Role Of Population Heterogeneity Research Articles

Toxin-antitoxin HicAB regulates the formation of persister cells responsible for the acid stress resistance in Acetobacter pasteurianus.

Elucidation of the acetic acid resistance (AAR) mechanisms is of great significance to the development of industrial microbial species, specifically to the acetic acid bacteria (AAB) in vinegar industry. Currently, the role of population heterogeneity in the AAR of AAB is still unclear. In this study, we investigated the persister formation in AAB and the physiological role of HicAB in Acetobacter pasteurianus Ab3. We found that AAB were able to produce a high level of persister cells (10-2 to 100 in frequency) in the exponential-phase cultures. Initial addition of acetic acid and ethanol reduced the ratio of persister cells in A. pasteurianus by promoting the intracellular ATP level. Further, we demonstrated that HicAB was an important regulator of AAR in A. pasteurianus Ab3. Strains lacking hicAB showed a decreased survival under acetic acid exposure. Deletion of hicAB significantly diminished the acetic acid production, acetification rate, and persister formation in A. pasteurianus Ab3, underscoring the correlation between hicAB, persister formation, and acid stress resistance. By transcriptomic analysis (RNA-seq), we revealed that HicAB contributed to the survival of A. pasteurianus Ab3 under high acid stress by upregulating the expression of genes involved in the acetic acid over-oxidation and transport, 2-methylcitrate cycle, and oxidative phosphorylation. Collectively, the results of this study refresh our current understanding of the AAR mechanisms in A. pasteurianus, which may facilitate the development of novel ways for improving its industrial performance and direct the scaled-up vinegar production. KEY POINTS: • AAB strains form persister cells with different frequencies. • A. pasteurianus are able to form acid-tolerant persister cells. • HicAB contributes to the AAR and persister formation in A. pasteurianus Ab3.

Role of population heterogeneity and pH factor in natural phenomenon of α-acetolactate overproduction in Lactococcus lactis ssp. lactis bv. diacetylactis B2103/74 diacetyl producer

The influence of population heterogeneity and medium pH factors on the effect of α-acetolactate (AL) overproduction that we found in L. lactis bv. diacetylactis B2103/74 culture was studied. The nature of the enzymatic system responsible for this effect (which is able to considerably block lactate dehydrogenase (LDH) by intercepting up to 80% of the NADH in it) is unknown; we designated this system as the heminindependent electron transferring system (HEMIETS). It was demonstrated that manifestation of the effect was masked by the culture heterogeneity and was especially strong in approximately neutral pH values (6.1–6.5). The presence in the population of at least three types of dissociants differing in the level of HEMIETS activity, and consequently AL synthesis, was established: an active dissociant (AL accumulation up to 30 mM), an inactive dissociant that had lost the HEMIETS (AL no more than 3 mM), and a dissociant with intermediate activity (AL 15–17 mM). It was demonstrated that the HEMIETS activity at a particular pH value had primary importance in the emerging general picture of pyruvate metabolism at different pH values and, finally, in overproduction. Thus, no overproduction effect was observed at a pH of 7.0 due to the low HEMIETS activity, and the pyruvate metabolism passed according to homolactic type. However, the HEMIETS activity was so high at pH values of 5.3–6.5 that this allowed it to take the function of the main regulator of NAD+/NADH oxidation–reduction balance and to give a minor role to LDH. The LDH- and acetolactate synthase pathway productivity depended on the HEMIETS activity at a particular pH, while the productivity of pyruvate dehydrogenase pathway directly depended on the external pH. The latter was relatively high in approximately neutral area (pH 6.0–6.5) and was noticeably decreased in neutral (pH 7.0) and weakly acid (pH ≤ 6.0) zones.

Individual-Based Modeling of Tuberculosis in a User-Friendly Interface: Understanding the Epidemiological Role of Population Heterogeneity in a City.

For millennia tuberculosis (TB) has shown a successful strategy to survive, making it one of the world’s deadliest infectious diseases. This resilient behavior is based not only on remaining hidden in most of the infected population, but also by showing slow evolution in most sick people. The course of the disease within a population is highly related to its heterogeneity. Thus, classic epidemiological approaches with a top-down perspective have not succeeded in understanding its dynamics. In the past decade a few individual-based models were built, but most of them preserved a top-down view that makes it difficult to study a heterogeneous population. We propose an individual-based model developed with a bottom-up approach to studying the dynamics of pulmonary TB in a certain population, considered constant. Individuals may belong to the following classes: healthy, infected, sick, under treatment, and treated with a probability of relapse. Several variables and parameters account for their age, origin (native or immigrant), immunodeficiency, diabetes, and other risk factors (smoking and alcoholism). The time within each infection state is controlled, and sick individuals may show a cavitated disease or not that conditions infectiousness. It was implemented in NetLogo because it allows non-modelers to perform virtual experiments with a user-friendly interface. The simulation was conducted with data from Ciutat Vella, a district of Barcelona with an incidence of 67 TB cases per 100,000 inhabitants in 2013. Several virtual experiments were performed to relate the disease dynamics with the structure of the infected subpopulation (e.g., the distribution of infected times). Moreover, the short-term effect of health control policies on modifying that structure was studied. Results show that the characteristics of the population are crucial for the local epidemiology of TB. The developed user-friendly tool is ready to test control strategies of disease in any city in the short-term.

Pressure-Based Strategy for the Inactivation of Spores.

Since the first application of high hydrostatic pressure (HHP) for food preservation more than 100 years ago, a wealth of knowledge has been gained on molecular mechanisms underlying the HHP-mediated destruction of microorganisms. However, one observation made back then is still valid, i.e. that HHP alone is not sufficient for the complete inactivation of bacterial endospores. To achieve "commercial sterility" of low-acid foods, i.e. inactivation of spores capable of growing in a specific product under typical storage conditions, a combination of HHP with other hurdles is required (most effectively with heat (HPT)). Although HPT processes are not yet industrially applied, continuous technical progress and increasing consumer demand for minimally processed, additive-free food with long shelf life, makes HPT sterilization a promising alternative to thermal processing.In recent years, considerable progress has been made in understanding the response of spores of the model organism B. subtilis to HPT treatments and detailed insights into some basic mechanisms in Clostridium species shed new light on differences in the HPT-mediated inactivation of Bacillus and Clostridium spores. In this chapter, current knowledge on sporulation and germination processes, which presents the basis for understanding development and loss of the extreme resistance properties of spores, is summarized highlighting commonalities and differences between Bacillus and Clostridium species. In this context, the effect of HPT treatments on spores, inactivation mechanism and kinetics, the role of population heterogeneity, and influence factors on the results of inactivation studies are discussed.

Population Heterogeneity and Between-Group Substitutability and Complementarity of Social Actions

This article extends a foundation for sociological theories of the micro-macro linkage in collective action. Key elements of the foundation are population heterogeneity and a model of interdependence of actions. By “population heterogeneity” I mean differences among people in the payoffs of their alternative choices. This article introduces the concepts of interpersonal substitutability and complementarity of actions between groups for analyzing their collective outcomes by extending similar concepts and methods previously introduced in the literature for interdependence of actions within a group. The article applies these theories and methods (1) to evaluate Tsebelis's theory of the relationship between crime and punishment and present distinct conclusions on the effectiveness of alternative crime control methods depending on the conditions of population heterogeneity, and (2) to clarify the role of population heterogeneity as a modifier for the effects of an increase in the gender equality of job opportunities on men's and women's gender role attitudes about the division of household labor.

The role of population heterogeneity and human mobility in the spread of pandemic influenza

Little is known on how different levels of population heterogeneity and different patterns of human mobility affect the course of pandemic influenza in terms of timing and impact. By employing a large-scale spatially explicit individual-based model, founded on a highly detailed model of the European populations and on a careful analysis of air and railway transportation data, we provide quantitative measures of the influence of such factors at the European scale. Our results show that Europe has to be prepared to face a rapid diffusion of a pandemic influenza, because of the high mobility of the population, resulting in the early importation of the first cases from abroad and highly synchronized local epidemics. The impact of the epidemic in European countries is highly variable because of the marked differences in the sociodemographic structure of European populations. R(0), cumulative attack rate and peak daily attack rate depend heavily on sociodemographic parameters, such as the size of household groups and the fraction of workers and students in the population.

Investigating Autocatalytic Gene Expression Systems through Mechanistic Modeling

A structured model of gene expression, which incorporates the stochastic behavior of cellular processes, was developed to examine the “all-or-none” phenomenon observed in autocatalytic systems (e.g. the lac operon). Autocatalytic expression systems typically have the genes encoding the inducer transport proteins controlled by internal inducer levels, so that transport of the inducer increases production of the transport protein. The model was able to predict the unique behaviors of autocatalytic expression systems that have been experimentally observed and provided valuable insight into the role of population heterogeneity in these systems. The simulations substantiate the importance of stochastic processes on induction of gene expression in autocatalytic systems. The simulation results show that the all-or-none phenomenon is governed largely by random cellular events, and that population-averaged variations in gene expression are due to changes in the frequency of full gene induction in individual cells rather than to uniform variations in gene expression across the entire population. In addition, the model shows how concentrations of inducer too low to induce expression in uninduced cells can maintain induction in pre-induced cultures. A comparison of induction behaviors from an autocatalytic system and a system having constitutive synthesis of the transport protein showed that transport protein levels must be decoupled from inducer control to achieve homogeneous expression of a gene of interest in all cells of a culture.