Coping with Biological Growth on Stone Heritage Objects

Methods, Products, Applications, and Perspectives

Daniela Pinna

• Editore: Apple Academic Press
• Anno: 2017
• ISBN:
  9781315341378
• Edizione: 1
• Argomento: Biological Sciences
• Categoria: Science General

Coping with Biological Growth on Stone Heritage Objects: Methods, Products, Applications, and Perspectives offers hands-on guidance for addressing the specific challenges involved in conserving historical monuments, sculptures, archaeological sites, and caves that have been attacked and colonized by micro- and macroorganisms. The volume provides many case studies of removal of biological growth with practical advice for making the right choices. It presents detailed and updated information related to biocides and to alternative substances, features that will be valuable to dealing with these challenges. The author's goal is to provide access to information and offer the conceptual framework needed to understand complex issues, so that the reader can comprehend the nature of conservation problems and formulate her/his own views.

From bacteria to plants, biological agents pose serious risks to the preservation of cultural heritage. In an effort to save heritage objects, buildings, and sites, conservators' activities aim to arrest, mitigate, and prevent the damages caused by bacteria, algae, fungi, lichens, plants, and birds. Although much has been learned about these problems, information is scattered across meeting proceedings and assorted journals that often are not available to restorers and conservators. This book fills the gap by providing a comprehensive selection and examination of international papers published in the last fifteen years, focusing on the appropriate methods, techniques, and products that are useful for the prevention and removal of micro- and macroorganisms that grow on artificial and natural stone works of art, including wall paintings. Results on new substances with antimicrobic properties and alternative methods for the control of biological growth are presented as well.

The book also emphasize issues on bioreceptivity of stones and the factors influencing biological growth and includes an outline of the various organisms able to develop on stones, a discussion on the bioprotection of stones by biofilms and lichens, a review of the main analytical techniques, and a section on bioremediation.

This volume will be a valuable reference for cultural heritage conservators and restorers, scientists, and heritage-site staff involved in conservation and maintenance of buildings, archaeological sites, parks, and caves.

CHAPTER 1

BASIC PRINCIPLES OF BIOLOGY*

*The data and information sources have been the books:

J. B. Reece, L. A. Urry, M. L. Cain, S. A. Wasserman, V. P. Minorsky, R. B. Jackson. Campbell Biology. Benjamin Cummings. San Francisco, 2014.

D. L. Nelson, M. M. Cox. Lehninger Principles of Biochemistry. W.H. Freeman and Company, New York, 2012.

R. F. Evert, S. E. Eichhorn. Raven Biology of Plants. W.H. Freeman/Palgrave Macmillan, New York, 2013.

CONTENTS

Abstract

1.1 The Cell

1.2 Biochemistry Basics

1.3 Organisms Responsible of Biodeterioration

Keywords

ABSTRACT

The smallest organisms consist of single cells and are microscopic. Multicellular organisms contain many different types of cells, which vary in size, shape, and specialized function. Cells are the structural and functional units of all living organisms. The structural features shared by cells of all kinds are described. The organisms are divided according to how they obtain the energy and carbon they need for synthesizing cellular material.

The chapter provides some fundamentals of biochemistry. Biochemistry describes in molecular terms the structures, mechanisms, and chemical processes shared by all living organisms. Thousands of different molecules constitute the cell’s intricate internal structures. Diverse living organisms share common chemical features. Besides water and electrically charged ions, the cell is composed of organic molecules, that is, of molecules that contain carbon—carbohydrates, lipids, proteins, and nucleid acids. The chapter includes an outline of the cell structure, and of the various micro-and macroorganisms able to develop on stones.

As the reader goes through the book, she/he may find it helpful to refer to this chapter at intervals to refresh the memory of this background material.

1.1 THE CELL

Some characteristics distinguish any forms of life:

The cell, the basic structural and functional unit of all living organisms;

A high degree of chemical complexity and microscopic organization;

The presence of systems for extracting, transforming, and using energy from the environment;

Defined functions for each component and regulated interactions among them;

The presence of mechanisms for sensing and responding to alterations in their surroundings;

The ability to grow and to reproduce;

A capacity to change over time by gradual evolution.

Cells are the smallest unit of life that can replicate independently. The cell membrane, or plasma membrane, surrounds the cytoplasm of a cell. It serves to separate and protect it from the free passage of inorganic ions and other charged or polar compounds. Plasma membranes are permeable to water. This permeability is due largely to protein channels in the membrane that selectively permit the passage of water. Plasma membrane mostly consists in a bilayer of phospholipids that are amphipathic: One end of the molecule is hydrophobic (insoluble in water), the other is hydrophilic (soluble in water) (Fig. 1.1). A phospholipid is made of a molecule of glycerol with a phosphate added to one end, and two side chains of fatty acids attached at the other end. In the cell membrane, the glycerol and phosphate part of the molecule hangs out at the surface with the long side chains sandwiched in the middle (Fig. 1.2).

FIGURE 1.1 Structure of the cell membrane, composed of the phospholipid bilayer with embedded proteins. It is involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signaling. It is a barrier for most molecules and serves as the location for the transport of molecules into the cell.

FIGURE 1.2 A phospholipid molecule is made of two fatty acids linked to a glycerol molecule. The third carbon of glycerol is linked to a phosphate group. The letter “X” indicates the atom or group of atoms that makes up the “rest of the molecule.” The phospholipid tail is nonpolar and uncharged and is thus hydrophobic, while the polar head, which contains the phosphate and X groups, is hydrophilic.

The lipid bilayer creates an effective chemical barrier around the cell. The cell membrane includes transport proteins that allow the passage of certain ions and molecules, receptor proteins that transmit signals into the cell, and membrane enzymes that participate in some reaction pathways. It contains also glycolipids and sterols. Sterols account for approximately 25% of the weight of the cell membrane. The type and content of sterols differ among plant, animal, and fungal cells. Whereas plant cell membranes contain primarily stigmasterol and animal cell membranes cholesterol, ergosterol is the predominant sterol in many fungi. Cells of archaea, bacteria, algae, fungi, and plants have also a cell wall around the membrane, a semi rigid layer that provides cells with structural support and protection. It plays key roles in cell differentiation, intercellular communication, water movement, and defense environment. It acts as a filtering mechanism as well. The plant cell wall is the primary source of cellulose, the most abundant and useful biopolymer on Earth.

Within the cell membrane, there is the cytoplasm, composed of an aqueous solution, the cytosol, and a variety of suspended particles with specific functions. It contains ribosomes, the complex processing molecules that assemble proteins for the cell. It also contains the genome—the complete set of genes composed of DNA (deoxyribonucleic acid). DNA and proteins are the major components of chromosomes. In the cytoplasm, there are also structures called organelles that carry out specific functions, from providing energy to producing hormones and enzymes.

Cells are too small to be seen without magnification. They range in size from 1 to 100 μm (Fig. 1.3).

There are two primary types of cells: prokaryotic cells and eukaryotic cells.

In prokaryotic cells (Greek pro, “before,” and karyon, “nucleus”), the nucleoid contains a single circular molecule of DNA that is not separated by a membrane from the rest of the cell. The cytoplasm contains also small, circular segments of DNA called plasmids. In bacteria, the plasmids can be transmitted from one cell to another. For this ability, genes, like those for antibiotic resistance, may be spread very rapidly through bacterial populations. All prokaryotic organisms are unicellular, meaning that the entire organism is only one cell. Most of them reproduce through a process called binary fission where the cell just splits in half after copying its DNA. Prokaryotic cells contain a few organelles that are not membrane-bound. Archaea and bacteria have prokaryotic cells (Fig. 1.4).

FIGURE 1.3 Size comparison among various atoms, molecules, and microorganisms (not drawn to scale) (From Motifolio Inc.).

FIGURE 1.4 Diagram of the prokaryotic cell structure (From Motifolio Inc.).

Eukaryotic (Greek eu, “true,” and karyon, “nucleus”) cells are more complex and, on average, 10 times larger than prokaryotic cells. They have a nucleus, separated by a double membrane from other cellular structures, which contains DNA. Eukaryotic cells have several types of membrane-enclosed organelles with specific functions: mitochondria, endoplasmic reticulum, Golgi complexes, peroxisomes, and lysosomes (Fig. 1.5). There are also differences within eukaryotic cells. Plant cells, for example, contain a cell wall, vacuoles and chloroplasts that are not present in animal cells (Fig. 1.5).

Most eukaryotic organisms are multicellular. This allows the eukaryotic cells to become specialized. Through a process called differentiation, the cells change from one type to another. Commonly, a less specialized type becomes a more specialized type during cell growth. Differentiation occurs many times during the development of a multicellular organism as it changes from a simple cell to a complex system of tissues and organs. Cell differentiation relates specifically to the formation of functional cell types (e.g., vascular tissue cell types in plants). Differentiated cells contain large amounts of specific proteins associated with cell function.

Eukaryotes may use either asexual or sexual reproduction depending on the organism complexity. Sexual reproduction allows more diversity in offspring by mixing the genes of the parents to form a new combination and hopefully a more favorable adaptation for the environment.

Organisms may also be classified by the source of the energy and carbon they need for synthesizing the cellular material. Autotrophs (from the Greek autos, meaning “self,” and trophos, meaning “feeder”) are able to make their own energy-rich molecules out of simple inorganic materials. They obtain all needed carbon from CO₂. Phototrophs utilize solar energy, whereas chemotrophs obtain energy by the oxidation of a chemical fuel. For example, the lithotrophs oxidize inorganic fuels: HS⁻ to S0 (elemental sulfur), S⁰ to SO₄²⁻, NO₂⁻ to NO₃⁻, or Fe²⁺ to Fe³⁺. Heterotrophs (from the Greek heteros, meaning “other,” and trophos, meaning “feeder”) require organic nutrients. They are dependent on an outside source of organic molecules for their energy. However, nearly all living organisms derive their energy, directly or indirectly, from the radiant energy of sunlight. The light-driven splitting of water during photosynthesis releases its electrons for the reduction of CO₂ and the release of O₂ into the atmosphere:

FIGURE 1.5 Diagrams of two major types of eukaryotic cell: (a) a representative animal cell and (b) a representative plant cell. Plant cells are usually 10–100 µm in diameter—larger than animal cells that typically range from 5 to 30 µm. Eukaryotic microorganisms (such as protists and fungi) have structures similar to those in plant and animal cells, but many also contain specialized organelles not illustrated here.

$\begin{array}{l}\stackrel{\underset{\downarrow }{\text{Light}}}{{\text{6CO}}_{\text{2}}{\text{+ 6H}}_{\text{2}}\text{O}\to {\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}{\text{+ 6O}}_{\text{2}}}\\ {\text{(Light-driven reduction of CO}}_{\text{2}}\text{)}\end{array}$

Non-photosynthetic organisms obtain the energy they need by oxidizing the energy-rich products of photosynthesis, then passing the electrons thus acquired to atmospheric O₂ to form water, CO₂, and other products, which are recycled in the environment:

$\begin{array}{l}{\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}{\text{+ 6O}}_{\text{2}}\to {\text{6CO}}_{\text{2}}{\text{+ 6H}}_{\text{2}}\text{O}+\text{energy}\\ \text{(Energy-yielding oxidation of glucose)}\end{array}$

All these reactions are oxidation-reduction reactions: One reactant is oxidized (loses electrons) as another is reduced (gains electrons). Energy is converted into the chemical bonds of adenosine triphosphate.

All living organisms fall into one of three large groups (domains) that define three branches of evolution from a common progenitor: archaea, bacteria, and eukarya. Archaea and bacteria are prokaryotic microorganisms (or prokaryotes). Eukarya (or eukaryotes) include protists, fungi, plants, and animals.

1.2 BIOCHEMISTRY BASICS

Water is the most abundant substance in living systems making to 70% or more of the weight of most organisms. The concentrations of solutes strongly influence the physical properties of aqueous solutions. When two aqueous solutions of different ...