Apparent contradiction: Psychrotolerant bacteria from hydrocarbon-contaminated Arctic tundra soils that degrade diterpenoids synthesized by trees

Resin acids are tricyclic terpenoids occurring naturally in trees. We inves tigated the occurrence of resin acid-degrading bacteria on the Arctic tundr a near the northern coast of Ellesmere Island (82 degreesN, 62 degreesW). A ccording to most-probable-number assays, resin acid degraders were abundant (10(3) to 10(4) propagules/g of soil) in hydrocarbon-contaminated soils, b ut they were undetectable (<3 propagules/g of soil) in pristine soils from the nearby tundra, Plate counts indicated that the contaminated and the pri stine soils had similar populations of heterotrophs (10(6) to 10(7) propagu les/g of soil). Eleven resin acid-degrading bacteria belonging to four phyl ogenetically distinct groups were enriched and isolated from the contaminat ed soils, and representative isolates of each group were further characteri zed. Strains DhA-91, IpA-92, and IpA-93 are members of the genus Pseudomona s, Strain DhA-95 is a member of the genus Sphingomonas, All four strains ar e psychrotolerant, with growth temperature ranges of 4<degrees>C to 30 degr eesC (DhA-91 and DhA-95) or 4 degreesC to 22 degreesC (IpA-92 and IpA-93) a nd with optimum temperatures of 15 to 22 degreesC. Strains DhA-91 and DhA-9 5 grew on the abietanes, dehydroabietic and abietic acids, but not on the p imaranes, isopimaric and pimaric acids. Strains IpA-92 and IpA-93 grew on t he pimaranes but not the abietanes, All four strains grew on either aliphat ic or aromatic hydrocarbons, which is unusual for described resin acid degr aders. Eleven mesophilic resin acid degraders did not use hydrocarbons, wit h the exception of two Mycobacterium sp, strains that used aliphatic hydroc arbons. We conclude that hydrocarbon contamination in Arctic tundra soil in directly selected for resin acid degraders, selecting for hydrocarbon degra ders that coincidentally use resin acids. Psychrotolerant resin acid degrad ers are likely important in the global carbon cycle and may have applicatio ns in biotreatment of pulp and paper mill effluents.