Metabolic cost of motility in planktonic protists: Theoretical considerations on size scaling and swimming speed

The metabolic cost of swimming for planktonic protists is calculated, on theoretical grounds, from a simple model based upon Stokes' law. Energetic expenditure is scaled over both typically encountered size ranges (1–100 µm) and swimming speeds (100–5,000 µm/sec). In agreement with previous estimates for typical flagellates, these estimates generally suggest a low (<1%) cost for motility, related to total metabolic rate of growing cells. However, the cost of motility in small, fast-moving forms, such as some ciliates and flagellates, may be significant (1–10%) and even substantial (10–100%+) for certain species. In accordance with these predictions, many fast-moving ciliates restrict motility to bursts of activity or jumps. In the absence of a reduction in swimming speed or in the frequency of jumps, it is predicted that this relative cost of motility will be significantly increased in starving heterotrophs or light-limited autotrophs, if such cells reduce cell volumes and specific rates of respiration.     

Proteolytic degradation of heterologous proteins expressed inAspergillus niger

Summary Proteolytic degradation of heterologous proteins expressed in the filamentous fungusAspergillus niger reduces the yield of authentic target protein. The activities ofA. niger proteases are differentiated by their effects on two proteins expressed and secreted fromA. niger: hen egg-white lysozyme and porcine pancreatic phospholipase A₂.     

Light,iron, Sam Granick and the origin of life

Living matter is an organized system which requires a continual flux of energy for its survival. As a working assumption, the flux of energy required for the origin of a self-duplicating cell is taken as the power required for the maintenance of a modern cell: 10 mW per g of carbon or some 10⁵ times the output per gram of the sun. Solar photochemistry supplies the energy for the continuing evolution of life and, by continuity, for its origin. The iron oxide-sulfide photosynthetic unit proposed by S. Granick 35 years ago was meant to supply this energy. The evolution of complex organic photosensitizers is rationalized by the Granick hypothesis that biosynthetic pathways recapitulate their evolution. These concepts are discussed in the context of the evolution of photosynthetic systems and the known properties of these pigments.     

The design and use of the bioethics consultation form

The emergence of the ethics consultation as a means to resolve moral crises in clinical medicine has revealed the need for a worksheet that would facilitate intake and analysis. The author developed the "Bioethics Consultation Form" as an attempt to remedy this need. The form is arranged in an outline format and is a useful asset to ethics committee discussions and record keeping. The first section covers basic intake data concerning the patient's medical and personal information, advance directives, and values, as well as the values of the physician and family. After the intake section is completed with the above data, the ethics consultant then turns to the analysis section. This second section allows for (1) the discussion of conflicting values, (2) the identification of priorities, and (3) the elucidation of ethical norms relevant to the case. The Bioethics Consultation Form was adopted by the Patient Care Advisory Committee of the Franklin Square Hospital Center in Baltimore, Maryland in 1986. The methodology in the use of the form will be discussed. Further, the potential spectrum of consultative cases that can be analyzed using the form will be highlighted.     

On the relationship between evolutionary and psychological definitions of altruism and selfishness

I examine the relationship between evolutionary definitions of altruism that are based on fitness effects and psychological definitions that are based on the motives of the actor. I show that evolutionary altruism can be motivated by proximate mechanisms that are psychologically either altruistic or selfish. I also show that evolutionary definitions do rely upon motives as a metaphor in which the outcome of natural selection is compared to the decisions of a psychologically selfish (or altruistic) individual. Ignoring the precise nature of both psychological and evolutionary definitions has obscured many important issues, including the biological roots of psychological altruism.     

Computer modelling of neural tube defects

Neurulation, the curling of the neuroepithelium to form the neural tube, is an essential component of the development of animal embryos. Defects of neural tube formation, which occur with an overall frequency of one in 500 human births, are the cause of severe and distressing congenital abnormalities. However, despite the fact that there is increasing information from animal experiments about the mechanisms which effect neural tube formation, much less is known about the fundamental causes of neural tube defects (NTD). The use of computer models provides one way of gaining clues about the ways in which neurulation may be compromised. Here we employ one computer model to examine the robustness of different cellular mechanisms which are thought to contribute to neurulation. The model, modified from that of Odell et al (Odell, G.M., Oster, G., Alberch, P. and Burnside, B., (1981)) mimics neurulation by laterally propagating a wave of apical contraction along an active zone within a ring of cells. We link the results to experimental evidence gained from studies of embryos in which neurulation has been perturbed. The results indicate that alteration of one of the properties of non-neural tissue can delay or inhibit neurulation, supporting the idea, gained from observation of embryos bearing genes which predispose to NTD, that the tissue underlying the neuroepithelium may contribute to the elevation of the neural folds. The results also show that reduction of the contractile properties of a small proportion of the neuroepithelial cell population may have a profound effect on overall tissue profiling. The results suggest that the elevation of the neural folds, and hence successful neurulation, may be vulnerable to relatively minor deficiencies in cell properties.     

How-possibly explanations in biology

Biologists in many different fields of research give how-possibly explanations of the phenomena they study. Although such explanations lack empirical support, and might be regarded by some as unscientific, they play an important heuristic role in biology by helping biologists develop theories and concepts and suggesting new areas of research. How-possibly explanations serve as a useful framework for conducting research in the absence of adequate empiri cal data, and they can even become how-actually explanations if they gain enough empirical support.I am grateful to Robert Brandon and Michael Resnik for helpful comments and criticism.     

High-mobility group and other nonhistone substrates for nuclear histoneN-acetyltransferase

A variety of nonhistone proteins and polyamines has been studied for their substrate activity for nuclear histone N-acetyltransferase. Nonhistone chromatin high-mobility group (HMG) proteins are found to be as good a substrate for the enzyme as histones. The enzyme also acetylates spermidine and spermine. However, protamine, bovine serum albumin, and ubiquitin are not substrates. Chymotryptic peptides of histone and HMGs retained about 64% of the substrate activity, but trypsin treatment reduced the substrate activity by more than 85%. Both N-acetyltransferase activities for HMGs and histones are copurified through salt extraction, polyethylene glycol fractionation, and chromatography on DEAE-cellulose, phosphocellulose columns, and a HPLC anionic-exchange column. The highly purified nuclear histone acetyltransferase shows similar optimal pH and ping-pong kinetics for both HMGs and histones. The Km for HMG is 0.25 mg/ml. HMGs are able to accept the acetyl group from isolated acetyl-enzyme intermediate. Denatured gel analysis shows that HMG 1 and HMG 2 are the major proteins acetylated. High salt concentrations, mononucleotides, and DNA, which inhibit histone substrate activity of the enzyme, also inhibit HMG substrate activity. These observations suggest that there is a major nuclear N-acetyltransferase which is responsible for the acetylation of both histones and HMGs and perhaps also of spermine and spermidine. Thus the regulation of the structure and function of chromatin through postsynthetic acetylation can be achieved by a single nuclear N-acetyltransferase.     

Optimizing the production of transformed pea (Pisum sativum L.) callus using disarmed Agrobacterium tumefaciens strains

For optimization of the transformation procedure with Pisum sativum L. stern explant callus was used to test the effect of disarmed Agrobacterium tumefaciens strains, cocultivation procedures (preconditioning of explants; use of Nicotiana tabacum L. nurse cultures), duration of cocultivation (2, 3 or 4 days), and agents for selection (kanamycin or hygromycin). The succinamopine strain EHA101(pBI1042) produced the highest percentage of transformed calli (77%) when used in conjunction with tobacco nurse culture during four days of cocultivation. Using this strain, kanamycin (76%) and hygromycin (77%) were equally effective selective agents, but for strain LBA4404(pBI1042) percentage of transformed calli was higher for hygromycin (63%) than for kanamycin (17%). The procedures and strains shown to be optimal for transformation of pea callus will now be complemented by a pea regeneration system.     

Cultivation of algae and nutrient removal in a waste heat utilization process

A process providing a beneficial use for waste heat and excess nutrients in the cooling waters of nuclear reactors and fossil-fueled power generating plants has been developed. The process involves the cultivation of selected strains of thermotolerant microalgae in heated discharge waters and the subsequent harvesting of the algal biomass for nutrient removal, recovery of energy and fertilizer, and extraction of high value products. The design of such a process is presented for a large cooling reservoir receiving a discharge of 10⁹1^?1 d^?1 of secondary cooling water containing 100 μg 1^?1 of available P and 400 μg 1^?1 of available N. Based on this nutrient load, with a 1% P content in the algal biomass and a productivity of 10 g m^?2 d ^?1, a 100 ha region would be needed for the process. Hydraulic barriers (submerged plastic curtains) would isolate the 100 ha algal production area “cultivation zone” in the influent end of the reservoir to create a hydraulic and thermal environment conductive to the selective growth of filamentous, thermotolerant, nitrogen-fixing, blue-green algae. The algal culture would be inoculated into the thermal plume and harvested near the distal barrier of the cultivation zone with rotating, backwashed, fine mesh screens (“microstrainers”). A portion of the harvested biomass would be recycled to the inoculation site to maintain a dense culture. This process could mitigate both thermal and nutrient loadings on receiving bodies of water.