Productivity and photosynthetic efficiency ofSpirulina platensis as affected by light intensity,algal density and rate of mixing in a flat plate photobioreactor

The effect of the rate of mixing on productivity of algal mass in relation to photon flux density and algal concentration was quantitatively evaluated in cultures ofSpirulina platensis grown in a newly designed flat-plate photobioreactor. Special emphasis was placed on elucidating the principles underlying efficient utilization of high photon flux density for maximal productivity of algal-mass. Whereas the rate of mixing exerted little influence on productivity and photosynthetic efficiency in cultures of relatively low algal density, its effect became ever more significant as algal concentration was increased. Maximal mixing-enhanced cell concentrations and productivity of biomass were obtained at the highest light intensity used. At each level of incident light intensity, maximum productivity and photosynthetic efficiency could be achieved only when algal concentration and mixing rates were optimized. The higher the intensity of the light source, the higher became the optimal culture density, highest algal concentrations and productivity of biomass being obtained at the highest light intensity used. The rate of mixing required careful optimization: when too low, maximal productivity resulting from the most efficient utilization of light could not be obtained. Too high a rate of mixing resulted in cell damage and reduced output rate.Author for correspondence     

The environmental and genetic determinants of chick telomere length in Tree Swallows (Tachycineta bicolor)

Conditions during early life can have dramatic effects on adult characteristics and fitness. However, we still know little about the mechanisms that mediate these relationships. Telomere shortening is one possibility. Telomeres are long sequences of DNA that protect the ends of chromosomes. They shorten naturally throughout an individual's life, and individuals with short telomeres tend to have poorer health and reduced survival. Given this connection between telomere length (TL) and fitness, natural selection should favor individuals that are able to retain longer telomeres for a greater portion of their lives. However, the ability of natural selection to act on TL depends on the extent to which genetic and environmental factors influence TL. In this study, we experimentally enlarged broods of Tree Swallows (Tachycineta bicolor) to test the effects of demanding early‐life conditions on TL, while simultaneously cross‐fostering chicks to estimate heritable genetic influences on TL. In addition, we estimated the effects of parental age and chick sex on chick TL. We found that TL is highly heritable in Tree Swallow chicks, and that the maternal genetic basis for TL is stronger than is the paternal genetic basis. In contrast, the experimental manipulation of brood size had only a weak effect on chick TL, suggesting that the role of environmental factors in influencing TL early in life is limited. There was no effect of chick sex or parental age on chick TL. While these results are consistent with those reported in some studies, they are in conflict with others. These disparate conclusions might be attributable to the inherent complexity of telomere dynamics playing out differently in different populations or to study‐specific variation in the age at which subjects were measured.     

Effects of pyruvate on the growth of normal and transformed hamster embryo fibroblasts

The growth of NIL and NILpy hamster embryo fibroblasts was determined in the presence and absence of pyruvate as a component of the growth medium. It was demonstrated that NIL cells respond to the presence of pyruvate by decreasing cell doubling time, glucose utilization, glutamine utilization, and increasing lactate production with the effects being more pronounced at low inoculum densities. Polyoma-virus transformed NIL cells (NILpy) demonstrate none of the above effects upon pyruvate addition regardless of initial cell inoculum density.     

Lymphocyte-mediated cytolysis of allogenic tumor cell in vitro. II. Binding of cytotoxic lymphocytes to formaldehyde-fixed target cells.

Allogeneic immune peritoneal exudate lymphocytes would bind to viable monolayers of EL4 target cells but not to EL4 monolayers killed by heat, dehydration, osmotic shock, or other procedures. Fixation with formaldehyde in low concentration killed the EL4 monolayers but did not abolish binding. Formaldehyde-treated EL4 cells also permitted binding to varying degrees after further manipulations which originally abolished binding to unfixed cells.     

Regulation of glucose utilization in chick embryo fibroblasts by bicarbonate ion

The amount of glucose consumed by chick embryo fibroblasts in primary culture is strongly influenced by the presence of bicarbonate ion in the culture medmum. Cells grown on glucose at physiologic concentration (5.5 mm) and in the absence of bicarbonate ion have a reduced rate of glucose utilization when compared to their counterparts cultivated in medium containing the usual 25 mM bicarbonate. The presence or absence of bicarbonate is without effect on chick embryo fibroblast proliferation over a 6-day growth period. Both lactic acid accumulation per mole of glucose consumed and the utilization of glutamine increase as a function of bicarbonate ion in the growth medium.     

Evidence for Nonindependent Evolution of Adjacent Microsatellites in the Human Genome

Microsatellites are short tandem repeats that evolve predominantly through a stepwise mutation model. Despite intensive study, many aspects of their evolution remain unresolved, particularly the question of how compound microsatellites containing two different motifs evolve. Previous work described profound asymmetries in the probability that any given second motif lies either 3′ or 5′ of an AC repeat tract. Here we confirm and extend this analysis to examine the length dependence of these asymmetries. We then use the differences in length between homologous human and chimpanzee microsatellites as a surrogate measure of the slippage-based mutation rate to explore factors that influence this process. We find that the dominant predictor of mutation rate is the length of the tract being considered, which is a stronger predictor than the length of the two tracts combined, but other factors also have a significant impact, including the length of the second tract and which of the two tracts lies upstream. We conclude that compound microsatellites rarely arise through random point mutations generating a second motif within a previously pure tract. Instead, our analyses point toward a model in which poorly understood mutation biases, probably affecting both slippage and point mutations and often showing 3′-5′ polarity, promote the formation of compound microsatellites. The result is convergent evolution. We suggest that, although their exact nature remains unclear, these biases are likely attributable to structural features, such as the propensity of AC tracts to form Z-DNA.     

Life-history decisions under predation risk: Importance of a game perspective

We model ontogenetic shifts (e.g. in food or habitat use) during development under predation risk. We ask whether inclusion of state and frequency dependence will provide new insights when compared with game-free life-history theory. We model a simple biological scenario in which a prey animal must switch from a low-predation, low-growth habitat to a high-predation, high-growth habitat. To assess the importance of frequency dependence, we compare the results of four scenarios of increasing complexity: (1) no predation; (2) constant predation; (3) frequency-dependent predation (predation risk diluted at high prey density); and (4) frequency-dependent predation as in (3) but with predators allowed to respond adaptively to prey behaviour. State dependence is included in all scenarios through initial size, assumed to be environmental. A genetic algorithm is used to search for optimal solutions to the scenarios. We find substantially different results in the four different scenarios and suggest a decision tree by which biological systems could be tested to ascertain which scenario is most applicable.     

Transient induction of intergration functions in lambda lysogens

Summary Transient heat induction of lambda prophage permits the synthesis of integration enzymes which can insert a superinfecting homoimmune phage into the bacterial chromosome. The integration system is stable for 1 h in growing cells.     

C-phycocyanin as a storage protein in the blue-green alga Spirulina platensis

The possibility that c-phycocyanin serves as a nitrogen source in Spirulina platensis during nitrogen starvation was studied. The following evidence was obtained in support of this idea. 1. Under favourable conditions for growth, c-phycocyanin existed in large excess in the algal cells. 2. When the supply of nitrogen was low, about 30–50% of the c-phycocyanin disappeared without any effect on the maximal growth rate. 3. A culture which was deprived of nitrogen continued to grow unaffectedly for a period, the duration of which depended on the c-phycocyanin content in the cell before nitrogen starvation was initiated. 4. c-phycocyanin was the only nitrogenous compound that was depleted during the course of nitrogen starvation when growth was yet unaffected. 5. When protein synthesis was inhibited either by nitrogen starvation or by methionine sulfoximine (MSO), phycocyanin content began to decline immediately and growth continued at normal rates as long as c-phycocyanin did not decline below 50%. 6. The decrease in c-phycocyanin content during nitrogen starvation was accompanied by an increase in proteolytic activity.     

Cuticular penetration of abscisic acid

Summary Penetration of 2-¹⁴C abscisic acid (ABA) through enzymatically isolated cuticles from tomato fruit and from the upper epidermis of apricot, pear and orange leaves was assessed. Penetration was linear with time, greater as the undissociated than the dissociated ion, and greater through dewaxed than non-dewaxed cuticles. Significantly less (3–6 times) (2-¹⁴C)ABA penetrated the tomato fruit cuticle than NAA or 2,4-D. The leaf cuticles were less permeable than the tomato fruit cuticle. There was no evidence that the ABA was altered during transfer across the cuticle.