Inhibitory Effects of Phenolic Ecotoxicants on Photobacteria at Various pH Values

Kinetic characteristics of light emission by intact cells of photobacteria Photobacterium phosphoreum and Vibrio harveyi were studied (at pH 5.5, 7.0, and 8.0), as well as inhibitory effects of 2,4-di- and 2,4,5-triphenoxyacetic acids (2,4-D and 2,4,5-T), pentachlorophenol (PCP), and 2,6-dimethylphenol (2,6-DMP) (at the same pH values). The emission kinetics lacked a steady state, irrespective of pH. At pH 5.5, luminescence decayed exponentially in the 60-s range; at pH 7.0 and 8.0, a 5-min luminescence activation was observed. The respiratory activity of the cells decreased by more than an order of magnitude at pH 5.5 (compared to the levels observed at pH 7.0 and 8.0). The inhibitory effects of 2,4-D, 2,4,5-T, and PCP differed by one to two orders of magnitude, depending on pH. Maximum cell sensitivity to these compounds appeared at pH 5.5; minimum sensitivity, at pH 8.0. The effect of 2,6-DMP was pH-independent. The inhibitory effect was determined by the hydrophobicity of the molecule and pK values of the toxicants. At all pH values, substrate-depleted cells of photobacteria were more sensitive to chlorophenolic compounds than cells supplied with energy.     

Response of two wetland plant species to Cd exposure at low and neutral pH

Emerged and submerged plants are used in treating various metal-containing wastewaters, such as stormwater (neutral pH) and acid mine drainage (low pH). The aim was to investigate the appearance of a set of possible mechanisms to detoxify Cd in plants and whether their appearance differ due to the surrounding pH and/or plant type. One emergent (Carex rostrata) and one submerged (Elodea canadensis) macrophyte were exposed to 0, 0.05, and 0.5 μM Cd for 3 d in hydroponic solutions at pH 3.5 and 6.9. We analysed cadmium accumulation, thiol-rich peptide concentrations and cell wall-bound Cd in plants, organic acid content and pH change in surrounding water cation exchange capacity (CEC) of plant tissue. Both plant species accumulated Cd in their tissues, and thus did not exclude it and C. rostrata decreased the relative Cd distribution to its shoots with increasing Cd addition. In both species, Cd was immobilized through cell wall binding, and thiol-rich peptides synthesized in the presence of Cd that may participate in Cd binding. In addition, E. canadensis increased its CEC by synthesizing new metal-binding sites in the cell walls. Organic acid composition in surrounding water did not change with Cd addition and had no effect on Cd detoxification. However, E. canadensis increased the surrounding pH from pH 3.5 in the presence of Cd; the surrounding pH did not, however, influence the detoxification mechanisms.     

Effect of External pH on the Internal pH of Chlorella saccharophila

The overall internal pH of the acid-tolerant green alga, Chlorella saccharophila, was determined in the light and in the dark by the distribution of 5,5-dimethyl-2-[¹⁴C]oxazolidine-2,4-dione ([¹⁴C]DMO) or [¹⁴C]benzoic acid ([¹⁴C]BA) between the cells and the surrounding medium. [¹⁴C]DMO was used at external pH of 5.0 to 7.5 while [¹⁴C]BA was used in the range pH 3.0 to pH 5.5. Neither compound was metabolized by the algal cells and intracellular binding was minimal. The internal pH of the algae obtained with the two compounds at external pH values of 5.0 and 5.5 were in good agreement. The internal pH of C. saccharophila remained relatively constant at pH 7.3 over the external pH range of pH 5.0 to 7.5. Below pH 5.0, however, there was a gradual decrease in the internal pH to 6.4 at an external pH of 3.0. The maintenance of a constant internal pH requires energy and the downward drift of internal pH with a drop in external pH may be a mechanism to conserve energy and allow growth at acid pH.     

Ozone-induced Loss of Intracellular Potassium Ion from Chlorella sorokiniana

The unicellular algae Chlorella sorokiniana was used as a model system to investigate the interaction of ozone with plant cell membranes. Ozone induces K⁺ leakage from Chlorella sorokiniana similar to the electrolytic loss observed from many higher plants under stressful conditions. The kinetics of this leakage indicate that ozone initially interacts reversibly (within sec) with sites on membranes allowing a passive efflux of K⁺. This efflux ceases within minutes after the ozone stress is removed. This return to normal efflux is very temperature dependent. High intracellular osmolarity seems to be an important criterion of susceptibility to ozone injury in this model system, since rates of ozone-induced K⁺ leakage are less when the external osmotic potential is decreased by suspension of the cells in mannitol. Cell interaction with ozone is further complicated by a saturating-type dependence of the K⁺ efflux upon ozone concentration within the medium.     

Cyclic Amp Response to Various Haemopoietic Regulators

Diffusible inhibitors and stimulators are involved in the regulation of bone marrow pluripotent stem cell (CFU-S) proliferation. We have previously shown the existence of CFU-S inhibitors in foetal calf marrow and liver and have started their purification. the lack of a simple and time-saving test to determine the kinetic state of CFU-S and the activity of the inhibitors led us to explore the possibility of a biochemical proliferation marker that could be used for screening purpose. Since it was shown that cyclic AMP was implicated in the regulation of CFU-S proliferation, it was of interest to study the variations in cAMP levels after stimulation and inhibition of CFU-S entry into cycle. the results of in vitro experiments showed that the increase in cAMP levels observed in bone marrow cells after incubation with different haemopoietic stimulators was specific neither for bone marrow cells nor for the various haematopoietic regulators. In the in vivo experiments, an increased cAMP level was observed 8 hr after one injection of Ara-C at the time when CFU-S are recruited into S phase. However, no modification of cAMP levels has been observed after injection of CFU-S inhibitors in the Ara C-treated mice. Although cAMP does not seem to be a suitable marker for testing the activity of inhibitory fractions during the purification process, this work has contributed to the study of CFU-S stimulators.     

进化与未进化小球藻响应苯酚的转录组学分析

苯酚是工业废水中典型的环境污染物。小球藻(Chlorella sp.)由于其生长快、抗逆性强,可以有效利用废水中的酚类化合物,是最有潜力的含酚废水处理藻株。但是高浓度苯酚产生的氧化压力会造成小球藻细胞的氧化损伤。通过实验室适应性进化已经得到了可以耐受500mg/L苯酚的小球藻藻株(L5)。通过无参比较转录组学数据,在基因组尺度上考察了原始小球藻(L3)和进化后小球藻对高浓度苯酚的响应差异。无参比较转录组学结果表明,进化后小球藻能够耐受并降解高浓度苯酚是多个代谢途径整体调控的结果。相比于原始小球藻,进化后小球藻在500mg/L苯酚浓度下对苯酚氧化胁迫的响应增强,主要体现在细胞信号转导、ABC转运蛋白、热休克蛋白、氮代谢和三羧酸循环(TCA)等相关的转录水平明显上调。进化后小球藻通过这些响应降低高浓度苯酚产生的氧化压力。     

Potassium/proton antiport system of growing Enterococcus hirae at high pH.

The cytoplasmic pH (pHin) of Enterococcus hirae growing at pH 9.2 was maintained at about 8.1. Membrane-permeating amines such as ammonia alkalinized the pHin from 8.1 to 9.0 at a high concentration and induced K+ extrusion. The pHin alkalinization was transient; the pHin fell from 9.0 to the original value of pH 8.1, at which point K+ extrusion ceased, and remained constant. Cells accumulated ammonium ion to an extent stoichiometrically equivalent to the K+ loss. This bacterium continued to grow well under this condition. These results suggest that the pHin-responsive primary K+/H+ antiport system (Y. Kakinuma, and K. Igarashi, J. Biol. Chem. 263:14166-14170, 1988) works for the pHin regulation of this organism growing at a high pH.     

The Hyperpolarization of the Chara Membrane at High pH: Effects of External Potassium, Internal pH, and DCCD

At high external pH, the Chara membrane is known to switch toa new state in which the membrane potential is highly negative;it has been characterized as a passive diffusion potential forH⁺ (or 0H^–). DCCD is shown to inhibit the increased conductanceand the highly negative membrane potential associated with thisstate. DCCD also inhibits the plasmalemma H⁺-ATPase, as wellas cytoplasmic streaming. The alkaline state of the membraneis shown to involve a decreased permeability to K⁺; this enhancesthe selectivity for H⁺ (or OH^–) which results from theincreased permeability to H⁺ (or OH^–). Altering the cytoplasmicpH affects the membrane potential at both neutral and alkalinepH. It can also affect the ability of the cell to make the transitionto the alkaline state.     

Potassium uptake with low affinity and high rate in Enterococcus hirae at alkaline pH

Two high-affinity K+ uptake systems, KtrI and KtrII, have been reported in Enterococcus hirae. A mutant, JEMK1, defective in these two systems did not grow at pH 10 in low-K+ medium (less than 1 mM K+), but grew well when supplemented with 10 mM KCl. In this mutant, we found an energy-dependent K+ uptake at pH 10 with a low affinity for K+ (Km of approximately 20 mM) and an extremely high rate [Vmax of 1.6 micromol x min(-1) (mg protein)(-1)]. Rb+ uptake [Km of approximately 40 mM and Vmax of 0.5 micromol x min(-1) (mg protein)(-1)], which was inhibited competitively by K+ and less prominently by Cs+, was also observed. The specificity of this transport is likely to be K+>Rb+>Cs+. This peculiar K+ transport plays a role as a salvage mechanism against defects in high-affinity systems in the K+ homeostasis of this bacterium.     

Potassium transport in Neurospora. Evidence for a multisite carrier at high pH

At low extracellular pH (4–6), net uptake of potassium by Neurospora is a simple exponential process which obeys Michaelis kinetics as a function of [K]_o. At high pH, however, potassium uptake becomes considerably more complex, and can be resolved into two distinct exponential components. The fast component (time constant = 1.2 min) is matched quantitatively by a rapid loss of sodium; it is attributed to ion exchange within the cell wall, since it is comparatively insensitive to low temperature and metabolic inhibitors. By contrast, the slower component (time constant = 10.9 min) is inhibited markedly at 0°C and by CN and deoxycorticosterone, and is thought to represent carrier-mediated transport of potassium across the cell membrane. This transport process exhibits sigmoid kinetics as a function of [K]_o; the data can be fitted satisfactorily by two different two-site models (one involving a carrier site and a modifier site, the other an allosteric model). Either of these models could also accommodate the simple Michaelis kinetics at low pH.     

Response of completely mixed systems to pH shock

The response of aerobically growing heterogeneous microbial populations of sewage origin to step increases and decreases in pH were studied in both once-through and cell recycle systems. The pH range studied was 2.7 to 8.0. All studies were conducted at a dilution rate of 0.125 hr^?1, and all shocks were administered from a base or preshock pH level of 6.4 to 6.7. In each experiment, the preshock or initial “steady state” was assessed, the pH of the feed changed, and the resulting transient behavior of the system examined until attainment of the new or final “steady state” was approached. The major objectives of the work were to characterize the nature of the response with respect to biomass and effluent substrate concentrations, types of microbial populations present and chemical composition of the biomass, and to obtain guidelines as to allowable change in pH in waste streams. It was found in once-through systems that substrate removal efficiency recovered from pH levels as low as 3.0 after rather long periods of transient leakage of substrate. Cell recycle attenuated the severity of substrate leakage. In all cases of severe acid shock, the microbial population changed from predominantly bacterial-protozoan to one consisting predominantly of filamentous fungi. Changes in chemical composition of the sludge (protein and carbohydrate content) were consistent with the population changes. Based upon the results, it can be conservatively estimated that changes in pH of no more than one unit from the neutral preshock range can be tolerated without possible disruption of biochemical efficiency of substrate removal.     

不同条件下鲤鱼鳃部对高岭土颗粒吸附态铜的吸收

在水相溶解态铜浓度和高岭土吸附态铜浓度保持不变,pH和高岭土粒径不同条件下,研究了鲤鱼鱼鳃对铜的吸收。结果表明在本研究范围内,吸附态铜的存在增加了鱼鳃吸收。鳃对铜的吸收随pH增加而递增,随高岭土粒径减少而递增。利用MINTEQA2软件分析了不同实验条件下鱼鳃微环境中铜的形态分布特征,对吸附态铜可能的生物有效性机制进行了说明。     

Denaturation and in Vitro Gastric Digestion of Heat-Treated Quinoa Protein Isolates Obtained at Various Extraction pH

The aim of this study was to determine the influence of heat processing on denaturation and digestibility properties of protein isolates obtained from sweet quinoa (Chenopodium quinoa Willd) at various extraction pH values (8, 9, 10 and 11). Pretreatment of suspensions of protein isolates at 60, 90 and 120 °C for 30 min led to protein denaturation and aggregation, which was enhanced at higher treatment temperatures. The in vitro gastric digestibility measured during 6 h was lower for protein extracts pre-treated at 90 and 120 °C compared to 60 °C. The digestibility decreased with increasing extraction pH, which could be ascribed to protein aggregation. Protein digestibility of the quinoa protein isolates was higher compared to wholemeal quinoa flour. We conclude that an interactive effect of processing temperature and extraction pH on in vitro gastric digestibility of quinoa protein isolates obtained at various extraction pH is observed. This gives a first indication of how the nutritional value of quinoa protein could be influenced by heat processing, protein extraction conditions and other grain components.