ABSTRACT
A major environmental problem facing most countries of the world today, regarding agricultural productivity and food availability, is drought. The aim of the study was to isolate and characterize drought tolerant bacteria from aloe vera rhizosphere soil. Soil samples were collected from National Root Crop Research Institute, Umudike. The soil samples were collected from the rhizosphere of aloe vera plant. A total of 12 bacterial isolates were isolated from rhizosphere of aloe vera soil for drought tolerance activity which were identified by different morphological and biochemical characterization. The total bacteria heterotrophic count which ranged from 1.28 x106 Cfu/g to 1.72 x 106 Cfu/g. The percentage occurrence of the isolates. Bacillus sp 41.7% had the highest percentage occurrence followed by Streptomyces sp 33% while Paenibacillus sp 25% showed the least percentage occurrence. The drought tolerance potential of the isolate determined using an OD reading at 600nm among the different osmotic stresses, all the bacteria attain maximum growth at 0.44MPa stress. Changes in climatic conditions can bring about undesirable environmental conditions, including drought which decrease crop productivity hence the importance of drought resisted microorganisms that are beneficial to plants.
TABLE OF CONTENTS
Title Page i
Certification ii
Dedication iii
Acknowledgements iv
Table of Contents v
Lists of Tables viii
List of Figures ix
Abstract
CHAPTER
ONE
1.0 Introduction 1
1.1 Aim and Objectives 3
1.2 Objectives 3
CHAPTER
TWO
2.0 Literature Review 4
2.1 Actinomycetes 7
2.1
Taxanomy 10
2.2
Bioactive Agents in Actinomycetes 12
2.2.1
Antibiotics 12
2.2.2 Antifungals 12
2.3 Plant Growth Bioactive Molecules. 13
2.3.1 Indole Acetic Acid 13
2.3.2 Hydrogen Cyanide 14
2.4
Soil Bacteria Community Responses to Drought 15
2.5
Potential Causes of Soil Community Trends under Drought 17
2.6
Causes for Bacterial Community Trends in Drought-Stressed Roots 19
CHAPTER
THREE
3.0 Materials and Methods 21
3.1
Sample Collection 21
3.2 Sterilization
of Materials 21
.3.3 Pre-Treatment
of Soil Samples 21
3.4 Media Used 21
3.5 Media
Preparation 21
3.6 Isolation and
Selection of Bacteria 22
.3.6.1
Identification 22
3.6.2
Sub-culturing 23
3.6.3 Gram
Staining 23
3.7 Biochemical
Test 23
3.7.1 Starch
hydrolysis test 23
3.7.2 Hydrogen
sulfide test. 24
3.7.3 Gelatin
hydrolysis 24
3.7.4 Catalase
test 25
3.7.5 Oxidase test 25
3.7.6 Carbohydrate
fermentation test 25
3.7.7 Test for
casein hydrolysis 26
3.7.8 Drought Tolerance Abilities of Bacterial
Isolates 26
CHAPTER
FOUR
4.0
Results 27
CHAPTER
FIVE
5.0
DISCUSSION, CONCLUSION AND RECOMMENDATION 32
5.1 Discussion 32
5.2 Conclusion 36
5.3 Recommendation 36
LIST OF TABLES
Table Title
Page
4.1 Total
Heterotrophic Bacterial Load (cfu/g) of Aloe Vera rhizosphere 28
4.2 Colonial
description and biochemical characteristics of isolated bacteria 29
4.3 Percentage
occurrence of isolates 30
4.4
Drought Tolerance potential of the isolate determined using an OD reading at
600nm 31
CHAPTER ONE
1.0
INTRODUCTION
A
major environmental problem facing most countries of the world today, regarding
agricultural productivity and food availability, is drought. Drought has been a
subject of concern as it has led to reduced plant growth and yield. It is
therefore very important to seek means of reducing this menace, to increase
food availability and sustain food security. At present, strategies like
breeding and genetic modifications are being used to manage this problem
(Langridge and Reynolds 2015; Maazou et
al., 2016). Agricultural practices including soil amelioration and mulching
have also been used (Jongdee et al.,
2012). However, these strategies are not very efficient as they are not only
time consuming but labor and cost intensive (Ashraf, 2014; Eisenstein, 2016).
Often times, some desirable plants traits in
the host plant gene pool can be unintentionally lost in the process of breeding
(Philippot et al., 2013). Moreover,
plant breeding transfers benefit to single host specie and not to other crop
systems, as it is usually difficult to identify the genetic component
responsible for this improvement (Coleman-Derr and Tringe, 2014). The drawbacks
mentioned above have made these technologies highly unreliable, leading to a
quest for better and more efficient means to tackle this problem. In recent
times, the use of beneficial microbial species with plant growth promoting
capabilities to relieve plants of the adverse effects of drought has become
more relevant in agriculture (Babalola and Glick, 2012). Bacteria are important
soil components, able to form mutualistic and beneficial associations with most
plants (Ndeddy Aka and Babalola, 2016). Symbiotic bacteria are capable of
conferring stress tolerance to a wide variety of plant hosts through
phytohormonal modifications, production of exopolysaccharides, accumulation of
osmolytes and acting as defense against reactive oxygen species (Zhang et al., 2012; Coleman-Derr and Tringe,
2015).
These
bacteria are also able to synthesize antibiotic substances, fix atmospheric
nitrogen, produce soluble iron compounds (siderophore), and solubilize
inorganic phosphates (Babalola, 2012; Adegboye and Babalola, 2013). In
addition, they serve as plant growth regulators by producing the phytohormones
indole-acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC),
cytokinins and gibberellins (GA) (Khantsi et
al., 2013; Ndeddy Aka and Babalola, 2017). These outstanding properties of
the plant growth promoting bacteria (PGPB) facilitate the efficient stimulation
of plant growth during unfavorable environmental conditions like drought
(Yandigeri et al., 2012). Several
studies have revealed the successful application of isolated PGPB on drought
stress improvement in plants (Figueiredo et
al., 2008; Yandigeri et al.,
2012; Gusain et al., 2015).
However, most of these studies have
concentrated on certain groups of bacteria species, mostly Pseudomonas and Bacillus.
The use of actinomycetes species to enhance stress tolerance in plants have
received very little attention over the years. Actinomycetes, found mostly in
soils, are widely known for their antibiotic and bioactive secondary
metabolites production as well as their outstanding ability to survive in
unfavorable environments (Adegboye and Babalola, 2013; Adegboye and Babaloa,
2015; Passari et al., 2015). Their
ability to produce certain plant growth promoting properties has also been
identified, but with little information on the extent of the properties
produced (Ali et al., 2014; Sreevidya
et al., 2016).
1.1 AIM AND OBJECTIVES
The
aim of this study is isolation and characterization of drought tolerant
bacteria from aloe vera rhizosphere soil.
1.2 OBJECTIVES
1. Isolate
drought tolerant bacteria from aloe vera rhizosphere soil.
2. Characterize
drought tolerant bacteria from aloe vera rhizosphere soil.
3. Determine
the drought tolerance level of bacteria from aloe vera rhizosphere soil.
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