Bioenergetic Strategies Research Articles

Seasonal variation in the biochemical composition of deep-sea nematodes:bioenergetic and methodological considerations

Deep-sea nematode assemblages from one station (950 m depth) in the Cretan Sea (Eastern Mediterranean) were studied for seasonal variations in the gross biochemical composition. Seasonal changes in nematode composition were related to qualitative and quantitative changes in the sedimentary organic detritus and particle fluxes. Additional coastal sediment samples were collected to evaluate the effects of preservative (4 % formalin) on biochemical determinations and to compare nematode body composition in coastal and deep-sea assemblages. Protein represented the major biochemical class of organic compounds in nematodes, accounting for 43.7 and 48.5 % of organic matter (on average 24 and 29% of dry weight [DW]) in coastal and deep-sea nematodes, respectively. Carbohydrate levels of nematodes (accounting on average for 8 and 26% of DW and for 16 and 40% of organic matter, respectively, in coastal and deep-sea nematodes) appeared to be rather high when compared to literature values dealing with other taxa. Carbohydrates were the dominant biochemical class both in the sediments and in particle fluxes. Body composition of nematodes revealed rather high lipid levels (on average 11 and 17% of DW and 16 and 35% of organic matter, respectively in coastal and deep-sea nematodes). Such discrepancy appears to indicate a different bioenergetic strategy by deep-sea organisms that develop efficient energy storage systems to be able to cope with long periods of very low food availability. Deep-sea nematode body weight decreased between February-March and September 1995 concomitantly with the decrease in particle flux. Coastal nematodes displayed higher individual biomass than the deep-sea ones (0.44 ± 0.06 vs 0.37 ± 0.06 μg DW ind. - 1 , respectively), but were characterised by lower caloric values (5.57 vs 6.68 cal mg -1 DW). The caloric value of deep-sea nematodes was close to that of high-energy zooplankton, indicating that nematodes might represent an important high-quality food source for higher trophic levels. The reduced food inputs (especially carbohydrates and proteins) observed from February to September 1995 determined a parallel decrease in the concentration of sedimentary labile compounds and induced a clear decrease of the nematode energy content. However, no equally large seasonal changes in the total energy content (expressed as J m 2 ) of the nematode assemblages were observed. We hypothesise that deep-sea nematodes might respond to diminished food inputs by changing their bioenergetic strategies to better exploit the available resources.

Comparative study on cytochrome content of alkaliphilic Bacillus strains

The cytochrome content was estimated in a wide range of alkaliphilic Bacillus strains with DNA G + C contents from 34.4 to 44.3%. Among the strains tested, four facultative alkaliphiles, whose G + C contents were around 36%, and one obligate alkaliphile, with a G + C content of 41.4%, possessed relatively high amounts of total cytochrome (more than 0.3 nmol · mg cells −1). These five alkaliphiles contained high amounts of cytochromes b and c compared with the other strains tested, but their cytochrome a contents were not noticeably different. All the tested alkaliphilic strains had much higher amounts of cytochrome than B. subtilis (neutrophile), except for two facultative alkaliphiles with G + C contents around 40%. These results suggest that various bioenergetic strategies are used by alkaliphilic Bacillus for adaptation to a high alkaline environment, and that cytochromes b and c have a bioenergetically very important role in certain kinds of alkaliphiles.

Developmental biology of Armases miersii (Grapsidae), a crab breeding in supratidal rock pools. I. Facultative lecithotrophy of larval stages

Starvation resistance in the larvae of a grapsid crab, Armases miersii, that breeds in supratidal rock pools in Jamaica was examined by point-of-no-return (PNR) and point-of-reserve- saturation (PRS) experiments. A. miersii shows an abbreviation of larval development (only 3 zoeal stages) and a high degree of lecithotrophy in the zoea I and II stages. In complete absence of food, larval development is possible from hatching to the zoea III stage. The potential for endotrophic development decreases during ontogeny: the zoea I is, in principle, entirely independent of food, without significant effects of starvation on survival; the zoea II shows significantly higher mortality under continued lack of food (since hatching) and delayed development after initial temporary starvation; the zoea III can also develop independently of food, but only if the preceding stages were fed continuously. Hence, no PNR or PRS can be given for individual zoeal stages of this species. Late effects of early feeding or starvation indicate that lecithotrophy in A. miersii is only facultative, i.e. food is not essential in the beginning of larval life, but it will be taken up when available. Conspicuous intraspecific variability in the degree of lecithotrophy was observed in larvae originating from 2 different females. In a hatch with particularly high endotrophic potential (but not in nutritionally more vulnerable larvae), development was significantly faster under starvation. This effect is interpreted as a change in energy partitioning: lack of food may induce a signal for switching from growth (accumulation of exogenous energy) to rapid mobilization of internal reserves (accelerated development, termination of the nutritionally vulnerable planktonic larval phase). Feeding after initial starvation may cause inverse effects, i.e. slower development, replacement of utilized reserves, and accumulation of additional energy for later stages. This switching should occur only in facultatively lecithotrophic larvae that have sufficient internal energy reserves to allow for this opportunistic bioenergetic strategy. Compared with most planktotrophic marine decapod larvae, the zoeal stages of A. miersii show higher starvation resistance and endotrophic potential. These ontogenetic traits are considered adaptations to breeding and larval development in a short-lived, nutritionally unpredictable habitat.

The strategies of energy conservation in helminths.

From the above discussion it is quite obvious that the bioenergetics in helminths are different in many ways from those found in higher organisms. All adult helminths appear to be able to consume oxygen when it is available but none of them can use it to drive the pathways of complete substrate degradation, like typical aerobic organisms, as a major strategy for energy generation. These properties hold also true for those worms residing in a highly aerobic environment, such as the blood stream or the muscle and lung tissues. Although in a number of recent studies oxygen was found to play apparently a greater role in the bioenergetics of adult helminths than originally thought, energy-generating mechanisms in adult worms seem to place greater emphasis on fermentations and anaerobic electron transport processes. These exhibit relatively low energy conservation efficiencies and result in the formation of a variety of organic end products, most of which must be excreted. The obvious correlation between the type of bioenergetic strategy operative in a particular helminth species and its environmental conditions is not well understood. The increased capacity to generate chemical energy and key metabolites of helminths possessing multiple fermentations and anaerobic respirations may give the organism greater versatility and metabolic flexibility to respond to the environmental changes observed in its corresponding habitat. Other helminths, such as schistosomes and filariids, which have continuous access to a fairly constant nutrient supply, were found to depend primarily on the more inefficiently functioning and primitive strategy of glycolysis for energy production. The reason for the occurrence in helminths of limited oxidative capacities is not completely clear. It may be assumed that the variety of alternative anaerobic pathways have evolved in response to the lack of a circulatory system and/or to the specific, often peculiar, environmental conditions prevailing in most parasitic habitats. An alternative idea put forward by Barrett [8] is that helminth metabolism represents a form of biochemical economy. Most endoparasites have an abundant supply of food and swim as if in a land of Cockain, obviously without any need to extract a maximum amount of chemical energy from the nutrients they take up. On the other hand, the fact that free-living and other larval or juvenile stages of helminths often have a typical aerobic bioenergetic pattern is a clear indication that the DNA of these organisms carries the genetic message for all the enzymes involved in complete substrate degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Bioenergetic Strategies of the Cotton Rat, Sigmodon hispidus

Bioenergetic strategies of hispid cotton rats on a relict grassland in west-central Kansas were assessed for the period December 1967 through November 1968. Less than 1.0 per cent of the yearly net primary production of the grassland was ingested by cotton rats. Of the energy assimilated throughout the year, all but 2.2 per cent was utilized in maintenance. Energy flow channeled into secondary production ranged from a low of −2.4 kilocalories per hectare per day in January to a high of 22.6 in September. Accordingly, population density was at a low of 8.8 rats per hectare in April but increased to 19.4 by September. Seasonal fluctuations in relative amounts of energy utilized in secondary production probably reflect physiological adaptations to withstand adversities of climatic seasonality.