Interactions of bactivorous grazers and heterotrophic bacteria with dissolved organic matter

Abstract

Ciliated Protozoa (Euplotes sp, and Uronema sp.) and natural microzooplankton assemblages (10 to 200 pm) -collected from Los Angeles Harbor, a coastal lagoon, and San Pedro Channelwere fed bacteria previously labeled with 14C(U)-glucose. Dissolved organic carbon-l4 (D014C) released during grazing was collected and subsequently fractionated by AMICON ultrafiltration into 5 nominal molecular weight (NMW) classes: > 105, 104 to 105, 103 to 104, 5 X 102 to 103, and < 5 X 102 daltons. Release of labeled organic compounds with low (< 5 X 102 daltons) and intermediate NMW (103 to 104 daltons) was most rapid in experimental and control samples and was enhanced in the presence of grazers. Unlabeled bacterioplankton assemblages were incubated 24 h with either fractionated or unfractionated DO14C which was released during grazing experiments. Bacterioplankton utilized 196 % d-I + 100 more of the DO14C released in presence of cultured ciliates or microzooplankton than D014C released in their absence. Low (< 5 X 102 daltons) and intermediate NMW (103 to 104 daltons) labeled fractions were incorporated and respired more rapidly by bacteria than the other 3 NMW labeled fractions. Fractionation of D014C after bacterial incubation revealed a decrease in all NMW classes and a shift toward a dominance of low NMW labeled fractions in the D0I4C released in the presence of grazers, but not in the controls. Bactivorous ciliates and microzooplankton contribute quantitatively and qualitatively to the dissolved organic matter pool in nearshore planktonic systems. Dissolved organic matter released in the presence of bactivores is a readily available carbon source for bacterioplankton and may thereby influence bacterioplankton metabolism and growth activity.

Unambiguous detection and improved quantification of phagotrophy in apochlorotic nanoflagellates using fluorescent microspheres and concomitant phase contrast and epifluorescence microscopy

“…Several of these methods assume that bacterial growth without grazers is similar to growth with grazers, although it has been shown that bacterivorous nanoflagellates release nutrients (Burney et al 1981, Andersson et al 1985, Goldman et al 1985, Giide 1985, Taylor et al 1985 and in turn nurture bacterial production (Sherr et al 1982. Radioisotope techniques suffer from several limitations including artifacts arising from isotopic label leaking into the medium.…”

The effect of protozoan grazers on the cycling of polychlorinated biphenyls (PCBs) in marine systems

“…KDOC was used as the partition coefficient for the remainder of the bacterial cell because I assumed that the bacterial-derived DOC was similar in composition to the non-lipid cellular components within the bacterial cell. This assumption was derived from studies of bacterial-derived and grazer-enhanced DOC which showed that the DOC composition was similar to that of the bacterial cell (Taylor et al, 1985). Using these approximations, KB was calculated to be 10563.…”

“…The dependence of Kp on organic carbon content and compound hydrophobicity in this model is assumed to be similar to that of Kp in the two-phase model described above. However, it is possible that colloidal material has a different composition than the larger particulate material (e.g., Taylor et al, 1985). As a 16 result, two different Kp's should be used to explain fully the partitioning behavior of PCBs (Gschwend and Wu, 1985).…”

“…Studies of DOM release have begun to elucidate the composition of this material (Taylor et al, 1985;Nagata and Kirchman, 1992b;Tranvik, 1994). Taylor et al (1985) stressed that DOC produced in grazing cultures was best described as "grazer-enhanced" release rather than "grazer-produced".…”

Microbial loop carbon cycling in ocean environments studied using a simple steady-state model

“…Direct excretory losses to DOC are probably small (Nagata 2000), e.g. 3 to 9% of intake (Taylor et al 1985). The final mode of zooplankton DOC release, from fecal pellets, has been proposed as an important source (Jumars et al 1989, Lampitt et al 1990, Nagata 2000, with as much as 50% of C in pellets being rapidly solubilized (Urban-Rich 1999).…”