Methanogenesis and methanotrophy within a Sphagnum peatland

Abstract: Methane production and consumption activities were examined in a Massachusetts peatland. Peat from depths of 5–35 cm incubated under anaerobic conditions, produced an average of 2 nmol CH₄ g⁻¹ h⁻¹ with highest rates for peat fractions between 25–30 cm depth. Extracted microbial nucleic acids showed the strongest relative hybridization with a 16S rRNA oligonucleotide probe specific for Archaea with samples from the 25–30 cm depth. In aerobic laboratory incubations, the peat consumed methane with a maximum velocity of 67 nmol CH₄ g⁻¹ h⁻¹ and a K _s of 1.6 μM. Methane consumption activity was concentrated 4–9 cm below the peat surface, which corresponds to the aerobic, partially decomposed region in this peatland. Phospholipid fatty acid analysis of peat fractions demonstrated an abundance of methanotrophic bacteria within the region of methane consumption activity. Increases in temperature up to 30°C produced an increase in methane consumption rates for shallow samples, but not for samples taken from depths greater than 9 cm. Nitrogen fixation experiments were carried out using ¹⁵N₂ uptake in order to avoid problems associated with inhibition of methanotrophy. These experiments demonstrated that methane in peat samples did not stimulate nitrogen fixation activity, nor could activity be correlated with the presence of methanotrophic bacteria in peat fractions.     

Assimilation of methane and inorganic carbon by microbial communities mediating the anaerobic oxidation of methane

The anaerobic oxidation of methane (AOM) is a major sink for methane on Earth and is performed by consortia of methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). Here we present a comparative study using in vitro stable isotope probing to examine methane and carbon dioxide assimilation into microbial biomass. Three sediment types comprising different methane-oxidizing communities (ANME-1 and -2 mixture from the Black Sea, ANME-2a from Hydrate Ridge and ANME-2c from the Gullfaks oil field) were incubated in replicate flow-through systems with methane-enriched anaerobic seawater medium for 5–6 months amended with either ¹³CH₄ or H¹³CO₃^-. In all three sediment types methane was anaerobically oxidized in a 1:1 stoichiometric ratio compared with sulfate reduction. Similar amounts of ¹³CH₄ or ¹³CO₂ were assimilated into characteristic archaeal lipids, indicating a direct assimilation of both carbon sources into ANME biomass. Specific bacterial fatty acids assigned to the partner SRB were almost exclusively labelled by ¹³CO₂, but only in the presence of methane as energy source and not during control incubations without methane. This indicates an autotrophic growth of the ANME-associated SRB and supports previous hypotheses of an electron shuttle between the consortium partners. Carbon assimilation efficiencies of the methanotrophic consortia were low, with only 0.25–1.3 mol% of the methane oxidized.     

Bacterivory by starved marine heterotrophic nanoflagellates of two species which feed differently, estimated by uptake of dual radioactive-labelled bacteria

Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h⁻¹ throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 10⁵ bacteria ml⁻¹, and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell⁻¹ h⁻¹ at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h⁻¹ at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 10⁶ bacteria ml⁻¹; their initial clearance rate of 1–2.5 nl cell⁻¹ h⁻¹ subsequently fell as low as 0.1 nl cell⁻¹ h⁻¹. Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food.     

The content of prostaglandins and their precursors in Mortierella and Cunninghamella species

Five strains of filamentous fungi belonging to the genera Mortierella and Cunninghamella were examined for the content of dihomo-γ-linolenic, arachidonic, eicosapentaenoic acids and prostaglandins (type E₂ and F _2α). Prostaglandins were detected using an ELISA method in mycelia of all tested strains (range 50–4800 ng g⁻¹ of PGE₂ and 6–30 ng g⁻¹ of PG F _2α). Several micro-organisms also produced prostaglandins in the culture medium (2·2–137·6 μg l⁻¹ for PGE₂ and 0·4–7·8 μg l⁻¹ for PG F _2α).     

Amazonian peatlands: an ignored C sink and potential source

In tropical lowlands, peatlands are commonly reported from Southeast Asia, and especially Indonesian tropical peatlands are known as considerable C sinks and sources. In contrast, Amazonia has been clearly understudied in this context. In this study, based on field observations from 17 wetland sites in Peruvian lowland Amazonia, we report 0–5.9 m thick peat deposits from 16 sites. Only one of the studied sites did not contain any kind of peat deposit (considering pure peat and clayey peat). Historic yearly peat and C accumulation rates, based on radiocarbon dating of peat samples from five sites, varied from 0.94 ± 0.99 to 4.88 ± 1.65 mm, and from 26 ± 3 to 195 ± 70 g C m⁻², respectively. The long-term apparent peat and C accumulation rates varied from 1.69 ± 0.03 to 2.56 ± 0.12 mm yr⁻¹, and from 39 ± 10 to 85 ± 30 g C m⁻² yr⁻¹, respectively. These accumulation rates are comparable to those determined in the Indonesian tropical peatlands. Under altered conditions, Indonesian peatlands can release globally relevant amounts of C to the atmosphere. Considering the estimated total area of Amazonian peatlands (150 000 km²) close to that of the Indonesian ones (200 728 km²) as well as several factors threatening the Amazonian peatlands, we suggest that the total C stocks and fluxes associated with Amazonian peatlands may be of global significance.     

Selective grazing of methanotrophs by protozoa in a rice field soil

Biological methane oxidation is a key process in the methane cycle of wetland ecosystems. The methanotrophic biomass may be grazed by protozoa, thus linking the methane cycle to the soil microbial food web. In the present study, the edibility of different methanotrophs for soil protozoa was compared. The number of methanotroph-feeding protozoa in a rice field soil was estimated by determining the most-probable number (MPN) using methanotrophs as food bacteria; naked amoebae and flagellates were the dominant protozoa. Among ten methanotrophic strains examined as a food source, seven yielded a number of protozoa comparable with the yield with Escherichia coli [10⁴ MPN (g soil dry weight)⁻¹], and three out of four Methylocystis spp. yielded significantly fewer numbers [10²–10³ MPN (g soil dry weight)⁻¹]. The lower edibility of the Methylocystis spp. was not explained either by their growth phase or by harmful effects on protozoa. Incubation of the soil under methane resulted in a higher number of protozoa actively grazing on methanotrophs, especially on the less-edible group. Protozoa isolated from the soil demonstrated a grazing preference on the different methanotrophs consistent with the results of MPN counts. The results indicate that selective grazing by protozoa may be a biological factor affecting the methanotrophic community in a wetland soil.     

Species of Anguilla as indicators of mercury in the coastal rivers and lakes of Victoria, Australia

Mercury concentrations in the axial muscle tissue of most (243) of the 254 Anguilla australis and most (20) of the 27 A. reinhardtii collected from 30 sites in coastal rivers and lakes in Victoria, Australia, during 1975–78 were well below the Australian statutory health limit (0.5 μg g⁻¹ wet weight). For A. australis the mean mercury concentration was 0.17 μg g⁻¹ (±0.16 s.d. , range 0.01–1.60 μg g⁻¹); for A. reinhardtii the values were 0.37 ± 0.23 μg g⁻¹ (range 0.12–1.10 μg g⁻¹). Statistical analyses showed that variation in mercury concentration due to total length accounted for only 13% of the total variation in A. australis and 2% in A. reinhardtii whereas locality accounted for 54 and 68%, respectively. Both species are thus considered suitable as indicators of mercury pollution.     

Anti-bacterial activity of synthetic N-heterocyclic oxidizing compounds

Synthetic chlorochromate derivatives of pyridine and quinoline were active in vitro against type cultures of Escherichia coli (ATCC 128), Staphylococcus aureus (ATCC 14775), Pseudomonas aeruginosa (ATCC 10145) and Bacillus subtilis (NCTC 8236). The minimum inhibitory concentrations (MIC) were 125–250 μg ml⁻¹ and 250–500 μg ml⁻¹ for pyridinium chlorochromate and quinolinium chlorochromate, respectively. An established derivative of quinoline (Perfloxacin) had an MIC of 125–250 μg ml⁻¹. The extinction time for 10⁵ cfu in broth was 90 min for pyridinium chlorochromate and 120 min for quinolinium chlorochromate, except for B. subtilis which survived up to about 180 min and 360 min. A combination of the two compounds produced an antagonistic effect. The 50% lethal dose (LD₅₀ toxicity) in mice was estimated at 76 μg g⁻¹ and 33 μg g⁻¹ body weight for the quinolinium and pyridinium chlorochromates. The compounds also exhibited some potential for suppressing a simulated staphylococcal infection in mice at the dosage levels of ca 22 μg g⁻¹ for pyridinium chlorochromate and 45 μg g⁻¹ for quinolinium chlorochromate.     

Soil microbial carbon uptake characteristics in relation to soil management

Abstract The kinetics of glucose uptake by soil microbial communities in 16 different soild (7 under monocultures and 9 under crop rotations) differing in microbial biomass content, % C_org, pH and clay content were investigated at 22°C. The V _max value of microbial bimasses under monoculture, was o.27 μg C_gluc · μg⁻¹ C_mic · h⁻¹ (range 0.18–0.44), twice as high as the mean value of V _max of microbial biomasses under rotations (0.13 μg C_gluc, range 0.07–0.19). Mean values of K _m were 714 μg C_gluc and 290 μg C_gluc · g⁻¹ soil, respectively.
These differences were highly significant ( P =0.001, based on SE) and could not be relate to particle size distribution of the soils, pH or C_org. A Michaelis-Menten type uptake response was apparent over the total range of glucose concentrations used (45.4–1453.3 μg C_gluc · g⁻¹ soil) for microbial biomasses under rotation while the majority of microbial biomasses under monocultures showed a similar response only at low glucose concentrations. A different uptake mechanism appeared to be involved at higher glucose concentrations (similar to diffusion) in monoculture soils.