Grazing of nonindigenous bacteria by nano-sized protozoa in a natural coastal system

Abstract

Mesocosms (∼4.5 m(3)) situated in a closed bay area were used to investigate the effect of protozoan predation on nonindigenous bacteria. Pseudomonas fluorescens strain Agl was released into mesocosms as a single inoculum of 1 × 10(5) cells ml(-1) (final concentration) or as four inocula (same concentration each) at intervals of 3 days. Mesocosms that had received growth media corresponding to the inoculum served as controls. Numbers of P. fluorescens Ag1 decreased rapidly whether released as single or multiple inocula. Direct estimation of protozoan predation using fluorescently labeled P. fluorescens from log phase and starved cultures, respectively, revealed that natural populations of heterotrophic nanoflagellates consumed substantial amounts of the nonindigenous bacterial strain. The volume of fluorescently labeled cells prepared from starved cells was 68% of log phase cell volume, but the individual clearance of the small cells was five to seven times higher than that of the log phase bacteria. The natural populations of nanoflagellates consumed 34-62% of P. fluorescens Ag1 daily if starved bacteria were offered as food, and 3-13% if the cells were in the logarithmic growth phase. This suggests that the effect of protozoan predation on nonindigenous bacterial strains is substantial because cultured bacteria are likely to starve in natural environments. The addition of P. fluorescens Ag1 and the growth medium enhanced the abundance of natural bacteria, chlorophyll a, heterotrophic nanoflagellates, and ciliates, but it did not improve the growth conditions for the released strain. The effects on the indigenous populations were more pronounced after addition of fresh medium than following inoculation with cells, which possibly was due to the lower nutrient content of spent medium. However, these results, based on direct estimation of protozoan predation on log phase and starved nonindigenous bacteria, point to the conclusion that mortality induced by bacterivorous predators is the key factor determining removal of nonindigenous bacteria introduced in natural aquatic systems.

Measurement of bacterivory by heterotrophic nanoflagellates using immunofluorescence labelling of ingested cells

“…feeding on strains MM1 and Agl which were of almost equal size. These findings are in accordance with several previous studies (Chrzanowski & Simek 1990, Gonzalez et al 1990, Simek & Chrzanowski 1992, Christoffersen et al 1995.…”

“…The specificity and utility of the antibody to Pseudomonas fluorescens Agl have been published previously (Nybroe et al 1990, Ahl et al 1995. Polyclonal antibodies against ON2 and MM1 were prepared by immunizing rabbits (strain Ssc: CPH, State Serum Institute, Copenhagen) with whole cells which had been incubated at 100°C for 2 h. The antisera were absorbed and purified as described by Nybroe et al (1990).…”

“…Fluorescent antibody techniques are widely used for detection and quantification of different specific types of planktonic microorganisms in aquatic environments (Nybroe et al 1990, Campbell et al 1994, Vrieling et al 1994, Ahl et al 1995, Rollo et al 1995, Zaccone et al 1995. Furthermore, immunochemical assays have recently been used for qualitative detection of cyanobacteria in the guts of copepods (Goarant et al 1994) but quantification of the ingested material was not possible.…”

Viable, but non-culturable, state of a green fluorescence protein-tagged environmental isolate of Salmonella typhi in groundwater and pond water

“…Grazing by protozoa has been regarded as one of the main factors that remove allochthonous bacteria from natural environments [27,28]. Therefore, S. typhi can survive relatively longer in groundwater, where grazing pressure is very low, than in stream, lake, and pond water.…”

Biocontrol of Fusarium wilt of banana: Key influence factors and strategies

“…Obstacles to the initial colonization refers to the first set of natural barriers encountered by the antagonistic microbes after the application of BCAs, including the predation and phagocytosis from soil protozoa (Ekelund et al, 2001;Ronn et al, 2002), inhibition from the exudates of indigenous microbes (Bolwerk et al, 2003) or plant roots (Chao et al, 1986), the competition with indigenous microbes for ecological sites, nutrients and energy. Normally, influenced by these barriers, the population of most antagonistic microbes reduced drastically in the first 2 to 3 days after the application of the BCAs (Christoffersen et al, 1995). However, BCAs usually must maintain a certain population of the antagonistic microbes to obtain acceptable levels of disease suppression .…”