Genetics of Ethanol-Producing Microorganisms

Abstract

Ethanol-Producing Microrganisms

A wide variety of microbial species are known to produce ethanol as a product of carbohydrate fermentation.¹ Organisms which have received attention in recent studies include a wide range of yeasts, some molds, and a number of specialized bacteria (Table 1). Traditionally, yeasts, particularly Saccharomyces cerevisiae, have been used for producing fermentation ethanol or alcoholic beverages in large-scale processes. In Table 1, Zymomonas mobilis, the predominant organism in fermentations producing Mexican “pulque” or palm wine,³⁴-⁴⁶ is the only bacterium of current economic significance. However, the development of interest in other species with the ability, for example, to convert xylose to ethanol or to ferment at high temperatures indicates that no existing strain of Saccharomyces or Zymomonas meets the specifications for all current and future uses. Certainly the use of alternative organisms, or even mixed cultures,⁴²⁴⁵ warrants investigation. However, this review will concentrate on proven ethanol producers (i.e., yeasts, particularly Saccharomyces spp., and Z. mobilis) and how these might be improved in a systematic way for ethanol production, using the wide range of genetic techniques which is now available.     

Algebraic Methods in Evolutionary Genetics

This paper is a survey of some results obtained in evolutionary genetics by algebraical methods. The main topics: 1. Some special classes of algebras which arising in population genetics (stochastic, baric, BERNSTEINian, genetic etc.). 2. The BERNSTEIN'S problem and the stationary genetic structure. 3. The convergence to an equilibrium, the rate of convergence. 4. The exact linearization of evolutionary equation. 5. The exact formulae for evolutionary spectrum and for solution of the evolutionary equation.     

Evolutionary Genetics of Animal Migration

Three primary approaches have been used to study the geneticsof migration: the analyses of population differences, of singlelocus effects, and of polygenic influences. Studies of populationsreared under similar conditions in "common garden" experimentsfrequently reveal gene effects contributing to differences inmigratory tendency. Single locus effects are known, but arenot common, a result to be expected given that migration iscomplex. Quantitative genetic studies reveal that heritabilitiesfor migration related traits are often high (approximately 0.5or more) suggesting significant amounts of genetic variationon which natural selection can act. Analyses of genetic correlationsdemonstrate that migratory behavior is part of a syndrome thatincludes aspects of both physiology and life history traits.The latter are characteristically those which contribute tocolonizing ability. Migratory behavior thus does not evolvein isolation. New migration patterns are still evolving, aswould be predicted from observed environmental changes and thegenetic variation present in migratory species.     

Evolutionary Genetics of Drosophila Mediopunctata

Drosophila mediopunctata belongs to the tripunctata group, which is the second largest Neotropical group of Drosophila with 64 species described. Here I review the work done with this forest dwelling species, and some applications of the methods developed using it as a model organism, to other species. Specifically I look at: the phylogenetic status of the tripunctata group and its relation with other groups in the Hirtodrosophila-immigrans radiation; D. mediopunctata’s chromosome inversion polymorphism (altitudinal cline of frequencies and evidences of selection); the morphological variation of the wing and the development and applications of the ellipse method to describe the morphology of the wing; the variation on the number of aristal branches; the genetic basis of the polychromatism present in D. mediopunctata and its association with chromosome inversions; the sex-ratio trait and its use in the demonstration of Fisher’s principle; and, finally, the finding of the transposable P-element in this species. This paper is respectfully dedicated to Prof. Sergio Olavo Pinto da Costa whose help was decisive in the initial stages of our work.     

Molecular Evolutionary Dynamics of Energy Limited Microorganisms

Microorganisms have the unique ability to survive extended periods of time in environments with extremely low levels of exploitable energy. To determine the extent that energy limitation affects microbial evolution, we examined the molecular evolutionary dynamics of a phylogenetically diverse set of taxa over the course of 1,000 days. We found that periodic exposure to energy limitation affected the rate of molecular evolution, the accumulation of genetic diversity, and the rate of extinction. We then determined the degree that energy limitation affected the spectrum of mutations as well as the direction of evolution at the gene level. Our results suggest that the initial depletion of energy altered the direction and rate of molecular evolution within each taxon, though after the initial depletion the rate and direction did not substantially change. However, this consistent pattern became diminished when comparisons were performed across phylogenetically distant taxa, suggesting that although the dynamics of molecular evolution under energy limitation are highly generalizable across the microbial tree of life, the targets of adaptation are specific to a given taxon.     

Effects of Continuous and Interrupted Radiation on Microorganisms

Various bacterial spores exhibited a wide range of radiation resistance to doses of 0.25 to 2.5 Mrad from a cobalt-60 radiation facility. Bacillus pumilus and Clos-tridium tetani were shown to have the highest degree of resistance when compared with other bacterial sporeformers. B. subtilis E163 was the least resistant of the bacterial spores studied. Dried spores contained on cellulose discs were more readily destroyed by gamma-rays than were wet spores under similar conditions. Mycobacterium tuberculosis was destroyed by radiation doses much lower than that required by the least resistant bacterial spores. Interrupted dosimetry tests performed with materials of various types showed that sutures and other similar materials were effectively sterilized when the total radiation dose was given in two separate exposures with periods of interruption of 1 to 19 days. When "agar dosimeters" were employed in similar interrupted dosimetry series, B. pumilus spores were recovered in a few tests after administration of a total combined dosage of 2.5 Mrad with interruption periods of 2 to 19 days. When the experiment was repeated with interruption for 14 days, no survivors were found after a total dose of 2.0 to 2.8 Mrad.     

微重力和宇宙射线对某些微生物的影响

随着科学的发展,人造卫星的发射成功,人类开始迈向空间,为揭示太空的真实情况,国内、外学者已进行了大量的探索工作(鲁子贤 1988)。我们利用我国发射的人造卫星进行了搭载试验。本文报道空间环境对微生物生长与遗传性状影响的