Characterisation of Novel Isosaccharinic Acid Degrading Bacteria and Communities

The current plan for the permanent disposal of Low Level and Intermediate Level nuclear wastes is the cement-based geological disposal where the wastes will be disposed off in geological disposal facility (GDF). The chemical evolution of the GDF is expected to cause cellulosic materials in the waste to degrade into cellulose degradation products (CDP) of which isosaccharinic acids (ISA) are the major components. ISAs are reported to form complexation reactions with radionuclides, potentially enhancing their migration out of the GDF.

Recent studies have shown that microbial consortia indigenous to anthropogenic sites can potentially degrade these ISAs but have focused on the use of different nitrogen sources Ca(ISA)2 as analogue for CDP. This study therefore aimed at characterizing novel ISA degrading bacteria and investigate the metabolic potentials of microorganism within soil sediments from Harpur Hill site to biodegrade ISAs and assess the impact of using Ca(ISA)2 or CDP with NH4+ against NH4+ free systems on the chemical and microbial community evolution under conditions representative of the GDF.

In a batch/fed microcosms, microorganisms within the soil sediment were able to biodegrade ISAs in pH ranging from 9-11.5 irrespective of the source. The microbial community evolution in these systems were however different suggesting that the type of carbon source and the presence of a nitrogen source impacted on the selection of these communities. The evolution of the microcosms gave rise to a complex methanogenic, polymicrobial communities where the degradation of ISAs led to the formation of acetic acid and gases including CH4, CO2 and H2. The formation of these gaseous products are likely to contribute to the pressurization of the GDF as a result of which the porosity and permeability factors should be taken into account in the formulation of the cement backfill materials. Molecular characterization of the ISA degrading communities and pure isolates (Exiguobacterium sp. strain Hud and Oceanobacillu sp. strain Hud) will allow for studies into genes associated with ISA degradation which is currently lacking in the literature. The Harpur Hill site presents a diverse pool of microorganisms with the metabolic potentials to degrade ISA hence it could be a good candidate site for the GDF.