Assessment of pleiotropic effects of a gene substitution in pea by two-dimensional polyacrylamide gel electrophoresis

We examined, by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), near-isogenic lines of the r-gene in pea (Pisum sativum) which determines round (RR) vs. wrinkled (rr) seed. The study was undertaken to assess the number of protein changes resulting from a single gene substitution as a means of quantifying pleiotropic effects. A total of 636 to 770 resolvable polypeptides were identical in all respects between RR and rr for roots, shoots, leaflets, stipules, young ovaries, and young embryos. A single difference between the lines became evident about 21-23 days after anthesis in the embryos. Mature seeds of the two lines showed 62 spot differences in addition to differences in four clusters of spots, representing about 10% of the total number of spots visible on the gels. The protein differences are presumably involved in the many known physiological differences of the two seed types. 2-D PAGE analyses of near-isogenic lines are likely to be valuable in a number of quantitative and developmental genetic contexts.     

Improved performance in viscous mycelial fermentations by agitator retrofitting

For viscous mycelial fermentations it was demonstrated at the pilot-plant scale that the replacement of standard radial flow Rushton turbines with larger diameter axial-flow Prochem hydrofoil impellers significantly improved oxygen transfer efficiency. It was also determined that the Streptomyces broth under evaluation is highly shear thinning. Separate experiments using a Norcardia broth with similar Theological properties demonstrated that the oxygen transfer coefficient, K(L)a, can be greatly increased by use of water additions to reduce broth viscosity. These observations are consistent with the hypothesis that the improvement in oxygen transfer by changing agitator types is primarily due to an improvement in bulk mixing. A model is presented, based on the concepts of Bajpai and Reuss, which explains this improvement in performance in terms of enlargement of the well mixed micromixer region for viscous mycelial broths.     

Revised enzyme synthesis rate expression in cybernetic models of bacterial growth

A revised enzyme synthesis rate expression for cybernetic models of bacterial growth is presented. The rate expression, which is comprised of inducible and constitutive contributions, provides for a basal enzyme level that is necessary to predict certain types of commonly observed continuous culture transients. The response of a continuous culture to a step change in feed stream composition is simulated using both the old and new formulations, and the ramifications for the "matching-law" formulation are discussed.     

New instrument for on-line viscosity measurement of fermentation media

In an attempt to resolve the difficult problem of on-line determination of the viscosity of non-Newtonian fermentation media, the authors have used a vibrating rod sensor mounted on a bioreactor. The sensor signal decreases nonlinearly with increased apparent viscosity. Electronic filtering of the signal damps the interfering effect of aeration and mechanical agitation. Sensor drift is very low (0.03% of measured value per hour).On the rheological level the sensor is primarily an empirical tool that must be specifically calibarated for each fermentation process. Once this is accomplished, it becomes possible to establish linear or second-degree correlations between the electrical signal from the sensor and the essential parameters of the ferementation process in question (pH of a feremented milk during acidification, concentration of extra cellular polysaccharide). In addition, by applying the power law to describe the rheological behavior of fermentation media, we observe a second-order polynomial correlation between the sensor signal and the behavior index (n).     

Influence of immobilization procedure and salt environment on functional stability of chloroplast membranes: experimental data and numerical analysis

The interactions between chloroplast membranes and their microenvironment within artificial matrices (albumin-glutaraldehyde matrix, polyurethane foam) where investigated. Particularly, the influence of a high-ionic-strength medium (0.75 M potassium citrate) on the stability of the photosynthetic ferricyanide reduction by immobilized thylakoids has been studied. A method of data analysis based on a nonlinear identification method combined with the numerical integration of the equation of the transient state of the continuous stirred tank reactor (CSTR) is proposed to estimate the actual degradation of the photosynthetic electron transfer. A statistical analysis achieved on the parameter values has allowed a quantitative assessment of the global behavior of immobilized chloroplast membranes. From the mathernatical analysis of the experimental data, we demonstrate that citrate used in the reaction media prevents the photoinactivation of the electron transfer chain whatever the nature of the matrix or the type of the reactor. The use of an albumin-glutaraldehyde matrix or an open reactor during experiments also has allowed a better stabilization of the photosystems under operational conditions.     

Improved performance of intensive semicontinuous cultures of Scenedesmus by biomass recirculation

The microscopic green alga, Scenedesmus obliquus, was used in a semicontinuous culture system for the tertiary treatment of urban wastewater, with the simultaneous production of usable biomass. Partial biomass recycling was used to increase the productivity of the system by overcoming the limits imposed by the low maximal growth rate of the alga. The biomass to be recycled was collected by simple gravity settling of the removed culture.The culture system was operated at different dilution rates and its productivity measured at each rate. An evaluation of the crude nutrient composition of the algae produced at each dilution rate was also carried out.The system was found to operate stably at dilution rates of up to 0.8 day(-1) which represents a 20% net increase over the maximum dilution rate allowed under the same conditions in a system without recirculation. The composition of the biomass produced varied little over a range of dilution rates, which may be of relevance to its projected end-use.The study indicated that such a system can exploit available light to the full and should be of particular value for the treatment of low-strength wastes such as we employed.     

On-line adaptive control of a fed-batch fermentation of Saccharomyces cerevisiae

The feasibility of applying an adaptive control technique to a fermentation process is investigated. The nonlinear, time-variant parameters of a fermentation process were estimated on-line as a series of linearized describing matrices. The matrices were used to update a suboptimal feedback law which controlled the process in real time over the linear region. Experiments were performed on a small-scale fully instrumented fermenter with the online, real-time adaptive control package. Results are presented for both single- and multivariable control, and indicate successful control of yeast cell growth.     

Interactions between WHITE Genes Carried by a Large Transposing Element and the ZESTE Allele in DROSOPHILA MELANOGASTER

TE146, a large transposing element of Drosophila melanogaster, carries two copies of the white and roughest genes in tandem. In consequence, z¹ w ^11E4; TE146(Z)/+ flies have a zeste (lemon-yellow) eye color. However, one in 10³ TE146 chromosomes mutates to a red-eyed form. The majority of these "spontaneous red" (SR) derivatives of TE146 have only one copy of the white gene and are, cytologically, two- to three-banded elements, rather than six-banded as their progenitor. The SR forms of TE146 are also unstable and give zeste-colored forms with a frequency of about one in 10⁴. One such "spontaneous zeste" (SZ) derivative carries duplicated white genes as an inverted, rather than a tandem, repeat. The genetic instability of this inverted repeat form of TE146 is different from that of the original tandem repeat form. In particular, the inverted repeat form frequently produces derivatives with internal rearrangements of the TE and gives a much lower frequency of SR forms. In addition, two novel features of the interaction between w⁺ alleles in a zeste background have been found. First, copies of w ⁺ can become insensitive to suppression by zeste even when paired. Second, an inversion breakpoint may disrupt the pairing between two adjacent w⁺ alleles, necessary for their suppression by zeste, without physically separating them.     

Effects of environmental stresses on the cell cycle of two marine phytoplankton species

Cell cycle phase durations of cultures of Hymenomonas carterae Braarud and Fagerl, a coccolithophore, and Thalassiosira weissflogii Grun., a centric diatom, in temperature-, light- or nitrogen-limited balanced growth were determined using flow cytometry. Suboptimal temperature caused increases in the duration of all phases of the cell cycle (though not equally) in both species, and the increased generation time of nitrogen-limited cells of both species was due almost wholly to expansion of G₁ phase. In H. carterae light limitation caused only G₁ phase to expand, but in T. weissflogii both G₂ + M and G₁ were affected. These results are discussed in relation to cell division phasing patterns of these two species and to models of phytoplankton growth. Simultaneous measurements of protein and DNA on individual cells indicated that under all conditions, the protein content of cells in G₁ was a constant proportion of that of G₂ + M cells. Simultaneous measurements of RNA and protein on each cell indicated that the amounts of these two cell constituents were always tightly correlated. Under conditions of nitrogen limitation both protein and RNA per cell decreased to less than one-third of the levels found in nonlimited cells. This indicates, at least for nitrogen-replete cells, that neither protein nor RNA levels are likely to act as the trigger for cell cycle progression. Strict control by cell size is also unlikely since mean cell volume decreased as growth rates were limited by light and nitrogen supply, but increased with decreasing temperature.