Substrate uptake and utilization by a marine ultramicrobacterium.
A facultatively oligotrophic ultramicrobacterium (strain RB2256) isolated from an Alaskan fjord by extinction dilution in seawater, was grown in batch culture and under single- and dual-substrate-limitation of alanine and glucose in a chemostat. The nature of the uptake systems, and the uptake kinetics and utilization patterns of alanine and glucose were investigated. Glucose uptake was inducible, the system exhibited a narrow substrate specificity, and part of the uptake system was osmotic-shock-sensitive. Half-saturation constants for glucose were between 7 and 74 microM during glucose limitation. The initial step in glucose metabolism was the synthesis of sugar polymers, even during glucose-limited growth. The alanine uptake system was constitutively expressed and was binding-protein-dependent. In addition to L-alanine, nine other amino acids inhibited accumulation of [14C]L-alanine, indicating broad substrate specificity of the alanine transporter. Half-saturation constants between 1.3 and 1.8 microM were determined for alanine uptake during alanine limitation. Simultaneous utilization of glucose and alanine occurred during substrate-limited growth in the chemostat, and during growth in batch culture at relatively high (mM) substrate concentrations. However, the half-saturation constant for alanine transport during dual-substrate-limitation, i.e. in the presence of glucose, increased almost fivefold. We conclude that mixed substrate utilization is an inherent property of this organism.
Schut
F
F
Department of Microbiology, University of Groningen, Haren, The Netherlands.
Jansen
M
M
Gomes
T M
TM
Gottschal
J C
JC
Harder
W
W
Prins
R A
RA
D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism*; D006088:Gram-Negative Aerobic Bacteria / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D012623:Seawater; D013379:Substrate Specificity; D014871:Water Microbiology
D000596:Amino Acids; D002352:Carrier Proteins; D005947:Glucose; D000409:Alanine