On the choice of the optimal periodic operation for a continuous fermentation process

In this contribution we investigate the impact of the forcing waveform on the productivity of a continuous bioreactor governed by an unstructured, nonlinear kinetic model. The (periodic) forcing is applied on the substrate concentration in the feed. To this end, some alternative waveforms commonly encountered in practice are evaluated and their performance is compared. An analytical/numerical approach is used. The preliminary analytical step is based on the π‐criterion that gives useful information for small amplitudes. The extension to larger amplitudes, when significant improvements are expected, is then performed through a continuation‐optimization procedure. It is found that the choice of the specific waveform has an impact on the performance of the process and there is no unique best forcing for any process condition, but its choice depends on the operating parameters and the forcing amplitude and frequency values. Further, the influence of the waveform functions on the wash‐out conditions are extensively examined. The analysis shows that all the waveforms examined in this work may lead to significant enlargement of the nontrivial regime with respect to a steady state operation. In particular, square‐wave forcing leads in practice to the extinction of the wash‐out conditions for any feed substrate concentration and for a well defined choice of the forcing parameters. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

The unpredictability of favourability: condition assessment and protected areas in England

The probability that protected areas will deliver their potential for maintaining or enhancing biodiversity is likely to be maximised if they are appropriately and effectively managed. As a result, governments and conservation agencies are devoting much attention to the management of protected areas. In the U.K., the demand for performance accountability has resulted in Public Service Agreements (PSA) that set out targets for government departments to deliver results in return for investments being made. One such target for England is to ensure that all nationally important wildlife sites are in favourable condition by 2010. Here, we tested the hypothesis, of potential strategic importance, that the ecological condition of these sites is predictable from relationships with a range of physical, environmental and demographic variables. We used binary logistic regression to investigate these relationships, using the results of English Nature’s 1997–2003 condition assessment exercise. Generally, sites in unfavourable condition tend to be larger in area, located at higher elevations, but with higher human population density and are more spatially isolated from units of the same habitat. However, despite the range of different parameters included in our models, the extent to which the condition of any given site could be predicted was low. Our results have implications for the delivery of PSA targets, funding allocation, and the location of new protected areas.     

Optimizing the expression of chimeric genes in plant cells

Summary The Serratia marcescens chiA gene encodes a secreted chitinase activity which contributes to the fungal growth inhibition exhibited by this bacterium. The coding region from the chiA gene was fused to the promoter and 3 polyadenylation region of the Agrobacterium nopaline synthase gene. Site-directed mutagenesis of specific nucleotides surrounding the initiating AUG of the coding sequence of this chimeric gene resulted in up to an eight-fold increase in the amount of chitinase protein detected in transformed plant tissue. Analysis of the chiA mRNA indicated that these nucleotides also affected mRNA levels. At least 50% of the chitinase protein produced in transformed tobacco cells was the same molecular weight as the S. marcescen secreted protein.     

Somatic characteristics of an Australian population of Oreochromis mossambicus (Pisces: Cichlidae)

Synopsis The Oreochromis mossambicus population of North Pine Dam, Brisbane, Queensland, Australia was studied over three years, from 1985 to 1988. Basic somatic data were obtained and characteristic values of condition factor, sex ratio, gonosomatic index and the relationships between total and standard lengths, and length and weight, were calculated. Standard length is proportional to total length by the formula SL = –0.321 + 0.799 TL. Weight is related to length by the isometric formula W = aL³. Condition factor values spanned the range 0.0254 to 0.0563, with an average of 0.04078 for males and 0.03877 for females. The sex ratio is 1: 1 until maturity is reached (21 cm SL), at which time the catch rate of the sexes varies due to divergent habitat selection behaviour. Average values of gonosomatic index, considered in relation to maturity classification, are similar to those obtained from other populations, however maximum values are generally much lower, at 0.47 for males and 3.62 for females. These characteristic values are compared, with varying degrees of concordance, with those for populations of this species in other countries.     

Preparative resolution of some 5,5-hydantoin derivatives via formation of diastereoisomeric salts

Several preparative resolutions of 5,5-disubstituted hydantoins have been achieved via fractional crystallization of diastereoisomeric salts. The process can be extended by making use of the difference between the variation of solubilities of the hydantoins and their salts with α-methylbenzylamine as a function of the alkalinity of the medium. Optimization for each resolution procedure involves a refinement of the excess amount of base needed. © 1992 Wiley-Liss, Inc.     

Ka'apor ritual hunting

Several investigators cite population control, frequent settlement relocation, trekking, expansion of diet breadth, and food taboos as strategic responses to game depletion by indigenous populations living in interfluvial zones of lowland South America. The Ka'apor Indians of the interfluvial forest of northern Maranhão, Brazil, employ other means of optimizing hunting efficiency, partly based on ritual. Menstruating women, pubescent girls, and parents of newborns can consume meat only of the tortoise (Gochelone denticulata), the first prey species to be hunted out of an area. Tortoise capture requires, on average, one full day of hunting. This means that the full potential of hunting pressure does not materialize near the settlement. Meat productivity is unusually high even near old settlements. I argue that ritual tortoise hunting helps to regulate environmental utilization, to maintain a sustained yield of meat protein, and to expand the catchment area gradually.     

A biological sampling problem illustrated by the population structure and growth patterns of Sardinella aurita at Tripoli,Libya

Synopsis Sardinella aurita were sampled from catches of the lampara fishery at Tripoli, Libya during October 1979 through to September 1980. Landings consisted mainly of adult fish with large (mode 21–26 cm total length), relatively fast growing 3–5-group individuals in winter and spring and smaller (mode 14–20 cm total length), slow growing 2- and 3-group fish in summer. Gonad growth commenced in April, when the fish were feeding on zooplankton, and continued at the expense of mesenteric fat until July. It is suggested that the older and bigger fish spawn first, probably after having moved westwards, and that this results in spatial and temporal differences in length at age within the population. There was no consistent difference in growth rate between the sexes, but because first maturity in males tends to occur earlier than in females, there were length distribution differences between the sexes in the youngest (2+) age group as sampled.     

THE EFFECTS OF PREDATION ON THE AGE AND SIZE OF MATURITY OF PREY

The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.     

A medium optimization strategy for improvement of growth and methane production by Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum, strain Hveragerdi, has been cultivated in a completely defined mineral salts medium, under strictly anaerobic conditions with CO₂ and H₂ as sole carbon and energy source, respectively. During optimization of the medium an iron limitation was identified that could not be overcome by the simple addition of iron—or iron complexed with nitrilotriacetate (NTA)—to the medium, due to the formation of insoluble FeS complexes. In order to define a medium optimization strategy, and to avoid laborious empirical optimization procedures, a theoretical model has been developed in order to describe the solubility of iron and other mineral species in the medium as a function of the concentration of sulfur and NTA. This model may be applied for the optimization of any medium component. With this information sulfide has been replaced by a combination of cysteine and thiosulphate in conjunction with a non-toxic reducing agent (titanium (III) citrate). Using this defined medium precipitation was avoided and an iron limitation was overcome resulting in a 5-fold improvement of the final biomass concentration from 2–3 g l⁻¹ to 11.2 g l⁻¹ together with a 2-fold increase (from 45 to almost 100%) in the conversion of CO₂ and H₂ to CH₄, even at gas flow rates as high as 6 l min⁻¹.