Use of bioluminescent bacteria, Xenorhabdus luminescens , to measure predation on bacteria by freshwater microflagellates

Light emitted by the bioluminescent bacterium, Xenorhabdus luminescens (isolated from a nematode host), can be measured to monitor reductions of these bacteria in the presence of phagotrophs. X. luminescens is relatively large (0.6 x 3 mu m), but comparable in size to many cyanobacteria. The authors used the light emission method to examine phagotroph feeding on X. luminescens using unispecific cultures of two chrysomonads, Ochromonas sp. and Spumella sp. From light decay rates in control and experimental vials, was computed an apparent filtration rate (FR), and for a concentration (C) of 1 multiplied by 10 super(6) bacteria/ml, capture rate (CR) estimated as FR multiplied by C. The Ochromonas) sp. did not ingest the bacterium. The maximum estimated FR for Spumella , observed at 6.0 multiplied by 10 super(3) flagellates/ml (medium density), was 0.37 ml/h, for a volume-specific clearance rate (FR/cell volume) of 7.9 multiplied by 10 super(5)/h and a CR of 62 bacteria/flagellate/h. Video microscopy indicated these were accurate estimates of capture rates.