Effect of Insulin on Microbial Growth

The ability of insulin to affect the growth kinetics of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa was measured. For all organisms, insulin, in the absence of a metabolizable sugar source, i.e., glucose or starch in Mueller-Hinton medium, had no effect on generation time as compared with a homologous control. Response to insulin, in the form of increased or decreased generation times, for both Gram-positive and Gram-negative bacteria, was dependent on the concentration of insulin, the concentration of glucose present, and the initial concentration of bacteria exposed to the glucose and insulin. Received: 18 January 2000 / Accepted: 10 February 2000     

一类带Monod增长率及脉冲状态反馈控制的微生物杀虫剂模型的周期解

研究了一类带Monod增长率及脉冲状态反馈控制的微生物杀虫剂模型．证明了无脉冲系统的负向全局渐近稳定性及带有脉冲状态反馈控制系统具有阶一周期解,并且给出阶一周期解存在和稳定的充分条件．数值模拟验证了理论结果．     

Microbial Growth under Supercritical CO2

Growth of microorganisms in environments containing CO₂ above its critical point is unexpected due to a combination of deleterious effects, including cytoplasmic acidification and membrane destabilization. Thus, supercritical CO₂ (scCO₂) is generally regarded as a sterilizing agent. We report isolation of bacteria from three sites targeted for geologic carbon dioxide sequestration (GCS) that are capable of growth in pressurized bioreactors containing scCO₂. Analysis of 16S rRNA genes from scCO₂ enrichment cultures revealed microbial assemblages of varied complexity, including representatives of the genus Bacillus. Propagation of enrichment cultures under scCO₂ headspace led to isolation of six strains corresponding to Bacillus cereus, Bacillus subterraneus, Bacillus amyloliquefaciens, Bacillus safensis, and Bacillus megaterium. Isolates are spore-forming, facultative anaerobes and capable of germination and growth under an scCO₂ headspace. In addition to these isolates, several Bacillus type strains grew under scCO₂, suggesting that this may be a shared feature of spore-forming Bacillus spp. Our results provide direct evidence of microbial activity at the interface between scCO₂ and an aqueous phase. Since microbial activity can influence the key mechanisms for permanent storage of sequestered CO₂ (i.e., structural, residual, solubility, and mineral trapping), our work suggests that during GCS microorganisms may grow and catalyze biological reactions that influence the fate and transport of CO₂ in the deep subsurface.     

Optimization and Control of Industrial Microbial Cultivation Processes

Compared to the immense achievements in fundamental molecular biological sciences, the improvements in the fermentation and downstream processing technologies used in industry have been less spectacular over the last decade. Hence, there is a misbalance between new cellular systems and production technologies, resulting in a decreasing annual rate of approved production processes. In its PAT initiative the U.S. Food and Drug Administration identifies the potential for continuous improvement and makes concrete suggestions how this can be achieved. Here, some of these suggestions were applied to recombinant protein production with Escherichia coli and Pichia pastoris cultures. Concretely, the development of process operational procedures is discussed that allow a more tight supervision of the processes and the automatic control in cases where processes deviate from their set‐point profiles.     

Calorimetric Studies of Microbial Growth: Quantitative Relation between Growth Thermograms and Inoculum Size

Heat evolution during growth of bakery yeast was studied in a heat-conduction calorimeter. Growth thermograms observed for yeast grown on liquid synthetic media with various inoculum sizes were compared. The quantitative relation between actual heat evolution and inoculum size was discussed in terms of the exponential growth function.     

ATP Modulates the Growth of Specific Microbial Strains

The regulatory function of extracellular ATP (exATP) in bacteria is unknown, but recent studies have demonstrated exATP induced enhanced secondary metabolite production and morphological differentiation in Streptomyces coelicolor. The growth of Streptomyces coelicolor, however, was unaffected by exATP, although changes in growth are common phenotypes. To identify bacteria whose growth is altered by exATP, we measured exATP-induced population changes in fast-growing microbes and actinomycetes in compost. Compared with the water-treated control, the addition of 10 ml 100 μM ATP to 10 g of compost enhanced the actinomycetes population by 30% and decreased fast-growing microbial numbers by 20%. Eight microbes from each group were selected from the most populated colony, based on appearance. Of the eight isolated fast-growing microbes, the 16S rRNA sequences of three isolates were similar to the plant pathogens Serratia proteamaculans and Sphingomonas melonis, and one was close to a human pathogen, Elizabethkingia meningoseptica. The growth of all fast-growing microbes was inhibited by ATP, which was confirmed in Pseudomonas syringae DC3000, a pathogenic plant bacterium. The growth of six of eight isolated actinomycetes strains, all of which were identified as close to Streptomyces neyagawaensis, was enhanced by ATP treatment. This study suggests that exATP regulates bacterial physiology and that the exATP response system is a target for the control of bacterial ecology.     

General Model of Microbial Growth and Decomposition in Aquatic Ecosystems

A model capable of simulating freely suspended and attached decomposers, particulate organic matter, labile and refractory dissolved organic matter, inorganic nitrogen, and phosphate in the open-water portion of lakes is presented. Examples are given showing the utility of the model when coupled to the whole-ecosystem model CLEANER.     

Dynamical Allocation of Cellular Resources as an Optimal Control Problem: Novel Insights into Microbial Growth Strategies

Microbial physiology exhibits growth laws that relate the macromolecular composition of the cell to the growth rate. Recent work has shown that these empirical regularities can be derived from coarse-grained models of resource allocation. While these studies focus on steady-state growth, such conditions are rarely found in natural habitats, where microorganisms are continually challenged by environmental fluctuations. The aim of this paper is to extend the study of microbial growth strategies to dynamical environments, using a self-replicator model. We formulate dynamical growth maximization as an optimal control problem that can be solved using Pontryagin’s Maximum Principle. We compare this theoretical gold standard with different possible implementations of growth control in bacterial cells. We find that simple control strategies enabling growth-rate maximization at steady state are suboptimal for transitions from one growth regime to another, for example when shifting bacterial cells to a medium supporting a higher growth rate. A near-optimal control strategy in dynamical conditions is shown to require information on several, rather than a single physiological variable. Interestingly, this strategy has structural analogies with the regulation of ribosomal protein synthesis by ppGpp in the enterobacterium Escherichia coli. It involves sensing a mismatch between precursor and ribosome concentrations, as well as the adjustment of ribosome synthesis in a switch-like manner. Our results show how the capability of regulatory systems to integrate information about several physiological variables is critical for optimizing growth in a changing environment.     

A Generic View of Classic Microbial Growth Models

General theoretical aspects are reviewed of models for microbial growth and endogenous metabolism. The focus is on a generic cell model with two components. Growth is represented as the increase of one of these components (the structural scaffolding or 'frame'). A novel feature of the present generic model is the explicit modelling of (partial) metabolic shutdown under conditions where maintenance requirements cannot be met.Two different approaches to mechanistic underpinnings for the classic models are outlined. The first approach is based on a bimolecular reaction between the non-permanent biomass component and the permanent biomass component. The second approach is based on cellular control systems.     

Anaerobic Microbial Growth from Components of Cretaceous Shales

Cretaceous rock formations have been shown to harbor extant sulfate-reducing microbial communities. At these sites, microbial activity is concentrated at rock interfaces where there is likely a diffusion of nutrients from low permeability organic rich shales to higher permeability sandstones. This study was undertaken to further characterize this process and to determine the components of shale that provide electron donors for sulfate reduction activity. To this end, samples of Cretaceous sandstones were incubated with ground shales from available depths at the Cerro Negro exploratory drilling site in northwestern New Mexico. Both sulfate consumption as an indicator of sulfate reduction and acetate production were stimulated in the sandstone-shale incubations. The greatest levels of stimulation were observed with shales originally closest to the lower sandstone-shale interface and a strong correlation was observed between shale organic carbon and microbial activity. These results suggested that the organic matter in shale was supplying the needed electron donor for the sulfate-reducing microbial community. Further evidence for this interpretation was provided when a pure culture of Acetobacterium psammolithicum , an acetogen isolated from this site, was stimulated to produce acetate by the addition of autoclaved shales. To investigate the components in shale that were responsible for stimulating microbial activity, we extracted shale organic material. Aqueous extracts and to a lesser extent neutral ether extractions stimulated activity although neither to the same extent as the shale itself. Alkaline aqueous extracts were fractionated using XAD-7 resin. Each of the fractions contributed to some degree, but the greatest stimulation in microbial activity was attributed to both the hydrophilic eluate and to the fulvic acid fraction. These data indicate that a relatively complex group of organic compounds supply electron donors to the sandstone microbial communities.     

Effect of Androgens and Glucocorticoids on Microbial Growth and Antimicrobial Susceptibility

The effects of androgens, testosterone and dihydrotestosterone (DHT), of an environmental anti-androgen, 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (DDE), and of glucocorticoids, hydrocortisone and dexamethasone, on growth kinetics and antibiotic susceptibility of E. faecalis, E. coli, P. aeurginosa, and S. aureus were measured. For P. aeurginosa, the presence of either DHT or DDE caused at least a fourfold shift in the minimum inhibitory concentration (MIC) of cefepime and tobramycin. DHT and DDE also affected the response of E. faecalis to meropenem and norfloxacin, resulting in a shift from sensitive to intermediate resistance (four-fold increase in MIC). Hydrocortisone (2 M) induced an increase in the sensitivity of S. aureus to erythromycin, as compared to hormone-free control (from 0.5 to 0.06 g/mL). The susceptibility pattern of E. coli was unaffected by the hormones tested. These changes in susceptibility to antibiotics were unrelated to alterations in growth kinetics. For all organisms tested, the alterations in MICs occurred only in the presence of hormone, indicative of changes in the phenotype of these stable quality control strains.