Who Puts the Tubercule in Tuberculosis?

Who Puts the Tubercule in Tuberculosis?

Introduction

A fundamental problem in developmental biology is the determination of how a dividing cell can give rise to specialized progeny. One of the simplest organisms in which this problem can be addressed experimentally is the common soil bacterium Bacillus subtilis. In response to conditions of nutrient limitation, B. subtilis undergoes metamorphosis into a spore that is remarkably resistant to environmental extremes of heat, desiccation, and radiation. This primitive developmental process was discovered by microbiologists Ferdinand Cohn and Robert Koch almost 120 years ago. But only in the last decade have there emerged insights into the underlying molecular mechanisms of cellular differentiation and differential gene expression that govern the conversion of a growing cell into a spore.

Part One: Scientific Review of the Article: Pathogenic neisseriae: surface modulation, pathogenesis and infection control

The article states that spore formation is a feature of the life cycle of a variety of organisms including bacteria, fungi, and plants. For example, the social bacterium Myxococcus xanthus and the cellular slime mold Dictyostelium discoidium produce and disperse spores at the end of the process of forming a fruiting body. Also, fungi, mosses, and ferns produce haploid spores as the culmination of meiosis Spore formation in B. subtilis and related Gram-positive bacteria represents a distinctive kind of sporulation process: The spores or, more properly, endospores are produced entirely inside another cell rather than by the simple conversion of a cell into a spore. Because of its simplicity and the facility with which it can be manipulated by the methods of classical and molecular genetics, endospore formation is the most intensively studied process of sporulation, and it ranks among the best-understood systems of cellular differentiation.

Endospore formation occurs by a modification of the process of cell division or binary fission (Errington 1993). During growth, B. subtilis and related endospore-forming bacteria divide by forming a medially positioned septum that splits the growing cell into two identical daughter cells. A septum is also produced during sporulation; however, the septum is formed near one pole of the developing cell (hereafter referred to as the sporangium), thereby partitioning it into two unequal-sized progeny cells. Unlike the situation during binary fission, the progeny do not separate but are retained next to each other by the cell wall that surrounds the sporangium. The smaller progeny cell is called the forespore (or prespore); it is destined to become the endospore. The larger cell is the mother cell, so called because it nurtures the developing endospore. As in binary fission, each of the two cells that result from septation receives a copy of the bacterial chromosome. In sporulation, the chromosome copy was generated by the final round of DNA replication during the transition from growth.

The article states that Initially, the two cells lie side-byside in the sporangium, but at the next stage of development, in a process that resembles phagocytosis in higher cells, the membrane that surrounds the mother cell starts to migrate around the ...