Abstract
Problem statement: Application of free-cell forms is usually impractical to achieve satisfactory bioremediative effect because the microbes are encumbered by the biotic and abiotic stresses from the environment. Approach: In this study, a hydrocarbon-degrading bacterium (Pseudomonas isolate UTAR EPA2) was formulated with various combinations of formulative materials, comprising of clay-based carrier materials such as Bentonite (B) and Kaolin (K), enrichment materials such as Non-fat skimmed milk (N) and Sucrose (S) and a UV-protectant agent Para-aminobenzoic acid (P). Formulated cells were treated to sunlight exposure for 6 h to mimic the conditions in the environment prior to testing for their efficacy in degrading petrol, a mixed hydrocarbon substrate. Results: Cells in all formulations including free-cell suspension were able to degrade petrol with a relatively high degradation efficacy of more than 66% even after exposure to sunlight. Degradation efficacy was slightly higher for kaolin-based formulated cells compared to bentonite-based formulations, especially after exposure to sunlight, although their percentages of degradation were not statistically different. Nevertheless, kaolin-based formulations have very low viable cell count especially in formulations with P (KP, KNP, KSP, KNSP). This suggested that aside from viable cells, the physical properties of the clays could have also contributed to the degradation of petrol. Conclusion: For storage purposes and applications in the field, we suggest that the bacterium is formulated with bentonite-based formulations especially using Bentonite (B) clay singly, as relatively high percentage of petrol degradation and viable cell count was achieved with this formulation.
Highlights
Formulation of microbial cells has long been established for applications in the agricultural (Meyer, 2003), pharmaceutical (Tanaka et al, 1993; Frokjaer and Hovgaard, 2000) and industrial (Tanaka et al, 1993) sectors
Efficacy of formulated Pseudomonas cells in degrading petrol: Generally, the degradation efficacy of Pseudomonas cells were relatively higher for cells in Free-Cell suspension (FC) compared to kaolin and bentonite-based formulations, with mean percentages of degradation of 96.01, 87.18 and 82.44%, respectively
For cells aimed for environmental application, they are highly recommended for formulation as they can be protected from the sunlight exposure compared to free-cell suspensions
Summary
Formulation of microbial cells has long been established for applications in the agricultural (Meyer, 2003), pharmaceutical (Tanaka et al, 1993; Frokjaer and Hovgaard, 2000) and industrial (Tanaka et al, 1993) sectors. The aims of formulating viable cells are to ensure that adequate cell viability is sustained to increase the efficacy of the cells and to facilitate the delivery and handling processes (Filho et al, 2001). This can be achieved by producing granular formulations, powder or dust formulations, microcapsules, or oilemulsion formulations (Brar et al, 2006). Formulations generally comprise of the active or core material, the carrier material and may or may not include the incorporation of enrichment materials or additives. In some formulations, enrichment materials comprising of nutrient-rich medium such as Nonfat Skim Milk (NFSM), skim milk, molasses, trehalose, maltose and sucrose, or additives such ParaAminobenzoic Acid (PABA) and cellulose, are incorporated to further enhance the viability of core materials (Brar et al, 2006; Tu and Randall, 2005)
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