The Diversity Of Alkane Degrading Bacteria In The Enrichments And The Screening For The Biosurfactant-producing Bacteria

With the exploitation of the earth resources, marine has been suffered from seriouspollutions. Bioremediation is now widely recognized as an effective way to remove marine oil pollution. It has long been recognized that many microorganisms can use medium or long-chain n-alkanes as sources of carbon and energy, which has stimulated many studies on the usefulness of these organisms in the bioremediation of oil spills and contaminated sites. It's very important and necessary to isolate and culture and detect petroleum-degrading microorganisms from the polluted environment. Oil is one of the most important pollutants in the marine environment, but its hydrophobicity inevitably slows the degradation by microorganisms. Although chemical surfactants can disperse oil or increase oil water-solublility, but they tends to impede the oil use by microorganisms because of their toxicity. Biosurfactants are non-toxic, biodegradable, and will not cause pollution to the environment. Meanwhile biosurfactants can enhance the bioavailability of hydrophobic and hydrophilic compounds, therefore increase the degradation rate of alkane. In addition, the biosurfactant have great potential application in the environmental protection, crude oil recovery, health care, and food-processing industries.Deep sea sediment samples of the South China Sea were used to isolate hydrocarbon degrading bacteria. As a result, forty eight isolates were obtained from the enrichments with hexadecane as the sole carbon sources. Among them, 27 isolates were capable of degrading alkane; and 4 could produce biosurfactant significantly as determined by the surface tension measurement. Two isolates belonging to Dietzia maris lowered water surface tension to 33 mN/m. This is the first report about D. maris in biosurfactant production. The results of polymerase chain reaction (PCR) followed by Denaturing Gradient Gel Electrophoresis (DGGE) and DNA sequencing suggested that Bacillus was the dominant member in the hexadecane enriched communities. Isolates of Bacillus aquimaris were demonstrated to be the most predominant degraders in all 7 samples at 2 sampling sites. In addition, Sporosarcina, Halomonas and Brevibacterium were also found as one of the dominant members in some samples. Therefore, species of Bacillus might play an important role in alkane degradation in te sediments of the sampling sites.By enrichment with crude oil and diesel as the sole carbon source, the diversity of petroleum-degrading bacteria in the surface water of Cape Town was surveyed. Ten samples resulted in 10 petroleum -degrading consortia, whose structures were analyzed by the combined methods of DGGE and CFU counting. DGGE revealed quite diversity in bacterial population. We isolated 94 strains in total and they belong to 23 different genus. They belong to Proteobacteria, Acinobacteria, Flavobacteria, Firmicutes, Sphingobacteria, respectively. The results showed that the dominant strains were detected phylogenetically close to Alcanivorax, Marinobacter, Martelella, Novosphingobium, and Tthalassospira respectively. Four alkane degrading bacteria were selected to examine their potential in alkane degradation. After three days in cubation, 43%, 37%, 40% and 46% of hexadecane were degraded as quantified by GC-MS, respectively.With two kinds of methods including measurement of surface tension and oil-displacement test, 27 biosurfactant-producing bacteria was isolated from the southwest ridge of Indian Ocean. On the basis of 16S rRNA gene sequence similarity, there are 9 strains are less than the maximum 97% similarity .Therefore, 9 novel species or genus were proposed. The surfactant composition generated by these bacteria has not yet been determined; perhaps have new biological activity, with the value of further study.