@article{mbs:/content/journal/micro/10.1099/13500872-141-2-351, author = "Schut, Frits and Jansen, Michel and Gomes, Teresa M. Pedro and Gottschal, Jan C. and Prins, Wim Harder and Rudolf A.", title = "Substrate uptake and utilization by a marine ultramicrobacterium", journal= "Microbiology", year = "1995", volume = "141", number = "2", pages = "351-361", doi = "https://doi.org/10.1099/13500872-141-2-351", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/13500872-141-2-351", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", keywords = "ultramicrobacteria", keywords = "uptake systems", keywords = "oligotrophy", keywords = "glucose", keywords = "alanine", abstract = "SUMMARY 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 μM 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 μM 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.", }