Intracellular Parasitism

James W. Moulder

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000141665
• Edition: 1
• Topic: Medicine
• Subtopic: Pathology

This publication is a collection of essays on the biology of intracellular parasitisms where both bacterial and protozoan parasites are discussed. The juxtaposition of authors representing fields of research emphasizes the many common problems facing intracellular parasites and the hosts that harbor them. In addition, numerous illustrations of how different parasites and host attempt to solve these problems in different ways are provided. The book includes one or more chapters on Bdellovibrio, Chlamydia, Rickettsia, Coxiella, Legionella, Shigellae, Mycobacterium, Microsporidium, Plasmodium, and Toxoplasma. The authors frequently speculate and generalize on the subject matter discussed.

Chapter 1

POLYPHYLETIC ORIGIN OF BACTERIAL PARASITES

William G. Weisburg

TABLE OF CONTENTS

I. Introduction

A. Bacterial Parasites Have Free-Living Ancestors

B. Gene Sequences as Archeological Records

II. Overview of Bacterial Phylogeny With Particular Attention to Pathogenic Species

A. Eukaryotes, Archaebacteria, and Eubacteria

B. Distribution of Pathogenic and Intracellular Species

III. The Rickettsias

A. Rochalimaea quintana, Agrobacteria, and Plant Pathogenic Species

B. The Tribe Rickettsiae

C. The Family Rickettsiaceae

IV. Do Chlamydiae Have Close Relatives?

V. Evolutionary Steps to Intracellular Parasitism

A. Spectrum of Host-Associated Bacterial Niches

B. Approximately When Did These Various Lineages Begin?

Acknowledgments

References

I. INTRODUCTION

A. Bacterial Parasites Have Free-Living Ancestors

Intracellular parasites offer a unique challenge to biologists, particularly the obligately intracellular bacteria. The challenge lies in that they cannot be studied free of their host; where the organism ends and the host begins can be vague. For this reason, and many others, it is important to consider the intracellular bacteria in an evolutionary context, apart from their present symbiotic state. The knowledge of an obligate parasite’s phylogenetic relatives, as well as a reasonable scenario for evolution into an intracellular niche, are useful for understanding these fastidious bacteria in a manner apart from their hosts.

There are numerous distinctions to consider when describing the intracellular bacteria. Division of the intracellular forms into obligate and facultative species, and division of host-associated bacteria into intracellular and epicellular groups is of dubious use.¹ The first dichotomy—obligate vs. facultative—may reflect our ability to culture them. The second pair of terms may be two stages of a dynamic process, for example, an organism has learned how to cope with the outside of a cell, and in (evolutionary) time its descendants may succeed in becoming intracellular. These distinctions are mentioned here because the primary focus of this chapter is to relate, by phylogenetic analysis, the intracellular bacteria to the overall scheme of bacterial evolution, as it is presently understood. The other goal is to speculate on the origin of parasitic bacteria from free-living species. What macroevolutionary steps were taken? When may these events have occurred, and how can these speculations be examined experimentally?

B. Gene Sequences as Archeological Records

The study of bacterial phylogeny has not always been fruitful. The natural classification of species according to their evolutionary diversion and ascent has traditionally relied on grouping together organisms with similar morphological features; for example, Linnaeus used the parts of flowers to classify plants. At the time that bacteria were being taxonomically and systematically ordered, the characteristics available for scrutiny included shape, stain affinity, color, motility, and a few specialized physiological and ecological properties.

In the mid-1960s, Zuckerkandl and Pauling suggested a novel approach to the study of the evolutionary history of species.² They proposed that the genes of organisms were archeological relics of their ancestors. The sequences of macromolecules behaved as chronometers, and changed at a predictable rate through evolutionary time. If a biologist examined the same gene in a set of species, the two most similar genes would represent the pair of organisms that diverged most recently. In fact, the organisms can be grouped into nested hierarchies and represented as a phylogenetic tree. This revolutionary approach to the study of evolution was particularly far-sighted in view of the crude technology that was available for studying the sequences of genes (nucleic acid sequences) or gene products (proteins). Several technical innovations have occurred since then to allow rapid sequencing of nucleic acids, including RNA fingerprinting, gene cloning, DNA sequencing, RNA sequencing, and DNA oligomer synthesis.

The first workers to apply the principles of Zuckerkandl and Pauling to the study of bacterial evolution were Schwartz and Dayhoff using cytochrome protein sequences,³ and Woese, who examined the sequences of ribosomal RNAs.^4,5,6 The ribosomal RNA sequence approach has proven to be more generally applicable. Ribosomes are found in all organisms, and their RNA constituents are approximately homologous in structure and function throughout the biological world.

The ribosomes of bacteria contain three RNA chains, designated 16S (in the small ribosomal subunit) and 23S and 5S (in the larger ribosomal subunit). Sequences of 16S rRNA have been the most widely used for phylogenetic studies. In Escherichia coli it contains 1542 nucleotides.⁷ In the earliest phylogenetic studies, sequences were partially determined by the oligonucleotide cataloging method.^4,5 Beginning in the 1980s, sequence determination of 16S rRNA has been primarily by the primer extension/dideoxynucleotide termination method of Sanger. This sequencing method has been used on two fronts: sequencing cloned rRNA genes, and directly from unfractionated cellular RNA using reverse transcriptase.^8,9

FIGURE 1. Secondary structure of Bacteroides fragilis 16S ribosomal RNA,^10,11,12 demonstrating the universal nature of eubacterial rRNA structure.¹¹ (Figure courtesy of R.R. Gutell).

Figure 1 shows the current model for the secondary structure of 16S ribosomal RNA.^10,11 Bacteroides fragilis is chosen as a representative eubacterium because of its prominence as an isolate from the human gastrointestinal tract and to exemplify the point that all 16S rRNA secondary structures are approximately identical.^11,12 The secondary structure is crucial for phylogenetic study because it serves as the basis for exact alignment of sequences. A group of 16S rRNA sequences are aligned based on the conserved regions as well as on the location of helices and unpaired regions. An alignment then serves as the basis for constructing similarity matrices, distance trees, parsimony analyses, and signature analyses.

The goal of a phylogenetic approach to the comparative study of bacteria is straightforward—to accurately describe the relatedness of species to one another. When the genetic relationships are clear, then one can examine phenotypic, morph...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• The Editors
• Contributors
• Table of Contents
• Chapter 1 Polyphyletic Origin of Bacterial Parasites
• Chapter 2 Cell Envelope Modifications Accompanying Intracellular Growth of Bdellovibrio bacteriovorus
• Chapter 3 The Host Cell/Host Immune Responses and the Intracellular Growth of Chlamydia
• Chapter 4 Antigenic Variation of Chlamydia trachomatis
• Chapter 5 Rickettsia rickettsii: An Enigmatic Pathogen
• Chapter 6 The Rickettsia - Host Interaction
• Chapter 7 A Preview of Rickettsial Gene Structure and Function
• Chapter 8 Persistent Infection with Coxiella burnetii in vitro and in vivo
• Chapter 9 Genetic Diversity of Coxiella burnetii
• Chapter 10 Molecular Strategies for Uptake and Intraphagosomal Growth of Coxiella burnetii in Non-Immune and Immune Hosts
• Chapter 11 The Immunobiology of Legionella pneumophila
• Chapter 12 Intracellular Parasitism of Shigellae
• Chapter 14 Microsporidian Spores as Missile Cells
• Chapter 15 Protein Transport and Membrane Biogenesis in Malaria-Infected Erythrocytes
• Chapter 16 Interactions of Malaria Parasites and Their Host Erythrocytes
• Chapter 17 Sexual and Mosquito Stages of Plasmodium falciparum
• Chapter 18 Active Modification of Host Cell Phagosomes by Toxoplasma gondii
• Chapter 19 Biology of Toxoplasma gondii Host Cell Entry — The Role of Recognition and Attachment for Invasion of Host Cells
• Index