Nutrient regulation of bacterial production and ectoenzyme activities in the subtropical North Paci"c Ocean

Interactions between Bacteria and dissolved organic matter (DOM) in the open ocean are poorly understood. While it is likely that particular compounds may disproportionately regulate heterotrophic activity, very little is known about the underlying processes. Through 10 cruises between December 1996 and April 1998 we investigated how heterotrophic (non-pigmented) Bacteria cell production, per cell and -glucosidase and leucine aminopeptidase (LAPase) activities, and C-glucose uptake in 0.8 m "ltered seawater (fsw) cultures at Station ALOHA (22345 N, 1583W) responded to organic and inorganic nutrient additions (glucose, single amino acids, NH , NO ). Bacterial cell production did not change signi"cantly in fsw with glucose (1 M) or single exogenous N sources (1 MN) compared to that in fsw alone. Furthermore, there was no signi"cant di!erence in heterotrophic bacterial cell production in fsw amended with organic or inorganic N, nor between that in fsw with organic N and glucose, or inorganic N and glucose. Cell production did increase signi"cantly, however, in fsw with exogenous glucose (0.38 M) plus 1 M inorganic N (NH ) relative to that in fsw only, in fsw with glucose, and in fsw with 1 M N as amino acids (His, Tyr, Leu). There was no signi"cant di!erence between heterotrophic bacterial cell production in fsw with glucose, glucose plus amino acids, and that in fsw alone. Cell-speci"c LAPase activity increased signi"cantly relative to that in unamended fsw when exogenous glucose plus NH or NO were provided, but amino acids, glucose, NH or NO alone had little or no e!ect. -Glucosidase activity tended to increase with exogenous His and Tyr additions. Our results suggest that heterotrophic activity at Station ALOHA can be regulated by the abundance of particular compounds, regardless of their total concentrations. It appears that auxotrophy and de novo synthesis of cell protein from glucose may coexist among Bacteria at Station ALOHA, and that regulation of ectoenzyme expression is independent of product availability. 2001 Elsevier Science Ltd. All rights reserved. *Corresponding author. Present address: Environmental Microbiology Laboratory, Department of Microbiology, Snyder Hall, University of Hawaii, The Mall, Honolulu, HI 96822, USA. E-mail address: [email protected] (S.P. Donachie). Present address: Universities Space Research Association, NASA Goddard Space Flight Center, Code 970.2, Greenbelt, MD 20771, USA. 0967-0645/01/$ see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 0 6 4 5 ( 0 0 ) 0 0 1 5 8 2