Martin E. Boraas

Phagotrophy by a flagellate selects for colonial prey: A possible origin of multicellularity

Predation was a powerful selective force promoting increased morphological complexity in a unicellular prey held in constant environmental conditions. The green alga, Chlorella vulgaris, is a well-studied eukaryote, which has retained its normal unicellular form in cultures in our laboratories for thousands of generations. For the experiments reported here, steady-state unicellular C. vulgaris continuous cultures were inoculated with the predator Ochromonas vallescia, a phagotrophic flagellated protist (‘flagellate’). Within less than 100 generations of the prey, a multicellular Chlorella growth form became dominant in the culture (subsequently repeated in other cultures). The prey Chlorella first formed globose clusters of tens to hundreds of cells. After about 10–20 generations in the presence of the phagotroph, eight-celled colonies predominated. These colonies retained the eight-celled form indefinitely in continuous culture and when plated onto agar. These self-replicating, stable colonies were virtually immune to predation by the flagellate, but small enough that each Chlorella cell was exposed directly to the nutrient medium.

Selenium uptake and transfer in an aquatic food chain and its effects on fathead minnow larvae

The transfer of Se (Na2SeO4) was followed through a laboratory food chain (wateralgae-rotifer-larval fish) and its effect on larval fathead minnows (Pimephales promelas). Selenium transfer between algae (Chlorella pyrenoidosa) and rotifers (Brachionus calyciflorus) was a function of time and food availability. Selenium concentrations in the rotifers ranged from 46 to 91Μg Se · g−1 dry weight after 5 hr of feeding. Selenium concentrations (±SD) in larval fish reached 61.1±1.1 Μg Se · g−1 dry weight for 9 day-old larvae and 51.7+1.6 Μg Se · g−1 for 17 day-old larvae after 7 and 9 days of feeding with Se-contaminated rotifers, respectively. Final dry weights of larvae fed Se-contaminated rotifers were significantly lower than those of controls, although acute toxicity (mortality) was not demonstrated. The biological halflife of food-derived Se in the larvae was 28 days.

Variations in Sediment Accumulation Rates and the Flux of Labile Organic Matter in Eastern Lake Superior Basins

Abstract Benthic environments in Lake Superior are variable and dynamic. The complex topography and morphology of eastern Lake Superior results in a variety of depositional environments, from shallow coastal bays to deep profundal basins. Direct observations of bottom types and collection of sediments across the gradient in environments reveal benthic systems that range in sediment accumulation rates from ∼1.7 mm per year to virtually zero net long-term accumulation. Diagenetic modeling of organic carbon and nitrogen under steady state conditions indicate that 15% to 40% of the organic carbon and nitrogen deposited is recycled into the overlying water. This “metabolizable” fraction has a residence time in the sediment column estimated to be 30 to 60 years for organic carbon and 15 to 30 years for nitrogen. Concentration gradients of total dissolved inorganic carbon, ammonium, and oxygen in sediment pore waters yield fluxes of remineralized carbon and nitrogen across the sediment-water interface consistent with diagenetically modeled fluxes. Spatial variability in sediment accumulation patterns, however, is great, particularly in the deep, steep relief basins in the open lake. Here, distances of a few kilometers can radically alter deposition patterns. Evidence of aperiodic bottom currents were observed in the deepest charted basin of the lake as extensive fields of sediment ripples over hard, compacted relict silt and clays. While no currents were observed in these summertime dives, it is assumed that storms during isothermal conditions generate suffficient bottom currents at depth to very effectively scour the bottom. Differences in sediment metabolism appear to be determined by the flux of labile organic matter to the bottom coupled to the physical processes of sedimentation, resuspension, and horizontal transport.

Isolation of a fast-growing strain of the rotifer Brachionus calyciflorus Pallas using turbidostat culture

Abstract The rotifer Brachionus calyciflorus Pallas was grown in turbidostat culture, where the population (a clone) was forced to grow at its maximum specific growth rate ( μ max ) for a 14-month period. During this period, the μ max increased 51% from 0.053/h (doubling time=13.1 h) to 0.080/h (d.t.=8.7 h) after 8 months, the highest growth rate yet reported for a metazoan. The ability to grow rapidly was not lost when the rotifers were maintained at a low growth rate for 5 months (50 culture generations), indicating the elevated μ max was due to a change in genetic composition or expression. Our procedure for increasing a populations μ max should be applicable to other rotifer and metazoan species, and be instrumental in increasing mass production of rotifers for aquacultural purposes.

Effects of sodium and phosphate on growth of cyanobacteria

Abstract We conducted laboratory experiments to evaluate the effects of NaCl and phosphorus enrichments on natural phytoplankton assemblages from Lake Michigan in continuous-flow systems, at a dilution rate of 0.25 d−1. The experiment was repeated four times, 1981–1982, using freshly-collected natural lakewater inocula and temperature regimes typical of near-surface waters at initiation (6, 12, 16 and 20°C), at two levels of PO4−P (1–2 vs 91–92 μg l−1) and of Na+ (3–4 vs 9–10 mg l−1) each time. As a single factor, sodium chloride enrichments had no significant effect on growth rates or densities of cyanobacteria in cultures containing natural phytoplankton assemblages from Lake Michigan. However, filamentous cyanobacteria proliferated in the presence of elevated phosphorus concentrations, both with and without concurrent NaCl additions, particularly in warmer waters. Our laboratory results were consistent with the hypothesis that cyanobacteria are favored in phytoplankton of large lakes with low N:P ratios.

Toxicity of the Chrysophyte flagellate Poterioochromonas malhamensis to the rotifer Brachionus angularis

The toxicity of the chrysophyte flagellate Poterioochromonas malhamensis to the rotifer Brachionus angularis was investigated. Fed rotifers exposed to the flagellate experienced a mortality rate indistinguishable from starvation. Unfed rotifers exposed to the flagellate experienced a higher mortality rate. The mortality rate appears to depend on the flagellate concentration. Higher doses of flagellates resulted in quicker rotifer death. These laboratory results are consistent with the hypothesis that the occurrence of B. angularis in the field may be negatively related to the presence of P. malhamensis and related flagellates.

Ecology of micro-organisms in a small closed system - Potential benefits and problems for Space Station

The inevitble presence on the space station of microorganisms associated with crew members and their environment will have the potential for both benefits and a range of problems including illness and corrosion of materials. This report reviews the literature presenting information about microorganisms pertinent to Environmental Control and Life Support (ECLS) on the space station. The perspective of the report is ecological, viewing the space station as an ecosystem in which biological relationships are affected by factors such as zero gravity and by closure of a small volume of space. Potential sites and activities of microorganisms on the space station and their environmental limits, microbial standards for the space station, monitoring and control methods, effects of space factors on microorganisms, and extraterrestrial contamination are discussed.

In vitro antagonism of bioluminescent fungi by Trichoderma harzianum

Two species of bioluminescent fungi, Panellus stypticus and Omphalotus olearius were placed in contact with three different strains of interfungal pathogenic Trichoderma harzianum. Subsequent light emission by the luminous fungi and advance of the interfungal pathogens were compared. Relative differences among the pathogens were reflected in their rate of mycelial advance, the total area over which they produced spores upon the host fungi, and decreases in host bioluminescence. After ten days differences in the total surface areas of spore production varied from 1 to 53 per cent. Differences in the reduction of bioluminescence of the same material ranged over 2 orders of magnitude. Final reduction in luminescence ranged over 6 orders of magnitude. A marked reduction in bioluminescence was observed to precede the advance of spore production. The greatest reduction in luminescence was correlated with the presence of T. harzianum hyphae. Two strains of T. harzianum, NRRL 1698 and ATCC 58674, were effective against both bioluminescent fungi within the study period while a third strain, NRRL 13019, was only effective against Omphalotus olearius.

Influence of experimental conditions on nitrogenous excretion by Lake MichiganMysis relicta (Lovén): laboratory studies with animals acclimated inFragilaria

In laboratory experiments, rates of excretion of ammonia and urea by Lake MichiganMysis relicta were compared for animals incubated in the presence and the absence of algal food (Fragilaria crotonensis chemostat outflow). Prior to experiments, all animals were acclimated to laboratory conditions and the experimental food for 2–4 weeks. Algae used in experiments were enriched in the dark with nutrients (N and P) prior to experimental incubation.There were no significant differences in the ammonia and urea excretion rates of mysids incubated in filtered water compared to those inFragilaria cultures, or in ammonia excretion rates either as a function of individual size or sex of the mysid or of its having been held at 5 °C, 10 °C, or 15 °C. Ammonia excretion rates measured between 4 and 8 h of incubation were significantly higher than those between 1–3 h and 8–15 h, for mysids held both in filtered water and inFragilaria cultures. The results are compared to those from shipboard incubations in a previous study and are discussed with respect to physiological regulation of nitrogenous waste production.

Comparison of population dynamics between slow- and fast-growing strains of the rotifer Brachionus calyciflorus pallas in continuous culture

SummaryThe population dynamics of a slow- and a fast-growing strain of the rotifer Brachionus calyciflorus are compared. Rotifers were grown in steady-states, at various specific growth rates (μ), in both two-stage chemostat and turbidostat cultures on the green alga Chlorella pyrenoidosa. Population variables, including specific ingestion (I), loss (L) and filtration (F) rates, yield (Y), production (P) and half-saturation coefficient of growth (Kg), were calculated using a growth model based on saturation kinetics. I, L, F and Kg were shown to be higher and Y and P lower for the fast-growing strain. Differences between the two strains with regard to these variables may represent tradeoffs associated with the faster potential growth rate. Steady-state relationships between these values and μ for the fast-growing strain, however, deviated from model predictions which suggest a possible shift from carbon to non-carbon growth limitation.