Impact of bacteria and zooflagellates on the composition of sinking particles: an in situ experiment

Abstract

Multiple sediment trap (MULTITRAP) arrays were deployed at 3 hydrographically and biologically distinct stations in the eastern North Pacific Ocean and used to evaluate experimentally the hypothesis that protozoan grazers are important in the diagenesis of sinking biogenic materials in the ocean. Measurements were made of adenosine triphosphate (ATP) concentrations and the abundances of bacteria and zooflagellates associated with sinking particles collected from in situ preserved and 2 sets of unpreserved (live) traps: one containing a selective eukaryote inhibitor (thiram) and the second without thiram which served as a live-control. Particulate organic carbon and nitrogen (POC and PON), NH:, NO;, NO;, dissolved organic nitrogen (DON), diatoms, and fecal pellets were quantified in live-control and live-thiram traps. In situ microbial production was estimated by measuring RNA and DNA synthesis in live-control and live-thiram traps pre-charged with 3H-adenine. Trap-collected bacteria and zooflagellates accounted for a low percentage of the total POC (2 to 11 % ) but a high percentage of the total microbial biomass (an estimated 25 to 2 100 % of total ATP). Zooflagellates were the principal protozoans collected and accounted for 2 to 25% of the total microbial biomass. Synthesis of RNA and DNA was observed at all stations and depths, indicating microbial growth in the live traps. ATP and microscopic analyses, however, independently confirmed that death rates exceeded growth rates on the sedimenting particles. Differences between the livecontrol traps (coupled microbial assemblage) and live-thiram traps (uncoupled assemblage, grazers inhibited) indicated slower decomposition and nutrient regeneration in the uncoupled system. In general, POC was higher and in the shallowest traps, NH: was lower, and DON was higher in the livethiram traps. Zooflagellates appear to strongly influence decomposition and nutrient recycling within the microbial assemblage associated with sedirnenting particles.

Testing assumptions of the eukaryotic inhibitor method for investigating interactions between aquatic protozoa and bacteria, applied to marine sediment

“…McCambridge and McMeekin 1980;Newell et al 1983;Sherr et al 1986;Bomo et al 2004), whereas in others, it was found to inhibit aerobic or anaerobic bacteria (Taylor and Pace 1987;Tremaine and Mills 1987). Taylor and Pace (1987) strongly advised caution in the use of eukaryotic inhibitors, and Tremaine and Mills (1987) concluded that cycloheximide should not be used in grazing Ramirez and Alexander (1980) Seston 1 Taylor et al (1986) experiments. Nonetheless, the majority of studies we found that used cycloheximide were published after these stern warnings, and they did not test any of the assumptions.…”

“…A literature search yielded over 30 publications (most shown in Table 1), none of which tested all three assumptions thoroughly. Of the studies that did address these assumptions to some extent, most notable are Newell et al (1983), Sherr et al (1986), Taylor et al (1986), Taylor and Pace (1987), Tremaine and Mills (1987), and Tso and Taghon (2006) who evaluated the first and third assumptions in some detail, but only Taylor and Testing assumptions of the eukaryotic inhibitor method for investigating interactions between aquatic protozoa and bacteria, applied to marine sediment…”

No sign of denitrification in a Baltic Sea cyanobacterial bloom

“…In ageing aggregates, senescent algae might not alone be able to provide a sufficient amount of degradable material for the maintenance of high standing stock of attached bacteria. Therefore, the role of 'recycling' of organic matter from microzooplankton (as excretion, dead cells, fecal pellets, sloppy feeding) to bacteria is emphasised as the aggregates get older (Hoppe 1981, Taylor et al 1986, Biddanda & Pomeroy 1988. Cyanobacterial aggregates can stay in the upper water layer for weeks because of their buoyancy and reach a steady state in which in-and output of organic matter is balanced (Hoppe 1981).…”

Active ingestion of fluorescently labeled bacteria by mesopelagic heterotrophic nanoflagellates in the East Sea, Korea

“…Recently, Steward et al (1996) presented evidence that viruses may cause substantial mortality of mesopelagic bacterioplankton, but other sources may contribute as well. Several studies reported the ubiquitous occurrence of heterotrophic nanoflagellates (HNF) in the mesopelagial (Pomeroy & Johannes 1968, Taylor et al 1986, Cho & Azam 1988, Steward et al 1996. However, nothing is known about their grazing impact on bacterioplankton.…”