Changes in morphology and elemental composition of Vibrio splendidus along a gradient from carbon-limited to phosphate-limited growth.
We examined morphology, elemental composition (C, N, P), and orthophosphate-uptake efficiency in the marine heterotrophic bacterium Vibrio splendidus grown in continuous cultures. Eight chemostats were arranged along a gradient of increasing glucose concentrations in the reservoirs, shifting the limiting factor from glucose to phosphate. The content of carbon, nitrogen, and phosphorus was measured in individual cells by x-ray microanalysis using a transmission electron microscope (TEM). Cell volumes (V) were estimated from length and width measurements of unfixed, air-dried cells in TEM. There was a transition from coccoid cells in C-limited cultures toward rod-shaped cells in P-limited cultures. Cells in P-limited cultures with free glucose in the media were significantly larger than cells in glucose-depleted cultures (P < 0.0001). We found functional allometry between cellular C-, N-, and P content (in femtograms) and V (in cubic micrometers) in V. splendidus (C = 224 x V(0.89), N = 52.5 x V(0.80), P = 2 x V(0.65)); i.e., larger bacteria had less elemental C, N, and P per V than smaller cells, and also less P relative to C. Biomass-specific affinity for orthophosphate uptake in large P-limited V. splendidus approached theoretical maxima predicted for uptake limited by molecular diffusion toward the cells. Comparing these theoretical values to respective values for the smaller, coccoid, C-limited V. splendidus indicated, contrary to the traditional view, that large size did not represent a trade-off when competing for the non-C-limiting nutrients.
Løvdal
Trond
T
Department of Biology, University of Bergen, Jahnebakken, Bergen, Norway. trond.lovdal@start.no
Skjoldal
Evy F
EF
Heldal
Mikal
M
Norland
Svein
S
Thingstad
T Frede
TF
D000469:Alkaline Phosphatase / Q000378:metabolism; D018533:Biomass; D002244:Carbon / Q000378:metabolism / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media; D004577:Electron Probe Microanalysis; D046529:Microscopy, Electron, Transmission; D009584:Nitrogen / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology*; D014733:Vibrio / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure
D003470:Culture Media; D010710:Phosphates; D002244:Carbon; D000469:Alkaline Phosphatase; D009584:Nitrogen