Yet another post on crude-oil bioremediation

19 Jul

On Friday, members of the the American Society for Microbiology (ASM) received our bi-monthly e-mail from the new President of our organization, Dr. Bonnie Bassler, in which she addressed the very two subjects I’ve been so interested in the last few months: the article in Science on the “synthetic cell”, and the oil spill disaster in the gulf. 

With regard to the JCVI “synthetic cell,” the official position statement of the organization is remarkably in-line with my own opinions as I’ve state in previous posts, albeit slightly more vague and probably a bit more polite.

As for the Deep Water Horizon debacle, she sent out a link to a video that I had not yet seen, which was recorded at this year’s annual ASM meeting in May (which I unfortunately missed due to my efforts to complete my dissertation right about then).  The video is roughly  a half-hour long interview of Dr. Jay Grimes of the University of Southern Mississippi and Dr. Ronald Atlas of the University of Louisville, two true experts in the field of marine biology and hydrocarbon bioremediation. 

The video is terribly slow and a bit boring (may as well skip the first 7 minutes, for sure), but they eventually cover some great information all about the state of the science when it comes to oil bioremediation… so check it out if you have a half-hour to kill watching scientists sit around discussing the gulf oil spill.  In the meantime, I found an interesting and relevant article I thought you all might like to know about which examines the efficacy and effects of crude oil bioremediation in marine systems.

Getting terms straight, again.

Before I launch into the paper, I want to make sure we’re all clear on the terms I’ll be using (and have used) a great deal.  First, the broad term that covers the use of any living organism (plant, fungus, bacterium, earthworm, what-have-you) to clean up some toxic problem is “bioremediation.”  There are hundreds of different ways to achieve bioremediation, including “natural attenuation” (essentially allowing mother-nature to do her thing, without further intervention) as well as the two methods that the authors of these papers examined and that I’ve mentioned in previous posts: biostimulation and bioaugmentation

Lots of syllables for some fairly straight-forward concepts:  biostimuation is as simple as fertilizing.  The idea is to stimulate the growth of the native microbial populations;  find out what they are lacking and give it to them (like the veggie garden).  In the case of microbes that eat oil and gas (which are essentially carbon), those microbes need nitrogen, phosphorus, potassium, and sometimes micronutrients (like vitamins and minerals for humans).  Bioaugmentation just as simply, means to add (or augment) beneficial microbes.  There are a number of different approaches to this idea, in terms of precisely which microbes to add, in what quantities (i.e., did you get the microbes from the site and just grow them in the lab to greater numbers, or did you genetically engineer organisms from someplace else?).  The issue is that the number of microbes naturally equipped to deal with the problem may not be great enough to break it down at the speed we think is best, so if we can add some players to the game we can more rapidly attain the goal.

How do these strategies effect the natives?

The article for the day (McKew, et al) addresses the issue of how the use of bioremediation technologies  impacts the indigenous populations of hydrocarbon-eating microbes, for which the authors actually use the term “hydrocarbonoclastic bacteria” (don’t bother trying to pronounce it because they abbreviate it as HCB for most of the paper).  For the most part, studies in the past have focused on how quickly the oil is degraded after applying bioremediation, but we know little about the dynamics of the native microbial populations.

So, to address this issue, the authors took natural seawater from estuaries surrounding oil refineries in the UK and added weathered crude oil.  Then they looked at how different treatments of nutrients, emulsifiers, and two species of known oil-degrading bacteria (Alcanivorax borkumensis and Thalassolituus oleivorans) would effect not only oil degradation rates, but also the natural microbial communitites in the sea water.

Result#1: Emulsifiers enhanced hydrocarbon degradation only when nutrients are not limiting.  When they added emulsifiers, the native HCB populations gew rapidly and had greater access to the carbon, but could only utilize it if they had all the additional nutrients they needed.  In other words, the scientists could add emulsifier (or dispersant) all day long, but it would not increase the break-down of the oil without the addition of the necessary nutrients as well.  Not an unexpected result when we consider the wealth of previous literature on the subject.

Result #2:  Addition of A. borkumensis enhanced degradation of specific components of the oil (polycyclic aromatic hydrocarbons – PAHs).  This is particularly interesting when we consider the fact that this species does not actually break down PAHs, but rather produces a natural emulsifier (also called a biosurfactant).  This species effectively made the oil more bioavailable to the native HCB species and allowed more rapid degradation.

Result #3: Addition of T. oleivorans actually reduced the numbers of native HCB and of A. borkumensis.  Apparently, competition between the different HCB species is fierce, andT. oleivorans  can produce metabolites that inhibit the growth of other organisms.  Chemical warfare in microbes is a common occurance, but in this case it actually excluded a number of different beneficial microbes – not such a good thing.

Result #4:  Combined treatments of bioaugmentation (addition of microbes) and biostimulation (addition of nutrients) were no more effective at enhancing degradation than simple biostimulation alone.  Addition of nutrients stimulated indigenous populations of Cycloclasticus, a native HCB, and overall oil break-down was the same as the treatments where HCB were added.  However, in the first five days of the experiment, there were higher rates of degradation in the experiments with A. borkumensis.

Conclusions:  Biostimulation is a no-brainer.  It could be aided by bioaugmentation of certain bacterial species very early on after an oil spill, but species interactions are extremely important and can not be overlooked in planning bioaugmentation strategies.  The authors put it succintly,

“For bioaugmentation to be successful the addition of appropriate bacteria, with consideration to both the environment and pollutant, is of paramount importance.”

… not to mention the effects on the native HCB. 

Of course, the authors only looked at vials of water (a.k.a. microcosms) which don’t exactly reflect the real ecosystem, for a variety of reasons.  One of the biggest hurdles to bioaumentation of open water is simple dilution effects.  Can we really add enough organisms to that amount of open sea to make a difference? 

Overall, a nice paper than demonstrates the utility of biostimulation and just the tip of the iceberg in terms of issues to overcome for successful bioaugmentation.

_________________________________________________________________________

McKew, B. et al. (2007)  Efficacy of intervention strategies for bioremediation of crude oil in marine systems and effects of indigenous hydrocarbonoclastic bacteria.  Environmental Microbiology, 9(6):1562-1571. doi:10.1111/j.1462-2920.2007.01277.x

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One Response to “Yet another post on crude-oil bioremediation”

  1. abidemi ajala December 26, 2010 at 11:49 am #

    it’s impactful material.

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