ABSTRACT
A total of Five (5) different types of wood were used for this research. The used and unused wood samples were gotten from buildings that had been used after standard microbial screening. A total of six (6) bacterial and four (4) fungal species were isolated from the used and unused wood screened for microbes involved in deteriorating used wood samples. The total heterotrophic plate count ranged from 4.1 x 105 cfu/g to 7.6 x105cfu/g, the total coliform count ranged from 3.9 x105 cfu/g to 6.7 x105 cfu/g while the total fungal count ranged from 1.7 x105 cfu/g to 4.7 x105 cfu/g. The mean microbial counts from the unused wood samples. The total heterotrophic plate count ranged from 0.9 x 105 cfu/g to 6.1 x105 cfu/g, the total coliform count ranged from 2.9 x105 cfu/g to 7.9 x105 cfu/g while the total fungal count ranged from 0.7 x105 cfu/g to 2.1 x105 cfu/g. Esch1erichia coli had the highest percentage occurrence at (20%) while the least occurring bacterial isolates are Staphylococcus aureus (15%) each. The percentage of occurrence of bacterial isolates for unused wood samples revealed that Citrobacter sp. (36%) were more predominant while Bacillus (18%) had the least occurence. The percentage of occurrence of fungal isolates from used wood samples showed that Aspergillus niger, Rhodotorula sp. and Mucor sp. had the highest percentage occurrence at (33, while the least occurring fungal isolates were Aspergillus fumigatus at (5). On the other hand, the percentage of occurrence of fungi isolates from used wood samples revealed Aspergillus niger (67%) being predominant while Aspergillus fumigatus (33%) was least predominant.
TABLE OF
CONTENTS
Title
Page i
Certification ii
Dedication iii
Acknowledgements iv
Table
of Contents vi
List
of Tables ix
Abstract x
1.0 CHAPTER ONE 1
1.1 Introduction 1
1.1.1 Wood 1
1.2 Types
of Wood 3
1.2.1 Beech Wood 4
1.2.2 Ash Wood 4
1.2.3 Fibreboard 4
1.2.4 Plywood 4
1.2.5 Veneer 5
1.3 Classification
of Wood 5
1.3.1 Hardwoods 6
1.3.1.1 Maple 6
1.3.1.2 Mahogany 6
1.3.1.3 Cherry 7
1.3.1.4 Walnut 7
1.3.2 Soft Woods 7
1.3.2.1 Pine 7
1.3.2.2 Ash 7
1.3.2.3 Birch 8
1.3.2.3 Cedar 8
1.3.2.4 Redwood 8
1.3.2.4 Hemlock 9
1.4 Factors That Promote Growth of
Microorganisms in Wood
1.4.1 Moisture 9
1.4.2 Temperature 9
1.5 Wood and Its Component 10
1.5.1 Cellulose 11
1.5.2 Hemicellulose 11
1.5.3 Lignin 11
1.6 Aim and Objectives 13
2.0 CHAPTER TWO 14
2.1 Literature
Review 14
2.1.1 Microbial Colonization of
Wood 14
2.2 Degradation of Wood by Fungi 14
2.2.1 White-rot Fungi 15
2.2.2 Brown-Rot Fungi 16
2.3 Diversity of Bacterial
Communities in Wood 17
2.3.1 Edaphic and Atmospheric Sources
of Bacteria 18
2.3.2 Bacterial Endophytes 19
2.4 Bacterial Wood Decomposition 19
2.5 Bacterial Nitrogen Fixation in
Wood 20
2.6 Isolation and
Characterization of Microorganisms Involved
in Degradation of Wood 22
3.0
CHAPTER THREE 24
3.0 Materials
and Method 24
3.1 Study
Area 24
3.2 Collection
of Samples 24
3.3 Sterilization
of Materials 24
3.4 Preparation
of Culture Media 25
3.5 Isolation
of Microorganisms from Wood 25
3.6 Identification
of the Isolates 25
3.7 Gram
Staining 26
3.8 Biochemical
Test 26
3.8.1 Catalase Test 26
3.8.2 Indole Test 26
3.8.3 Citrate Utilization Test 27
3.8.4 Hydrogen Sulphide (H2S) Production Test 27
3.8.5 Starch Hydrolysis 27
3.8.6 Motility, Indole, Urease (MIU) 27
3.8.7 Coagulase Test 28
3.8.8 Oxidase Test 28
3.9 Identification
of Fungal Isolates 29
3.9.1 Wet Preparation 29
3.9.2 Colonial Morphology 29
4.0 CHAPTER FOUR 30
4.0 Results 30
5.0 CHAPTER FIVE 41
5.0
Discussion, Conclusion and Recommendation 41
5.1 Discussion 41
5.2 Conclusion 43
5.3 Recommendation 43
References 44
Appendix 50
LIST OF
TABLES
|
TABLE
|
TITLE
|
PAGE NO
|
|
1a
|
Mean Microbial Counts from Deteriorating Used Wood Samples
|
32
|
|
1b
|
Mean Microbial Counts
from Unused Wood Samples
|
33
|
|
2
|
Morphological
Identification of Bacterial Isolates from Deteriorating Wood Samples
|
34
|
|
3
|
Cultural
Morphology and Microscopic Characteristics Fungal Isolates from Deteriorating
Wood Samples
|
35
|
|
4
|
Biochemical
Identification, Gram Reaction and Sugar Utilization Profile of Bacterial
Isolates
|
36
|
|
5a
|
Percentage of
Occurrence of Bacterial Isolates from Deteriorating Used Wood Samples
|
37
|
|
5b
|
Percentage of
Occurrence of Bacteria Isolates from Unused Wood Samples
|
38
|
|
6a
|
Percentage of
Occurrence of Fungi Isolates from Used Wood Samples
|
39
|
|
6b
|
Percentage of
Occurrence of Fungi Isolates from Deteriorating Unused Wood Samples
|
40
|
CHAPTER
ONE
INTRODUCTION
1.1.1 Wood
Wood is a porous and fibrous structural
tissue found in the stems and roots of trees and other woody
plants. It is an organic
material a natural composite of cellulose fibers that are strong in tension and embedded in
a matrix of lignin that resists compression. Wood is sometimes defined as
only the secondary xylem in the stems of trees, or
it is defined more broadly to include the same type of tissue elsewhere such as
in the roots of trees or shrubs (Hoppe et
al., 2015). In a living tree it performs a support function, enabling
woody plants to grow large or to stand up by themselves. It also conveys water
and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer
to other plant materials with comparable properties, and to material engineered
from wood, or wood chips or fiber. Wood
has been used for thousands of years for fuel, as a construction material, for
making tools and weapons, furniture and paper. More recently it emerged as a feedstock for the production
of purified cellulose and its derivatives, such as cellophane and cellulose
acetate. As of 2005, the growing stock
of forests worldwide was about 434
billion cubic meters, 47% of which was commercial. As an abundant, carbon-neutral renewable resource, woody materials have been of
intense interest as a source of renewable energy. In 1991 approximately 3.5
billion cubic meters of wood were harvested. Dominant uses were for furniture
and building construction (Pan et al.,
2005).
Wood, in the strict sense, is yielded by trees, which increase in diameter by the formation, between the existing wood and the
inner bark, of new woody layers which
envelop the entire stem, living branches, and roots. This process is known
as secondary growth; it is
the result of cell division in the vascular
cambium, a lateral meristem, and
subsequent expansion of the new cells. These cells then go on to form thickened
secondary cell walls, composed mainly of cellulose, hemicellulose and lignin. Where the differences between the four seasons are
distinct, e.g. New Zealand,
growth can occur in a discrete annual or seasonal pattern, leading to growth
rings; these can usually be most
clearly seen on the end of a log, but are also visible on the other surfaces.
If the distinctiveness between seasons is annual (as is the case in equatorial
regions, e.g. Singapore), these growth rings are
referred to as annual rings. Where there is little seasonal difference growth
rings are likely to be indistinct or absent. If the bark of the tree has been
removed in a particular area, the rings will likely be deformed as the plant
overgrows the scar. If there are differences within a growth ring, then the
part of a growth ring nearest the center of the tree, and formed early in the
growing season when growth is rapid, is usually composed of wider elements. It
is usually lighter in color than that near the outer portion of the ring, and
is known as early wood or springwood. The outer portion formed later in the
season is then known as the latewood or summerwood. However, there are
major differences, depending on the kind of wood. As a tree grows, lower branches often die,
and their bases may become overgrown and enclosed by subsequent layers of trunk
wood, forming a type of imperfection known as a knot (Stokland et al., 2012).
The dead branch may not be attached to the trunk
wood except at its base, and can drop out after the tree has been sawn into
boards. Knots affect the technical properties of the wood, usually reducing the
local strength and increasing the tendency for splitting along the wood grain,
but may be exploited for
visual effect. In a longitudinally sawn plank, a knot will appear as a roughly
circular "solid" (usually darker) piece of wood around which
the grain of the rest of the wood
"flows" (parts and rejoins). Within a knot, the direction of the wood
(grain direction) is up to 90 degrees different from the grain direction of the
regular wood. In the tree a knot is
either the base of a side branch or a dormant bud. A knot (when the base of a side
branch) is conical in shape (hence the roughly circular cross-section) with the
inner tip at the point in stem diameter at which the plant's vascular cambium
was located when the branch formed as a bud (Frey-Klett et al., 2005).
In grading lumber and structural timber, knots are classified according
to their form, size, soundness, and the firmness with which they are held in
place. This firmness is affected by, among other factors, the length of time
for which the branch was dead while the attaching stem continued to grow. Knots
materially affect cracking and warping, ease in working, and cleavability of
timber. They are defects which weaken timber and lower its value for structural
purposes where strength is an important consideration. The weakening effect is
much more serious when timber is subjected to forces perpendicular to the grain
and/or tension than when under load
along the grain and/or compression. The
extent to which knots affect the strength of a beam depends upon their position, size, number, and
condition. A knot on the upper side is compressed, while one on the lower side
is subjected to tension. If there is a season check in the knot, as is often
the case, it will offer little resistance to this tensile stress. Small knots,
however, may be located along the neutral plane of a beam and increase the
strength by preventing longitudinal shearing. Knots in a board or plank are least injurious when they
extend through it at right angles to its broadest surface. Knots which occur
near the ends of a beam do not weaken it. Sound knots which occur in the
central portion one-fourth the height of the beam from either edge are not
serious defects (de Boer et al.,
2005).
1.2 TYPES OF WOOD
Wood is one of the most commonly
used materials in the world, and almost any type of wood can be used to build
furniture. Each type of wood has its own unique characteristics, which in turn
can add different degrees of warmth, emphasis and beauty to its surrounding
decor (James et al., 2012). The types
of wood are as follows;
1.2.1 Beech Wood
Beech is a hard, strong and heavy
wood. It has a fine, tight grain and even texture. Beech wood is very light in
colour and has a high shock resistance. It is a popular wood for furniture and
will give your room a warm feeling. With its smooth finish it is a great wood
to polish. Wood produced by Gmelina
arborea is an example of beech wood that can be found in Nigeria (de Boer et al., 2005).
1.2.2 Ash Wood
Ash is a tough hardwood which is
known for its excellent bending abilities. It is primarily used for bent pieces
of furniture such as a chair with curved backrests. Ash is light brown in
colour with a straight grain. The Oil Bean tree produces such type of wood and
it can be found in abundance in Nigeria (de Boer et al., 2005).
1.2.3 Fibreboard
Fibre board is an inexpensive
manufactured wood made from the breaking down of hard or soft woods into fibres
which are then bonded together with wax, resin and heat to create a dense piece
of wood. One of the most popular fibreboards is constructed of medium density
fibres that are known for their strength and durability and lend themselves
ideally to furniture products. Medium Density Fibreboard is very strong and is
considerably more popular than people think. In-fact many will be surprised as
to how much medium density fibres furniture is around them (de Boer et al., 2005).
1.2.4 Plywood
Plywood is a very strong
manufactured wood as it is build-up of layers of wood veneers which are bonded
together to create a flat smooth sheet of wood. It is popular in the furniture
and flooring industries due to its inherent strength and resistance to warping
due to the bonded cross-ply construction (de Boer et al., 2005).
1.2.5 Veneer
A veneer refers to a thin layer of
wood which is cut from the circumference of a tree. It is then bonded onto a
dense piece of wood, which is typically medium density fibres chipboard or
plywood. Veneers are available in many sizes, ranging from 3 to 6mm thick.Many
people mistakenly assume that veneered furniture is cheaper than solid wood;
however, veneers quite often are used in high end furniture pieces and it can
be more costly than solid wood.The way to find out if your piece of furniture
is veneered is by looking at the edges, and checking if the grain lines run off
the top and over the edges of the wood. As a veneer is real wood, it will
accept stains and finishes much like solid wood. Example of such wood in
Nigeria is the Iroko wood (de Boer et al., 2005).
1.3 CLASSIFICATION OF WOOD
The more one knows about the unique
characteristics of wood and its source, the better one can understand the
degree of warmth and beauty that it brings to our everyday décor. Furniture
made of wood is one of the few things in the world that all people can own and
know that they are the only person in the world who owns that particular grain
pattern and its inherent beauty. Each grain pattern is a unique masterpiece of
design, texture and splendor. Even what some may view as a defect, like a knot
or other natural blemishes, can add more beauty and character to any given
piece of furniture (James et al.,
2012). The classification of wood has historically always been either hard
wood; any leaf bearing tree, and soft wood; any cone bearing tree. These terms
can be confusing since some leaf bearing trees can have very soft wood and some
coniferous trees can have very hard woods. To make this easier, below you will
find a list of different tree types, classification and then individual wood
characteristics. There are two basic classification of wood, which are
1.3.1 HARDWOODS
1.3.1.1 Maple
There are 55 species of maple. Only
5 commercially important species grow in Nigeria Two of the five are hard rock
maple and sugar maple. Maple is so
hard and resistant to shocks that it is often used for bowling alley floors.
Its diffuse evenly sized pores give the wood a fine texture and even grain.
Maple that has a curly grain is often used for violin backs (the pattern formed
is known as fiddle-back). Burls, leaf figure, and birds-eye figures found in
maple are used extensively for veneers. The Birds eye figure in maple is said
to be the result of stunted growth and is quite rare. Maple is used extensively
for American colonial furniture, especially in medium and lower priced
categories. It can also be stained to simulate cherry wood, which it resembles.
1.3.1.2 Mahogany
Mahogany, also known as Honduras
mahogany is a tropical hardwood indigenous to Africa. There are many different
grades and species sold under this name, which vary widely in quality and
price. Mahogany which comes from the Caribbean is thought to be the hardest,
strongest and best quality. Logs from Nigeria, though highly figured, are of
slightly lesser quality. Philippine mahogany has a similar color, but is not
really mahogany at all. It is a much less valuable wood, being less strong, not
as durable or as beautiful when finished.
Mahogany is strong, with a uniform pore structure and poorly defined annual
rings. It has a reddish - brown color and may display stripe, ribbon, broken
stripe, rope, ripple, mottle, fiddleback or blister figures. Crotch mahogany
figures are widely used and greatly valued. Mahogany is an excellent carving
wood and finishes well. Mahogany is used extensively in the crafting and
production furniture. Mahogany is also used in making styles on woods.
1.3.1.3 Cherry
Cherry is grown in the Western part
of Nigeria, it is sometimes called fruitwood. The term fruitwood is also used
to describe a light brown finish on other woods. A moderately hard, strong,
closed grain, light to red-brown wood, cherry resists warping and checking. It
is easy to carve and polish.
1.3.1.4 Walnut
Walnut is one of the most versatile
and popular cabinet making woods. It grows in Europe, Africa, America and Asia.
There are many different varieties. Walnut is strong, hard and durable,
without being excessively heavy. It has excellent woodworking qualities, and
takes finishes well. The wood is light to dark chocolate brown in color with a
straight grain in the trunk. Wavy grain is present toward the roots, and walnut
stumps are often dug out and used as a source of highly figured veneer. Large
burls are common. Walnut solids and veneers show a wide range of figures,
including strips, burls, mottles, crotches, curls and butts. European walnut is
lighter in color and slightly finer in texture than American black walnut, but
otherwise comparable. Walnut is used
in all types of fine cabinet work, especially 20th century productions (de Boer et al., 2005).
1.3.2 Soft Woods
1.3.2.1 Pine
Pine is softwood which grows in most
areas of the Northern Hemisphere. There are more than 100 species worldwide. Pine is a soft, white or pale yellow
wood which is light weight, straight grained and lacks figure. It resists
shrinking and swelling. Knotty pine is often used for decorative effect. Pine
is often used for country or provincial furniture. Pickled, whitened, painted
and oil finishes are often used on this wood.
1.3.2.2 Ash
There are 16 species of ash which
grow in the eastern United States. Of these, the white ash is the largest and
most commercially important. Ash is a hard, heavy, ring porous hardwood. It has
a prominent grain that resembles oak, and a white to light brown color. Ash can
be differentiated from hickory (pecan) which it also resembles, by white dots
in the darker summerwood which can be seen with the naked eye. Ash burls have a
twisted, interwoven figure. Ash is widely used for structural frames
and steam bent furniture pieces. It is often less expensive than comparable
hardwoods.
1.3.2.3 Birch
There are many species of birch. The
yellow birch is the most commercially important. European birch is fine
grained, rare and expensive. Birch is a hard, heavy, close grained hardwood
with a light brown or reddish colored heartwood and cream or light sapwood.
Birch is often rotary or flat sliced, yielding straight, curly or wavy grain
patterns. It can be stained to resemble mahogany or walnut.
1.3.2.3 Cedar
Several species of cedar grow in the
southern Nigeria, and Central part of Africa. Cedar is knotty softwood which
has a red-brown color with light streaks. Its aromatic and moth repellent
qualities have made it a popular wood for lining drawers, chests and boxes.
Simple cases and storage closets are also constructed from this light, brittle
wood.
1.3.2.4 Redwood
This is indigenous to the Pacific
United States, redwood trees grow to more than 300 feet tall and 2,500 years
old. The best quality redwood comes from the heartwood which is resistant to
deterioration due to sunlight, moisture and insects. It is used to craft
outdoor furniture and decorative carvings. Redwood burls have a "cluster
of eyes" figure. They are rare and valuable (de
Boer et al., 2005).
1.3.2.4 Hemlock
Light in weight, uniformly textured,
It machines well and has low resistance to decay and non-resinous. Used for
construction lumber, planks, doors, boards, paneling, sub flooring and crates.
1.4 FACTORS THAT PROMOTE GRWOTH OF MICROORGANISMS IN WOOD
1.4.1 Moisture
Moisture and temperature
affect the chemical, biological, and mechanical processes of decay. The
formation of a moisture layer on the material surface is dependent upon
precipitation. It may also be generated as a result of the reaction of adsorbed
water with the material surface, deposited particles with the material surface,
and deposited particles with reactive gases. On a surface with moisture,
particles have a better possibility of adhering and water-soluble gases are
more readily captured. Both gas and particle fluxes increase when condensation
takes place on the material surface and decrease when evaporation occurs. A
moisture layer is a medium for the chemical and photochemical reactions of
surface contaminants and is also a conductive path for the electrochemical
reactions. Two variables are important from the viewpoint of the damage caused
by moisture: dew point and relative humidity of air. Dew point is a
characteristic of the water content of the large-scale air mass, whereas
relative humidity depends on the local temperature and therefore on the local
meteorological parameters. When the temperature of a material is below the
ambient dew point, water condenses on the material, a moisture layer
(condensation) can form, and the material damage may proceed. In most
materials, an increase in relative humidity causes further deterioration due to
more prolonged wetness time, higher deposition rates of pollutants and better
conditions for biodeterioration.
1.4.2 Temperature
Temperature affects the
processes of deterioration of a material gradually and in a variety of ways.
Changes in temperature induce a thermal gradient between the surface layer and
the inner layer of materials (particularly in materials with lower thermal
conductivity), which may result in the degradation of the mechanical properties
of the material and can lead to the formation of fine cracks. The formation of
cracks is accompanied by a loss of strength and by an increase in material
porosity, which may lower the chemical resistance of the material. Temperature
fluctuation of materials may influence bulk expansion, such as the expansion of
stone grains, the dilatation of different materials in joints, and the
expansion of water in material capillaries. Increased ambient air temperature is
one of the reasons why the rate of wet deposition is more important for
deterioration processes in tropical and subtropical regions than in temperate
regions. Higher ambient temperature reduces the effects of freeze–thaw cycles
(Kuhad et al., 2007).
1.5 WOOD AND ITS
COMPONENT
The major components in
wood are cellulose, hemicellulose and lignin. Woody and dead agricultural plant
materials constitute more than 60% of the total biomass produced on the earth.
The degradation of lignocellulosic materials is considered the most important
of biological processes, leading to production of carbon dioxide, water and
humic substances in the earth’s carbon cycle (Kuhad et al., 2007). Concern over food and energy sufficiency became
apparent for more than 30 years ago, due to the first so-called oil crisis of
1973. Interest in the use of abundant renewable lignocellulose as an energy
source has again been kindled worldwide. Lignocellulosic biomasses, such as
agricultural and forestry residues, were recognized as a potential source of
energy that could replace the future transport of unstable and uncertain
petroleum and fossil fuel (Himmel et al.,
2002). The most common renewable fuel is ethanol, which could be derived
from lignocellulosic material, cellulose and hemicellulose, as an attractive
future raw material (Gray et al., 2006).
In many countries there are research and development programmes in renewable
energy sources; e.g. the European Union has envisions a future in which one
fourth of fuel will be derived from biomaterials by 2030 (Mosier et al., 2005) and in Finland there are
plans to take lignocelluloses in to use more than ever before.
1.5.1 Cellulose
The main structural
component in the cell wall of green plants is cellulose. Cellulose molecules
form linear homopolysaccharide chains of β-D-glucopyranose
units, which are joined together by β (1–>4)-glycosidic
bonds. Cellulose molecules are strongly associated through inter- and
intermolecular hydrogen bonds and bundles of cellulose molecules form micro
fibrils. They are organized into strong fibrous structures, in which the highly
oriented regions are called crystalline cellulose and the less oriented region
amorphous cellulose. Most of the plant cell wall cellulose is crystalline.
Cellulose micro fibrils are embedded in a lignin-hemicellulose matrix (Daniel,
2003).
1.5.2 Hemicellulose
Hemicelluloses are short
chains of frequently branched heteropolysaccharides, containing two or more
different sugar monomers, both hexoses and pentose. Hemicelluloses are named
after their main sugar constituents, such as galactoglucomannans, which are the
principal hemicelluloses in softwoods and which are formed of galactose,
glucose and mannose units. Glucuronoxylans predominate in hemicelluloses of
hardwood, and are composed of β-D-xylose
and 4-O-methyl-α-D-glucopyranosyluronic acid units. Hemicelluloses and lignin
give the cell structure rigidity (Kuhad et
al., 2007).
1.5.3 Lignin
Lignin is the second
most abundant biopolymer next to cellulose in terrestrial vascular plants. Lignin
is a highly branched, amorphous and water-insoluble high-molecular weight (MW)
natural polymer built of phenyl propane units (Sjostrom, 2003). Lignin is
closely associated with cellulose and hemicelluloses in plant cell walls and
attaches to polysaccharide polymers in the cell walls both physically and
chemically. It binds the fibrous cell walls together and this gives plants
mechanical strength. Lignin resists chemical and enzymatic degradation and
makes wood resistant against microbial attack. The phenyl propane units of
lignin are linked together by different types of bonds (Eriksson et al., 2010). The most common bond is
the β-aryl ether (β-O-4) linkage,
which may account for 50% and 60% of the inter-monomeric bonds in softwood
lignin and hardwood lignin, respectively (Sjostrom, 2003). Lignin is
synthesized with the fixation of CO2 in plant cell walls and finally
by the polymerization of radicals generated by the one-electron oxidation of
lignin precursors (Chiang, 2006). The lignin monomeric precursors, p-hydroxycinnamyl alcohols, are
synthesized from L-phenylalanine or L-tyrosine through the shikimic acid
pathway. The intermediates are formed by deamination and several successive
hydroxylation and methylating with enzyme reactions, leading to p-coumaric, caffeic, ferulic,
5-hydroxyferulic and sinapic acid. Enzyme-mediated reductions create p-hydroxycinnamyl alcohols: coniferyl,
sinapyl and coumaryl alcohol, which are the primary precursors and building
units of lignin. Of these coniferyl alcohol is the most common precursor
(Fengel and Wegener, 2009). Softwood consists mainly of tracheids and ray cells
that give strength to wood and provide water transport. Either bordered pits or
large simple pits connect the softwood tracheids.Hardwood possesses an array of
vessels, fibres and ray parenchyma cells that are connected by bordered or simple
pits (Sjostrom 2003). The woody cell wall is composed of secondary and primary
walls. The secondary wall has three distinct layers, thin outer (S1) and inner
layers (S3) and a thick middle layer (S2) (Sjostrom, 2003). Adjacent cells are
separated by the pectin-rich middle lamella. The lignin content is highest in
the S2 layer because it is the thickest layer, but the greatest lignin
concentration is in the middle lamella between cells (Kuhad et al., 2007). Fungal hyphae penetrate
from one cell to another through existing pores and pits in the cell walls
(Eriksson et al., 2010).
1.6 AIM AND OBJECTIVES
To characterize and
identify microorganisms involved in wood degradation, while the specific
objectives are;
•
To isolate and identify bacteria present in different
wood samples
•
To isolate and identify fungi present in
different wood samples
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