STUDIES ON SALT ACTION
Ih an earlier paper (Falk, 1923) our present state of knowledge in regard to the physiological influence of mineral salts upon bacteria has been somewhat comprehensively reviewed. The experiments here reported were designed to determine with some exactness the effect upon bacterial viability of sodium and calcium chlorides, alone and in combination. Our work has extended over a long period, the first preliminary communications (Winslow and Falk, 1918) having been made over four years ago. The early experiments at times yielded conflicting results and it was only by a careful study of the hydrogen ion factor (Falk, 1920) that we succeeded in explaining these inconsistencies along the lines since so well worked out for problems of bacterial growth by Holm and Sherman (1921) and Sherman and Holm (1922). The study presented here deals with the viability of Bactenium coli in distilled water, in various concentrations of NaCl, and in various concentrations of CaCl2 with varying hydrogen ion concentrations for each solution; while a following paper (IJX) deals with viability in various mixtures of the two salts mentioned above.
STUDIES ON THE RELATIONSHIP OF POTASSIUM TO METABOLISM AND PURINE BIOSYNTHESIS IN ESCHERICHIA COLI
During inhibition of the growth of Escherichia coli by sulfonamides, a diazotizable amine is formed (Fox, 1942). Following its isolation (Stetten and Fox, 1945) and identification as 4-amino5-imidiazolecarboxamide (Shive et al., 1947), its important roles in purine (Buchanan, 1952) and nucleic acid metabolism (Brown et al., 1952) were disclosed. Accordingly the relationships of the chief intracellular cation, potasium to growth, metabolism and the bacterial synthesis of this metabolite were investigated. The importance of potassium in cellular physiology has received an increasing appreciation (McQuarrie, 1953; Sheppard, 1951). In contrast to sodium, potassium functions in numerous metabolic reactions. Its role in phosphorylations, i.e., in fructokinase, phosphofructokinase, and pyruvate phosphopherase activity, as well as stimulation of oxidative phosphorylation, carbohydrate metabolism, respiration, fatty acid oxidation, and decarboxylation of malate has been reviewed (Lardy, 1951; Lehninger, 1950). Potassium also stimulates metaphosphate (Schmidt et al., 1949), acetoin (Nossal, 1952), and pantothenate formation (Maas, 1952); aldehyde dehydrogenase (Black, 1951) and lactase activity (Cohen and Monod, 1951); acetate activation by coenzyme A (Stadtman, 1952); various oxidations (Quastel and Webley, 1942); and this cation is required for the growth of several microorganisms (MacLeod and Snell, 1947; Rahn, 1936; Falk, 1923) and other forms of life. The present study illustrates some aspects of the role that potassium exerts on the anabolic metabolism of E8cherichia coli. Data are presented indicating that within defined limits the extent of uptake of assimilable carbon, phos-
Genetics of the phenotypic evolution in sheep: a molecular look at diversity-driving genes
Background After domestication, the evolution of phenotypically-varied sheep breeds has generated rich biodiversity. This wide phenotypic variation arises as a result of hidden genomic changes that range from a single nucleotide to several thousands of nucleotides. Thus, it is of interest and significance to reveal and understand the genomic changes underlying the phenotypic variation of sheep breeds in order to drive selection towards economically important traits. Review Various traits contribute to the emergence of variation in sheep phenotypic characteristics, including coat color, horns, tail, wool, ears, udder, vertebrae, among others. The genes that determine most of these phenotypic traits have been investigated, which has generated knowledge regarding the genetic determinism of several agriculturally-relevant traits in sheep. In this review, we discuss the genomic knowledge that has emerged in the past few decades regarding the phenotypic traits in sheep, and our ultimate aim is to encourage its practical application in sheep breeding. In addition, in order to expand the current understanding of the sheep genome, we shed light on research gaps that require further investigation. Conclusions Although significant research efforts have been conducted in the past few decades, several aspects of the sheep genome remain unexplored. For the full utilization of the current knowledge of the sheep genome, a wide practical application is still required in order to boost sheep productive performance and contribute to the generation of improved sheep breeds. The accumulated knowledge on the sheep genome will help advance and strengthen sheep breeding programs to face future challenges in the sector, such as climate change, global human population growth, and the increasing demand for products of animal origin.