Risk-related standards of competence: continuing the debate over risk-related standards of competence

This discussion paper addresses Ian Wilks' defence of the risk-related standard of competence that appears in Bioethics 11 . Wilks there argues that the puzzle posed by Mark Wicclair in Bioethics 5 against Dan Brock's argument in favour of a risk-related standard of competence — namely that Brock's argument allows for situations of asymmetrical competence — is not a genuine problem for a risk-related standard of competence. To show this, Wilks presents what he believes to be two examples of real situations in which asymmetrical competence arises.
I argue that insofar as Wilks equivocates two senses of competence in his examples — namely, competence to perform a task and competence in performing a task — Wilks is unable to illustrate the existence of real situations of asymmetrical competence. By examining the way in which Wilks equivocates two senses of competence in his examples, and by applying the results of this examination to the problem of patient competency within the medical field, I argue that not only does Wilks fail to show that situations of asymmetrical competence exist, but he is also unable to provide a foundation for understating how the risk-related standard of competence can strike a balance between an individual's autonomy and benevolent intervention.
I thus conclude that insofar as Wilks fails to answer the objections raised by Wicclair and others against the risk-related standard of competence, the risk-related standard of competence continues to be undermined by the problem of asymmetrical competence.     

Regulation by the precompetent cell culture of the appearance of spontaneous and induced competence

Biochemical and biophysical changes in the precompetent cell culture, rather than merely the cell size, regulate the appearance of competence. The more physiologically mature the incompetent cell culture is, the less competence substance is required for maximal induction of competence. The kinetics of induction of competence as the function of the physiological state of the incompetent culture and as the function of the concentration of the competence substance seems to support the idea that the competent cell is a temporary spheroplast.     

The acquisition of competence as a possible source of cell cycle variability in mouse fibroblasts

The kinetic analysis of the competence induction in Balb/c-3T3 cells shows that competence is acquired with a first order kinetics, whose rate depends on the concentration of the competence factor. Thus it is suggested that the competence induction may be a source of cell cycle variability for mouse fibroblasts.     

Regulation of competence development in Haemophilus influenzae

Development of competence for DNA uptake by the bacterium Haemophilus influenzae is tightly regulated, and expression of the cell's complement of competence genes is absolutely dependent on the cAMP-CRP complex. A second regulator of competence may maximize competence under starvation conditions. Several investigators have recently identified a consensus sequence (competence regulatory element, CRE) in the promoter regions of some competence genes and have proposed that this may be a binding site for Sxy (TfoX), a putative positive regulator of competence. However, a scoring method that reliably ranks candidate binding sites according to affinity for the cognate binding protein predicts that the cAMP-CRP complex will bind CRE sequences with high affinity. Moreover, the predicted Sxy protein lacks recognizable DNA-binding motifs and has not been shown to bind DNA. No other consensus sequences (putative binding sites) were identified in the promoter regions of competence genes. These observations suggest that the proposed competence-specific regulatory elements are in fact CRP-binding sites, and highlight the central role of cAMP-an established bacterial mediator of the response to nutritional stress-in competence regulation. Minor sequence elements uniquely conserved in the set of CRE sequences are predicted to reduce CRP affinity, and a model is suggested in which a secondary regulator of competence genes may interact with CRP under certain conditions to stabilize the initiation complex.     

Suppression of early competence mutations in Bacillus subtilis by mec mutations.

Although competence normally develops only in glucose-minimal salts media, mecA and mecB mutations permit the expression of competence and of late competence genes in complex media as well (D. Dubnau and M. Roggiani, J. Bacteriol. 172:4048-4055, 1990). The expression of late competence genes is dependent on the products of the regulatory genes comA, comB, comP, sin, abrB, spo0H, and spo0A. We show here that this list must be extended to include degU, csh-293, and spo0K. mecA and -B mutations bypass most of these requirements, making the expression of late competence genes and of competence itself independent of all of these regulatory genes, with the exceptions of spo0A and spo0K (in the case of mecB). The expression of late competence genes in mec mutants that are deficient for each of the bypassed regulatory functions is still under growth stage-specific regulation. The implications of these findings are discussed, and a provisional scheme for the flow of information during the development of competence is proposed.     

The development of meiotic competence in the rat: Role of hormones and of the stage of follicular development

Hypophysectomy of 15-day-old rats (hypox) markedly reduced the normal development of meiotic competence and abolished the development of antral follicles between days 21 and 31 postpartum (pp). Here the correlation among age of the rats, stage of follicular development, and meiotic competence was examined. Administration of pregnant mare's serum gonadotropin (PMSG-3IU) or insertion of an estradiol-17β (E₂) capsule to hypox rats induced the development of meiotic competence provided the treatment started after day 20 pp. Hormonal treatments at an earlier age were not effective in inducing meiotic competence in hypox rats. The induction of meiotic competence by PMSG or E₂ was associated with an increase in the number of granulosa cells and formation of follicular antrum. The finding that PMSG and E₂ failed to induce meiotic competence when administered prior to day 21 pp suggests that the development of meiotic competence is an age-dependent process. When the hormonal treatments commenced after day 21, both follicular development and meiotic competence were induced.     

Defined Nongrowth Media for Stage II Development of Competence in Haemophilus influenzae

The composition of a defined nongrowth medium used in stage II development of competence of Haemophilus influenzae affects the course of this development. The development of competence in two nongrowth media, M-IV and M-V, is rapid, logarithmic, and independent of the cell concentration. This last property indicates that there is probably no transfer of a competence factor from competent to noncompetent cells, in contrast to results reported for other organisms. Levels of competence reached in these completely defined media are such that 1 to 5% of the cells are transformed in the presence of an excess of marked deoxyribonucleic acid. The method of evaluating competence, which depends on the frequency of multiple independent transformations, has been reexamined. This and other methods are compared on samples taken from a culture during development of competence.     

Intercellular Effects on Development of Competence in Bacillus subtilis

The intercellular transfer of competence during growth under the conditions specified by the transformation procedure of Spizizen was investigated with Bacillus subtilis 168. The rate of competence development as assayed uniformly in medium B was not affected by variations in the cell concentration, although the first appearance of transformants occurred earlier with high cell densities in medium A, approximately in proportion to the onset of the stationary phase in the culture. Growth in the presence of Pronase enhanced the frequency of transformation, but did not detectably alter the kinetics of competence development. The rate of competence increase in physiologically noncompetent cultures was not changed by mixing with competent cultures either in medium A or in medium B; however, an early appearance of transformants was noted in mixed cultures in which the proportion of competent to noncompetent cells prevented exponential growth of the noncompetent strain. These experiments indicate that the normal development of competence in B. subtilis is not mediated by a soluble or loosely bound protein factor capable of transmitting competence directly via cell contact. The onset of competence is thus a function of internal physiological changes which are induced by the overall metabolic state of the culture.     

Role of the ø11 Phage Genome in Competence of Staphylococcus aureus

Both phage ?11 and 83A, when present as prophage or when used as helper phage, induce competence for transfection and transformation to the same level in Staphylococcus aureus, strain 8325-4. Cells lysogenized with certain temperature-sensitive (ts) mutants of phage ?11 show competence at the nonpermissive temperature (41 C) without production of infectious phages. Phage ?11ts allele 31 can neither as a prophage nor as a helper phage develop competence under nonpermissive conditions. This mutant appears, therefore, to be mutated in the region of the phage genome controlling competence. The competence level for both transfection and transformation is increased by superinfecting strain 8325-4 (?11) or 8325-4 (83A) at high multiplicities with phage ?11 with some of its mutants or with phage 83A. This superinfection enhancement appears to require protein synthesis but not deoxyribonucleic acid synthesis as judged from studies with inhibitors of macromolecular synthesis. Besides the phage particle, no extracellular or cell-bound factors so far detected can induce competence. The phage-induced product conferring competence is rapidly synthesized by strain 8325-4 (ts?11(31)) after shift to permissive conditions, but requires deoxyribonucleic acid and protein synthesis to be expressed. Recombination between the sus mutants of phage ?11 of Kretschmer and Egan and ts?11(31) indicate that competence is controlled by an early gene in the lytic cycle which may be expressed also in lysogenic cells. The phage product inducing competence appears to have a half-life of 10 to 15 min in the conditional lethal mutant at shift to nonpermissive temperature. Ultraviolet inactivation of phage ?11 infectivity occurs more rapidly than inactivation of competence induction. In fact, the number of transformants is increased at low doses of irradiation. Competence induction is, however, decreased at high does of ultraviolet irradiation.     

Mechanism of binding of the competence substance to the cell wall receptor sites

The induction of competence by the competence substance is strongly inhibited in the presence of phytohemagglutinins. A great inhibition effect is also found when the competence substance is preincubated with some amino sugars. Both the phytohemagglutinins and the competence substance exhibit a similar binding affinity to cross-linked dextran (Sephadex) and to the cell surfaces, as both are inhibited by some sugars in their interaction with the sensitive cells. It is proposed that they are bound to similar or identical cell receptor sites. These seem to be some specific sugar molecules forming a part of cell wall structures of the transformable and to competence inducible bacterial strains. This paper is part XIV of the series “Studies on phytohemagglutinins”; part XIII:Biochim. Biophys Acta,304, 93 (1973)     

Amino-acylation site mutations in amino acid-activating domains of surfactin synthetase: effects on surfactin production and competence development in Bacillus subtilis.

The part of the srfA operon of Bacillus subtilis that contains the region required for competence development is composed of the first four amino acid-activating domains which are responsible for the incorporation of Glu, Leu, D-Leu, and Val into the peptide moiety of the lipopeptide surfactin. Ser-to-Ala substitutions were made in the amino-acylation site of each domain, and their effects on surfactin production and competence development were examined. All of the mutations conferred a surfactin-negative phenotype, supporting the finding that the conserved Ser in the amino-acylation site is required for peptide synthesis. However, none of the mutations affected significantly competence development or the expression of a lacZ fusion to the late competence operon comG. This, coupled with recent findings that only the fourth, Val-activating, domain is required for competence, suggests that some activity, other than amino-acylation and perhaps unrelated to peptide synthesis, possessed by the fourth domain is involved in the role of srfA in regulating competence development.     

Modulation of competence for genetic transformation in Streptococcus pneumoniae

The spontaneous development of competence by cultures of Streptococcus pneumoniae in casein hydrolysate medium was strongly dependent on the initial pH of the culture medium. Cells growing in cultures beginning with a wide range of initial pH values (6.8 to 8.0) all developed competence, as measured by [3H]DNA uptake, [3H]DNA degradation and genetic transformation; but the initial pH of the medium affected both the timing of the occurrence of competence and the number of times the culture became competent. In cultures grown in media of lower initial pH, competence occurred only once, at high population densities, while in more alkaline media a succession of competence cycles occurred, beginning at lower cell densities. The critical population density required for the initiation of competence varied tenfold over the pH range studied. Successive competence cycles in an alkaline medium were not equivalent: while the percentage of competent cells in the first competence cycle was high (approximately 80%), that in the second competence cycle was lower (approximately 12%). Correspondingly, competence-specific proteins were less prominent in the labelled-protein pattern of the second competence cycle than in that of the first. These features of the physiology of competence control make it possible to adjust the expression of competence to suit various experimental requirements.     

Analysis of stochastic strategies in bacterial competence: a master equation approach

Competence is a transiently differentiated state that certain bacterial cells reach when faced with a stressful environment. Entrance into competence can be attributed to the excitability of the dynamics governing the genetic circuit that regulates this cellular behavior. Like many biological behaviors, entrance into competence is a stochastic event. In this case cellular noise is responsible for driving the cell from a vegetative state into competence and back. In this work we present a novel numerical method for the analysis of stochastic biochemical events and use it to study the excitable dynamics responsible for competence in Bacillus subtilis. Starting with a Finite State Projection (FSP) solution of the chemical master equation (CME), we develop efficient numerical tools for accurately computing competence probability. Additionally, we propose a new approach for the sensitivity analysis of stochastic events and utilize it to elucidate the robustness properties of the competence regulatory genetic circuit. We also propose and implement a numerical method to calculate the expected time it takes a cell to return from competence. Although this study is focused on an example of cell-differentiation in Bacillus subtilis, our approach can be applied to a wide range of stochastic phenomena in biological systems.