BIODEGRADATION OF CRUDE OIL BY BACTERIA ISOLATED FROM PRISTINE SOIL

ABSTRACT

The demand for petroleum as a source of energy and raw materials for chemical industries in recent years has resulted in a tremendous increase in world exploration. This increase in exploration of crude oil has also brought with it an ever increasing problem of environmental pollution. This present study was designed to identify crude oil degrading microorganisms from pristine soil and crude oil degradation capacity. Soil samples were collected from a pristine soil. The soil had a pH of 5.65 with total organic matter and organic carbon of 5.22% and 5.27% respectively. The isolates were identified based on morphological observation, physiological and biochemical tests. The isolates belong to species of Bacillus and Staphylococcus. Biodegradation of crude oil by the two isolates was 28.57% and 31.70% for Bacillus subtilis and Staphylococcus aureus respectively after 28 days. The components degraded from the crude oil were majorly the n-alkane. Some of the aromatic hydrocarbons were converted into an intermediate product. Bacillus and Staphylococcus species could be good candidate microorganisms in the bioremediation of crude oil contaminated sites. The isolates demonstrated ability to degrade petroleum hydrocarbon.

CHAPTER ONE

1.0    INTRODUCTION

1.1    Background to the Study

In recent  years, the demand for petroleum as a source of energy and raw material for chemical industries has resulted in a tremendous increase in world production. This increase in production, refining and distribution of crude oil has also brought with it an ever- increasing problem of environmental pollution (Gopinathan et al., 2012; Abioye et al., 2013; Sojinu and Ejeromedoghene, 2019).

Petroleum hydrocarbons can seep into the soil and contaminate underlying ground water. Runoff from unregulated sites can carry petroleum contaminants off site into nearby waterways. Indiscriminate dumping of petroleum waste products can lead to an elevated level of   petroleum hydrocarbons in the soil, which results in a significant decline in the quality  of  the  soil,  makes  it  unfit  for  use  and  becomes  a  threat  to  healthy  soil microorganisms. Oil spills and waste discharges into the sea from refineries, factories or shipping contain poisonous compounds that are potentially dangerous to plants and animals. These poisons can pass through the food web which may eventually be eaten by humans (Abioye et al., 2013; Ikuesan, 2017).

Several methods are used to remediate a contaminated site or oil polluted soil and these include the use of physical, chemical and biological methods. The biological method is the use of a biological agent such as microorganisms and green plants. Microorganisms are also equipped with a metabolic machinery to use petroleum as carbon and energy source. Crude oil by its nature is biodegradable, thus, biological methods (bioremediation technique) have been developed and improved for cleaning up oil contaminated sites and have become alternatives to chemical and physical techniques (Abioye et al., 2013; Kure et al., 2018).

The degradation of hydrocarbon which is one of the trait possess by microbes is not limited to  certain  genera  but  widely  distributed  in  nature.  Some  genera  of  bacteria  with  the capability to degrade hydrocarbon includes Pseudomonas, Rhodococcus, Bacillus, Xanthomonas, Cornybacterium, Acinetobacter (Morais  and Tauk-Tornisielo, 2009 ;Ajao et al., 2014; Hamzah et al., 2017).

The genus Pseudomonas and Bacillus in particular have been the subject of numerous studies. The Pseudomonas sp is one of the best crude oil degraders. An interesting and useful characteristic of many Pseudomonas sp. is their ability to utilize a wide variety of organic substrates for growth. Pseudomonas sp. utilizes crude oil organic compounds as sole source of nutrients which includes saturated and aromatic compounds (Gopinathan et al., 2012).

Bacillus on the other hand has the ability to grow on different substrates. They have the ability to degrade different hydrocarbons by the production of biosurfactants, which facilitates the hydrocarbon degradation. They also produce a variety of enzymes, which are involved in biodegradation (Gopinathan et al., 2012).

Biodegradation efficiency is determined with the provision of favourable conditions to the microbes which will enhance their rapid growth, such condition include oxygen, nutrient, pH, temperature other  conditions.  Only then  will these organisms  able to  degrade  and breakdown pollutants (e.g hydrocarbon) at a correspondingly faster rate. The most important principle  of  biodegradation  is  that  microorganisms  can  be  used  to  destroy  hazardous contaminants or transform them to less harmful forms (Abioye et al., 2013; El-Borai et al., 2016).

Several catabolic pathways that controls biodegradation have been identified and are generally located on the large, transmissible plasmids usually found in Pseudomonas sp. Molecular information  about an ecosystem contamination  is useful in order to develop improve bioremediation  strategies (Arvanitis, 2008).

1.2    Statement of the Research Problem

Industrialization, discovery of crude oil as a source of fuel and most human activities have impacted the soil and water directly or indirectly. Human and other life forms depend on the soil directly or indirectly for their survival. The negative impact of crude oil pollution on the soil  and  other  environment  is  overwhelming  and  this  has  led  researchers  in  search  of possible ways to ameliorate this problem using a quick, safe, beneficial, benign and cheap method with the understanding that the cost of managing impacted soil is very expensive. Crude oil contamination of the environment has become a global challenge. Whenever there is a crude oil contamination, there adverse effects are always enormous both on land and on the aquatic life. The soil structure, composition and nutrient are also affected by oil spillage or contamination, some of these oil spill get seeped into ground water which can adversely affect human health. More so, developing effective strategies for biodegradation has been a problem.

1.3    Justification for the study

Biodegradation of crude oil by microorganisms has received enormous attention over the past  decades  using  indigenous  microbes  (Abioye  et  al.,  2012;  Vinothini  et  al.,  2015;

Benchouk and Chibani,   2017). However, few studies are available regarding the biodegradation of crude oil by bacteria isolated from pristine soil.  Attention has been focused on isolating microbes from contaminated environment neglecting those from the pristine environment. Some of the microbes from the pristine environment could do well. It is also possible that there may not be contaminated environment to isolate these microbes from. Successful biodegradation techniques require the right combination of microbes and environmental conditions. Therefore, there is need to screen for oil degrading bacteria from pristine soil best suited to degrade petroleum based contaminants.

1.4 Aim and Objectives of the Study

The aim of this study was to investigate the biodegradation of crude oil by bacteria isolated from pristine soil.

The objectives of the study were to:

I.      determine the physicochemical properties of the pristine soil

II.      isolate and identify the selected bacteria from the soil

III.      investigate the crude oil biodegradation potential of the isolated bacteria

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