Aliphatic compounds in crude oil and petroleum products are readily degraded, with a prominent initial microbial preference for straight chain compounds e.
Photosynthetic activity is absent as light does penetrate surface layers, be it soil, sediment, or rock. Two types of systems have been proposed for SLiMEs: List of microbial processes that can occur in the subsurface.
Information taken from Todd, S. The organisms in a detrital system are primarily heterotrophic and however nutrient supply is very limited . Furthermore, low-molecular weight organics are preferentially consumed, leaving the remainder of energy and carbon in increasingly recalcitrant forms .
While these are an integral part of productive systems, chemolithoautotrophs are also present in detrital systems though in quantities nowhere near large enough to sustain the primarily heterotrophic community.
Because this system is more reliant on photochemical energy, detrital systems are classified as SLiME-like . These ecosystems are completely independent of photosynthetic based energy and fixed carbon . The ecosystem energetics of phototrophs is replaced by chemolithoautotrophic based chemical energy in the form of hydrogen gas .
A key point to productive systems is that both the original electron donor and ultimate electron acceptor will be derived from abiotic geochemical sources .
Oxygen cannot be used as an electron acceptor because it is a by-product of photosynthesis, which does not occur in the subsurface. Due to the complete independence from photosynthesis, productive systems would be considered to be true SLiMEs .
H2 Formation and H2 Driven Chemolithoautotrophy The reason the majority of subsurface chemolithoautotrophs use hydrogen as their energy source is due to its availability and energetic potential.
Hydrogen is able to travel through water easily, with high concentrations present in aquifers and possesses a strong reducing power . There are many ways that hydrogen can be generated within the subsurface, including but not limited to: All of these processes ensure that there is a steady supply of hydrogen for chemolithoautotrophs to utilize.
Subsurface Environments Diagram of an aquifer, detailing energy movement and locations of microbes. Image from Griebler, C and Lueders, T. Groundwater ecosystems such as aquifers are very common SLiMEs.
The complexity and size of groundwater ecosystems are quite variable, they can range from small alluvial aquifers to large regional aquifers hundreds of kilometers long . The larger groundwater systems are usually part of cavernous karstic environments . Deep marine hydrothermal vent subsurfaces are another well studied area when it comes to SLiMEs  ; .
Related to the hydrothermal vents is the hydrothermal sediment biosphere.monly employed technology used to clean up aquifers, but it is widely recognized that progress is slow.
Bioremediation, the process of stimulating microbes to rapidly microbial population responsible for hydrocarbon degradation. populations which have adapted to the subsurface environment .
Rhizofiltration of uranium contaminated waste water (Photo courtesy Department of Energy Subsurface Contaminants Focus Area) Metals are not the only toxins that can be cleaned up using plants.
Microbial clean-up of these DRO compounds is claimed to be an efficient, economical, and versatile alternative to the established physicochemical treatments that are prone to cause recontamination by secondary contaminants (Hong et al., ; Megharaj et al., ).
Microbial adaptations may result from chronic exposure to elevated concentrations as shown by the The rate and ability of microbes to degrade a compound are dependent on the ability of the subsurface environment to support a healthy community of microbes.
This section describes the main processes for the clean-up of the Nakhodka oil. This paper describes a new product for the clean-up of PAHs in a subsurface environment. A new product for the clean-up of PAHs will be described including factors that could enhance or limit its potential, based on technical and literature reviews.
This is significant in the event of a spill, as a quick response and an efficient clean‐up will be dependent on identifying and specifying the substrate environment, with a view to inoculating with the appropriate microbial .