title: Light dependence of [3H]leucine incorporation in the oligotrophic North Pacific ocean.
abstract: The influence of irradiance on bacterial incorporation of [(3)H]leucine was evaluated at Station ALOHA in the oligotrophic North Pacific subtropical gyre. Six experiments were conducted on three cruises to Station ALOHA to examine how [(3)H]leucine incorporation varied as a function of irradiance. Two experiments were also conducted to assess the photoautotrophic response to irradiance (based on photosynthetic uptake of [(14)C]bicarbonate) in both the upper and lower photic zones. Rates of [(3)H]leucine incorporation responded to irradiance in a photosynthesis-like manner, increasing sharply at low light and then saturating and sometimes declining with increasing light intensity. The influence of irradiance on bacterial growth was evaluated in both the well-lit (5 to 25 m) and dimly lit regions of the upper ocean (75 to 100 m) to determine whether the bacterial response to irradiance differed along the depth-dependent light gradient of the photic zone. [(3)H]leucine incorporation rates were analyzed with a photosynthesis-irradiance model for a quantitative description of the relationships between [(3)H]leucine incorporation and irradiance. Maximum rates of [(3)H]leucine incorporation in the upper photic zone increased 48 to 92% relative to those of dark-incubated samples, with [(3)H]leucine incorporation saturating at light intensities between 58 and 363 micromol of quanta m(-2) s(-1). Rates of [(3)H]leucine incorporation in the deep photic zone were photostimulated 53 to 114% and were susceptible to photoinhibition, with rates declining at light intensities of >100 micromol of quanta m(-2) s(-1). The results of these experiments revealed that sunlight directly influences bacterial growth in this open-ocean ecosystem.
authors.affiliation: School of Marine Science, The College of William and Mary, Gloucester Point, Virginia 23062, USA. mchurch@es.ucsc.edu
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Church
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Ducklow
authors.forename: David M
authors.initials: DM
authors.lastname: Karl
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D005618:Fresh Water / Q000382:microbiology*; D007930:Leucine / Q000378:metabolism*; D008027:Light; D010140:Pacific Ocean; D010788:Photosynthesis
chemical_list: D001426:Bacterial Proteins; D007930:Leucine