Abstract
Bio-surfactants are amphiphilic molecules possessing both hydrophilic and hydrophobic moieties. They are surface active agents that are produced extracellularly or as a part of the cell membrane by bacteria, yeast, and fungi. In the present study, the screening and optimization of bio-surfactant production were carried out using oil-contaminated soil sample. The cultural, morphological and biochemical tests as well as 16s rRNA analysis identified the most efficient bio-surfactant producer as Azorhizobium strain. The preliminary screening of bio-surfactant production was done with the help of oil displacement test, drop collapse test and observed hemolysis on superimposed blood agar plates. Optimization studies revealed that 2% inoculum size of test strain (1.0 O.D 530 nm) can be exploited for bio-surfactant production using 2% coconut oil and ammonium nitrate with a C: N ratio of 20:1 in MSM medium (pH 8.5) and incubation conditions of 30 ˚C for 96 h. The crude yield of bio-surfactant produced was estimated as 2.5 g/L. Further purification of crude bio-surfactant was carried out using acid hydrolysis and rotary vacuum evaporator. The bio-surfactant thus obtained successfully reduced the surface tension of the medium from 59 mN/m to 38 mN/m with E24 60%. The characterization studies of the purified bio-surfactant carried out by FTIR analysis confirmed it to be lipopolysaccharide type of bio-surfactant. Thus our current study suggests useful application of bio-surfactant producing bacterial strain that may be helpful in the petroleum industry for the purpose of recovery of petroleum and other oils from oily sludge, cleaning of oil storage tanks and bioremediation of oil-contaminated sites.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants that result primarily from the incomplete combustion of organic matter associated with coal and crude oil processing
Primary screening of bio-surfactant producers Screening for bio-surfactant production was carried out by qualitative methods viz., Oil displacement test, Blood hemolysis test and Drop collapse test using the supernatant obtained by centrifuging pre-grown culture medium at 8000 rpm for 20 min
It was identified as Azorhizobium strain on the basis of morphological cultural, biochemical and 16s rRNA analysis
Summary
Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants that result primarily from the incomplete combustion of organic matter associated with coal and crude oil processing. Surfactants can accumulate between fluid phases such as oil/water or air/water due to the presence of both hydrophobic (non-polar) and hydrophilic (polar) moieties in their structures This reduces the surface and interfacial tensions forming emulsions [10]. The microbial-derived surfactants have gained popularity since the late 1960s as an improved alternative to chemical surfactants primarily because of their specific action, low toxicity, higher biodegradability, and effectiveness at extremes of temperature, pH, and salinity Their unique structures provide new properties that classical surfactants may lack. The optimization studies w.r.t growth conditions for production of bio-surfactants may be subjected to genetic modifications, use of combined omics analysis and computational modeling [14] These efforts will allow the bio-surfactants to be used in large quantities and as preferred replacements for synthetic surfactants in several industrial processes [13, 15]. The current study was carried out with an aim to optimize bio-surfactant production from Azorhizobium species and characterize the same in order to obtain high yields
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