Biogeochemical processes in the groundwater discharge zone of urban streams

The influence of biogeochemical processes on nitrogen and organic matter transformation and transport was investigated for two urban streams receiving groundwater discharge during the dry summer baseflow period. A multiple lines of evidence approach involving catchment-, and stream reach-scale investigations were undertaken to describe the factors that influence pore water biogeochemical processes. At the catchment-scale gaining stream reaches were identified from water table mapping and groundwater discharge estimated to be between 0.1 and 0.8 m³ m^?2 d^?1 from baseflow analysis. Sediment temperature profiles also suggested that the high groundwater discharge limited stream water infiltration into the sediments. At the stream reach-scale, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were higher in stream water than in groundwater. However, DOC and DON concentrations were greatest in sediment pore water. This suggests that biodegradation of sediment organic matter contributes dissolved organic matter (DOM) to the streams along with that delivered with groundwater flow. Pore water ammonium (NH₄ ⁺) was closely associated with areas of high pore water DOM concentrations and evidence of sulfate (SO₄ ^2?) reduction (low concentration and SO₄:Cl ratio). This indicates that anoxic DOM mineralization was occurring associated with SO₄ ^2? reduction. However the distribution of anoxic mineralization was limited to the center of the streambed, and was not constrained by the distribution of sediment organic matter which was higher along the banks. Lower sediment temperatures measured along the banks compared to the center suggests, at least qualitatively, that groundwater discharge is higher along the banks. Based on this evidence anoxic mineralization is influenced by groundwater residence time, and is only measurable along the center of the stream where groundwater flux rates are lower. This study therefore shows that the distribution of biogeochemical processes in stream sediments, such as anoxic mineralization, is strongly influenced by both the biogeochemical conditions and pore water residence time.     

Contrasting life histories of the predatory cladocerans Leptodora kindtii and Bythotrephes longimanus

The predatory cladocerans, Leptodora kindtii (Focke, 1844) andBythotrephes longimanus (Leydig, 1860), express markedly differentlife-history traits. Leptodora produce small-bodied neonatesthat mature at small sizes but continue to grow throughout life.Bythotrephes produce larger neonates in both relative and absoluteterms that grow rapidly to a large size at maturity whereuponthey curtail somatic growth and divert resources mainly to reproduction.Despite their remarkable differences, the sets of life-historytraits of both species appear to be solutions to the same basicselection pressures imposed by visually discriminating gape-limitedfishes and foraging constraints imposed by prey size. Leptodorastresses pre-contact (transparency) while Bythotrephes stressespostcontact (caudal spine) modes of morphological defense againstfishes. Mounting these disparate modes of defense has consequencesfor selection on timing and allocation to body growth that mayunderlie competitive imbalance between the species. Owing tothe production of large-bodied neonates that grow rapidly, Bythotrephesquickly attain body sizes that both admit them to a broaderprey base in size and taxonomic variety, and allow shorter preyhandling times, in comparison to Leptodora. This provides Bythotrepheswith a wider and more exploitable prey base from an earlierage and may explain why Leptodora has declined in density followingBythotrephes invasion into some North American lakes. The divergentsets of life-history traits expressed by Leptodora and Bythotrephesparallel two dominant life-history strategies evolved by phytoplanktivorousspecies of the order Cladocera.     

Generational and dual-species exposures to invertebrate predators influence relative head size in Daphnia mendotae

Laboratory cyclomorphosis experiments with crustacean zooplanktonoften fail to produce morphological trait expression as extremeas that observed in field populations. A seven-generation laboratoryexperiment found that the maximum expression of relative headarea in a round-helmet morph of Daphnia mendotae was delayeduntil the third generation of non-lethal, chemical exposureto Leptodora kindtii. By the third generation and after, relativehead area remained high and comparable in degree to field specimens.The induction pattern from parents to offspring was statisticallypositive into the fourth generation. Published studies on kairomoneinduction of morphological trait expression extending only onegeneration may fail to measure transgenerational effects, whichcould account for mismatch between laboratory and field results.In a second laboratory experiment with a pointed-helmet morphof D. mendotae exposed to L. kindtii and Chaoborus punctipennis,we show that induction levels are not the same for all predatorsor combinations of predators. The maximum relative head areafor pointed morph individuals exposed to both predator cueswas still not as extreme in the laboratory as in the field.This is the first demonstration that delayed generational effectsof kairomone induction of helmet expression in the Cladoceracan reconcile laboratory experiments with the field observationsof cyclomorphosis.     

Effects of cellulose on growth,enzyme production,and ultrastructure of a Cellulomonas species

Cellulomonas sp. (NRCC 2406) was grown on complex medium (peptone-tryptone-yeast extract) alone, or with the addition of different celluloses (solka floc, avicel, CF 11 cellulose or Whatman No. 1 filter paper) and/or glucose. Cultures growing on the complex medium without cellulose produced low levels of endo- and exo-cellulases and very little -glucosidase. Adding cellulose stimulated growth, as measured by cellular protein or by viable counts, and also stimulated production of cellulases. Adding glucose in the prescene of cellulose inhibited growth and cellulose breakdown. Glucose also inhibited attachment of growing cells to cellulose fibres. Electron microscope studies showed that Cellulomonas sp. adhered to the cellulose fibers. In the presence of cellulose in the media, the cells developed a thicker outer layer which probably helps in the adhesion process.Abbreviations PTYE peptone, tryptone, yeast extract medium - DNS dinitrosalicylic acid - CMC carboxymethyl cellulose - cfu/ml colony-forming units per ml     

Dominant expression of a gene amplification-related herbicide resistance in medicago cell hybrids

Protoplasts from phosphinotricin resistant M. sativa and M. varia cell lines carrying an amplified glutamine synthethase gene were fused with leaf protoplasts of kanamycin resistant M. varia transformants. The dominant nature of both PPT and kanamycin resistant traits was shown by the double resistant phenotype of the intra- and interspecific cell hybrids obtained. The presence of amplified GS gene in the hybrid genomes and the expression of chimeric neomycin phosphotransferase II gene was detected. The highly embryogenic character of the M. varia parent was not expressed after cell fusion. All hybrid cell lines with the double resistant phenotype showed non-morphogenic growth similarly to the PPT resistant parent. The possible role of GS gene amplification and other factors in the dominant behaviour of unorganized cell growth in alfalfa somatic hybrids is discussed.     

Factors regulating cryIVB expression in the cyanobacterium Synechococcus PCC 7942

The expression of the larvicidal Bacillus thuringiensis subsp. israelensis cryIVB gene in cyanobacteria has been suggested to be an effective means of controlling mosquito populations. Using a variety of cryIVB constructs, in this study we have examined the effect of Synechococcus PCC 7942 culture age on intracellular toxin levels and have attempted to determine the mechanisms by which cryIVB gene expression is regulated. The data suggest that specific degradation of the cryIVB mRNA limits toxin production; however, the addition of cyanobacterial 3 untranslated DNA sequences to the cryIVB gene did not improve mRNA stability or toxin levels. An analysis of the cryIVB sequence and comparison of codon usage patterns with highly expressed cyanobacterial genes suggest that inefficient translation and intragenic ribosomal binding sites impede protein synthesis and result in rapid turnover of the toxin mRNA.     

A bacteriophage of a moderately halophilic bacterium

A bacteriophage of an aerobic, gram-negative, rod-shaped halophilic bacterium, provisionally named Pseudomonas sp. G3, is described. The phage has a head and a tail and is similar in appearance to Salmonella phage Beccles. It infects its bacterial host at all salt concentrations in which the bacteirum is able to grow. In contrast to phages of halophilic archaebacteria, the newly-described phage is relatively stable in the absence of salt. It also infects Vibrio costicola and two unidentified halophilic eubacteria.Abbreviations PPT proteose peptone-tryptone medium - pfu plaque-forming unit - G+C guanine + cytidine content, mol %     

Alteration of proteoglycan metabolism during the differentiation of 3T3- L1 fibroblasts into adipocytes

3T3-L1 fibroblasts were induced to differentiate to 3T3-L1 adipocytes by dexamethasone, isobutyl-methylxanthine, and insulin. To study how differentiation affects extracellular matrix production, the accumulation of proteoglycans was studied by labeling the 3T3-L1 cells with [35S]sulphate for 24 h. The labeled proteoglycans were isolated from the medium and cell layer extracts by anion-exchange chromatography. They were then taken to gel filtration chromatography on Superose 6 before or after chondroitin ABC lyase digestion. Hyaluronan was determined by radioimmunoassay. The rate of accumulation of proteoglycans and hyaluronan in the control 3T3-L1 fibroblasts increased with time whereas it decreased slightly in the age matched adipocytes where the differentiation had proceeded, as judged by the change of morphology and increase of the activity of the adipose conversion markers glycerol-3-phosphate dehydrogenase and hormone sensitive lipase. The main change noted was that the adipocytes accumulated 50-70% less amount of small proteoglycans (decorin) in the medium than the fibroblasts did. The amount of large chondroitin/dermatan sulphate proteoglycans was also decreased but to a considerably smaller extent (30%). In the cell layer, heparan sulphate proteoglycan decreased by 60% as compared with the control cells. Thus, the differentiation of 3T3-L1 fibroblasts into adipocytes, which changes the morphology and the function of the cells, is also accompanied by a decreased net production especially of proteoglycans typical of fibrous connective tissue.