Abstract
BackgroundSustainable management of voluminous and hazardous oily sludge produced by petroleum refineries remains a challenging problem worldwide. Characterization of microbial communities of petroleum contaminated sites has been considered as the essential prerequisite for implementation of suitable bioremediation strategies. Three petroleum refinery sludge samples from North Eastern India were analyzed using next-generation sequencing technology to explore the diversity and functional potential of inhabitant microorganisms and scope for their on-site bioremediation.ResultsAll sludge samples were hydrocarbon rich, anaerobic and reduced with sulfate as major anion and several heavy metals. High throughput sequencing of V3-16S rRNA genes from sludge metagenomes revealed dominance of strictly anaerobic, fermentative, thermophilic, sulfate-reducing bacteria affiliated to Coprothermobacter, Fervidobacterium, Treponema, Syntrophus, Thermodesulfovibrio, Anaerolinea, Syntrophobacter, Anaerostipes, Anaerobaculum, etc., which have been well known for hydrocarbon degradation. Relatively higher proportions of archaea were detected by qPCR. Archaeal 16S rRNA gene sequences showed presence of methanogenic Methanobacterium, Methanosaeta, Thermoplasmatales, etc. Detection of known hydrocarbon utilizing aerobic/facultative anaerobic (Mycobacterium, Pseudomonas, Longilinea, Geobacter, etc.), nitrate reducing (Gordonia, Novosphigobium, etc.) and nitrogen fixing (Azovibrio, Rhodobacter, etc.) bacteria suggested niche specific guilds with aerobic, facultative anaerobic and strict anaerobic populations. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) predicted putative genetic repertoire of sludge microbiomes and their potential for hydrocarbon degradation; lipid-, nitrogen-, sulfur- and methane- metabolism. Methyl coenzyme M reductase A (mcrA) and dissimilatory sulfite reductase beta-subunit (dsrB) genes phylogeny confirmed methanogenic and sulfate-reducing activities within sludge environment endowed by hydrogenotrophic methanogens and sulfate-reducing Deltaproteobacteria and Firmicutes members.ConclusionRefinery sludge microbiomes were comprised of hydrocarbon degrading, fermentative, sulfate-reducing, syntrophic, nitrogen fixing and methanogenic microorganisms, which were in accordance with the prevailing physicochemical nature of the samples. Analysis of functional biomarker genes ascertained the activities of methanogenic and sulfate-reducing organisms within sludge environment. Overall data provided better insights on microbial diversity and activity in oil contaminated environment, which could be exploited suitably for in situ bioremediation of refinery sludge.
Highlights
Sustainable management of voluminous and hazardous oily sludge produced by petroleum refineries remains a challenging problem worldwide
Physicochemical analysis, and enumeration of microorganisms Refinery waste sludge samples were collected in sterile screw-capped glass bottles (1 l capacity) using sterilized stainless steel scoops from storage tank/pit of Indian Oil Corporation Limited (IOCL) at Guwahati (26.18° N, 91.80° E and 26.14° N, E 91.73° E, designated as GR1 and GR3 respectively) and Digboi (27.39° N, 95.61° E designated as DB2), Assam, India and immediately stored in ice
The temperature of the two samples GR1 and DB2 obtained from sludge storage pits were close to the local daytime temperature of the regions (35.2–35.6 °C), whereas GR3, collected from tank receiving the effluent from the refinery plant showed an elevated temperature of 44.9 °C
Summary
Sustainable management of voluminous and hazardous oily sludge produced by petroleum refineries remains a challenging problem worldwide. Characterization of microbial communities of petroleum contaminated sites has been considered as the essential prerequisite for implementation of suitable bioremediation strategies. Eco-friendly, cost-effective and sustainable microbe-based in situ bioremediation of contaminated sites has gained considerable importance, as bioremediation technology is relying on the metabolic activity of the native microbial populations contributing in hydrocarbon mineralization through natural biogeochemical cycles [5, 6]. Characterization of contaminated sites and inhabitant microbial populations have been considered as essential prerequisites for the development of bioremediation strategies as the success of bioremediation is very much influenced by the available physicochemical conditions and nutrient availability [9,10,11]. Bioremediation efficiency could be accelerated either by stimulating the metabolic activity of native microorganisms by nutrient amendments and/or by alterations in physicochemical conditions or by introducing more efficient microbes isolated from exogenous or endogenous sources [12,13,14]
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