Photosynthetic accumulation of poly-(hydroxybutyrate) by cyanobacteria--the metabolism and potential for CO2 recycling.
Regulatory mechanism in PHB [poly-(hydroxybutyrate)] accumulation by cyanobacteria, especially by a thermophilic isolate, Synechococcus MA19 was reviewed in comparison with a genetically engineered strain. The strain, MA19 accumulates PHB under nitrogen starved and photoautotrophic conditions (MA19-N). Little PHB synthase activity was detected in crude extracts from the cells grown in nitrogen sufficient conditions (MA19 + N). The activity was detected exclusively in membrane fractions from MA19 + N. The change of the enzyme activity was insensitive to chloramphenicol, which suggests post-translational activation. In vitro, acetyl phosphate activated PHB synthase in membrane fractions from MA19 + N, and the extent of activation depended on the concentration of acetyl phosphate. Phosphotransacetylase which catalyzes the conversion of acetyl-CoA to acetyl phosphate was detected in crude extracts from MA19-N but not in those from MA19 + N. These results suggested that intracellular acetyl phosphate concentration could be controlled, depending on C-N balance and intracellular acetyl-CoA concentration. On the contrary, in genetically-engineered cyanobacterium (transformant with PHB synthesizing genes from Ralstonia eutropha), it did not seem to be PHB synthase but acetyl-CoA flux that limits PHB synthesis. The closer association of PHB granules with thylakoid membranes in MA19 is suggested than that in the genetically-engineered cyanobacterium, which may reflect the difference of distribution of PHB synthase. Transposon-mutagenesis was used to acquire mutants of its altered PHB regulatory mechanism. PHA production by cyanobacteria was considered from the aspects of photobioreactors.
National Institute of Bioscience and Human-Technology, Tsukuba, Ibaraki, Japan. yasada@ccmail.nibh.go.jp
Y
Y
Asada
M
M
Miyake
J
J
Miyake
R
R
Kurane
Y
Y
Tokiwa
D000217:Acyltransferases / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism* / Q000648:ultrastructure; D006885:Hydroxybutyrates / Q000378:metabolism*; D010788:Photosynthesis; D011091:Polyesters / Q000378:metabolism*; D000091402:Prohibitins; D000094122:Polyhydroxybutyrates
D000217:Acyltransferases; D002245:Carbon Dioxide; D006885:Hydroxybutyrates; D011091:Polyesters; D000091402:Prohibitins; C000717328:PHB protein, human; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C060970:poly-beta-hydroxybutyrate polymerase