Predatory Organisms Research Articles

A performance evaluation of a full scale rotating biological contactor (RBC) system

Abstract A full‐scale rotating biological contactor (RBC) was tested for its performance in removing soluble BOD and nitrogen. The system removed 88 percent of the incoming EOD, with an average effluent soluble BOD of 10 mg/l. The ammonia nitrogen removal efficiency was only 70 percent, much lower than expected. Considering the fact that conditions were favourable for the growth of nitrifying bacteria, the problem was thought to be due to the heavy population of predator organisms residing on the last stage of the system.

Boring Late Cambrian organisms

Specimens of inarticulate brachiopods (family Acrotrctidae) with boreholes were found in Upper Cambrian carbonates in the southern Great Basin of the United States. Some morphologic features and preferred orientation of the borings are similar to those made by predators and previously reported in the fossil and Holocene record. Such predatory activity on brachiopods is previously unknown in Cambrian rocks. Taxa associated with these specimens are not known to have been predators and identity of the predatory organism is unknown. Cambrian brachiopods, predation, paleoecology.

Cell-Cell Interactions and Development in Myxococcus Xanthus

Myxococcus xanthus is a gram-negative, rod-shaped bacterium which shows complex cell-cell interactions during vegetative growth and fruiting-body formation. In nature, Myxococcus xanthus grows and moves as a large community of food gathering and predatory organisms. Cell-cell contact is maintained throughout vegetative growth and characteristic behaviors are exhibited in the presence of certain stimuli. In addition, cell-cell stimulation can be observed in the movement of cells. Thus there must exist specific chemical signals that help direct the movement of individual cells within the community. The most dramatic behaviors exhibited by Myxococcus xanthus are associated with starvation. Starved cells aggregate and then sporulate within raised mounds. Complex biochemical changes which are part of a developmental program occur in these cells. For example, protein S first appears in the cytoplasmic fraction of cells, and is later translocated to the cell surface where it self-assembles to form a spore surface coat. Another new developmental protein that is synthesized at this time is myxobacterial hemagglutinin, a lectin that accumulates in the shockable fraction of developmental cells and that has been located in distinct patches at the cell poles. This protein may be important in end-to-end associations during cellular aggregation. Cell-cell signalling has also been found to be important during fruiting-body formation. Certain non-fruiting mutants can be stimulated to fruit by wild-type cells or by mutants from a different extracellular complementation group. Analysis of mutants has shown that the developmental program in Myxococcus xanthus appears to have two major components: one controls aggregation; the other regulates sporulation. Links exist between these two components, since some developmental mutants are defective in both functions. The study of cell-cell interactions during vegetative growth and fruiting-body formation in M. xanthus provides an opportunity to analyze complex interactions in a simple model system.

Mathematical models for continuous culture growth dynamics of mixed populations subsisting on a heterogeneous resource base. II. Predation and trophic structure

Models are presented for the joint dynamics of predators and prey, maintained in continuous flow chemostat culture. The predators are visualized as subsisting on one or more prey organisms, which in turn are visualized as subsisting on one or more substrate resources supplied by the investigator. The dynamic equations are translated into an analogous Lotka-Volterra predation model, and the criteria for the existence and stability of various equilibria are indicated. Denoting the number of different predator organisms as N H , the number of different prey organisms by N I and the number of different substrates as N J , it is shown that the joint coexistence of all components requires 0 ⩽ N I − N H ⩽ N J . The model is extended to more complex situations by including additional trophic layers and by allowing trophic layer “leap-frogging.” The model may always be translated into an approximately quadratic differential equation of the Lotka-Volterra type. The α- and β-coefficients of these latter are really variables, and become quite complex for some of the multi-layered models.

Internal nitrogen cycling compared in surface samples of an Andept and a Mollisol

This study was conducted to examine the hypothesis that slow N mineralization and associated organic matter accumulation in Andept, was related to the internal N cycling regime, and if so, to determine at what stage. The results indicated that N was mineralized from native organic matter in an Andept less rapidly than occurred in a Mollisol of similar organic matter content but N mineralization from added alfalfa was similar in both soils. Both soils immobilized N rapidly in the presence of glucose, but remineralization of immobilized N was more rapid in the Mollisol than in the Andept samples. Partial sterilization resulted in substantial remineralization of N from both soils. It was concluded that slow N mineralization in the Andept soil is due to slow N recycling from recently synthesized biomass. Associated with this is a low supply of soluble C in the Andept soil. Whether slow N recycling from recently synthesized biomass results from some toxic effect on predatory organisms, from lytic enzyme adsorption, adsorption of lytic products or some mineral nutrient deficiency awaits further study.

Dietary habits of fish populations in the Lower Medway Estuary

Populations of mainly first‐year fish overwinter in the Medway Estuary, an area offering shelter and a rich and varied food supply. In the absence of previous investigations, the present study examines the dietary habits of four fish species; gadoids Merlangius merlangus and Trisopterus luscus, and pleuronectids Platichthys flesus and Pleuronectes platessa.Gadoids fed predominantly on fast moving nektonic organisms such as brown shrimps, mysids and fish while pleuronectids preferred the slower moving tubificid and polychaete worms. Seasonal fluctuations of the dietary constituents are considered in relation to changes within the populations of both prey and predator organisms.

Report on a biochemical red tide repressive agent.

Organisms were isolated from the November 1973 red tide outbreak in a search for a naturally occurring predator organism. Two organisms were found which look promising as a means of biocontrol: a Tintinnideae spp., ciliate and Gomphosphaeria aponina Kutzing, a blue-green algae. This report characterizes a blue-green algal toxin found to be lethal to the Florida red tide organism Gymnodinium breve Davis.

Experimental and mathematical modeling studies of protozoan predation on bacteria

AbstractThe predation of bacteria by protozoan in both continuous and batch cultures was studied using experimental and modeling techniques. The predator organism was the ciliate, Tetrahymena pyriformis. The bacterium, Aerobacter aerogenes, served as the prey. Several batch growth responses were observed each initiated at a different nutrient level. Continuous cultures were conducted over a range of dilution rates. The models studied were partially successful in simulating the empirical data. Deviations between the model and the actual population behavior are discussed and possible explanations for the differences proposed.

Notes on Some Natural Enemies of Utah Black Flies (Diptera: Simuliidae)

Immature and adult black flies are often victims of various predatory or parasitic organisms. Observations on certain of these organisms were made in Utah over a period of several years, and are presented below to stimulate further interest in the natural enemies of the Simuliidae.

SOUND PRODUCTION IN THE SPINY LOBSTER PANULIRUS ARGUS (LATREILLE) ,

1. The intricate stridulatory mechanism of the West Indian spiny lobster Panulirus argus, and the sounds it produces are described. The sounds are related to various patterns of behavior.2. On the basis of behavioral evidence it is suggested that a slow rattle is characteristic of spiny lobsters when contained in groups, and that a rasp is a usual component of defensive behavior.3. The characteristics of the sounds of P. argus are compared to those of other marine sounds of biological origin. On the basis of this comparison, an attempt is made to generalize(a) the type of sound which accompanies defensive behavior of marine fishes and crustaceans, and (b) the type of sound stemming from marine fishes and crustaceans when undisturbed.4. It is concluded that the intricacy of the sound-producing mechanism of P. argus, and of other palinurids, justifies a conclusion of a significance of sound to the biology of spiny lobsters. While certain suggestions of a possible value of the rasp to survival of spiny lobsters are presented, a consistent effect of the rasp on the behavior of other spiny lobsters and on predator organisms has yet to be demonstrated.