‘Waste materials’: an economic and sustainable ‘fuel’ for hydrocarbon-loving marine microbes involved in oil remediation?

Contamination of oil pollutants in marine environments has long lasting, catastrophic effects. The current methods used to degrade the emollient spills are limited. Currently conventional treatments are: the application of blooms, skims, adsorbents and dispersants. However, these techniques have been found only recover approximately 10-15% of the oil impurity. Furthermore, research has suggested that using these dispersants; the particularly the surfactants involved, have an acute and chronic effect of the surrounding ecosystem (Singer et al. 2001), to add insult to injury; it’s expensive!

One alternative approach to ‘clean up’ these spills is the addition of biological systems. This process is called Bioremediation, it can be enhanced through bio-augmentation; addition of microbes and bio-stimulation: the supplementation of nutrients. For degradation to occur, there must be direct contact between microbes and the hydrocarbon substrate within the spill. This interaction enables marine microorganisms to metabolize the present oil compounds. Applied combinations of bio-augmentation and bio-stimulation have not been shown to be very effective at remediating oil spills; the mix can become diluted and washed away from tidal action. To over come this problem, the uses of ‘carriers’ as mediators in this mix have been considered. Carriers are materials that carry inoculants and nutrients to the oil spill. The use of carriers is thought to enhance the process of oil degradation by marine bacteria; it supplies more nutrients and counteracts the mixing of water, increasing the longevity of bioremediation. Characteristics of model carriers are: not soluble, highly stable, not readily degraded, natural and economical. Consequently, a natural waste product would be ideal.  

Simons et al. (2012) investigated the application of three different natural carrier materials: mussel shells, coir peat and a mussel shell and agar complex. This study wad conducted over a 30-day period. Six hydrocarbon-degrading microbes, previously isolated and characterised by Kadali et al. (2012) were used. The ID strains of the isolates were: Pseudomonas mendocina, Planomicrobuim alkanoclasticum, Bacillus sp, Bacillus sp, Arthrobacter pascens and Arthrobacter nitrogujacolicus. The samples were cultured until an OD₆₀₀ of 1.0 was obtained. For the carriers: waste mussel shells were acquired from Woolworths and ground, Coir peat bricks obtained from Bunnings and the mussel shell and agar complex was made by adding molten agar to ground mussel shells. Erlenmeyer flask biodegradation experiments were carried out. For each isolate and carrier material: the flasks contained mineral salts medium made in seawater containing weathered oil. To specify; the process by which an oil spill changes both physically and chemically is called oil weathering. Weathered oil was used in these experiments because the stage of which ‘weathered oil’ is degraded by marine microbes is responsible for eliminating last traces of an oil spill. At days: 0, 15 and 30 samples were collected to measure the Total Petroleum hydrocarbon (TPH). DGGE fingerprinting analysis and PCR amplification of 16s DNA was used to analyse the microbial community at those intervals.

Simons et al. (2012) considered whether the application of natural carriers to the process of bioremediation, would improve the efficiency of an important stage in the mechanism of oil remediation. The main findings in this study were that the flasks containing the carrier consisting of solely of mussel shells exhibited the greatest degree of oil degradation: 55% reduction of the weathered oil. The mussel and agar complex carrier closely followed this; with a reduction of 49%. Coir peat displayed a 36% decrease. The first two carriers were shown to be convincing, significantly different to the control flasks. Flasks in which just nutrients was added to the isolates was not shown to beneficial in improving the extent of degradation, it was only the combination of the carriers, nutrients and hydrocarbon-loving microbes that resulted in significant bioremediation.    

This particular paper was chosen because it advocates that inexpensive, accessible ‘waste’ materials could potentially be used as carriers for hydrocarbonoclastic bacteria to significantly degrade hydrocarbon contaminants in seawater oil spills. The paper also begins to investigate the community composition of these noteworthy microbes. This was a topic that was discussed in the previous post: “Obligate oil-degrading marine bacteria” Sophie suggested that more knowledge of population dynamics and ecophysiological functioning of marine oil-degrading communities are needed. Simons et al. (2012) have started to explore this. The DGGE analysis carried out during the experiments indicated that the there was an increase in community complexity over time. The microbial population was suggested to be adapting and growing in the presence of weathered oil. The presence of the carrier material was also shown to not to affect the community structure. Further studies could investigate what effects the previously discussed carriers could have on in situ spills. Other natural waste products could also be examined as potential carriers, which theoretically would make this method globally applicable.       

Simons, K. L., Ansar, A., Kadali, K. K., Bueti, A., Adetutu, E. M. and Bali, A. S. (2012)

“Investigating the effectiveness of economically sustainable carrier material complexes for marine oil remediation”

Bioresource Technology, 126: 202-207.

http://www.sciencedirect.com/science/article/pii/S1369527412000938

Kadali, K. K., Simons, K. L., Skuza, P. P., Moore, R. B. and Ball, A. S. (2012)

“A complementary approach to identify and assessing the remediation potential of hydrocarbonoclastic bacteria”

Microbiol. Methods, 88: 348-355.

Singer, M. M., Jacobson, S., Tjeerderm, R. S. and Sowby, M. (2001)

“Acute effects of fresh versus weathered oil to marine organisms: California findings”

Int. Oil Spill Conf, 2: 1263-1268.