Need and Background
Detergents are extensively used in household cleaning products, cosmetics, pharmaceuticals as well as in agriculture as adjuvants changing the features of pesticides or other crop protection agents. The constant increase use of these products means that water-soluble detergents have become one of the major problematic classifications of pollutants for the aquatic and terrestrial habitats. Sodium dodecyl sulfate (SDS), a widely used anionic surfactant accounts for approximately 25% to 30% of the world’s total synthetic surfactants. SDS is majorly used because of its less cost and excellent foaming characteristics. SDS otherwise was popularly known as sodium lauryl sulfate (SLS) is used in household products such as toothpaste, shampoos, shaving foams, and bubble baths, in laboratories and in various other industries.
The molecular structure of SDS (C12H25NaO4 ) is composed of two units namely, (1) A hydrocarbon chain (C1- C12), (2) A sulfate group attached to the carbon (Schleheck et al, 2003). The molecule has a tail of 12 carbon atoms, attached to a sulfate group contributing to the molecule its amphiphilic properties required of a detergent.
The presence of sufficiently high concentrations of SDS in the environment may cause dermatitis and inflammation. SDS is found to be toxic even to aquatic flora and fauna.
According to the latest assessment by WaterAid, an international organization working for water sanitation and hygiene reported that an alarming 80% of India’s surface water is polluted. The report, based on latest data from the ministry of urban development (2013), census 2011 and Central Pollution Control Board, estimated that 75-80% of water pollution by volume is from domestic sewage, while untreated sewage flowing into water bodies including rivers have almost doubled in recent years. On the biological level, anionic surfactants have a major negative effect on the normal functioning of the sludge microbial consortium on several levels, destroying the biodiversity and decomposition of numerous xenobiotics.
Thus it is utterly important to identify a bacterial strain that has the capability to survive in the presence of such extreme quantities of detergent and efficiently degrade it to non-surface active compounds although degradation of SDS is a major challenge for bacteria because this detergent solubilizes biological membrane and denatures proteins. Our project focuses on Isolation, screening, and identification of efficient Sodium dodecyl sulfate degrading bacteria.
Considering the working of a top loader washing machine, it uses up to 120 liters of water per cycle and consumption of water daily on 4 cycles estimates around 480 liters of water per day. On an average, total water usage yearly roughly estimates to 876,000 liters. An apartment with an in-unit washer wastes approximately 8,500 gallons of water per year on laundry. These figures gave us motivated us to do a thorough literature search to come up with a novel solution to this urgent problem.
Background Literature Survey
Biodegradation of surfactants is often performed by diverse soil or aquatic microorganisms ultimately forming water and carbon dioxide (Schleheck et al. 2000). The discovery that many bacterial isolates from environmental niches not contaminated by detergents exhibits alkyl sulfatase activity indicates that such enzymes may also play a major role in natural environments. Thus, it seems that bacteria may have the ability to mobilize organically bound sulfur for growth, and experimental studies have provided evidence that bacterial sulfatase could play a role in sulfur scavenging.
It has been reported that the degradation of SDS is started by alkyl sulfatases which hydrolyze SDS to sulfate and 1-dodecanol (Thomas and White 1989). The resulting parent alcohol is further decomposed and converted to CO2 and H2O by β-oxidation (Dodgson et al. 1984) (Thomas and White 1989). The molecular analysis of Pseudomonas C12B, a well studied SDS degrading bacteria, revealed that two chromosomally coded genes viz, sdsA and sdsB played a major role in surfactant remediation (Davison et al. 1992). SdsA codes for alkyl sulfatase enzyme, the primary enzyme responsible for SDS degradation, whereas SdsB codes for transcriptional regulator protein promoting SdsA activity that has extensive similarity with the lysR family of helix-turn-helix DNA-binding activator protein.
The LysR-type transcriptional regulator (LTTR) family is a well-studied group of transcriptional regulators. They are highly conserved and ubiquitous amongst bacteria, with functional orthologs identified in archaea and eukaryotic organisms.
Dodecanol is an organic compound produced industrially mainly from palm kernel oil and coconut oil. Dodecanol is used to make surfactants, lubricating oils, pharmaceuticals, in the formation of monolithic polymers and as a flavor enhancing food additive. In cosmetics, dodecanol is used as an emollient. It is also the precursor to dodecanal, an important fragrance.
The desperate need of land for agricultural purposes, urban development, and industrial expansions are bringing untold adversity upon our planet and threatening our continuous existence. Industrial deforestation is harming our globe in many ways. We aim to separate out dodecanol, an intermediate product of SDS degradation pathway of bacteria, which would be much pure in quality and of high yield, utilizing a renewable strategy and aiming strictly towards less environmental destruction.