ORIGINAL PAPER S. Manohar á T. B. Karegoudar Degradation of naphthalene by cells of Pseudomonas sp. strain NGK 1 immobilized in alginate, agar and polyacrylamide Received: 21 October 1997 / Received revision: 15 January 1998 / Accepted: 18 January 1998 Abstract A Pseudomonas sp. strain NGK 1 (NCIM 5120) was immobilized in various matrices, namely, al- ginate, agar (1.8 ´ 10 11 cfu g )1 beads) and polyacryl- amide (1.6 ´ 10 11 cfu g )1 beads). The degradation of naphthalene was studied, by freely suspended cells (4 ´ 10 10 cfu ml )1 ) and immobilized cells in batches, with shaken culture and continuous degradation in a packed-bed reactor. Free cells brought about the com- plete degradation of 25 mmol naphthalene after 3 days of incubation, whereas, a maximum of 30 mmol naph- thalene was degraded by the bacteria after 3±4 days of incubation with 50 mmol and 75 mmol naphthalene, and no further degradation was observed even after 15 days of incubation. Alginate-entrapped cells had de- graded 25 mmol naphthalene after 3.5 days of incuba- tion, whereas agar- and polyacrylamide-entrapped cells took 2.5 days; 50 mmol naphthalene was completely degraded by the immobilized cells after 6±7 days of in- cubation. Maximum amounts of 55 mmol, 70 mmol and 67 mmol naphthalene were degraded, from an initial 75 mmol naphthalene, by the alginate-, agar- and poly- acrylamide-entrapped cells after 15 days of incubation. When the cell concentrations were doubled, 25 mmol and 50 mmol naphthalene were degraded after 2 and 5.5 days of incubation by the immobilized cells. Complete degradation of 75 mmol naphthalene occurred after 10 days incubation with agar- and polyacrylamide- entrapped cells, whereas only 60 mmol naphthalene was degraded by alginate-entrapped cells after 15 days of incubation. Further, with 25 mmol naphthalene, alginate-, agar- and polyacrylamide-entrapped cells (1.8 ´ 10 11 cfu g )1 beads) could be reused 18, 12 and 23 times respectively. During continuous degradation in a packed-bed reactor, 80 mmol naphthalene 100 ml )1 h )1 was degraded by alginate- and polyacrylamide-en- trapped cells whereas 80 mmol naphthalene 125 ml )1 h )1 was degraded by agar-entrapped cells. Introduction Polycyclic aromatic hydrocarbons in nature are envi- ronmental pollutants, owing to their inferred recalci- trance to microbial degradation and potential toxicity to higher organisms (Gundlach et al. 1983; Vandermeulen 1981). Naphthalene is considered to be a primary irritant and the US Environmental Protection Agency (EPA) has classi®ed it as a ``priority toxic pollutant'' (US EPA 1980a, b). Exposure to naphthalene has been shown to cause a decrease in haemoglobin concentration and in- hibit oxygen consumption in various organisms (Darv- ille and Wilhm 1984; Strubble and Harmon 1983). Exposure to naphthalene has been implicated in hae- molytic anaemia in people with glucose-6-phosphate dehydrogenase de®ciency and in newborn infants (Sit- ting 1985). Naphthalene and its methyl derivatives are considered some of the most acutely toxic compounds (Anderson et al. 1974). Naphthalene, being the simplest homologue in the polycyclic series, has received con- siderable interest. Several reports are available on the degradation of naphthalene by various microorganisms with free cells (Gibson and Subramanian 1984; Kuhm et al. 1991; Grund et al. 1992; Eaton and Chapman 1992; Manohar and Karegoudar 1995, 1996; Atlas and Cerniglia 1995; Ashok and Saxena 1995). However, bioremediation of naphthalene using immobilized cells has not been investigated. Many microorganisms have been immobilized by entrapment methods. The potential of using immobilized cells in industrial processes is re- garded as a valuable application (Cheetam 1980; Bisping and Rehm 1988). Cells at dierent stages (viable, resting, dead etc.) have been successfully entrapped in various matrices (Mattiasson 1983; Brodelius and Vandamme 1987; Trevors et al. 1992). Immobilized viable cells stay alive for a long time in the immobilized stage when the conditions are optimal. Bioremediation using Appl Microbiol Biotechnol (1998) 49: 785±792 Ó Springer-Verlag 1998 S. Manohar á T.B. Karegoudar (&) Department of Biochemistry, Gulbarga University, Gulbarga-585 106, India Telex: +91 0895 208 GULU-IN Fax: +91 08472 21632