Immobilization of Pseudomonas sp strain ADP: A stable inoculant for the bioremediation of atrazine

Storage and delivery of beneficial microorganisms are fundamental issues determining their value and effectiveness for a wide range of industrial and environmental purposes. One such application is the use of bacteria for the remediation of soil pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and persistent pesticides. Liquid cultures of a candidate for atrazine degradation in soil and water, Pseudomonas sp. strain ADP (3.67×109 colony-forming units, cfu/mL), when stored at 4 and 25°C, showed a 1 log reduction in cfu/mL occurs after approximately 4 and 2weeks, respectively. When immobilized onto natural zeolite from two sources (a New Zealand and an Australian quarry) and stored in open containers exposed to the atmosphere, survival at 25°C was poor. However, when the cells were immobilized onto the Australian zeolite with xanthan gum and stored in closed containers, survival at 25°C was superior to control cells stored at 4°C. The initial growth medium, zeolite substratum and immobilization matrix excipients all appear to play an important role in the stabilization of Pseudomonas sp. strain ADP. The bacteria immobilized onto Australian zeolite with xanthan remained viable within 1 log unit of initial cfu/g loading and retained their ability to degrade atrazine (as measured by zone clearance on atrazine containing plates) for at least 10weeks at 25°C.