Growth characteristics of a new methylomonad.

A methylomonad culture was isolated from pond water and examined as a potential source of single-cell protein. A medium containing magnesium sulfate, ammonium hydroxide, sodium phosphate, tap water, and methanol supported the growth of the isolate. Optimal growth conditions in batch cultures for the organism were: temperature, 30 to 33 degrees C; pH 7.1; and phosphate concentration, 0.015 M. The minimum doubling time obtained was 1.6 h. The specific growth rate in batch culture was dependent on the methanol concentration, reaching a maximum around 0.2% (wt/vol). Growth inhibition was apparent above 0.3% (wt/vol), and growth was completely inhibited above 4.6% (wt/vol) methanol. Although the inhibitory effect of formaldehyde on the specific growth rate was much greater than that of formate, the organism utilized formaldehyde, but not formate, as a sole carbon and energy source in batch cultures. The isolate was identified primarily by its inability to utilize any carbon source other than methanol and formaldehyde for growth. Although it is capable of rapid growth on methanol, the organism showed a very weak catalase activity. The amino acid content of the cells compared favorably with the reference levels for the essential amino acids specific by the Food and Agricultural Organization of the United Nations.     

Growth characteristics of a new methylomonad.

A methylomonad culture was isolated from pond water and examined as a potential source of single-cell protein. A medium containing magnesium sulfate, ammonium hydroxide, sodium phosphate, tap water, and methanol supported the growth of the isolate. Optimal growth conditions in batch cultures for the organism were: temperature, 30 to 33 degrees C; pH 7.1; and phosphate concentration, 0.015 M. The minimum doubling time obtained was 1.6 h. The specific growth rate in batch culture was dependent on the methanol concentration, reaching a maximum around 0.2% (wt/vol). Growth inhibition was apparent above 0.3% (wt/vol), and growth was completely inhibited above 4.6% (wt/vol) methanol. Although the inhibitory effect of formaldehyde on the specific growth rate was much greater than that of formate, the organism utilized formaldehyde, but not formate, as a sole carbon and energy source in batch cultures. The isolate was identified primarily by its inability to utilize any carbon source other than methanol and formaldehyde for growth. Although it is capable of rapid growth on methanol, the organism showed a very weak catalase activity. The amino acid content of the cells compared favorably with the reference levels for the essential amino acids specific by the Food and Agricultural Organization of the United Nations.     

网柄细胞状黏菌生物学特性及其应用研究进展

网柄细胞状黏菌是一类介于植物和动物之间的原生生物。尽管形态微小,但因为同时具有动物细胞和植物细胞的特点,且生命周期短暂易重复,故而对其进行生物学特性及应用的研究具有重要价值。本文从网柄细胞状黏菌的生活史循环、生物学特性、生态多样性、在医学和药物领域的探索及其与其他微生物关系等5个方面探讨网柄细胞状黏菌的生物学特性及应用的研究进展及意义,展望网柄细胞状黏菌未来在医学和生态等方面的研究前景及其潜在的应用价值,旨在为我国网柄细胞状黏菌同其他领域的交叉研究相结合提供视野,探索其在促进人类的科学进步、改善生活环境及攻克疾病方面的作用及意义。     

Growth of myxamoebae of the cellular slime mould Dictyostelium discoideum in axenic culture

1. A simple axenic medium suitable for the growth of the myxamoebae of a strain of the cellular slime mould Dictyostelium discoideum is described. 2. Procedures suitable for the growth of this strain in liquid and on solid media are described. 3. Conditions suitable for initiating the cell differentiation of myxamoebae grown axenically are described.     

菹草无性系季节生长速度和生物量分配特征

研究了菹草(Potamogeton crispus L.)无性系在典型发育阶段的生长特征, 结果表明: 随着无性系的生长, 叶生物量比例增高, 茎生物量比例降低, 根状茎和根生物量占总生物量的比例较稳定, 成熟无性系各组分所占比例依次为叶＞茎＞根状茎和根。各发育阶段无性系小株生物量增长特征不同, 越冬期和繁殖期小株叶、茎生物量均与小株株高呈幂函数异速生长, 而指数生长期叶生物量与小株株高呈指数生长, 各发育阶段小株总生物量向叶茎组分的分配比例不同。无性系小株上部、中部、下部叶面积与小株株高之间在幼苗生长期和越冬期呈幂函数异速生长, 而在指数生长期和繁殖期呈线性同速生长, 尤其上部叶面积与高度间极显著正相关的水平最高。     

Growth characteristics of Candida utilis in a multistage culture system

The effect of increasing ethanol concentration in the feed on the growth and physiological activity of the yeast Candida utilis was studied. At steady-state of continuous culture with constant values of dilution rate, temperature, and pH in all fermenters in series biomass, ethanol and volatile acid concentrations, biomass yield and productivity and respiration activity were measured. In the three-stage system the maximum biomass concentration in the effluent and maximum productivity was achieved between 20 and 25 g ethanol/l in the feed. At higher concentrations, ethanol negatively affects the coupling of oxidative phosphorylation and respiratory control of cells resulting in a decrease in biomass yield and intracellular protein content. It was shown that the presence of acetate in the medium inhibits the respiration activity of yeasts growing on ethanol.     

Cell density dependence of the aggregation characteristics of the cellular slime mould Dictyostelium discoideum.

We have measured fruiting body density and spore formation efficiency in Dictyostelium discoideum as functions of initial cell density. Experiments were performed on agar made up with distilled water and on buffered agar. Minor differences are seen; these are discussed. The functions show 4 regions of density dependence which can be accounted for by changes in aggregation characteristics with density and changes in the efficiency of spore differentiation. The results are discussed in terms of the relaying mechanism for signal propagation controlling cell aggregation. They extend earlier measurements by Bonner & Dodd and by Hohl & Raper, supply data for a quantitative model of the aggregation process, allow estimates of signal range, and show the importance of entrainment between neighbouring centres in defining aggregation territories.     

Galvanotaxis of slime mold

The plasmodium of Physarum polycephalum reacts to direct current by migration toward the cathode. Cathodal migration was obtained upon a variety of substrata such as baked clay, paper, cellophane, and agar with a current density in the substratum of 1.0 microa./mm.(2) Injury was produced by current densities of 8.0 to 12.0 microa./mm.(2) The negative galvanotactic response was not due to electrode products. Attempts to demonstrate that the response was due to gradients or orientation in the substratum, pH changes in the mold, cataphoresis, electroosmosis, or endosmosis were not successful. The addition of salts (CaCl(2), LiCl, NaCl, Na(2)SO(4), NaHCO(3), KCl, MgSO(4), sodium citrate, and sea water) to agar indicated that change of cations had more effect than anions upon galvanotaxis and that the effect was upon threshold values. K ion (0.01 M KCl) increased the lower threshold value to 8.0 microa./mm.(2) and the upper threshold value to 32.0 microa./mm.(2), whereas the Li ion (0.01 M LiCl) increased the lower threshold to only 4.0 microa./mm.(2) and the upper threshold to only 16.0 microa./mm.(2) The passage of electric current produced no increase in the rate of cathodal migration; neither was there a decrease until injurious current densities were reached. With increase of subthreshold current densities there was a progressive decrease in rate of migration toward the anode until complete anodal inhibition occurred. There was orientation at right angles to the electrodes in alternating current (60 cycle) with current density of 4.0 microa./mm.(2) and in direct current of 5.0 microa./mm.(2) when polarity of current was reversed every minute. It is concluded that the negative galvanotactic response of P. polycephalum is due to inhibition of migration on the anodal side of the plasmodium and that this inhibition results in the limitation of the normal migration of the mold to a cathodal direction. The mechanism of the anodal inhibition has not been elucidated.     

The control of re-invasion by rats of part of a sewer network

Re-infestation by rats (Rattus norvegicus Berk.) of a section of a sewer network was studied by recording bait consumption in the manhole chambers for periods up to 18 weeks after each of three attempts to rid the section of rats. The mean rate of increase of the rat population was of the order of 20 % per week both when the section was surrounded by a permanently poison-baited zone as a barrier against re-invasion from the connected, still heavily-infested sewers, and when this barrier was absent. When, however, infestation in the connected sewers was reduced by poisoning, and the poison-bait barrier was maintained, the mean weekly rate of increase in the section declined to 4·4% and could be attributed substantially to breeding. It is concluded that the type of poison-bait barrier used in the present trials is insufficient to prevent invasion of one part of a sewer network from another if the population density in the latter is high.     

Growth characteristics of ultrahigh-density microalgal cultures

The physiological characteristics of cultures of very high cell mass (e.g. 10 g cell mass/L), termed “ultrahigh cell density cultures” is reviewed. A close relationship was found between the length of the optical path (OP) in flat-plate reactors and the optimal cell density of the culture as well as its areal (g m⁻² day⁻¹) productivity. Cell-growth inhibition (GI) unfolds, as culture density surpasses a certain threshold. If it is constantly relieved, a 1.0 cm OP reactor could produceca. 50% more than reactors with longer OP,e.g. 5 or 10 cm. This unique effect, discovered by Hu et al. [3], is explained in terms of the relationships between the frequency of the light-dark cycle (L-D cycle), cells undergo in their travel between the light and dark volumes in the reactor, and the turnover time of the photosynthetic center (PC). In long OP reactors (5 cm and above) the L-D cycle time may be orders of magnitude longer than the PC turnover time, resulting in a light regime in which the cells are exposed along the L-D cycle, to long, wasteful dark periods. In contrast, in reactors with an OP ofca. 1.0 cm, the L-D cycle frequency approaches the PC turnover time resulting in a significant reduction of the wasteful dark exposure time, thereby inducing a surge in photosynthetic efficiency. Presently, the major difficulty in mass cultivation of ultrahigh-density culture (UHDC) concerns cell grwoth inhibition in the culture, the exact nature of which is awaiting detailed investigation.