzed cell walls of anaerobic fungiin vitro and inhibited the activity of fungal β-1,4-endoglucanases. Of the two bacteria examined, one was more effective in both antifungal effects.     

Microbial activity profiles in Tagus estuary salt marsh sediments

This study provides some results about microbial activity in salt marsh sediments. Microbial activity was determined by profiling extracellular enzyme activities in three Tagus estuary marshes and in two sediments horizons: surface layer (0–2 cm) and depth (8–10 cm). Five enzymatic activities were examined (β-glucosidase, cellulase, alkaline phosphatase, potential nitrification and nitrate reductase). All extracellular enzymatic activities were highest in the surface layer and decreased with depth. β-glucosidase and alkaline phosphatase prevailed both in surface sediments (1150 and 1200 ηmol h⁻¹ g⁻¹, respectively) and in deeper sediments (150 and 200 ηmol h⁻¹ g⁻¹, respectively). Microbial activities differed significantly between salt marshes. The marsh location in the estuary seemed to contribute to these differences: marshes located in the proximity of urbanised and industrial areas had higher microbial activities.     

Evaluation of hydrolysis and fermentation rates in microbial fuel cells

This study determined the influence of substrate degradation on power generation in microbial fuel cells (MFCs) and microbial community selection on the anode. Air cathode MFCs were fed synthetic medium containing different substrates (acetate, glucose and starch) using primary clarifier sewage as source of electroactive bacteria. The complexity of the substrate affected the MFC performance both for power generation and COD removal. Power output decreased with an increase in substrate complexity from 99 ± 2 mW m⁻² for acetate to 4 ± 2 mW m⁻² for starch. The organic matter removal and coulombic efficiency (CE) of MFCs with acetate and glucose (82% of COD removal and 26% CE) were greater than MFCs using starch (60% of COD removal and 19% of CE). The combined hydrolysis–fermentation rate obtained (0.0024 h⁻¹) was considerably lower than the fermentation rate (0.018 h⁻¹), indicating that hydrolysis of complex compounds limits current output over fermentation. Statistical analysis of microbial community fingerprints, developed on the anode, showed that microbial communities were enriched according to the type of substrate used. Microbial communities producing high power outputs (fed acetate) clustered separately from bacterial communities producing low power outputs (fed complex compounds).     

Metabolic energy utilization during development of Antarctic naked dragonfish (Gymnodraco acuticeps)

We have capitalised on the availability of eggs and adults of the naked dragonfish Gymnodraco acuticeps (Sub-order Notothenioidei, F. Bathydraconidae) near McMurdo Station, Antarctica to examine metabolic energy utilization at different stages of its life cycle. Average egg respiration rates were found to increase from 2.17±1.02 nmol O₂ h⁻¹ ind⁻¹ at about 17 h post-fertilization (hpf) to 5.72±0.56 nmol h⁻¹ ind⁻¹ at about 24 hpf, during which time the eggs underwent first cleavage. The respiration rates of embryos from 2–20 days post-fertilization (dpf) averaged 4.11±1.47 nmol O₂ h⁻¹ ind⁻¹. About 10 months post-fertilization, oxygen consumption rates of 27.14±3.92 nmol O₂ h⁻¹ ind⁻¹ were recorded immediately prior to hatching, with a peak of 112.41±31.38 nmol O₂ h⁻¹ ind⁻¹ at the time of hatch. Larvae aged 46–63 days post-hatch had an average respiration rate of 64.4±15.11 nmol O₂ h⁻¹ ind⁻¹. Mass-specific respiration rates of hatched larvae (approximately 1–2 months old) were calculated using dry weights (DW) and averaged 16.1±3.4 nmol O₂ h⁻¹ mg⁻¹ DW. Adult dragonfish respiration rates (corrected for a 100 g fish and using a 0.8 scaling exponent) averaged 0.91±0.36 mmol O₂ kg⁻¹ h⁻¹ after a 48 h acclimatization period, which is not indicative of significant metabolic cold adaptation. The energy contents of dragonfish eggs and larvae were also measured by microbomb calorimetry and used, along with the respiration data, in an initial approach to estimate an energy budget. In order to balance the budget, the bulk of the available post-gastrulation respiratory energy (during 213 days of embryonic incubation) must be consumed at a relatively low average rate (7.1 nmol O₂ h⁻¹ ind⁻¹), which supports the possibility that advanced dragonfish embryos overwinter in a relatively quiescent metabolic state while awaiting a suitable stimulus (such as the return of the sun) to initiate hatching.     

Variations of soil enzyme activities in a temperate forest soil

Soil enzyme activities (dehydrogenase, urease, phosphatase, and arylsulfatase) in a temperate forest soil were determined in relation to landscape position and seasons. Overstory of the area is dominated by Quercus mongolica, Kalopanax pictus, Carpicus cordata, and Acer pseudo-sieboldianum. The activities were measured in three patches, namely a north-facing backslope, a ridge, and a south-facing backslope in autumn and spring over 2 years. In addition, spatially more detailed analysis for phosphatase was conducted before and after litterfall production in six patches. Dehydrogenase, urease, phosphatase, and arylsulfatase activities varied 1.8–18.5 μg INT-formazan g⁻¹ h⁻¹, 45.4–347.0 μg NH₄ ⁺ g⁻¹ h⁻¹, 0.9–4.5 mmol pNP g⁻¹ h⁻¹, and 0.7–2.6 mmol pNP g⁻¹ h⁻¹, respectively. In general, higher enzyme activities were found in the northern aspect than in the southern aspect. This variation appears to be related to differences in chemical properties (e.g., Fe, Al, and Mg) of soil as well as distribution of leaf litter. Two patterns were discernible in relation to seasonal variations. Dehydrogenase and urease exhibited a positive correlation with mean air temperature, suggesting that temperature would be a major controlling variable for those enzymes. In contrast, higher activities were detected in autumn for phosphatase and arylsulfatase activities, which appeared to be closely related to litter production and distribution. Overall results of this study indicate that soil enzyme activities in a forest floor are influenced by several variables such as temperature, nutrient availability, and input of leaf litter, which are closely related to landscape position.     

Production of 1,3-Propanediol by Clostridium butyricum VPI 3266 in continuous cultures with high yield and productivity

The effects of dilution rate and substrate feed concentration on continuous glycerol fermentation by Clostridium butyricum VPI 3266, a natural 1,3-propanediol producer, were evaluated in this work. A high and constant 1,3-propanediol yield (around 0.65 mol/mol), close to the theoretical value, was obtained irrespective of substrate feed concentration or dilution rate. Improvement of 1,3-propanediol volumetric productivity was achieved by increasing the dilution rate, at a fixed feed substrate concentration of 30, 60 or 70 g l⁻¹. Higher 1,3-propanediol final concentrations and volumetric productivities were also obtained when glycerol feed concentration was increased from 30 to 60 g l⁻¹, at D=0.05–0.3 h⁻¹, and from 60–70 g l⁻¹, at D=0.05 and 0.1 h⁻¹·30 g l⁻¹ of 1,3-propanediol and the highest reported value of productivity, 10.3 g l⁻¹ h⁻¹, was achieved at D=0.30 h⁻¹ and 60 g l⁻¹ of feed glycerol. A switch to an acetate/butyrate ratio higher than one was observed for 60 g l⁻¹ of feed glycerol and a dilution rate higher than 0.10 h⁻¹; moreover, at D=0.30 h⁻¹ 3-hydroxypropionaldehyde accumulation was observed for the first time in the fermentation broth of C. butyricum.     

Microbial acetate oxidation in horizontal rotating tubular bioreactor

The aim of this work was to investigate the possibility of conducting a continuous aerobic bioprocess in a horizontal rotating tubular bioreactor (HRTB). Aerobic oxidation of acetate by the action of a mixed microbial culture was chosen as a model process. The microbial culture was not only grown in a suspension but also in the form of a biofilm on the interior surface of HRTB. Efficiency of the bioprocess was monitored by determination of the acetate concentration and chemical oxygen demand (COD). While acetate inlet concentration and feeding rate influenced efficiency of acetate oxidation, the bioreactor rotation speed did not influence the bioprocess dynamics significantly. Gradients of acetate concentration and pH along HRTB were more pronounced at lower feeding rates. Volumetric load of acetate was proved to be the most significant parameter. High volumetric loads (above 2 g acetate l⁻¹ h⁻¹) gave poor acetate oxidation efficiency (only 17 to 50%). When the volumetric load was in the range of 0.60–1.75 g acetate l⁻¹ h⁻¹, acetate oxidation efficiency was 50–75%. At lower volumetric loads (0.14–0.58 g acetate l⁻¹ h⁻¹), complete acetate consumption was achieved. On the basis of the obtained results, it can be concluded that HRTB is suitable for conducting aerobic continuous bioprocesses.     

Major substrates for microbial sulfate reduction in the sediments of Ise Bay, Japan

To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments, the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan, in autumn 1990. Sulfate reduction rates (51–210 nmol ml⁻¹ day⁻¹ at 24°C) were much higher than the methane production ones (<1.78 nmol ml⁻¹ day⁻¹) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l⁻¹ molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate. The maximum rate of methane production was 1.2–1.9 μmol ml⁻¹ day⁻¹, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population density and activity.     

Seasonal changes in digestive enzyme (trypsin) activity of the copepods <Emphasis Type="Italic">Pseudocalanus minutus</Emphasis> (Calanoida) and <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)

Seasonal activities of the digestive enzyme trypsin were measured between August 1998 and May 1999 to study different nutritional strategies of the two copepods Pseudocalanus minutus and Oithona similis in the Arctic Kongsfjorden (Svalbard) using a highly sensitive fluorescence technique. Stage-, depth- and season-specific characteristics of digestive activity were reflected in the trypsin activity. P. minutus females and stage V copepodids (C) had highest trypsin activities in spring during reproduction (197.5 and 145.7 nmol min⁻¹ ng C⁻¹, respectively). In summer stages CIII–V and in autumn stages CIV and V had high activities (80–116 nmol min⁻¹ ng C⁻¹) in the shallow layer (< 100 m) presumably as a consequence of prolonged feeding before descending to overwintering depth. Trypsin activities at depth (> 100 m) in summer and autumn were low in stages CIII and CIV (29–60 nmol min⁻¹ ng C⁻¹) and in winter in all stages in both layers (20–43 nmol min⁻¹ ng C⁻¹). Based on low trypsin activity, males most likely did not feed. In O. similis, the spring phytoplankton bloom did not significantly affect trypsin activity as compared to the other seasons. O. similis CV and females had high trypsin activities in summer in the deep stratum (304.5 nmol min⁻¹ ng C⁻¹), which was concomitant with reproductive processes and energy storage for overwintering. In autumn, stage CV and female O. similis had significantly higher activities than stage CIV (130–152 versus 78 nmol min⁻¹ ng C⁻¹), which is in accordance with still ongoing developmental and reproductive processes in CVs and females. Comparisons of both species revealed different depth-related responses emphasizing different nutritional preferences: the mainly herbivorous P. minutus is more actively feeding in the shallow layer, where primary production occurs, whereas the omnivorous O. similis is not as much restricted to a certain depth layer, when searching for food. P. minutus had lower levels of trypsin activity during all seasons. In contrast to P. minutus, higher enzyme activities in males of O. similis suggest that they continue to feed and survive after fertilization of females.     

Oxygenic Photosynthesis and Respiratory Activity in Microbial Mats of the Ebro Delta, Spain, by Oxygen Exchange Method

Photosynthetic and respiratory activities at low light intensities (300 μE m⁻² s⁻¹) in the microbial mats of the Ebro Delta were measured by the oxygen exchange method in the laboratory. The response to H₂S concentration, a significant factor in the dynamics of that ecosystem, was assessed. Total photosynthesis reached 23.78–28.17 μg O₂ cm⁻² h⁻¹. Photosynthetic activity was not significantly different at the two temperatures tested. Respiratory activity reached a consumption of 6.95–8.56 μg O₂ cm⁻² h⁻¹ at 25°C and 11.42–11.70 μg O₂ cm⁻² h⁻¹ at 35°C. The Q₁₀ value for respiration was 1.37–1.64. Oxygen production in Microcoleus chthonoplastes, the most abundant cyanobacterium in those microbial mats, was highly resistant to sulfide inhibition. Concentrations less than 0.02 mM sulfide did not affect the rate of photosynthesis. Concentrations up to 0.1 mM sulfide caused different degrees of partially reversible inhibition, with a maximum of 67% at 0.78 mM sulfide. Primary production (g C assimilated/m²/year) in those microbial mats was also assessed and compared with data from other ecosystems. Received: 24 October 1997 / Accepted: 18 December 1997     

Protozoan growth rates in Antarctic lakes

The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h⁻¹), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029–0.0059 h⁻¹ and 0.0056–0.0127 h⁻¹, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h⁻¹ for heterotrophic ciliates, 0.0143 h⁻¹ for a mixotrophic Plagiocampa species and 0.0075 h⁻¹ for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes. Accepted: 7 December 1999     

High rates of nitrogen fixation (acetylene reduction) on coral skeletons following bleaching mortality

Nubbins of the coral Acropora aspera were artificially bleached and nitrogen fixation (acetylene reduction) rates were measured on the developing epilithic communities. Seasonal comparisons were made between corals that died in summer of heat stress and corals that died in winter from natural cold stress. Rates of acetylene reduction from artificially bleached corals peaked at 26.66 nmol cm⁻² h⁻¹ 2 weeks after summer mortality, while rates from natural winter mortality peaked at 18.07 nmol cm⁻² h⁻¹ 12 days after coral death. Comparative rates of acetylene reduction taken from live corals and coral rubble ranged between 0.56 and 1.16 nmol cm⁻² h⁻¹, and 0.15 and 12.77 nmol cm⁻² h⁻¹, respectively. N₂-fixation rates from dead corals were up to 30 times greater than those measured on live corals. The observed increase in N₂-fixation from dead corals may increase the availability of nitrogen for use in trophic processes within the reef for an extended period following the initial mortality event. If the spatial scale over which coral mortality has occurred in past thermal bleaching events is considered the ramifications of such an increase may be substantial.     

Dynamics of a benthic microbial community in a riverine environment subject to hydrological fluctuations (Mulargia River,Italy)

Temporary rivers are characterized by recurrent dry phases, and global warming will stress their hydrology by amplifying extreme events. Microbial degradation and transformation of organic matter (OM) in riverbed sediment are key processes with regard to carbon and nutrient fluxes. In this study, we describe structural and functional changes of benthic microbial communities in a riverine environment subject to hydrological fluctuation. Sampling was carried out in the outlet section of the Mulargia River (Sardinia, Italy) under various water regimes, including one flood event. Overall, sediments were characterized by low bacterial cell abundance (range 0.6–1.8 × 10⁹ cell g⁻¹) as a consequence of their low nutrient and OM concentrations. No major differences were found in the community composition. Alpha-Proteobacteria dominated during the whole year (range 21–30%) followed by Beta-Proteobacteria, Gamma-Proteobacteria, and Cytophaga-Flavobacteria which always contributed <18%. Planctomycetes and Firmicutes were found in smaller amounts (<7%). In spring, when the highest total organic carbon content was also detected (0.42% w/w), both bacterial abundance and C production (BCP, 170 nmol C h⁻¹ g⁻¹) reached relatively high values. During the flood event, an increase in BCP and the highest values of community respiration (CR, 74 nmol C h⁻¹ g⁻¹) were observed. Moreover, most of the extracellular enzyme activities (EEA) changed significantly during the flood. The variation of the water flow itself can explain part of these changes and other factors also come into play. The presence of different patterns of functional parameters could suggest that the quality of the OM could be the major driving force in nutrient flux.     

Production of fructose from inulin using mixed inulinases from <Emphasis Type="Italic">Aspergillus niger</Emphasis> and <Emphasis Type="Italic">Candida guilliermondii</Emphasis>

Two new effective microbial producers of inulinases were isolated from Jerusalem artichoke tubers grown in Thailand and identified as Aspergillus niger TISTR 3570 and Candida guilliermondii TISTR 5844. The inulinases produced by both these microorganisms were appropriate for hydrolysing inulin to fructose as the principal product. An initial inulin concentration of ∼100 g l⁻¹ and the enzyme concentration of 0.2 U g⁻¹ of substrate, yielded 37.5 g l⁻¹ of fructose in 20 h at 40°C when A. niger TISTR 3570 inulinase was the biocatalyst. The yield of fructose on inulin was 0.39 g g⁻¹. Under identical conditions, the yeast inulinase afforded 35.3 g l⁻¹ of fructose in 25 h. The fructose yield was 0.35 g g⁻¹ of substrate. The fructose productivities were 1.9 g l⁻¹ h⁻¹ and 1.4 g l⁻¹ h⁻¹ for the mold and yeast enzymes, respectively. After 20 h of reaction, the mold enzyme hydrolysate contained 53% fructose and more than 41% of initial inulin had been hydrolysed. Using the yeast enzymes, the hydrolysate contained nearly 38% fructose at 25 h and nearly 36% of initial inulin had been hydrolysed. The A. niger TISTR 3570 inulinases exhibited both endo-inulinase and exo-inulinase activities. In contrast, the yeast inulinases displayed mainly exo-inulinase activity. The mold and yeast crude inulinases mixed in the activity ratio of 5:1 proved superior to individual crude inulinases in hydrolysing inulin to fructose. The enzyme mixture provided a better combination of endo- and exo-inulinase activities than did the crude extracts of either the mold or the yeast individually.     

Bacterial growth and substrate degradation by BTX-oxidizing culture in response to salt stress

Interactions between microbial growth and substrate degradation are important in determining the performance of trickle-bed bioreactors (TBB), especially when salt is added to reduce biomass formation in order to alleviate media clogging. This study was aimed at quantifying salinity effects on bacterial growth and substrate degradation, and at acquiring kinetic information in order to improve the design and operation of TBB. Experiment works began by cultivating a mixed culture in a chemostat reactor receiving artificial influent containing a mixture of benzene, toluene, and xylene (BTX), followed by using the enrichment culture to degrade the individual BTX substrates under a particular salinity, which ranged 0–50 g l⁻¹ in batch mode. Then, the measured concentrations of biomass and residual substrate versus time were analyzed with the microbial kinetics; moreover, the obtained microbial kinetic constants under various salinities were modeled using noncompetitive inhibition kinetics. For the three substrates the observed bacterial yields appeared to be decreased from 0.51–0.74 to 0.20–0.22 mg mg⁻¹ and the maximum specific rate of substrate utilization, declined from 0.25–0.42 to 0.07–0.11 h⁻¹, as the salinity increased from 0 to 50 NaCl g l⁻¹. The NaCl acted as noncompetitive inhibitor, where the modeling inhibitions of the coefficients, K _T(S), were 22.7–29.7 g l⁻¹ for substrate degradation and K _T(μ), 13.0–19.0 g l⁻¹, for biomass formation. The calculated ratios for the bacterial maintenance rate, m _S, to further indicated that the percentage energy spent on maintenance increased from 19–24 to 86–91% as salinity level increased from 0 to 50 g l⁻¹. These results revealed that the bacterial growth was more inhibited than substrate degradation by the BTX oxidizers under the tested salinity levels. The findings from this study demonstrate the potential of applying NaCl salt to control excessive biomass formation in biotrickling filters.     

Comparison of relative rates of BTEX biodegradation using respirometry

Biodegradation of BTEX by a microbial consortium isolated from a closed municipal landfill was studied using respirometric techniques. The kinetics of biodegradation were estimated from experimental oxygen uptake data using a nonlinear parameter estimation technique. All of the six compounds were rapidly degraded by the microbial culture and no substrate inhibition was observed at the concentration levels examined (200 mg L⁻¹ as COD). Microbial growth and contaminant degradation were adequately described by the Monod equation. Considerable differences were observed in the rates of BTEX biodegradation as seen from the estimates of the kinetic parameters. A three-fold variation was seen in the values of the maximum specific growth rate, μ_max. The highest value of μ_max was 0.389 h⁻¹ for p-xylene while o-xylene was characterized by a μ_max value of 0.14 h⁻¹, the lowest observed in this study. The half saturation coefficient, K _s, and the yield coefficient, Y, varied between 1.288–4.681 mg L⁻¹ and 0.272–0.645 mg mg⁻¹, respectively. Benzene and o-xylene exhibited higher resistance to biodegradation while toluene and p-xylene were rapidly degraded. Ethylbenzene and m-xylene were degraded at intermediate rates. In biodegradation experiments with a multiple substrate matrix, substrate depletion was slower than in single substrate experiments, suggesting an inhibitory nature of substrate interaction. Received 15 February 1998/ Accepted in revised form 5 July 1998     

Physical characteristics of olive stone wooden residues: possible bulking material for composting process

The present work focuses on the study of the physical characteristics of olive stone wooden residues at the prospect of its use as a bulking material in compost process. The physical characteristics that were studied according to particle mesh classification, were the apparent density, porosity, water holding capacity, air free space and air pressure drop. From the experimental results, it was proved that only the fraction of 6.8–12.5 mesh, which is 29.40% of the substrate, could maintain the moisture in the optimum range 40–60%. The fraction of the particles of 2.6–23.6 mesh, which was 74.68% of the substrate, had appropriate porosity for composting. It was also proved that for dried substrate and air velocity 300 m h⁻¹, acceptable pressure drop (10 cm H₂O m⁻¹) was observed for the fraction of the particles of 2.6–27.5 mesh, which was 80.08% of the substrate, while for dried substrate and air velocity 150 m h⁻¹, the respective fraction was particles of 2.6–37.9 mesh which accounted for the 89.48% of the substrate. Conclusively, olive oil processing solid residues have the physical characteristics, so as to be used for composting or as a substrate for co-composting with high strength wastewater.     

On-line screening of soil VOCs exchange responses to moisture, temperature and root presence

The exchanges of volatile organic compounds (VOCs) between soils and the atmosphere are poorly known. We investigated VOC exchange rates and how they were influenced by soil moisture, temperature and the presence of plant roots in a Mediterranean forest soil. We measured VOC exchange rates along a soil moisture gradient (5%–12.5%–20%–27.5% v/v) and a temperature gradient (10°C–15°C–25°C–35°C) using PTR-MS. Monoterpenes were identified with GC-MS. Soils were a sink rather than a source of VOCs in both soil moisture and temperature treatments (−2.16 ± 0.35 nmol m⁻² s⁻¹ and −4.90 ± 1.24 nmol m⁻² s⁻¹ respectively). Most compounds observed were oxygenated VOCs like alcohols, aldehydes and ketones and aromatic hydrocarbons. Other volatiles such as acetic acid and ethyl acetate were also observed. All those compounds had very low exchange rates (maximum uptake rates from −0.8 nmol m⁻² s⁻¹ to −0.6 nmol m⁻² s⁻¹ for methanol and acetic acid). Monoterpene exchange ranged only from −0.004 nmol m⁻² s⁻¹ to 0.004 nmol m⁻² s⁻¹ and limonene and α-pinene were the most abundant compounds. Increasing soil moisture resulted in higher soil sink activity possibly due to increases in microbial VOCs uptake activity. No general pattern of response was found in the temperature gradient for total VOCs. Roots decreased the emission of many compounds under increasing soil moisture and under increasing soil temperature. While our results showed that emission of some soil VOCs might be enhanced by the increases in soil temperature and that the uptake of most soil VOCs uptake might be reduced by the decreases of soil water availability, the low exchange rates measured indicated that soil-atmosphere VOC exchange in this system are unlikely to play an important role in atmospheric chemistry. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Fungal control of nitrous oxide production in semiarid grassland

Fungi are capable of both nitrification and denitrification and dominate the microbial biomass in many soils. Recent work suggests that fungal rather than bacterial pathways dominate N transformation in desert soils. We evaluated this hypothesis by comparing the contributions of bacteria and fungi to N₂O production at control and N fertilized sites within a semiarid grassland in central New Mexico (USA). Soil samples were taken from the rhizosphere of blue grama (B. gracilus) and the microbiotic crusts that grow in open areas between the bunch grasses. Soils incubated at 30% or 70% water holding capacity, were exposed to one of three biocide treatments (control, cycloheximide or streptomycin). After 48 h, N₂O and CO₂ production were quantified along with the activities of several extracellular enzymes. N₂O production from N fertilized soils was higher than that of control soils (165 vs. 41 pmol h⁻¹ g⁻¹), was higher for crust soil than for rhizosphere soil (108 vs. 97 pmol h⁻¹ g⁻¹), and increased with soil water content (146 vs. 60 pmol h⁻¹ g⁻¹). On average, fungicide (cycloheximide) addition reduced N₂O production by 85% while increasing CO₂ production by 69%; bactericide (streptomycin) reduced N₂O by 53% with mixed effects on CO₂ production. N₂O production was significantly correlated with C and N mineralization potential as measured by assays for glycosidic and proteolytic enzymes, and with extractable nitrate and ammonium. Our data indicate that fungal nitrifier denitrification and bacterial autotrophic nitrification dominate N transformation in this ecosystem and that N₂O production is highly sensitive to soil cover, N deposition and moisture.     

Influence of net ecosystem metabolism in transferring riverine organic carbon to atmospheric CO<Subscript>2</Subscript> in a tropical coastal lagoon (Chilka Lake,India)

Studies on biogeochemical cycling of carbon in the Chilka Lake, Asia’s largest brackish lagoon on the east coast of India, revealed, for the first time, strong seasonal and spatial variability associated with salinity distribution. The lake was studied twice during May 2005 (premonsoon) and August 2005 (monsoon). It exchanges waters with the sea (Bay of Bengal) and several rivers open into the lake. The lake showed contrasting levels of dissolved inorganic carbon (DIC) and organic carbon (DOC) in different seasons; DIC was higher by ∼22% and DOC was lower by ∼36% in premonsoon than in monsoon due to seasonal variations in their supply from rivers and in situ production/mineralisation. The DIC/DOC ratios in the lake during monsoon were influenced by physical mixing of end member water masses and by intense respiration of organic carbon. A strong relationship between excess DIC and apparent oxygen utilisation showed significant control of biological processes over CO₂ production in the lake. Surface partial pressure of CO₂ (pCO₂), calculated using pH–DIC couple according to Cai and Wang (Limnol and Oceanogr 43:657–668, 1998), exhibited discernable gradients during monsoon through northern (1,033–6,522 μatm), central (391–2,573 μatm) and southern (102–718 μatm) lake. The distribution pattern of pCO₂ in the lake seems to be governed by pCO₂ levels in rivers and their discharge rates, which were several folds higher during monsoon than premonsoon. The net CO₂ efflux, based on gas transfer velocity parameterisation of Borges et al. (Limnol and Oceanogr 49(5):1630–1641, 2004), from entire lake during monsoon (141 mmolC m⁻² d⁻¹ equivalent to 2.64 GgC d⁻¹ at basin scale) was higher by 44 times than during premonsoon (9.8 mmolC m⁻² d⁻¹ ≈ 0.06 GgC d⁻¹). 15% of CO₂ efflux from lake in monsoon was contributed by its supply from rivers and the rest was contributed by in situ heterotrophic activity. Based on oxygen and total carbon mass balance, net ecosystem production (NEP) of lake (−308 mmolC m⁻² d⁻¹ ≈ −3.77 GgC d⁻¹) was found to be almost in consistent with the total riverine organic carbon trapped in the lake (229 mmolC m⁻² d⁻¹ ≈ 2.80 GgC d⁻¹) suggesting that the strong heterotrophy in the lake is mainly responsible for elevated fluxes of CO₂ during monsoon. Further, the pelagic net community production represented 92% of NEP and benthic compartment plays only a minor role. This suggests that Chilka lake is an important region in biological transformation of organic carbon to inorganic carbon and its export to the atmosphere.