Light-Induced Body Movement of Euglena gracilis Coupled to Flagellar Photophobic Responses by Mechanical Stimulation*†

SYNOPSIS. In low viscosity media, Euglena gracilis strain Z responds to a sudden change in light intensity by a cessation of forward movement, followed by a reorientation of the locomotor flagellum which results in turning of the cell around the lateral axis (photophobic response). At a viscosity interface between low [～ 1 cP (centipoise)] and high (4000 cP) media, the cells exhibit avoidance responses or become immobilized in the higher viscosity medium. Upon changing the light intensity, free swimming cells have photophobic responses, while immobilized ones undergo body contractions. For cells immersed in media of varying viscosity, the delay between light stimulation and body contraction (transduction time) is shortest at high viscosities. From 500 to 2000 cP, where the cells are capable of both movement and light-induced body contractions, there is a logarithmic dependence of the transduction time on the viscosity. The transduction time does not vary appreciably with the intensity of the primary light stimulus within a range of 0.14-1.13 kW/m².     

Ammonium uptake in carrot cell structures is influenced by pH-dependent cell aggregation

Semicontinuously grown wild carrot ( Daucus carota L.) cells were used in an investigation of the effect of culture medium pH on ammonium uptake in suspension cultures as a first step in exploring the relationship between pH and anthocyanin biosynthesis. In contrast to published data showing decreasing uptake rates with decreasing culture medium pH, ammonium-limited, semicontinuous carrot cell cultures showed a 25% greater ammonium uptake rate at pH 4.5 than at pH 5.5. When cells that had been grown semicontinuously in medium with a pH of 4.5 or 5.5 were grown in batch cultures at pH 4.5, 5.5 or 6.5 the ammonium uptake rates were those of the semicontinuous cultures, indicating that the pH of the batch culture medium had no effect on ammonium uptake rates over 7 days. The cell culture was composed of very small aggregates when it was grown semicontinuously in medium at pH 4.5, but was composed of large aggregates when it was grown semicontinuously in medium at pH 5.5. The aggregation/disaggregation of the cells was pH dependent, as changing the pH of the semicontinuous culture medium altered the extent of the aggregation. We conclude that the change in culture medium pH caused the cells to aggregate or disaggregate which in turn decreased or increased the rate of ammonium uptake from the medium.     

Kinetic model of the inhibition of respiration by endogenous nitric oxide in intact cells

Nitric oxide (NO) inhibits mitochondrial respiration by decreasing the apparent affinity of cytochrome c oxidase (CcO) for oxygen. Using iNOS-transfected HEK 293 cells to achieve regulated intracellular NO production, we determined NO and O₂ concentrations and mitochondrial O₂ consumption by high-resolution respirometry over a range of O₂ concentrations down to nanomolar. Inhibition of respiration by NO was reversible, and complete NO removal recovered cell respiration above its routine reference values. Respiration was observed even at high NO concentrations, and the dependence of IC₅₀ on [O₂] exhibits a characteristic but puzzling parabolic shape; both these features imply that CcO is protected from complete inactivation by NO and are likely to be physiologically relevant. We present a kinetic model of CcO inhibition by NO that efficiently predicts experimentally determined respiration at physiological O₂ and NO concentrations and under hypoxia, and accurately predicts the respiratory responses under hyperoxia. The model invokes competitive and uncompetitive inhibition by binding of NO to the reduced and oxidized forms of CcO, respectively, and suggests that dissociation of NO from reduced CcO may involve its O₂-dependent oxidation. It also explains the non-linear dependence of IC₅₀ on O₂ concentration, and the hyperbolic increase of c₅₀ as a function of NO concentration.     

Optimal surveillance strategy for invasive species management when surveys stop after detection

Invasive species are a cause for concern in natural and economic systems and require both monitoring and management. There is a trade‐off between the amount of resources spent on surveying for the species and conducting early management of occupied sites, and the resources that are ultimately spent in delayed management at sites where the species was present but undetected. Previous work addressed this optimal resource allocation problem assuming that surveys continue despite detection until the initially planned survey effort is consumed. However, a more realistic scenario is often that surveys stop after detection (i.e., follow a “removal” sampling design) and then management begins. Such an approach will indicate a different optimal survey design and can be expected to be more efficient. We analyze this case and compare the expected efficiency of invasive species management programs under both survey methods. We also evaluate the impact of mis‐specifying the type of sampling approach during the program design phase. We derive analytical expressions that optimize resource allocation between monitoring and management in surveillance programs when surveys stop after detection. We do this under a scenario of unconstrained resources and scenarios where survey budget is constrained. The efficiency of surveillance programs is greater if a “removal survey” design is used, with larger gains obtained when savings from early detection are high, occupancy is high, and survey costs are not much lower than early management costs at a site. Designing a surveillance program disregarding that surveys stop after detection can result in an efficiency loss. Our results help guide the design of future surveillance programs for invasive species. Addressing program design within a decision‐theoretic framework can lead to a better use of available resources. We show how species prevalence, its detectability, and the benefits derived from early detection can be considered.     

产小檗碱诱变菌株培养条件的优化

S-NU-3-2菌株是对源自药用植物黄檗的内生真菌S6进行诱变获得的小檗碱产量比出发菌株有明显提高的突变株,本研究对其培养条件进行了优化,以期进一步提高其产量,为开发利用真菌发酵生产植物活性成分的新途径奠定基础。以菌丝生长和小檗碱产量为指标,筛选出了适宜该菌株发酵的基本培养基、碳源、氮源、光照和培养温度,并经进一步的正交试验优化,得出该高产菌株的最佳培养条件为豆芽汁基本培养基含蔗糖3%,酵母膏0.2%,pH7.0,温度26℃,全光照培养。与初始培养条件相比,在优化后的条件下,该菌株的小檗碱得率提高了47.2%,菌体生物量提高了24%。     

Common co-lipids, in synergy, impart high gene transfer properties to transfection-incompetent cationic lipids

Efficacious cationic transfection lipids usually need either DOPE or cholesterol as co-lipid to deliver DNA inside the cell cytoplasm in non-viral gene delivery. If both of these co-lipids fail in imparting gene transfer properties, the cationic lipids are usually considered to be transfection inefficient. Herein, using both the reporter gene assay in CHO, COS-1 and HepG2 cells and the whole cell histochemical X-gal staining assay in representative CHO cells, we demonstrate that common co-lipids DOPE, Cholesterol and DOPC, when act in synergy, are capable of imparting improved gene transfer properties to a novel series of cationic lipids (1-5). Contrastingly, lipids 1-5 became essentially transfection-incompetent when used in combination with each of the pure co-lipid components alone.     

Microtubule destruction induces tau liberation and its subsequent phosphorylation

Neurofibrillary tangle-bearing neurons, a pathological hallmark of Alzheimer’s disease, are mostly devoid of normal microtubule (MT) structure and instead have paired helical filaments that are composed of abnormal hyperphosphorylated tau. However, a causal relationship between tau phosphorylation and MT disruption has not been clarified. To examine whether MT disruption induces tau phosphorylation, stathmin, an MT-disrupting protein, was co-expressed with tau in COS-7 cells. Stathmin expression induced apparent MT catastrophe and tau hyperphosphorylation at Thr-181, Ser-202, Thr-205, and Thr-231 sites. In contrast, c-Jun N-terminal kinase activation, or phosphatase inhibition, led to significant tau phosphorylation without affecting MT structure. These findings suggest that MT disruption induces subsequent tau phosphorylation.     

Evolutionary and swarm intelligence‐based approaches for optimization of lipase extraction from fermented broth

Evolutionary and swarm intelligence‐based optimization approaches, namely genetic algorithm (GA) and particle swarm optimization (PSO), were utilized to determine the optimal conditions for the lipase extraction process. The input space of the nonlinear response surface model of lipase extraction served as the objective function for both approaches. The optimization results indicate that the lipase activity was significantly improved, more than 20 U/g of dry substrate (U/gds), in both approaches. PSO (133.57 U/gds in the 27th generation) outperforms GA (132.24 U/gds in the 320th generation), slightly in terms of optimized lipase activity and highly in terms of convergence rate. The simple structure associated with the effective memory capability of PSO renders it superior over GA. The proposed GA and PSO approaches, based on a biological phenomenon, are considered as natural and thus may replace the traditional gradient‐based optimization approaches in the field of downstream processing of enzymes.     

Critical adjustment of cysteine and glutamine concentrations for improved clonal growth of WI-38 cells

Summary Clonal growth of WI-38 cells with a plating efficiency of 45% has been achieved in a synthetic nutrient mixture (MCDB 102) supplemented with either whole or dialyzed fetal bovine serum. For optimum growth, the concentration of cysteine in the medium must be adjusted precisely. Deviation by a factor of three in either direction from the optimum concentration (9.0×10⁻⁵M) eliminates essentially all clonal growth. A high concentration of glutamine (2.5×10⁻³M) is also needed for, optimum clonal growth. Presented in preliminary form at the 26th Annual Meeting of the Tissue Culture Association, June 4, 1975. This work was supported by Grant No. HD-08181 from the National Institute of Child Health and Human Developement, Grant No. AG-00310 from the National Institute on Aging, and by Contract No. 223-74-1156 from the Bureau of Biologics, Food and Drug Administration.