Bio-Engineering High Performance Microbial Strains for MEOR

Abstract

The main objectives of this three-year research project are: 1) to employ the latest advances in genetics and bioengineering, especially Directed Protein Evolution technology, to improve the effectiveness of the microbial enhanced oil recovery (MEOR) process. 2) to improve the surfactant activity and the thermal stability of bio-surfactant systems for MEOR; and 3) to develop improved laboratory methods and tools that screen quickly candidate bio-systems for EOR.Biosurfactants have been receiving increasing attention as Enhanced Oil Recovery (EOR) agents because of their unique properties (i.e., mild production conditions, lower toxicity, and higher biodegradability) compared to their synthetic chemical counterparts. Rhamnolipid as a potent natural biosurfactant has a wide range of potential applications, including EOR and bioremediation.During the three-year of the project period, we have successfully cloned the genes involved in the rhamnolipid bio-synthesis. And by using the Transposon containing Rhamnosyltransferase gene rhlAB, we engineered the new mutant strains P. aeruginosa PEER02 and E. coli TnERAB so they can produce rhamnolipid biosurfactans. We were able to produce rhamnolipds in both P. aeroginosa PAO1-RhlA -strain and P. fluorescens ATCC15453 strain, with the increase of 55 to 175 fold in rhamnolipid production comparing with wild type bacteria strain. We have also completed the first round direct evolution studies using Error-prone PCR technique and have constructed the library of RhlAB-containing Transposon to express mutant gene in heterologous hosts. Several methods, such as colorimetric agar plate assay, colorimetric spectrophotometer assay, bioactive assay and oil spreading assay have been established to detect and screen rhamnolipid production.Our engineered P. aeruginosa PEER02 strain can produce rhamnolipids with different carbon sources as substrate. Interfacial tension analysis (IFT) showed that different rhamnolipids from different substrates gave different performance. Those rhamnolipids with plant oil as substrateshowed as low an IFT as 0.05mN/m in the buffer solution with pH5.0 and 2% NaCl. Core flooding tests showed that rhamnolipids produced by our engineered bacteria are effective agents for EOR.At 250ppm rhamnolipid concentration from P. aeruginosa PEER02, 42% of the remaining oil after waterflood was recovered. These results were therefore significant towards considering the exploration of the studied rhamnolipids as EOR agents.2