Methylotrophs : Microbiology. Biochemistry and Genetics

Ching T. Hou

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351091411
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Microbiología

This book offers a comprehensive examination of the microbiology, biochemistry, genetics, and applied aspects of methylotrophsThis book is intended for reference purposes at the professional level and for students at the graduate level. It is hoped that it will provide researchers with not only basic science, but also applied aspects of methylotrophs.

Chapter 1
Microbiology and Biochemistry of Methylotrophic Bacteria

Ching T. Hou

Table of Contents

I. Introduction

II. Microbiology

A. Taxonomy

B. Morphology

C. Fine Structure

1. Typel

2. Type II

D. Role of Intracytoplasmic Membranes

E. Classification

1. Group Methylomonas

2. Group Methylobacter

3. Group Methylococcus

4. Group Methylosinus

5. Group Methylocystis

6. Group Methylobacterium organophilum

F. Phospholipid and Fatty Acid Compositions of Methanotrophs

G. Tricarboxylic Acid Cycle

III. Biochemistry

A. Carbon Assimilation Pathways

1. The Ribulose Monophosphate Pathway

2. The Enzymes of the Ribulose Monophosphate Pathway

3. The Serine Pathway

4. The Enzymes of the Serine Pathway

5. Production of Intracellular and Extracellular Polymers

B. Energy Generation

1. Oxidation of Methane to Methanol

2. Possible Free Radical Mechanism for Methane Oxidation

3. Oxidation of Methanol (Methanol Dehydrogenase)

4. Oxidation of Formaldehyde (Formaldehyde/Aldehyde Dehydrogenase)

5. Oxidation of Formate (Formate Dehydrogenase)

6. Secondary Alcohol Dehydrogenase

7. Oxidation of Compounds with Carbon-Carbon Bonds

8. Electron Transfer and Energy Transducing Systems

9. Oxidation of Methylamine

10. Oxidation of Dimethylamine and Trimethylamine

C. Anaerobic Methane Oxidation

D. Nitrogen Metabolism

E. The Nature of Obligate Methanotrophy

References

I. Introduction

Methylotrophic bacteria are recognized by their ability to use, as sole carbon and energy sources for growth, compounds that contain no carbon-carbon bonds and to assimilate carbon as formaldehyde or a mixture of formaldehyde and carbon dioxide.^1–6 They are different from methanogenic bacteria which produce methane from organic compounds. Growth substrates often used by methylotrophs are the following: methane, methanol, formaldehyde, formate, dimethyl ether, methyl formate, formamide, and methylamines. Not all of the methylotrophs can grow on methane. Those microorganisms capable of growth on methane are called methanotrophs. No obligate methylotrophs so far described are capable of growth on formate. Facultative methylotrophs can also grow on a variety of organic multicarbon compounds.

Methylotrophs play an important role in carbon recycling in the biosphere. The stability of the biosphere carbon cycle depends on the uninterrupted balance among methanogens which produce C₁-compounds from organic compounds anaerobically, methylotrophs which oxidize C₁-compounds to carbon dioxide or cell mass aerobically, and heterotrophs which degrade methylotroph biomass. Much of the methane arising from methanogenesis in the deeply submerged sediment does not reach the atmosphere due to its aerobic and anaerobic oxidation by methane-utilizing bacteria in both aquatic and soil environments.⁷

The progress in the understanding of the microbiology and biochemistry of methylotrophs can be attributed largely to Whittenbury and co-workers who isolated and characterized many methane-oxidizing bacteria,⁸ and to Quayle and co-workers who unveiled the metabolic pathways of C₁ compounds in methylotrophs.² However, the importance of specific methylotrophic microorganisms in nature has not been established. We cannot be certain that the dominant methylotrophs in nature have been isolated and characterized.

The purpose of this chapter is to review in detail up-to-date information on microbiology and biochemistry of methylotrophic bacteria. The following excellent reviews were often used as sources of information during the preparation of this chapter: Quayle,^2–3 Anthony,⁴ Colby et al.,⁵ Hanson,⁷ Wolf and Higgins,⁹ and Higgins et al.¹⁰

II. Microbiology

A. Taxonomy

The first methane-utilizing microorganisms, Bacillus methanicus, was isolated by Söhngen in 1906.¹¹ The name was changed to Methanomonas methanica by Orla-Jensen,¹² to Pseudomonas methanica by Dworkin and Foster,¹³ and finally to Methylomonas methanica by Foster and Davis.¹⁴ Aside from this M. methanica, only three additional species were well documented prior to 1970. They are Pseudomonas methanitrificans,¹⁵ Methylomonas methanooxidans,^{16, 17} and Methylococcus capsulatus.¹⁴ In 1970, Whitten bury and co-workers isolated over 100 methane-utilizing bacteria and classified these bacteria into several groups on the basis of morphology, fine structure, and type of resting stage formed. All of the strains isolated were Gram-negative, catalase-positive, aerobic bacteria that utilized compounds without carbon-carbon bonds as substrates. All were obligate methylotrophs utilizing methane, methanol, and dimethylether as carbon and energy sources.⁸ Many of the isolates formed heat- or desiccation-resistant resting stages. All of the strains contained complex intracytoplasmic membrane structures and utilized different carbon assimilation pathways.^{2, 18–20} Based on the differences in intracytoplasmic membrane arrangement and in carbon assimilation pathways, Whittenbury et al. classified the isolates into two types (Table 1). Most workers accept this as a basis for the development of a formal classification, and most organisms isolated since then fall more or less into one of these groups. Romanovskaya et al.²¹ have reviewed the information about genera and species of methylotrophs and have corrected nomenclature where it did not follow the project for an International Code of Bacterial Nomenclature. As more detailed knowledge has accumulated, the need for two subgroups (A and B) above the genus level has arisen for classification of type I organisms. The new genus of facultative methylotrophs, Methylobacterium^{22, 23} needs to be accommodated. A tentative classification scheme for methane-oxidizing bacteria including obligate and facultative methylotrophs was proposed (Table...