Preserving Biological Materials in Protective Polymers

Abstract

Acacia gum (AG) is a water soluble natural polymer that has many desirable properties for a vast range of applications including those which are used in pharmaceutical, textile and food industries. In this study, a novel hypothesis utilizing AG as a protectant for biological materials during desiccation and storage was tested. Preserving biological materials in AG may be applied to large scale applications, for example, preservation of bacteria for crop protection and bioremediation. In addition, forensic and pathological samples of unknown content may be preserved in AG. The goal of this project was to develop a simple process and formulas for preserving biological materials in AG without applying specialized equipment and refrigeration. Biologicals tested were Escherichia coli, Bacillus subtilis, single-stranded DNA and double stranded dsDNA.

There were two types of experiments performed for all biologicals: (1) storage at various temperatures and low humidity and (2) storage at various humidity and ambient temperature. The level of protective effect on preserving biological materials in AG was object-specific. E. coli dried in AG was less sensitive to degradation compared to controls under all storage conditions. E. coli maintain viability up to day 128 when stored at 5 and 15°C and up to day 64 when stored at 25 and 40°C. For humidity experiments, E. coli remained viable up to day 32 for humidity levels of 46, 76 and 86%. For B. subtilis cultures, the viability remained constant for all storage conditions up to the maximum time tested for both experiments: 615 days for temperature experiments and 128 days for humidity experiments. It was determined that AG provides an adequate environment for B. subtilis spore formation. Electron micrographs of E. coli cells in AG had distorted morphologies and invaginations in cell walls and membranes compared to control. Electron micrographs of B. subtilis illustrated spore formation in AG samples but not in control samples. ssDNA was protected in AG when stored at low temperatures and humidity. On day 118 of the long-term temperature experiment, PCR were performed on ssDNA samples preserved in AG which were stored at all experimental temperatures. The PCR products obtained from one set of primers were of the same size as ssDNA control stored at -20°C. The DNA sequences of experimental PCR products were identical to control. dsDNA samples were successfully protected in AG stored at 5, 15, 25 and 40° C up to 64 days. For humidity experiments, more dsDNA was recovered from AG samples stored at low humidity (46 and 53%) up to 64 days. Examples of potential applications for preserving biologicals in AG include pesticides, bacterial preparations for bioremediation, oral vaccines, and probiotics.