Organization of Prokaryotic Cell Membranes

Volume III

Ghosh, Bijan K. Ghosh

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315896120
• eBook ISBN: 9781351092128
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

These volumes include a collection of authoritative articles covering the most active areas of prokaryotic biomembrane investigations, and will provide a great service not only to those interested in the field but also to microbiologists in general. These monographs will also serve to focus attention on prokaryotic membranes that are so often ignored by eukaryoticmembraneologists and proved an excellent reference source for many years to come.

Chapter 1
Membranes of Hydrocarbon-Utilizing Microorganisms

W. R. Finnerty and M. E. Singer

Table of Contents

I. Introduction

II. Ultrastructure of Hydrocarbon-Utilizing Microorganisms

A. Hydrocarbon Inclusions

B. Intracytoplasmic Membranes

III. Ultrastructure of Alkane-Grown Yeasts

A. Cell Envelope

B. Microbodies

C. Plasma Membrane

IV. Membranes of Acinetobacter

A. Lipids of Hexadecane-Grown Acinetobacter

1. Cellular Phospholipids

2. Cellular Neutral Lipids

3. Extracellular Lipids

B. Isolation of Membranes from Acinetobacter sp. H01-N

1. Membranes Derived from Nutrient Broth-Grown Cells

2. Membranes Derived from Hexadecane-Grown Cells

3. Isolation of Hydrocarbon Inclusions

4. Isolation of Extracellular Membrane Vesicles

C. Biochemical Composition of Acinetobacter Membranes

1. Membrane Phospholipids

2. Membrane Neutral Lipids

3. Membrane Proteins

4. Membrane-Localized Cytochromes

V. Phospholipid Metabolism in Acinetobacter sp. H01-N

A. Phospholipid Biosynthesis

1. Stimulation of Phosphatidic Acid Cytidyl Transferase by Exogenous Phospholipid

2. Lipid Depletion of UAT Membranes

B. Phospholipid Catabolism

1. General

2. Outer Membrane Phospholipases of Acinetobacter

VI. Conclusions

A. Intracytoplasmic Membranes

B. Hydrocarbon Inclusions

C. Extracellular Membrane Vesicles

D. Cytoplasmic Membranes

E. Outer Membrane

F. Membrane Biogenesis

G. An Overview — Membranes and Hydrocarbon Metabolism

References

I. Introduction

Hydrocarbons are organic molecules that contain only the elements of carbon and hydrogen. Such molecules range in size from methane to large polycyclic aromatic molecules of undetermined weight and structure. Most hydrocarbons are, at best, only sparingly soluble in an aqueous environment.

The ability of diverse genera of microorganisms to degrade a wide variety of hydrocarbons is ubiquitous in nature, with microbial degradation of hydrocarbons receiving extensive study over the last three decades.¹ Such studies have been mainly limited to investigations concerning the metabolic interaction between a single, simple hydrocarbon and a single microorganism, Research efforts in microbial hydrocarbon metabolism have largely concentrated on whole cell physiology, primarily describing various substrate-product interrelationships. Several biochemical pathways of hydrocarbon dissimilation and mechanisms of hydrocarbon oxidation have been formulated, although significant gaps in our knowledge remain. Information at the molecular level is notably lacking in hydrocarbon microbiology. The ability of microorganisms to metabolize such hydrophobic molecules poses questions of basic interest regarding the evolution of the genetic information encoding alkane oxidation in some genera but not in others. Further, the organization and regulation of genetic information specifying alkane oxidations is poorly understood, with these genes being plasmid-encoded in Pseudomonas species and chromosome-encoded in Acinetobacter species.² To date, the genetics and regulation of alkane metabolism have been examined only in Pseudomonas putida, a bacterium capable of utilizing low-molecular-weight, simple hydrocarbons.

Major questions remain unanswered and often unrecognized concerning the growth of microorganisms at the expense of these water-insoluble substrates:

1. How do hydrocarbons enter the microbial cell?
2. How do microorganisms respond metabolically and biochemically to such physiologically unusual hydrophobic substrates for purposes of energy production and carbon assimilation?
3. What are the mechanisms of genetic regulation of microbial hydrocarbon metabolism?

Accordingly, it is important to recognize that microbial hydrocarbon metabolism requires further research at more sophisticated levels of analysis to resolve these fundamental questions.

Hydrocarbon microbiology has largely focused on studies relating to the cellular physiology of alkane metabolism. A number of basic and fundamental generalizations have emerged which collectively serve to characterize those prokaryotic and eukaryotic microorganisms exhibiting the ability to grow at the expense of alkanes as a sole source of carbon and energy.

First, a large number of bacteria, yeast, and fungi grow at the expense of alkanes varying in carbon number from 1 to 40 carbon atoms. A few representative genera capable of alkane metabolism are Acinetobacter, Pseudomonas, Brevibacterium, Arthrobacter, Mycobacterium, Nocardia, Corynebacterium, Candida, Cladosporium, Penicillium, Cunnhighamella, Fusarium, Mucor, and Aspergillus. These microorganisms are natural soil inhabitants of ubiquitous distribution. Such alkane-utilizing microorganisms are easily isolated from soil by appropriate selective enrichment procedures.

Second, the mechanism(s) of oxidation employed by these various microorganisms are obligately oxygen-dependent processes involving mono-, di-, and subterminal oxilation of the alkane molecule:

The initial oxidative enzymes are membrane-bound dioxygenases which catalyze the insertion of molecular oxygen into the alkane molecule,¹ This n-alkyl hydroperoxide is reduced to fatty alcohol which is oxidized to fatty acid by way of alcohol and aldehyde dehydrogenases.

Finally, the oxidation of alkanes yield a variety of products, many of which accumulate in the culture broth. Products characterizing alkane oxidations are fatty acids, fatty alcohols, fatty aldehydes, wax esters, ketones, dicarboxylic acids, and hydroxy fatty acids.

This chapter discusses the membrane biochemistry and unique ultrastructural features of alkane-utilizing microorganisms with special attention to Acinetobacter. Acinetobacter represents an environmentally ubiquitous and nutritionally diverse genus of Gram-negative bacteria capable of growth on n-alkanes (C10 to C30), fatty alcohols and aldehydes, fatty acids, and dicarboxylic acids, as well as certain amino acids and a few carbohydrates.The physiological attributes exhibited by hexadecane-grown Acinetobacter sp. H01-N provide a unique model system for studying the metabolism of hydrophobic, water-insoluble compoun...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Volume III
• Chapter 2 The Biosynthesis of Bacterial Outer Membrane Proteins
• Chapter 3 Functional Organization of Bacterial Membrane Proteins
• Chapter 4 Protein Secretion in Bacteria
• Index