Methodological problems in evolutionary biology VII. The species plague

Various philosophers and evolutionary biologists have recently defended the thesis that species are individuals rather than sets. A decade of debates, however, did not suffice to settle the matter. Conceptual analysis shows that many of the key terms involved (individuation, evolutionary species, spatiotemporal restrictedness, individual) are ambiguous. Current disagreements should dissolve once this is recognized. Explication of the concepts involved leads to new programs for philosophical research. It could also help biology by showing how extant controversies concerning evolution may have conceptual rather than factual roots.     

Isolation and characterization of butanol-resistant mutants of Clostridium acetobutylicum.

In a wild-type strain of Clostridium acetobutylicum isolated from soil, solvent production appeared limited by butanol toxicity. Butanol-resistant mutants have been obtained which produced significantly higher solvent concentrations (about 30%) than the wild-type strain. Some other physiological differences were observed between a selected resistant mutant and the wild-type strain at the level of solvent resistance and sporulation.     

Dynamics of bryophytes in a chalk grassland

Dynamics of bryophytes were followed in a chalk grassland in 4 plots, 25×25 cm, each subdivided in to 400 subplots, in which every 3–4 months the presence of all bryophyte species was recorded. During the first 14 months no successional trends were visible. However, dynamics on the scale of one subplot were considerable. Degree of dynamics was markedly negatively correlated with original presence in the plots. Several explanations for this correlation are discussed.     

Responses of a Mutant Strain of Chlamydomonas reinhardi to Prolonged Organotrophic Growth

The responses of the wild type strain and of the y-2 mutant strain of Chlamydomonas reinhardi to long term organotrophic growth were studied. It was shown that wild type can be cultured as an organotroph for at least a month with little decrease in chlorophyll content and no loss of viability. On the other hand, the mutant strain y-2 dies during such organotrophic growth, death beginning after 5 to 6 days in the dark. The kinetics of death indicate that the loss of 95% of the chlorophyll precedes death and that revertants to wild type overgrow such a culture. The results suggest that death of y-2 is correlated with the loss of chlorophyll rather than simple metabolic response to organotrophy and that the chloroplast or a chloroplast related factor may perform certain nonphotosynthetic functions in C. reinhardi. The activities of nicotine adenine dinucleotide and nicotine adenine dinucleotide phosphate dependent triose phosphate dehydrogenases were studied during long term organotrophic growth of y-2. It was found that the activities of these enzymes varied in a manner consistent with previous findings under these conditions. The activity of glutamic dehydrogenase was found to vary as a function of chlorophyll content in the mutant strain y-2.     

Evaluation of two unstructured mathematical models for the penicillin G fedbatch fermentation

The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes.     

Degradation of some phenols and hydroxybenzoates by the imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans: evidence for an operative gentisate pathway

The imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans degraded 3-hydroxybenzoic acid via gentisate which was the cleavage substrate. 4-Hydroxybenzoic acid was metabolized via protocatechuate. No cleavage enzyme for the latter was detected. In stead of this NADH- and NADPH-dependent monooxygenases were present. In cells grown at the expense of hydroquinone and 4-hydroxygenzoic acid, enzymes of the hydroxyhydroquinone variant of the 3-oxoadipate pathway were demonstrated, which also took part in the degradation of 2,4-dihydroxybenzoic acid byC. parapsilosis.Abbreviations HHQ Hydroxyhydroquinone (1,2,4-trihydroxybenzene) - GSH reduced Glutathione     

Determination of mercury in human serum and packed blood cells by neutron activation analysis

A method is described for the determination of mercury in human blood serum and packed blood cells employing neutron activation analysis. Great attention was devoted to the collection and manipulation of the samples. The accuracy and precision of the method were tested by analyzing biological reference materials and by comparing the concentrations measured in a number of serum samples to those obtained by another, independent technique (cold vapor atomic absorption spectrometry) in the same samples. The article reports the levels measured in blood serum and packed blood cells samples from 15 adult volunteers, as well as the figures determined in a “second-generation” biological reference material (freeze-dried human serum), prepared and conditioned at the University of Ghent.     

The microbiological fate of polycyclic aromatic hydrocarbons: carbon and oxygen balances for bacterial degradation of model compounds

A series of pure bacterial strains belonging mainly to theRhodococcus andPseudomonas genera were grown on one of the following polycyclic aromatic hydrocarbons (PAH) supplied as sole carbon and energy source: naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene. In each case, a quantitative evaluation of the carbon repartition of the PAH degraded into CO₂, biomass and water-soluble metabolites was carried out. In addition, the kinetics of oxygen consumption and of water-soluble metabolite accumulation during PAH biodegradation was followed with respirometric equipment. Satisfactory carbon balances were obtained and the data correlated well with oxygen consumption values. The results show that growth on PAH presents high mineralization yields (from 56% to 77% of carbon) and sizeable production of biomass (from 16% to 35% of carbon) and limited but significant accumulation of metabolites (from 5% to 23% of carbon). The mineralization yields were higher and biomass yields lower in the case of higher PAH. Some differences between strains were also observed.     

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A _t). Various approaches to estimatingA _t for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates ofA _t differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measureA _t for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured asA _t than as the transfer or apparent absorption coefficients sinceA _t does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed.