Phagotrophy and NH4+ regeneration in a three-member microbial food loop

In a series of batch experiments we compared the efficiencyof nitrogen regeneration of a two- and three-member microbialfood loop consisting of a mixed bacterial assemblage, a small(3–5 µm) heterotrophic flagellate (Paraphysomonassp.), and a large (7–12 µm) heterotrophic flagellate(Paraphysomonas imperforata). In the two-member system the nitrogenregeneration efficiency for NH₄⁺ (R_n) was 41% and the grossgrowth efficiency (GGE) was 57% during active grazing by thesmall flagellate on bacteria. Regeneration of NH₄⁺ continuedduring the stationary phase so that R_n was 75% after 6 daysincubation. When the larger flagellate was introduced at theend of exponential growth of the smaller grazer in the three-membersystem, initially there was rapid regrowth of bacteria, tyingup 15% of the nitrogen originally in the bacteria. The largerflagellate grazed the smaller one with a GGE of 55%. Total nitrogenregeneration efficiency through exponential growth of the largerflagellate was 73%. Because microbial food loops in naturalwaters are far more complicated and with more grazing stepsthan portrayed in this study, we would expect the bulk of nutrientswithin these systems to be recycled with little transfer tohigher trophic levels.     

Inorganic carbon uptake by phytoplankton in vineyard sound,Massachusetts. I. Measurements of the photosynthesis-irradiance response of winter and early-spring assemblages

The photosynthesis-irradiance dependence of natural phytoplankton assemblages from surface waters of Vineyard Sound, Massachusetts, was investigated over a several month period during late winter —early spring, 1982, when water temperatures were ? 0.5 to 8.5°C. Maximal photosynthetic rates not only were consistently observed between 7–15% I₀, but were substantially higher than previously reported rates for cold-water assemblages, averaging 10–20 μg C · μg Chl a^?1 · h^?1. At higher light intensities photo-inhibition was severe and developed within minutes to tens of minutes of the start of the experiment. Several lines of evidence, however, suggest that photoinhibition in situ may be much less that that measured in incubations of > 30 min duration; residence time of phytoplankton at surface light intensities is sufficiently short, and adaptation of photosynthetic capacity appears to have occurred to approximately the mean depth of the water column. These results further highlight the importance of establishing the time-dependent photosynthetic responses of phytoplankton and the relationship to the physical mixing regime in estimating primary productivity.     

Individual differences in the ability to recognise facial identity are associated with social anxiety

Previous research has been concerned with the relationship between social anxiety and the recognition of face expression but the question of whether there is a relationship between social anxiety and the recognition of face identity has been neglected. Here, we report the first evidence that social anxiety is associated with recognition of face identity, across the population range of individual differences in recognition abilities. Results showed poorer face identity recognition (on the Cambridge Face Memory Test) was correlated with a small but significant increase in social anxiety (Social Interaction Anxiety Scale) but not general anxiety (State-Trait Anxiety Inventory). The correlation was also independent of general visual memory (Cambridge Car Memory Test) and IQ. Theoretically, the correlation could arise because correct identification of people, typically achieved via faces, is important for successful social interactions, extending evidence that individuals with clinical-level deficits in face identity recognition (prosopagnosia) often report social stress due to their inability to recognise others. Equally, the relationship could arise if social anxiety causes reduced exposure or attention to people's faces, and thus to poor development of face recognition mechanisms.     

Video plankton recorder reveals high abundances of colonial Radiolaria in surface waters of the central North Pacific

Colonial spumellarian Radiolaria are heterotrophic protiststhat form large (up to several meters in length), gelatinousstructures in the surface waters of all tropical and subtropicaloceanic ecosystems. These species are morphologically and trophicallycomplex and some, but not all, produce silica skeletal structuresof considerable paleontological significance. Skeletonless speciesof Radiolaria are poorly sampled by plankton nets, which canseverely damage these delicate organisms. Therefore, abundancesof colonial Radiolaria typically have been underestimated inquantitative studies of zooplankton abundance and biomass. Herewe document the abundances of colonial Radiolaria in the centralNorth Pacific based on analysis of video images from a miniaturizedvideo plankton recorder. We observed abundances of radiolariancells in colonies that exceeded previous reports of total Radiolariaby more than ten-fold, and counts of skeleton-bearing Radiolariaby more than two to three orders of magnitude. Biomass (carbon)within these colonies was similar to or greater than the totalradiolarian biomass (i.e. including all solitary species) previouslyreported for the Pacific. Symbiont productivity within colonialRadiolaria was estimated to constitute a modest but significantfraction of total primary productivity (up to     

Mitochondrial genome distribution in histochemically cytochrome c oxidase-negative muscle fibres in patients with a mixture of deleted and wild type mitochondrial DNA.

In situ hybridization studies were performed on a series of chronic progressive external ophthalmoplegia patients harbouring large mitochondrial DNA deletions, using intra- and extra-deletional probes. Clear differences in the distribution of wild type and deleted mitochondrial genomes were seen in both ragged-red and non-ragged red, cytochrome c oxidase-negative fibres, with an accumulation of deleted genomes in the subsarcolemmal zone. Wild type genome content was normal or decreased in the cytochrome c oxidase-negative regions of one case, but in two patients, wild type mtDNA content in cytochrome c oxidase-negative regions was either normal (most fibres) or increased (occasional fibres). The latter observation suggests there may be a stage in the natural history of ragged-red fibre evolution where wild type genomes are transiently increased. The significance of this finding is discussed.     

Inorganic carbon sources and biomass regulation in intensive microalgal cultures

Three freshwater and one marine algal species were grown under inorganic carbon limitation in laboratory continuous cultures. Comparisons were made between HCO₃^? alkalinity and bubbled CO₂ as carbon sources. HCO₃^? alkalinity was an excellent source of inorganic carbon below specific pH levels, but chemical precipitation at high pH placed an upper limit on productivity that was far lower than potential light-limiting levels. With bubbled CO₂ it was possible to achieve light limitation. The main factor controlling productivity was the mass flux of inorganic carbon added to the culture, which is the product of gas flow rate and influent P level. Small bubbles were more efficient than large bubbles at low gas flow rates and P levels, but led to froth flotation of algal cells and concomitant reductions in productivity at high bubble rates. At 1% CO₂ productivity was still dependent on mass fluxes of added carbon, but was independent of bubble size. At high bubble rates with 1% CO₂ narcosis was evident. Maximum yields occurred at intermediate dilution rates when inorganic carbon was supplied via bubbled gas.