Isolation and Characterization Of Antibiotic Producing Actinomycetes In A Rhizosphere Environment
– Isolation and Characterization of Antibiotic Producing Actinomycetes in a Rhizosphere Environment –
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ABSTRACT
This research work was carried out to isolation and characterization of antibiotic producing actinomycetes in rhizosphere environments using the standard microbiological method, crowded plate method, streak plate method and pour plate method.
Starch casein agar and Nutrient agar were used for the characterization of the growth organisms and tests such as gram staining, starch hydrolysis, casein hydrolysis, lipid hydrolysis, citrate, methyl red, catalase and indole were carried out.
After culturing only 5 out of the 13 isolates (from a total of 25 soil samples) showed visible growth and had antimicrobial activity on selected organisms(Stapylococus aureus, Bacillus subtilis and Escherichia coli), the total count for the colony forming units ranged from 3.9×106– 5.2×106.
The five isolates gotten from this work had four of them from the genus Streptomycetes (denoted as B, F, H and M) and the other from the genus Nocardia (L).
Isolate B was active against Escherichia coli with a zone of inhibition measuring 26mm, isolate F, H, L and M were active against Staphylococcus aureus with zones of inhibition measuring 8mm, 9mm16mm and 9mm respectively, while isolate B, F, H, L and M were active against Bacillus subtitis with zones of inhibition measuring 5mm, 11mm, 11mm, 19mm and 7mm respectively.
This study shows that Streptomyces are the most prevalent antibiotic producing actinomycetes in the soil. Therefore antibiotics should be taken only when needed to avoid antibiotic resistance by certain organisms and stored at appropriate conditions (temperature and pressure) hence, further purification, elucidation, and characterization are recommended to know the quality and novelty and commercial values of antibiotics.
INTRODUCTION
Rhizosphere is the narrow region of soil that is directly influenced by root secretion and associated soil microorganisms (Bacteria, fungi, protozoa etc). The rhizosphere by definition is the soil region in close contact with the plant root.
The term “rhizosphere soil” generally refers to thin layer of soil adhering to a root system after the loose soil has been removed by shaking (Atlas 1981) the rhizosphere is basically divided into two general areas, the inner rhizosphere at the very root surface and the outer rhizosphere embracing the immediate adjacent soil.
Soil which is not part of rhizosphere is known as bulk soil, with the recent description and ecological characterization of plant growth –promoting rhizosphere –bacteria (PGPR).
The use of bacteria from the root zone to enhance plant growth has been given attention to Kloepper (1980) showed that certain rhizosphere bacteria can metabolize seed exudates actively at cool temperature and that these bacteria can encourage seedling emergence in field soil.
Kloepper (1980) also revealed that root colonization by some PGPR strains displaced native root micro flora thereby enhancing crop growth.
Alexander (1977) reported that the interactions between these microorganisms in the root of plant can have a considerable significance for crop production and soil fertility hence providing food for man and feed for animals.
The microbial population is more in the inner zone where the biochemical interaction between organisms are most pronounced.
In the rhizoplane which is the surface directly covering the root within the rhizosphere and rhizoplane, the inner organism contribute excretory products. Some of the interactions (such as mutualisms) are beneficial to the plant while some (like parasitism) are detrimental.
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