Nutrient regulation of bacterial production and ectoenzyme activities in the subtropical North Pacific Ocean

Interactions between Bacteria and dissolved organic matter (DOM) in the ope n ocean are poorly understood. While it is likely that particular compounds may disproportionately regulate heterotrophic activity, very little is kno wn about the underlying processes. Through 10 cruises between December 1996 and April 1998 we investigated how heterotrophic (non-pigmented) Bacteria cell production, per cell alpha- and beta -glucosidase and leucine aminopep tidase (LAPase) activities, and C-14-glucose uptake in 0.8 mum filtered sea water (fsw) cultures at Station ALOHA (22 degrees 45 'N, 158 degreesW) resp onded to organic and inorganic nutrient additions (glucose, single amino ac ids, NH4+, NO3-). Bacterial cell production did not change significantly in fsw with glucose (1 muM) or single exogenous N sources (1 muM N) compared to that in fsw alone. Furthermore, there was no significant difference in h eterotrophic bacterial cell production in fsw amended with organic or inorg anic N, nor between that in fsw with organic N and glucose, or inorganic N and glucose. Cell production did increase significantly, however, in fsw wi th exogenous glucose (0.38 muM) plus 1 muM inorganic N (NH4+) relative to t hat in fsw only, in fsw with glucose, and in fsw with 1 muM N as amino acid s (His, Tyr, Leu). There was no significant difference between heterotrophi c bacterial cell production in fsw with glucose, glucose plus amino acids, and that in fsw alone. Cell-specific LAPase activity increased significantl y relative to that in unamended fsw when exogenous glucose plus NH4+ or NO3 - were provided, but amino acids, glucose, NH4+ or NO3- alone had little or no effect. alpha -Glucosidase activity tended to increase with exogenous H is and Tyr additions. Our results suggest that heterotrophic activity at St ation ALOHA can be regulated by the abundance of particular compounds, rega rdless of their total concentrations. It appears that auxotrophy and de nov o synthesis of cell protein from glucose may coexist among Bacteria at Stat ion ALOHA, and that regulation of ectoenzyme expression is independent of p roduct availability. (C) 2001 Elsevier Science Ltd. All rights reserved.