Substrate uptake and utilization by a marine ultramicrobacterium

Microbiology (Reading). 1995 Feb;141 ( Pt 2):351-61. doi: 10.1099/13500872-141-2-351.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / metabolism*
  • Amino Acids / metabolism
  • Amino Acids / pharmacology
  • Biological Transport / drug effects
  • Carrier Proteins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Glucose / metabolism*
  • Gram-Negative Aerobic Bacteria / genetics
  • Gram-Negative Aerobic Bacteria / growth & development
  • Gram-Negative Aerobic Bacteria / metabolism*
  • Gram-Negative Aerobic Bacteria / ultrastructure
  • Seawater
  • Substrate Specificity
  • Water Microbiology*


  • Amino Acids
  • Carrier Proteins
  • Glucose
  • Alanine