Carboxysomes, microcompartments that enhance the fixation of carbon dioxide by
Rubisco, are found in several chemoautotrophs and in all cyanobacteria thus
far examined. The genes for Rubisco large (cbbL) and
small (cbbS) subunits (cbb for
Calvin-Benson-Bassham), along with the genes (csoS) for
the carboxysome shell peptides, are organized in a putative operon in
Halothiobacillus neapolitanus in the following order:
cbbL,cbbS,
csoS2, csoS3,
orfA, orfB,
csoS1C, csoS1A, and
csoS1B. DNA sequencing has revealed essentially the same
operon in three other thiobacilli,
Acidithiobacillus ferrooxidans,
Thiomonas intermedia, and
Thiobacillus denitrificans. The carboxysome genes are
also clustered inSynechococcus sp. and
Synechocystis sp., although in some cases certain genes
lie outside the cluster. The genes, labelled ccm for
CO2 concentrating mechanism, exist in
Synechococcus PCC7942 in the order
ccmK, ccmL,
ccmM, ccmN, and
ccmO, and are located upstream of the Rubisco genes.
ccmO is absent, and multiple copies of
ccmK exist in some species. The
ccmK/ccmO and ccmL genes are
homologues of csoS1CAB andorfAB,
respectively. The ccmM and ccmN
genes have no apparent counterpart in the thiobacilli. More recently, the
genome sequence of four additional cyanobacteria has become available. The
carboxysome genes in Nostoc punctiforme are clustered
like, and are similar to, the genes of the earlier mentioned cyanobacteria.
However, the three marine organisms
Prochlorococcus marinus MIT9313,
P. marinus MED4, and Synechococcus
WH8102, possess an operon nearly identical to that found in thiobacilli.
Furthermore, the genes exhibit surprising sequence identity to the carboxysome
genes of the thiobacilli.
Potential Application of Halothiobacillus Neapolitanus for Hydrogen Sulfide Removal in Biogas
