Changes in soil microbial community composition induced by cometabolism of toluene and trichloroethylene

The effects of trichloroethylene (TCE) on microbial community composition were analyzed by reverse sample genome probing. Soil enrichments were incubated in dessicators containing an organic phase of either 1 or 10% (w/w) toluene in vacuum pump oil, delivering constant equilibrium aqueous concentrations of 16 and 143mg/l, respectively. Increasing the equilibrium aqueous concentration of TCE from 0 to 10mg/l led to shifts in community composition at 16, but not at 143mg/l of toluene. In closed system co-degradation studies, TCE at an aqueous concentration of 1mg/1 was effectively degraded by toluene-degrading soil enrichments once the aqueous toluene concentration dropped below 25mg/l. Little TCE degradation was observed at higher toluene concentrations (50–250mg/l). The results indicate that TCE changes microbial community composition under conditions where it is being actively metabolized.     

Rapid nutrient cycling in leaf litter from invasive plants in Hawai’i

Physiological traits that contribute to the establishment and spread of invasive plant species could also have impacts on ecosystem processes. The traits prevalent in many invasive plants, such as high specific leaf areas, rapid growth rates, and elevated leaf nutrient concentrations, improve litter quality and should increase rates of decomposition and nutrient cycling. To test for these ecosystem impacts, we measured initial leaf litter properties, decomposition rates, and nutrient dynamics in 11 understory plants from the Hawaiian islands in control and nitrogen + phosphorus fertilized plots. These included five common native species, four of which were ferns, and six aggressive invasive species, including five angiosperms and one fern. We found a 50-fold variation in leaf litter decay rates, with natives decaying at rates of 0.2–2.3 year^–1 and invaders at 1.4–9.3 year^–1. This difference was driven by very low decomposition rates in native fern litter. Fertilization significantly increased the decay rates of leaf litter from two native and two invasive species. Most invasive litter types lost nitrogen and phosphorus more rapidly and in larger quantities than comparable native litter types. All litter types except three native ferns lost nitrogen after 100 days of decomposition, and all litter types except the most recalcitrant native ferns lost >50% of initial phosphorus by the end of the experiment (204–735 days). If invasive understory plants displace native species, nutrient cycling rates could increase dramatically due to rapid decomposition and nutrient release from invasive litter. Such changes are likely to cause a positive feedback to invasion in Hawaii because many invasive plants thrive on nutrient-rich soils.     

Treatment of the yeast<Emphasis Type="Italic"> Rhodotorula glutinis</Emphasis> with AlCl<Subscript>3</Subscript> leads to adaptive acquirement of heritable aluminum resistance

When aluminum (Al) was added to a culture, growth of Rhodotorula glutinis IFO1125 was temporarily arrested, showing longer lag phases, depending on the Al concentrations (50–300 M) added, but the growth rates were not affected at all. Resistant strains obtained by one round of plate treatment containing Al reverted the resistance level to the wild-type level when cultivated without Al. Repeated Al treatments, however, induced heritable and stable Al resistance, the level of which was increased up to 4,000 M by stepwise increments in Al concentrations. Thus, the heritable Al resistance adaptively acquired was due neither to adaptation nor to mutation, but to a mechanism which has yet to be studied. Heritable Al resistance seemed to release the Al inhibition of magnesium uptake.     

The effect of insularity on the diversity of land birds in the Fiji islands: implications for refuge design

Ecologists have argued over rules of thumb that could be used to set priorities in configuring systems of reserves for preserving biological diversity. To evaluate these simple strategies, I assembled a particularly large and comprehensive data set on the land birds of the Fiji archipelago. I analyzed the species distribution on 220 islands to compare the running total of species preserved by differènt sequences of adding nature reserves to a hypothetical reserve system, treating each island as if it were a potential reserve. A strategy of maximizing the number of islands contributing to any given reserve area (maximum fragmentation) is much more effective at including species than a strategy of maximizing the size of the island components of a reserve (minimum fragmentation). Nevertheless the maximum fragmentation strategy is not a very good one. It is less effective than many random strategies, especially when about 2–10% of total area is to be set aside as reserve, and when only rare species are considered. A computer program was used to determine an optimal strategy by maximizing the number of additional species added for each unit of area added. This strategy is always substantially more effective at encompassing species diversity than either the maximum or minimum fragmentation strategies. It is suggested that the poor performance of the minimum fragmentation strategy is due principally to the presence of many smaller-island endemics within the Fiji archipelago. More generally, it is argued that the effect of fragmentation on species diversity depends on the geographic scale and isolation of the region under consideration. In these respects the Fiji Archipelago may be a particularly good model for continental reserve systems.     

Macrobenthic community structure before and after pollution abatement in the Neches River estuary (Texas)

Macrobenthos and physicochemical conditions in the lower 39 km of the Neches River estuary were studied from August, 1984 to May, 1985. The results were compared with data collected in 1971–1972. Between 1972 and 1984 the permitted BOD waste load in the tidal Neches River was reduced from 123 125 kg d to 8717 kg d. River discharge and dissolved oxygen concentrations were consistently higher and salinity was lower, during the same seasons, during the 1984–1985 study. A total of 50 taxa of macrobenthos were collected in 1971–1972 and 104 taxa were collected in 1984–1985. The numbers of taxa per collection at each station in 1984–1985 were at least twice those found in 1971–1972. Minimum densities in 1984–1985 were much higher than the maximum densities in 1971–1972 at all stations. Patterns of dominance, Sorenson's similarity index, and diversity ( ) values indicated improved water quality in 1984–1985. Statistical analysis of macrobenthic diversity indicated significant differences between upper estuary and lower estuary stations in 1971–1972. No significant differences were found in 1984–1985. Significant differences in numbers of taxa, macrobenthos densities, and values between the two studies were found. Reductions of waste loads, increased river discharge, and deepening of the navigation channel were among the factors that probably contributed most to the changes in community structure of the macrobenthos observed.     

Structure,biomass distribution,and energetics of the pelagic ecosystem in the Barents Sea: A synopsis

Biomass distribution and energetics of trophic levels in the pelagic ecosystem of the Barents Sea are presented as averages over several years for the whole Barents Sea using data from the research programme Pro Mare in 1984–1989 and mathematical ecosystem models. Average biomasses range from more than 3 tonnes carbon km^–2 (zooplankton) to 0.1 kg C km^–2 (polar bears) and P/B ratios from 300 (bacteria) to 0.035 (minke whales). However, the Barents Sea ecosystem is in a far from steady state with, for instance, capelin stocks ranging from 30–700 kg C km^–2 between years and cod stocks from 150–700 kg C km^–2. As a general rule, the various fish stocks grow adequately, albeit at different rates, in warm years characterized by large influxes of Atlantic water and high zooplankton productivity. The skewed populations distribution which arises in warm years may lead to grave imbalances in cold years and even to the collapses of stocks, such as of capelin in the eighties. The food requirements of average-sized stocks of cod, seabirds and marine mammals correspond to more than twice the average productivity of capelin. Thus other species of pelagic fish (herring, polar cod) and zooplankton obviously play major roles as prey for these animals.     

Organochlorine and mercury residues in fish from Lake Simcoe,Ontario 1970–76

Synopsis Lake Simcoe located in the central Ontario plain has four major streams draining the watershed. Persistent organochlorine insecticides were used in the basin for mosquito control and agricultural production until restricted. Methyl mercury compounds have been phased out and a voluntary restriction occurred for PCB.Ten species of fish were collected between 1970 and 1976 for organochlorine and mercury analysis. DDT residues significantly declined between 1970 and 1975–76 in all species except small Stizostedion vitreum vitreum and large Salvelinus namaycush. Eggs taken 1975–76 from small S. namaycush had DDT residues below the critical level reported for the production of viable offspring, but this was not so for large members.HEOD residues between 1970 and 1975–76 significantly declined in five species, showed no change in two, whereas in two species the Larger members of one had Lower residues and the smaller members of the other showed no change.PCB residues declined.in all species except the larger Perca flavescens. Chlordane and heptachlor-epoxide were identified in S. namaycush for the first time in 1975–76. Mercury residues showed no change between 1970 and 1975–76 in five species, it declined in two species and increased in small S. v. vitreum.Correlations existed between Levels of organic contaminant and Lipid content of fish especially in the immediate post period of their use. Where the increasing Lipid content was associated with an increasing trophic level a preypredator relationship existed for contaminant accumulations. However, where Lipid contents were Low, no correlation appeared to exist in the prey-predator.     

Investigations on macrozoobenthos in Lake Grevelingen,with special emphasis on the role of polychaetes (V)

Summary An outline has been given of the soft-bottom macrozoobenthic research in Lake Grevelingen, after its creation in 1971. A faunistic study aims at assessing the effect of the closure of the former estuary on the species composition, diversity, and distribution of the benthic macrofauna. The main project is a study into the biomass and production of the macrozoobenthos, in order to estimate its role in the carbon cycle in the lake.As regards the faunistic work, a preliminary species-balance has been presented for molluscs and polychaetes. The total number of mollusc species hardly changed after the closure, the number of polychaetes decreased with about one quarter. Nearly all disappeared species were rare or rather scarce in the Grevelingen estuary and most of them may be regarded as typical North Sea species. Several newcomers have also been recorded after the closure. The strong river influence in the former estuary causing wide salinity fluctuations, possibly selected for more hardy species, and these species obviously are able to survive quite well in the present brackish lake.Mean mollusc biomass in April decreased in the first years after the closure. In 1973 it amounted to only 11 g ash-free dry weight.m^–2. In view of the preliminary estimate for 1977 (over 50g ash-free dry weight.m^–2) a recovery has taken place.Up till 1976 polychaete biomasses were assumed to be unimportant in Lake Grevelingen, reason to ignore them in benthic production studies. A survey with a Van Veen bottom grab seemed to confirm this: mean April biomass in 1977 was only 2.6 g ash-free dry weight.m^–2. However, especially in coarser sediments this bottom grab inadequately samples the bottom fauna. Diver-taken cores proved that, on average, polychaetes live deeper than molluscs and are relatively much more underestimated with the Van Veen grab. Moreover, sieving techniques used are not appropriate for many of the fragile polychaete species. In a special polychaete research at three permanent stations a mean annual biomass of 7.5–12.4 g ash-free dry weight was estimated. Mainly based on P/B ratios from the literature a conservative production estimate for these three stations gave values of 16–25 g ash-free dry weight.m^–2.yr^–1. This indicates an important role for polychaetes in the benthic ecosystem of Lake Grevelingen.     

Changes in the flora of some Aegean islets 1968–2000

The flora of 17 islets was studied during the period 1968–2000, with thorough inventories from 1971. At each visit the species present and their population sizes were noted. The flora of the smallest islets of hard rock consisted mainly of perennials, and remained unchanged in terms of species present throughout the period of study. In the larger and more complex islets the major part of the flora consisted of islet-specialised taxa staying for long periods of time. To them are added some other mostly casual species from the close large islands, introduced by human influence, birds or winds and standing for most of the turnover in the islets flora. Few changes were observed in the plant communities of rock crevices, the spray zone of the shores and other constant habitats. The dominant perennial species forming layer of shrubs or subshrubs also mostly remained the same. Most of the changes concerned soil spaces opened by animals or erosion. Most annual species were found to survive by an extreme seed bank strategy. Many taxa common on the neighbouring islands were lacking or casual on the islets. Some others reached dominance or high frequencies that have not been observed on islands or in mainland areas. The conditions for the flora on the Aegean islets are considered to differ fundamentally from that on large isolated islands because they are situated comparatively close among each other and to islands and mainland areas. They are also vulnerable towards catastrophic events and therefore frequently presenting opened targets for invasions. The islet-specialised taxa are found to retain good ability for dispersal over moderately long distances. The grazing of the islets is stated to be an important factor for the evolution of islet adapted and specialised taxa.     

The Planktonic Index of Biotic Integrity (P-IBI): An approach for assessing lake ecosystem health

Using historical (1970) and more recent (1996) Lake Erie plankton and trophic status data, we developed a Planktonic Index of Biotic Integrity (P-IBI) to measure changes in lake ecosystem health. We used discriminant analysis to determine phytoplankton and zooplankton community characteristics (metrics) that distinguished among levels of impairment. Traditional measures of lake trophic status classes (i.e., oligotrophic, mesotrophic, eutrophic), such as chlorophyll a and total phosphorus concentrations, were used to classify sites on a gradient of impairment. We then judged the ability of plankton metrics to distinguish among trophic status classes. Because of the temporal variability found in plankton communities, we conducted analyses on a monthly basis (May–September). For June, July and August we found five unique metrics that could distinguish among trophic status classes. The P-IBI showed an increase in water quality in Lake Erie between 1970 (<3 = eutrophic) and the mid-1990s (1996 and 1997) (3–4 = mesotrophic) (which reflected mean (±standard error) total phosphorus concentrations (μg/L) 1970 > 1996; western basin (41.53 ± 2.68 > 29.75 ± 1.39), eastern basin (14.84 ± 0.82 > 7.74 ± 0.28) and mean (±standard error) chlorophyll a concentrations (μg/L) uncorrected for pheophytin 1970 > 1996; western basin (12.58 ± 1.82 > 5.40 ± 0.22), central basin (5.90 ± 0.36 > 3.17 ± 0.54), and eastern basin (5.17 ± 0.38 > 1.67 ± 0.18)), with declining water quality in the late 1990s (1998 and 1999) (3) and 2002 (<3). We recommend that the techniques used in creating the P-IBI be investigated for determining ecosystem health of other lakes.     

Zooplankton community response to reservoir aging

Changes in zooplankton diversity and density in response to reservoir aging in Pawnee Reservoir were investigated. Zooplankton samples collected from April 1992 through April 1993, were compared to a similar study conducted after initial impoundment by Helzer (1971), in 1968–1970. Since this initial study, increases in turbidity and resulting changes in biotic interactions significantly altered the zooplankton community. A significant increase in total zooplankton density and a decrease in species richness were observed between study periods. Density increased from 24.6 to 95.4 individuals L^–1, while the number of taxa declined from fourteen to ten. During this time period, Cyclops vernalis became the dominant zooplankter in the reservoir. The density of this predatory copepod increased significantly, from 0.1 l^–1 in 1968–1970, to 44.3 l^–1 in 1992–1993, which accounted for most of the increase in total zooplankton density. Though a greater spring maximum of another dominant, Bosmina spp. was found during the 1992–1993 study period, the annual density of this cladoceran was not significantly different between study periods. Similar trends for Daphnia ambigua and D. parvula were also observed, as greater spring maxima levels were attained, however overall annual densities were not significantly different. The dominance of C. vernalis (46% of annual density) and Bosmina spp. (33%), indicate that these two zooplankters were tolerant of changes in physical conditions resulting from reservoir aging and biotic interactions that followed in the reservoir during the 22 years between study periods.     

Introduced species as moving targets: changes in body sizes of introduced lizards following experimental introductions and historical invasions

Introduced species usually fail to establish, but when they succeed, may undergo character release and rapid evolutionary divergence in novel environments. We collected brown anoles (Anolis sagrei: Lacertilia: Iguanidae) from a single Florida population and released them onto two ecologically different dredge-spoil islands in central Florida (forested and non-forested) and measured differences in population growth, individual growth, body size, and condition over four years. The population on the non-forested island expanded twice as fast as the forested island population and reached a density of ca. 12,000 lizards ha^–1 and a biomass of ca. 43.3 kg ha^–1, among the largest values recorded for non-aggregated terrestrial vertebrates. First-year progeny grew larger than their surviving parents on both islands, indicating character release occurred in early stages of both invasions. However, in subsequent years, lizards became larger on the forested island, but smaller on the non-forested island. Body condition declined over time on both islands, but the effect was most dramatic on the non-forested island. Lizards on the forested island had the lowest survival rates and highest tail autotomy frequencies. These results were attributed to differences in abiotic and biotic conditions on the two islands. Brown anoles are generally larger on islands where they have been introduced than on their native Caribbean islands, and are much larger on mainlands than on islands, indicating character release occurred at larger geographic scales as well. Habitat influences the morphology of introduced species possessing the ability to rapidly adapt to local conditions, presenting invasive species managers with moving targets.     

Genetic Diversity in Remnant Mainland and “Pristine” Island Populations of Three Endemic Australian Macropodids (Marsupialia): Macropus Eugenii, Lagorchestes Hirsutus and Petrogale Lateralis

Since European settlement, mainland Australia has experienced a wave of mammal extinctions and population declines. However, some species have persisted on off-shore islands, which are now viewed as important wildlife refuges. In this study, we assessed the level of genetic diversity, at 7–11 microsatellite loci, in island and remnant mainland populations of three endemic species of macropodid marsupial; the tammar wallaby Macropus eugenii(n = 92); rufous hare-wallaby Lagorchestes hirsutus(n = 40) and black-footed rock-wallaby Petrogale lateralis(n = 164). There was a consistent pattern of significantly higher levels of microsatellite diversity in the remnant mainland population (A= 4.9–13.9; He= 0.61–0.86) of each species compared to conspecific pristine island populations (A= 1.2–3.7; He= 0.05–0.44). These marked differences are even apparent where island populations currently have a substantially larger census size. In addition, island populations were substantially inbred (Fe= 0.49–0.91). Although island populations have been insulated from the relatively recent threatening processes operating on the mainland, they have nevertheless been significantly impacted by increased inbreeding and the substantial erosion of genetic diversity. Despite the difficulties of ensuring the survival of remnant mainland populations, they appear to retain substantially more genetic diversity than their island counterparts and therefore are more likely to contribute to the long-term persistence of their species. These data also demonstrate that small remnant mainland populations (n < 10–20) are often capable of rapid recovery and are not necessarily genetically depauperate.     

Nitrogen isotope ratios shift with plant size in tropical bromeliads

We describe an ontogenetic shift in nitrogen (N) isotopic values in two rosette-forming epiphytic bromeliads. Leaf tissue N isotope values of small individuals of two bromeliad species (mean –6.2) differed from those of large individuals within each species (mean –0.5). Using references for potential N sources, we calculated the relative contribution of autochthonous (soil-derived through leaf litter) and allochthonous (atmospheric deposition) N with a two-member mixing model. Atmospheric sources contributed as much as 77–80% of the N in small individuals, whereas soil-derived N contributed 64–72% (conservative reference value) to 100% (less conservative reference value) of leaf tissue N in large plants. Shifts in N source with increasing plant size may be important aspects of rainforest complexity, an understudied aspect of ecosystem diversity.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Rotifer communities of floodplain lakes of the Brahmaputra basin of lower Assam (N.E. India): biodiversity, distribution and ecology

The rotifer communities of 15 acidic – alkaline and soft – marginally hard water floodplain lakes of the lower Assam valley of the Brahmaputra river basin, characterized by low ionic concentrations, reveal 164 species (178 taxa) belonging to 39 genera and 20 families and represent the richest biodiversity known to date in these ecotones of the Indian subcontinent. Nine species are new to the Indian Rotifera. Cosmopolitan (59.7%) > pantropical (15.2%) > cosmotropical (12.2%) species dominate the taxocoenosis. Biogeographically interesting elements constitute a notable component (13.4%); important members of this category include six Oriental, two Australasian and seven Palaeotropical species. The examined fauna depicts a tropical character with predominance of Lecanespp. (28.0%). Littoral or periphytic rotifers (76.2%) dominate the planktonic species. Rotifers comprise a dominant qualitative (67–103, 79.1±11.0 species) and an important quantitative (mean: 41.1–65.9%) component of zooplankton in all floodplain lakes, register a moderate diversity (mean: 2.036–2.642), low dominance (mean: 0.019–0.216) and high evenness (mean: 0.840–0.893). The examined material indicates several interesting acidophilous elements. Richness depicts significant inverse correlation with pH. Water temperature, conductivity, dissolved oxygen and alkalinity record significant direct relationships with the rotifer abundance. Diversity is influenced by abundance and is also directly correlated with water temperature and conductivity. Canonical analysis shows a notable cumulative impact of six abiotic factors on richness, density and diversity.     

Environmental controls on the photosynthesis and respiration of a boreal lichen woodland: a growing season of whole-ecosystem exchange measurements by eddy correlation

Measurements of net ecosystem CO₂ exchange by eddy correlation, incident photosynthetically active photon flux density (PPFD), soil temperature, air temperature, and air humidity were made in a black spruce (Picea mariana) boreal woodland near Schefferville, Quebec, Canada, from June through August 1990. Nighttime respiration was between 0.5 and 1.5 kg C ha^–1 h^–1, increasing with temperature. Net uptake of carbon during the day peaked at 3 kg C ha^–1 h^–1, and the daily net uptake over the experiment was 12 kg C ha^–1 day^–1. Photosynthesis dropped substantially at leaf-to-air vapor pressure deficit (VPD) greater than 7 mb, presumably as a result of stomatal closure. The response of ecosystem photosynthesis to incident PPFD was markedly non-linear, with an abrupt saturation at 600 mol m^–2 s^–1. This sharp saturation reflected the geometry of the spruce canopy (isolated conical crowns), the frequently overcast conditions, and an increase in VPD coincident with high radiation. The ecosystem light-use efficiency increased markedly during overcast periods as a result of a more even distribution of light across the forest surface. A mechanistic model of forest photosynthesis, parameterized with observations of leaf density and nitrogen content from a nearby stand, provided accurate predictions of forest photosynthesis. The observations and model results indicated that ecosystem carbon balance at the site is highly sensitive to temperature, and relatively insensitive to cloudiness.     

Can ecology help genomics: the genome as ecosystem?

Ecologists study the rules that govern processes influencing the distribution and abundance of organisms, particularly with respect to the interactions of organisms with their biotic and abiotic environments. Over the past decades, using a combination of sophisticated mathematical models and rigorous experiments, ecologists have made considerable progress in understanding the complex web of interactions that constitute an ecosystem. The field of genomics runs on a path parallel to ecology. Like ecology, genomicists seek to understand how each gene in the genome interacts with every other gene and how each gene interacts with multiple, environmental factors. Gene networks connect genes as complex as the webs that connect the species in an ecosystem. In fact, genes exist in an ecosystem we call the genome. The genome as ecosystem is more than a metaphor – it serves as the conceptual foundation for an interdisciplinary approach to the study of complex systems characteristic of both genomics and ecology. Through the infusion of genomics into ecology and ecology into genomics both fields will gain fresh insight into the outstanding major questions of their disciplines.     

Fish populations in the Paraná River: Lentic environments of Diamante and San Pedro Areas (Argentine Republic)

Data on the fish populations of lentic water bodies of the Lower Paraná River in the Diamante and San Pedro areas (33°40–31°55 S, 59°40'–60°40 W), sampled during 1971 are given. Limnological characteristics such as surface area and depth of ponds, water turbidity, and plant cover are included. Differences in fish population size, structure, specific diversity, dominance, and biomass of particular species are established between two areas in a dry season.     

Carbon dioxide and water vapor exchange in a warm temperate grassland

Grasslands cover about 40% of the ice-free global terrestrial surface, but their contribution to local and regional water and carbon fluxes and sensitivity to climatic perturbations such as drought remains uncertain. Here, we assess the direction and magnitude of net ecosystem carbon exchange (NEE) and its components, ecosystem carbon assimilation (A _c) and ecosystem respiration (R _E), in a southeastern United States grassland ecosystem subject to periodic drought and harvest using a combination of eddy-covariance measurements and model calculations. We modeled A _c and evapotranspiration (ET) using a big-leaf canopy scheme in conjunction with ecophysiological and radiative transfer principles, and applied the model to assess the sensitivity of NEE and ET to soil moisture dynamics and rapid excursions in leaf area index (LAI) following grass harvesting. Model results closely match eddy-covariance flux estimations on daily, and longer, time steps. Both model calculations and eddy-covariance estimates suggest that the grassland became a net source of carbon to the atmosphere immediately following the harvest, but a rapid recovery in LAI maintained a marginal carbon sink during summer. However, when integrated over the year, this grassland ecosystem was a net C source (97 g C m^–2 a^–1) due to a minor imbalance between large A _c (–1,202 g C m^–2 a^–1) and R _E (1,299 g C m^–2 a^–1) fluxes. Mild drought conditions during the measurement period resulted in many instances of low soil moisture (<0.2 m³m^–3), which influenced A _c and thereby NEE by decreasing stomatal conductance. For this experiment, low had minor impact on R _E. Thus, stomatal limitations to A _c were the primary reason that this grassland was a net C source. In the absence of soil moisture limitations, model calculations suggest a net C sink of –65 g C m^–2 a^–1 assuming the LAI dynamics and physiological properties are unaltered. These results, and the results of other studies, suggest that perturbations to the hydrologic cycle are key determinants of C cycling in grassland ecosystems.     

Electrophoretic behavior of the H+-ATPase proteolipid from bovine heart mitochondria

The proteolipid subunit of H⁺-ATPase was labeled by [¹⁴C]N,N-dicyclohexylcarbodiimide in bovine heart mitochondria. The radioactive labeling was followed using various systems of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). When using discontinuous SDS-PAGE (Laemmli, U.K., 1970,Nature (London)227, 680–685) a monomeric (Mr 7600±1500) and a dimeric form (Mr 17,800±1200) of the proteolipid were detected, while only the monomeric form was found on urea (8 M) containing gels (SDS-PAGE according to Laemmli; or Swank, R. T., and Munkers, K. D., 1971,Anal. Biochem. 39, 462–477). When using SDS-PAGE with Na-P_i buffer (Weber, K., and Osborn, M., 1969,J. Biol. Chem. 244, 4406–4442), only a dimeric form of the proteolipid (Mr 15,000±1000) was detected. Experimental data indicate that the different patterns of proteolipid separation are related to the presence of the two distinct proteolipid conformations in the SDS solution.