Habitat choice by juvenile cod (Gadus morhua L.) on sandy soft bottoms with different vegetation types

Habitat choice by juvenile cod (Gadus morhua L.) on sandy bottoms with different vegetation types was studied in laboratory. The experiment was conducted day and night in flow-through tanks on two different size-classes of cod (7–13 and 17–28 cm TL). Four habitats, typical of shallow soft bottoms on the Swedish west coast:Fucus vesiculosus, Zostera marina, Cladophora sp. and bare sand, were set up pair-wise in six combinations. The main difference between habitats in this study was vegetation structure, since all parameters except vegetation type was considered equal for both sides of the experimental tanks and natural prey was eliminated. The results showed a difference in habitat utilization by juvenile cod between day (light) and night (dark). During day time the fishes showed a significant preference for vegetation, while nocturnally no significant choice of habitat was made. Both size-classes preferredFucus, considered the most complex habitat in this study, when this was available. The smaller size-class seemed to be able to utilize the other vegetation types as well, always preferring vegetation over sand. Larger juvenile cod, on the other hand, appeared to be restricted toFucus. This difference in habitat choice by the two size-classes might be due to a greater dependence on shelter from predation by the smaller juveniles, causing them to associate more strongly with vegetation. The larger juveniles avoidedCladophora, since they might have difficulties in entering the compact structure of this filamentous algae. Availability of vegetation at day time, as a predation refuge, as well as of open sandy areas for feeding during night, thus seems to be important for juvenile cod. It is concluded that eutrophication-induced changes in habitat structure, such as increased dominance by filamentous algae, could alter the availability of predation refuges and foraging habitats for juvenile cod.     

New fluorophore-forming reactions for histochemical visualization of N-acetylated and tertiary indolamines using glyoxylic acid,aluminum-formaldehyde and trifluoroacetic acid anhydride as reagents

Summary N-acetylated and tertiary indolamines, some of which are possible neurotransmitter candidates in the CNS, cannot be visualized with the standard Falck-Hillarp histofluorescence method and very little is known about their cellular localization. The present investigation demonstrates that glyoxylic acid (GA), formaldehyde (FA) in combination with aluminum ions (the ALFA method) and trifluoroacetic acid anhydride (TFAA) are capable of forming fluorescent compounds from N-acetylated (e.g. melatonin and N-acetyl-5-hydroxytryptamine) and tertiary (e.g. bufotenin) indolamines in histochemical protein models. With GA and FA-aluminum more vigorous reaction conditions were required for demonstration of these compounds compared to those needed for optimal visualization of primary catecholand indolamines (prolonged reaction time and higher concentration of GA and FA and aluminum ions). The fluorophore formation from N-acetylated and tertiary indolamines, which represents a new reaction principle in amine fluorescence histochemistry, is proposed to proceed as follows. In the first step, the indole reacts in 2-position with the reagent. The intermediate formed is dehydrated in the second step, yielding a strongly fluorescent 2-methylene derivative, which either per se or as the corresponding autoxidized dimer constitutes the main fluorophore. TFAA and related anhydrides represent new and potent reagents for histochemical visualization of N-acetylated indolamines such as melatonin. In contrast to the GA and ALFA reactions the optimal formation of fluorphores with TFAA required only mild reaction conditions (2–10 min at 0–20° C). The main fluorophore formed from melatonin has been identified and the reaction with TFAA is proposed to proceed as follows. An unstable intermediate, the isoimidinium carboxylate, is formed in the first step and this compound is then cyclized to form the fluorophore, 6-methoxy-1-methyl-3,4-dihydro--carboline. The GA and ALFA methods are already widely used for visualization of catecholamine systems. The fluorescence microscopical and microspectrofluorometric analysis did not, however, veveal any specific structures containing N-acetylated or tertiary indolamines in the rat CNS. The TFAA reaction was highly specific for N-acetylated indolamines when applied to protein models. However, in tissue a disturbing background fluorescence appeared, which under all reaction conditions tested, developed concomitantly with the specific fluorescence from melatonin. The problem with this background reaction has to be solved before the TFAA reaction can be applied for demonstration of N-acetylated indolamines in tissue.     

The influence of artificial colonization withE. coli strain O83 on the intestinal flora in infants

Dominant bacterial strains present in stool (with particular emphasis onE. coli strains) were examined in 4 groups of healthy infants: breast-fed and bottle-fed, colonized withE. coli O83, and control (non-colonized) breast-fed and bottle-fed newborns. The presence of fimbriae was examined by hemagglutination, the P-fimbriae-bearing strains were tested by the PPA latex test. In addition, adherence to cell line HT-29 and serotyping was performed in selected strains. TheE. coli strain O83 was found to possess type 1 fimbriae. Fewer bacterial strains possessing type 1 fimbriae were found inE. coli O83-colonized infants (except the O83 serotype) than in control infants. TheE. coli O83 strain colonized significantly better the breast-fed than the bottle-fed infants; its higher adherence activity was demonstrated even in cell line HT-29. Finally, colonization withE. coli O83 influenced the character of microbial intestinal flora: the frequency of positiveE. coli isolates was significantly higher in colonized (both breast- and bottle-fed) than noncolonized infants.     

Surface Attachment of Ammonia-Oxidizing Bacteria in Soil

Abstract Indigenous ammonia-oxidizing bacteria (AOB) in a clay loam soil were extremely difficult to release from soil particles compared to most heterotrophic bacteria; less than 1% of indigenous AOB (estimated as potential ammonia oxidation rate) were extractable by the dispersion-density-gradient centrifugation technique. This is at least 10-fold less than the extractability of heterotrophic bacteria. Urea applications to the same soil induced a 5-fold increase in the potential ammonia oxidation rate, and this resulted in a much higher percentage (8%) extractability of AOB. Thus, the newly grown AOB in the urea-treated soil were less strongly attached to the soil particles. The contrast suggests that the strong attachment of indigenous AOB is a gradual process taking place due to a long residence time (infrequent/slow cell division) compared to heterotrophic organisms. However, the contrast could also reflect differences in species composition of the original AOB community and those growing in response to urea inputs. Specific detection of AOB in extinction dilution cultures was done by PCR and sequencing of the products. Considerable diversity was found within the genus Nitrosospira, but severe problems with the specificity of the primers were observed. Two allegedly AOB specific PCR primers pairs were used: one specific for Nitrosospira (SPIRA) and one which should encompass all AOB within the β-Proteobacteria (GAOB). Only 33% of the cultures that gave PCR products with GAOB also gave products with the SPIRA primer pair, suggesting the presence of AOB other than Nitrosospira. However, the phylogeny based on the sequencing placed all the cultures in various clusters of the Nitrosospira clade, suggesting that the SPIRA primers do not match all members of the Nitrosospira genus. The cultures obtained from the urea-treated soil were different from the others in giving PCR products only with the SPIRA primers and not with the GAOB. Since sequencing also here confirmed the presence of Nitrosospira, these observations suggest that the GAOB primers do not match all AOB species. Received: 15 September 1999; Accepted: 8 November 1999; Online Publication: 28 April 2000     

Temperature sensitivity and substrate quality in soil organic matter decomposition: results of an incubation study with three substrates

Kinetic theory suggests that the temperature sensitivity of decomposition of soil organic matter should increase with increasing recalcitrance. This ‘temperature–quality hypothesis’ was tested in a laboratory experiment. Microcosms with wheat straw, spruce needle litter and mor humus were initially placed at 5, 15 and 25 °C until the same cumulative amount of CO₂ had been respired. Thereafter, microcosms from each single temperature were moved to a final set of incubation temperatures of 5, 15 and 25 °C. Straw decomposed faster than needle litter at 25 and 15 °C, but slower than needle litter at 5 °C, and showed a higher temperature sensitivity (expressed as Q₁₀) than needle litter at low temperatures. When moved to the same temperature, needle litter initially incubated at 5 and 15 °C had significantly higher respiration rates in the final incubation than litters initially placed at 25 °C. Mor humus placed at equal temperatures during the initial and final incubations had higher cumulative respiration during the final incubation than humus experiencing a shift in temperature, both up‐ and downwards. These results indicate that other factors than substrate quality are needed to fully explain the temperature dependence. In agreement with the hypothesis, Q₁₀ was always higher for the temperature step between 5 and 15 °C than between 15 and 25 °C. Also in agreement with the temperature–quality hypothesis, Q₁₀ significantly increased with increasing degree of decomposition in five out of the six constant temperature treatments with needle litter and mor humus. Q₁₀s for substrates moved between temperatures tended to be higher than for substrates remaining at the initial temperature and an upward shift in temperature increased Q₁₀ more than a downward shift. This study largely supports the temperature–quality hypothesis. However, other factors like acclimation and synthesis of recalcitrant compounds can modify the temperature response.