Carbon cycling by microbes influenced by light in the Northeast Atlantic Ocean

Abstract

The goal of this study was to examine the relationships between phytoplankton and heterotrophic bacteria and the effect of light on bacterial growth and respiration in the Northeast Atlantic Ocean in summer. Heterotrophic microbes were a substantial component of the plankton as indicated by the ratio of bacterial biomass to phytoplankton biomass, which varied from 0.15 to 0.83, averaging 0.60. Aerobic anoxygenic phototrophic (AAP) bacteria made up on average 10% of bacterial abundance and 13% of bacterial biomass. AAP bacterial biomass was on average 2-fold higher than Synechococcus sp. biomass, whereas Prochlorococcus sp. was never more than 1% of bacterial biomass. The bacterial production to primary production ratio ranged from 0.04 to 0.14 and was on average 0.07. The bacterial growth efficiency (BGE) in light incubations (10%) was 3-fold lower than in the dark (32%). Consequently, the calculated flux of carbon through bacteria in the light was also about 3-fold lower in the dark, since ratios of bacterial carbon demand (BCD) to primary production inferred from light and dark estimates of BGE were 0.7 and 0.2, respectively. However, BCD and respiration rates were not greater than primary production, suggesting that this region of the North Atlantic was net autotrophic even after the spring bloom. The BGE data and the abundance of photoheterotrophic microbes, such as AAP bacteria, highlight the importance of the effects of light on carbon cycling by bacteria in the Northeast Atlantic Ocean.

Diel variability of heterotrophic bacterial production and underwater UV doses in the eastern South Pacific

“…Second, Prochlorococcus contributed on average to 36% of the sum 'heterotrophic bacteria' + Prochlorococcus between 120 and 140 m, and still represented 15% down to 190 m at GYR (Grob et al 2007). It is thus possible that some patterns in leucine incorporation rates at these very deep layers, not influenced by UV, could be due to the circadian cell cycle of some cyanobacteria able to assimilate leucine (Cottrell et al 2008, Mary et al 2008.…”

“…Second, Prochlorococcus contributed on average to 36% of the sum 'heterotrophic bacteria' + Prochlorococcus between 120 and 140 m, and still represented 15% down to 190 m at GYR (Grob et al 2007). It is thus possible that some patterns in leucine incorporation rates at these very deep layers, not influenced by UV, could be due to the circadian cell cycle of some cyanobacteria able to assimilate leucine (Cottrell et al 2008, Mary et al 2008.The pronounced diel pattern observed in the eastern South Pacific for heterotrophic bacterial production, delayed with that of primary production, suggests a probable interactive control on a daily scale by bottom-up resources (phytoplankton and regenerating micro organisms as producers of labile organic carbon and nitrogen source) and by the quality and intensity of natural solar radiation (UV-B, UV-A and PAR). Further measurements on a daily scale of DNA damages, fluxes of DOM release and regeneration, as well as bacterial re-assimilation of these by-products are necessary in these original, unique, transparent oceanic waters of the South Pacific Gyre to validate these hypotheses.…”

Bacteriochlorophyll and community structure of aerobic anoxygenic phototrophic bacteria in a particle-rich estuary

“…value for 20 fields of view were estimated. The AAP bacteria were enumerated using an Intensified Retiga charge-couple device camera (Qimaging, Surry, BC Canada) and image analysis routines to enumerate cells that fluoresce blue when stained with 4 0 ,6-diamidino-2-phenylindole and have infra-red fluorescence, but not red or orange fluorescence (Cottrell et al, 2008;Cottrell and Kirchman, 2009). …”

Photoheterotrophic Microbes in the Arctic Ocean in Summer and Winter

“…AAP bacteria have been found in freshwater high-latitude waters (20,35), but sequence analysis of pufM genes indicates that these AAP bacteria are distinct from those found in marine systems (50). The abundance of AAP bacteria decreases with latitude within the North Atlantic Ocean, from the central gyre to the waters near Greenland (13). Although these photoheterotrophic microbes are still present at 65°N, extrapolation of the trend suggests that AAP bacteria might be absent from the high-latitude waters of the Arctic Ocean.…”

“…Enumeration by infrared epifluorescence microscopy indicates that the abundance of AAP bacteria in environments such as the North Pacific Gyre and the Northeast Atlantic Ocean ranges from 1% to 10% (12,13,42) and can exceed 10% of the total prokaryotic community in estuaries (41,50). AAP bacteria have been found in freshwater high-latitude waters (20,35), but sequence analysis of pufM genes indicates that these AAP bacteria are distinct from those found in marine systems (50).…”