Fate of particle-bound bacteria ingested by Calanus pacificus

Abstract

Bacteria bound to particles can be ingested by marine calanoid copepods, thus potentially providing a direct trophic link between bacteria and metazoa provided the microbes are digested by the animals. If some bacteria survive gut passage, they might play a role in fecal pellet solubilization and fragmentation (via ectoenzymes) and decomposition. We examined whether Calanus pacificus could assimilate bacterial biomass and whether a significant fraction of the ingested bacteria passed into the fecal pellets alive. We fed adult female copepods on freeze-thawed diatoms (Cylindrotheca fusiformis and Chaetoceros sp.) which had been colonized by natural populations of seawater bacteria labeled with 3H-leucine. The copepods retained 26 to 31 % of the label 43 h after ingestion and subsequent gut clearance, indicating that a substantial fraction of bacterial biomass bound to particulates of appropriate size can be directly ava~lable to this copepod as a source of material and energy. Bacteria were present at very high concentrations (10' to 101° ml-l) in the fecal pellets of copepod fed on bacterized food, but were absent in the fecal pellets of copepods fed axenic food. When fecal pellets freshly ejected by copepods fed bacterized food were incubated in seawater, bacteria abundances in them increased, yielding minimum specific growth rates of 0.08 h-' (generation time g = 8.7 h) at 16 "C and 0.19 and 0.20 h-' ( g = 3.6 and 3.5 h) at 22 "C. Since bacteria grew within the fecal pellets, at least some of the bacteria we found in the freshly egested fecal pellets must have survived gut passage In order to determine whether bacteria imparted aminopeptidase activity to copepod fecal pellets, the enzyme activity of fecal pellets produced on uncolonized and colonized freeze-thawed diatoms was compared. This comparison showed that bacteria in the fecal pellets account for 68 to 84 %of the aminopeptidase activity of fecal pellets, indicating a potential role for the interior bacteria in fecal pellet solubilization and fragmentation. We conclude that feeding of these copepods on attached bacteria not only serves to link the microbial loop with the grazing food chain but, because of the passage of viable bacteria into the fecal pellet, may also influence fecal pellet degradation.

Biogeochemical significance of attached and free-living bacteria and the flux of particles in the NE Atlantic Ocean

“…The concentration of bacteria associated with faecal pellets was generally higher than the concentration on the amorphous aggregates (Table 2) and was in the same range as those found in laboratory-produced faecal pellets from zooplankton fed on bacterized food (10' to 10tO ml-l). This may be due to the rapid growth of a significant fraction of bacteria which survive gut passage (Lawrence et al 1993). These investigators also found that a high proportion of aminopeptidase activity was carried out by bacteria in the faecal pellets and proposed that they may be important in faecal pellet solubilization and degradation.…”

“…They may be a food-chain short cut whereby material normally too small for organisms higher in the food chain can be ingested (Lampitt et al 1993a). Cyanobacteria can survive the passage through zooplankton and nekton guts (Johnson et al 1982, Lampitt et al 1993a) while around 30% of attached bacteria may be assimilated (Lawrence et al 1993). The ability of cyanobacteria to survive gut passage are reflected in the concentrations found in faecal pellets (Table 2b) …”

Bacteria dispersal by hitchhiking on zooplankton

“…However, the significance of zooplankton association goes beyond pathogenic bacteria, because zooplankton harbors very diverse bacterial phylotypes (19) in great abundances. For example, a single zooplankter can harbor up to 10 9 bacteria (27,28), which is equivalent to or higher than ambient bacterial concentrations. With 10 zooplankters·L −1 , not uncommon for lakes during the growth season (29), up to 10 10 bacteria/L could be associated with the animals.…”

Significance of bacteria in the flux of organic matter in the tidal creeks of the mangrove ecosystem of the Indus River delta, Pakistan

“…8; but these may be overestimates, as discussed). Depending on the size of the particles to which bacteria were attached, this bacterial production could be directly available to a variety of detritivores (Lawrence et al 1993, Crump & Baross 1996. Such transfer of bacterial product~on to the higher trophic levels is probably quite important because of the direct nature of the transfer.…”