Editorial: Essential Biomolecules Caught in the Food Web?

Peer Reviewe

Improving the application of quantitative fatty acid signature analysis in soil food webs: The effects of diet fat content

Quantitative fatty acid signature analysis (QFASA) as a biochemical tool to study the diet composition of predators is frequently used in marine ecology to infer trophic links in vertebrate consumers. However, the potential and challenges of this method in other ecosystems have only recently been studied. The application in soil ecosystems leads to hurdles not encountered in the marine, such as the low similarity of fatty acid signatures between resource and consumer. So far, diet estimation attempts have been semisuccessful, necessitating to adapt QFASA for use in soil food webs. Dietary fat content may play an important role, as it influences consumer metabolism, and thus calibration coefficients for fatty acid trophic transfer. A series of feeding trials with baker's yeast spiked with five different pure fatty acids at various concentrations was conducted with Collembola, and the changes in calibration coefficients were observed. From there, equations were gained through regression analysis and new sets of calibration coefficients were calculated. QFASA was applied on a range of basal resources and the results compared with previously defined calibration coefficients. Calibration coefficients changed with the proportion of fatty acids in the diet and differed between the three Collembolan species. The re-estimation of diets showed an improvement of model performance by the new calibration coefficients and indicated several modes of fatty acid assimilation. These greatly influence the outcome of diet estimation, for example, algal and bacterial diets are likely underestimated due to high metabolic turnover rates. The application of QFASA in soil ecosystems remains challenging. The variation in calibration coefficients and the resulting decrease in estimation deviation indicate the merit of calculating calibration coefficients from consumer signatures through linear or exponential equations. Ideally, the method should, when extended to the entire fatty acid signature, allow correct determination of consumer diets in soil food webs.Peer Reviewe

Legionella pneumophila and Free-Living Nematodes: Environmental Co-Occurrence and Trophic Link

Free-living nematodes harbor and disseminate various soil-borne bacterial pathogens. Whether they function as vectors or environmental reservoirs for the aquatic L. pneumophila, the causative agent of Legionnaires’ disease, is unknown. A survey screening of biofilms of natural (swimming lakes) and technical (cooling towers) water habitats in Germany revealed that nematodes can act as potential reservoirs, vectors or grazers of L. pneumophila in cooling towers. Consequently, the nematode species Plectus similis and L. pneumophila were isolated from the same cooling tower biofilm and taken into a monoxenic culture. Using pharyngeal pumping assays, potential feeding relationships between P. similis and different L. pneumophila strains and mutants were examined and compared with Plectus sp., a species isolated from a L. pneumophila-positive thermal source biofilm. The assays showed that bacterial suspensions and supernatants of the L. pneumophila cooling tower isolate KV02 decreased pumping rate and feeding activity in nematodes. However, assays investigating the hypothesized negative impact of Legionella’s major secretory protein ProA on pumping rate revealed opposite effects on nematodes, which points to a species-specific response to ProA. To extend the food chain by a further trophic level, Acanthamoebae castellanii infected with L. pneumphila KV02 were offered to nematodes. The pumping rates of P. similis increased when fed with L. pneumophila-infected A. castellanii, while Plectus sp. pumping rates were similar when fed either infected or non-infected A. castellanii. This study revealed that cooling towers are the main water bodies where L. pneumophila and free-living nematodes coexist and is the first step in elucidating the trophic links between coexisting taxa from that habitat. Investigating the Legionella–nematode–amoebae interactions underlined the importance of amoebae as reservoirs and transmission vehicles of the pathogen for nematode predators.Deutsche Forschungsgemeinschaft (DFG)Peer Reviewe

Chemical characterization of pitch deposits produced in the manufacturing of high-quality paper pulps from hemp fibers

Instituto de Recursos Naturales y Agrobiología, CSIC, P.O. Box 1052, E-41080, Seville, Spain E-mail address: [email protected] composition of pitch deposits occurring in pulp sheets and mill circuits during soda/anthraquinone pulping and elemental chlorine-free pulp bleaching of bast fibers of industrial hemp (Cannabis sativa) has been studied. Pitch deposits were extracted with acetone, and the extracts analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Acetone extracts (15-25% of pitch deposits) were constituted by the defoamers used at the mill and by lipophilic extractives from hemp fibers. Acetone-insoluble residues (75-85% of pitch deposits) were analyzed by pyrolysis-GC/MS in the presence and absence of tetramethylammonium hydroxide. These residues were constituted by salts of fatty acids (arising from hemp fibers) with calcium, magnesium, aluminum and other cations that were identified in the deposits. It was concluded that inappropriate use of defoamer together with the presence of multivalent ions seemed to be among the causes of hemp extractives deposition in the pitch problems reported here.This study has been supported by the Spanish Ministerio de Ciencia y Tecnología (MCYT) and FEDER funds (projects 2FD97-0896-C02-02 and AGL2002-00393). A.G. acknowledges a "Ramón y Cajal" contract of the Spanish MCYT. We also thank CELESA (Tortosa, Spain) for providing the samples.Peer reviewe

Flooding forested groundwater recharge areas modifies microbial communities from top soil to groundwater table

Subsurface microorganisms are crucial for contaminant degradation and maintenance of groundwater quality. This study investigates the microbial biomass and community composition [by phospholipid fatty acids (PLFAs)], as well as physical and chemical soil characteristics at woodland flooding sites of an artificial groundwater recharge system used for drinking water production. Vertical soil profiles to c. 4 m at two watered and one nonwatered site were analyzed. The microbial biomass was equal in watered and nonwatered sites, and considerable fractions (25-42%) were located in 40-340 cm depth. The microbial community structure differed significantly between watered and nonwatered sites, predominantly below 100 cm depth. Proportions of the bacterial PLFAs 16:1ω5, 16:1ω7, cy17:0 and 18:1ω9t, and the long-chained PLFAs 22:1ω9 and 24:1ω9 were more prominent at the watered sites, whereas branched, saturated PLFAs (iso/anteiso) dominated at the nonwatered site. PLFA community indices indicated stress response (trans/cis ratio), higher nutrient availability (unsaturation index) and changes in membrane fluidity (iso/anteiso ratio) due to flooding. In conclusion, water recharge processes led to nutrient input and altered environmental conditions, which resulted in a highly active and adapted microbial community residing in the vadose zone that effectively degraded organic compound

Functional microbial community response to nutrient pulses by artificial groundwater recharge practice in surface soils and subsoils

Subsurface microorganisms are essential constituents of the soil purification processes associated with groundwater quality. In particular, soil enzyme activity determines the biodegradation of organic compounds passing through the soil profile. Transects from surface soil to a depth of 3.5 m were investigated for microbial and chemical soil characteristics at two groundwater recharge sites and one control site. The functional diversity of the microbial community was analyzed via the activity of eight enzymes. Acid phosphomonoesterase was dominant across sites and depths, followed by l-leucine aminopeptidase and β-glucosidase. Structural [e.g. phospholipid fatty acid (PLFA) pattern] and functional microbial diversities were linked to each other at the nonwatered site, whereas amendment with nutrients (DOC, NO3−) by flooding uncoupled this relationship. Microbial biomass did not differ between sites, whereas microbial respiration was the highest at the watered sites. Hence, excess nutrients available due to artificial groundwater recharge could not compensate for the limitation by others (e.g. phosphorus as assigned by acid phosphomonoesterase activity). Instead, at a similar microbial biomass, waste respiration via overflow metabolism occurred. In summary, ample supply of carbon by flooding led to a separation of decomposition and microbial growth, which may play an important role in regulating purification processes during groundwater recharg

Flux of Root-Derived Carbon into the Nematode Micro-Food Web: A Comparison of Grassland and Agroforest

Carbon (C) cycling is crucial to agroecosystem functioning. Important determinants for the belowground C flow are soil food webs, with microorganisms and microfaunal grazers, i.e., nematodes, as key biota. The present study investigates the incorporation of plant-derived C into the nematode micro-food web under two different cropping systems, grassland (ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.)) and agroforest (willow (Salix schwerinii Wolf and Salix viminalis L)). To quantify the C flux from the plant into the soil micro-food web, grass and willow were pulse-labeled with 13CO2 and the incorporation of 13C into the nematode trophic groups was monitored 3, 7, 14 and 28 days after labeling. The natural stable isotope signals (13C/12C, 15N/14N) were analyzed to determine the structure of the nematode micro-food web. The natural isotopic δ15N signal revealed different trophic levels for omnivores and predators in grassland and agroforest soils. The incorporation of plant C into nematode tissue was detectable three days after 13CO2 labeling with the highest and fastest C allocation in plant feeders in grassland, and in fungal feeders in agroforest soil. C flux dynamics between the aboveground vegetation and belowground micro-food web varied with cropping system. This demonstrates that crop-specific translocation of C affects the multitrophic interactions in the root environment, which in turn can alter soil nutrient cycling.Peer Reviewe

Toxicity Assay for Citrinin, Zearalenone and Zearalenone-14-Sulfate Using the Nematode Caenorhabditis elegans as Model Organism

To keep pace with the rising number of detected mycotoxins, there is a growing need for fast and reliable toxicity tests to assess potential threats to food safety. Toxicity tests with the bacterial-feeding nematode Caenorhabditis elegans as the model organism are well established. In this study the C. elegans wildtype strain N2 (var. Bristol) was used to investigate the toxic effects of the food-relevant mycotoxins citrinin (CIT) and zearalenone-14-sulfate (ZEA-14-S) and zearalenone (ZEA) on different life cycle parameters including reproduction, thermal and oxidative stress resistance and lifespan. The metabolization of the mycotoxins by the nematodes in vivo was investigated using HPLC-MS/MS. ZEA was metabolized in vivo to the reduced isomers α-zearalenol (α-ZEL) and β-ZEL. ZEA-14-S was reduced to α-/β-ZEL-14-sulfate and CIT was metabolized to mono-hydroxylated CIT. All mycotoxins tested led to a significant decrease in the number of nematode offspring produced. ZEA and CIT displayed negative effects on stress tolerance levels and for CIT an additional shortening of the mean lifespan was observed. In the case of ZEA-14-S, however, the mean lifespan was prolonged. The presented study shows the applicability of C. elegans for toxicity testing of emerging food mycotoxins for the purpose of assigning potential health threats.Peer Reviewe