Transgenic nematodes as biosensors for metal stress in soil pore water samples

Caenorhabditis elegans strains carrying stress-reporter green fluorescent protein transgenes were used to explore patterns of response to metals. Multiple stress pathways were induced at high doses by most metals tested, including members of the heat shock, oxidative stress, metallothionein (mtl) and xenobiotic response gene families. A mathematical model (to be published separately) of the gene regulatory circuit controlling mtl production predicted that chemically similar divalent metals (classic inducers) should show additive effects on mtl gene induction, whereas chemically dissimilar metals should show interference. These predictions were verified experimentally; thus cadmium and mercury showed additive effects, whereas ferric iron (a weak inducer) significantly reduced the effect of mercury. We applied a similar battery of tests to diluted samples of soil pore water extracted centrifugally after mixing 20% w/w ultrapure water with air-dried soil from an abandoned lead/zinc mine in the Murcia region of Spain. In addition, metal contents of both soil and soil pore water were determined by ICP-MS, and simplified mixtures of soluble metal salts were tested at equivalent final concentrations. The effects of extracted soil pore water (after tenfold dilution) were closely mimicked by mixtures of its principal component ions, and even by the single most prevalent contaminant (zinc) alone, though other metals modulated its effects both positively and negatively. In general, mixtures containing similar (divalent) metal ions exhibited mainly additive effects, whereas admixture of dissimilar (e.g. trivalent) ions often resulted in interference, reducing overall levels of stress-gene induction. These findings were also consistent with model predictions

Nutrient limitations to bacterial and fungal growth during cellulose decomposition in tropical forest soils

Nutrients constrain the soil carbon cycle in tropical forests, but we lack knowledge on how these constraints vary within the soil microbial community. Here, we used in situ fertilization in a montane tropical forest and in two lowland tropical forests on contrasting soil types to test the principal hypothesis that there are different nutrient constraints to different groups of microorganisms during the decomposition of cellulose. We also tested the hypotheses that decomposers shift from nitrogen to phosphorus constraints from montane to lowland forests, respectively, and are further constrained by potassium and sodium deficiency in the western Amazon. Cellulose and nutrients (nitrogen, phosphorus, potassium, sodium, and combined) were added to soils in situ, and microbial growth on cellulose (phospholipid fatty acids and ergosterol) and respiration were measured. Microbial growth on cellulose after single nutrient additions was highest following nitrogen addition for fungi, suggesting nitrogen as the primary limiting nutrient for cellulose decomposition. This was observed at all sites, with no clear shift in nutrient constraints to decomposition between lowland and montane sites. We also observed positive respiration and fungal growth responses to sodium and potassium addition at one of the lowland sites. However, when phosphorus was added, and especially when added in combination with other nutrients, bacterial growth was highest, suggesting that bacteria out-compete fungi for nitrogen where phosphorus is abundant. In summary, nitrogen constrains fungal growth and cellulose decomposition in both lowland and montane tropical forest soils, but additional nutrients may also be of critical importance in determining the balance between fungal and bacterial decomposition of cellulose

Ecotox-evaluation strategy for soil bioremediation exemplified for a PAH-contaminated site

Hund K, Traunspurger W. Ecotox-evaluation strategy for soil bioremediation exemplified for a PAH-contaminated site. Chemosphere. 1994;29(2):371-390

Predator-prey interaction in soil food web: functional response, size-dependent foraging efficiency, and the influence of soil texture

Hohberg K, Traunspurger W. Predator-prey interaction in soil food web: functional response, size-dependent foraging efficiency, and the influence of soil texture. BIOLOGY AND FERTILITY OF SOILS. 2005;41(6):419-427.In a series of laboratory experiments, we presented carnivorous Macrobiotus richtersi (Tardigrada, Macrobiotidae) with nematode prey to assess their importance as predator. We investigated consumption rate for (a) different prey densities (10-400 prey individuals), (b) different prey biomasses (22-80 ng), (c) different prey species (Pelodera teres, Rhabditidae, versus Acrobeloides nanus, Cephalobidae) and (d) different environments (2-D agar surface versus 3-D sand fractions of three different textures). M. richtersi consumed up to 4.6 mu g nematode prey in 4 h, that is, 43% of the tardigrade's body mass. Predation rate was positively correlated with prey density. The optimal prey in the present investigation was the biggest prey because it yielded the highest biomass uptake per time. In addition, the size of M. richtersi played an important role in consumption rate. Bacterivorous nematodes reacted differently to attack. Even in a water film on stiff agar where nematode agility was limited, a vigorous undulation reaction of P. teres led to a measurable reduction in consumption rate. A. nanus, in contrast, showed little response to attack. Microcosm experiments with sands of different particle size demonstrated that M. richtersi is able to chase and consume small bacterivorous nematodes in a 3-D soil matrix. However, consumption rate in sand microcosms was significantly reduced compared with pure agar. The sand matrix improved nematode agility and possibly provided small pores as refuge for the nematodes. The lowest consumption rate was observed in fine sand. Effects of predatory tardigrades on nematode numbers in the field are discussed

Colonization of exclosures in a Costa Rican Stream: Effects of macrobenthos on meiobenthos and the nematode community

Duft M, Fittkau K, Traunspurger W. Colonization of exclosures in a Costa Rican Stream: Effects of macrobenthos on meiobenthos and the nematode community. JOURNAL OF FRESHWATER ECOLOGY. 2002;17(4):531-541.Interactions of macro- on meiobenthos were studied in the sediment of a small stream in northwestern Costa Rica. Three different exclosure types (n = 5) were exposed for 21 days: (1) treatment macrofauna (2 mm mesh size) allowed meiobenthic plus macrobenthic colonization; (2) treatment meiofauna (500 Am mesh size) allowed meiobenthic colonization but reduced macrobenthic colonization; and (3) plastic pipe exclosures (35 Am mesh size lid) inhibited access of both meio- and macrobenthos. In each cage, standardized hard substrates were provided for algal colonization. We postulated impacts of macrobenthos on (1) meiofaunal abundance, (2) algal biomass, and (3) nematode community composition. Reduction of macrobenthos did not result in increased population densities for any meiobenthic taxonomic group, but gastropods were more abundant in macro treatments. Ambient population densities were not reached inside the exclosures except for ostracods. Algal biomass significantly increased when macrobenthos was reduced, yet the influence of a caging effect during the experiment cannot be ruled out. Bacterivorous nematodes were dominant in both treatments. Species of the genera Eumonhystera and Plectus (colonizers) were predominantly found in meio treatments, while the genera Rhabdolaimus and Dorylaimus/Mesodorylaimus (persisters) were mainly present in macro treatments

Toxicity of ingested cadmium to the nematode Caenorhabditis elegans

Hoess S, Schlottmann K, Traunspurger W. Toxicity of ingested cadmium to the nematode Caenorhabditis elegans. Environmental Science & Technology. 2011;45(23):10219-10225

Effects of nutrient enrichment on the trophic structure and species composition of freshwater nematodes - A microcosm study

Ristau K, Faupel M, Traunspurger W. Effects of nutrient enrichment on the trophic structure and species composition of freshwater nematodes - A microcosm study. Freshwater Science. 2013;32(1):155-168

Meiobenthos of some Estonian coastal lakes.

Timm T, Kumari M, Kübar K, Sohar K, Traunspurger W. Meiobenthos of some Estonian coastal lakes. Proc. Estonian Acad. Sci. Biol. Ecol. 2007;56:179-195