Staphylococcus aureus Genomes Harbor Only MpsAB-Like Bicarbonate Transporter but Not Carbonic Anhydrase as Dissolved Inorganic Carbon Supply System.

ABSTRACT

In recent years, it became apparent that not only autotrophic but also most other bacteria require CO2 or bicarbonate for growth. Two systems are available for the acquisition of dissolved inorganic carbon supply (DICS) the cytoplasmic localized carbonic anhydrase (CA) and the more recently described bicarbonate transporter MpsAB (membrane potential generating system). In the pathogenic species Staphylococcus aureus, there are contradictions in the literature regarding the presence of a CA or MpsAB. Here, we address these contradictions in detail. We could demonstrate by careful BLASTp analyses with 259 finished and 4,590 unfinished S. aureus genomes that S. aureus does not contain CA and that the bicarbonate transporter MpsAB is the only DICS system in this species. This finding is further supported by two further pieces of evidence (i) mpsAB deletion mutants in four different S. aureus strains failed to grow under atmospheric air, which should not be the case if they possess CAs, since we have previously shown that both CA and MpsAB can substitute for each other, and (ii) S. aureus is completely resistant to CA inhibitors, whereas Staphylococcus carnosus, which has been shown to have only CA, was inhibited by ethoxyzolamide (EZA). Taken together, we demonstrate beyond doubt that the species S. aureus possesses only the bicarbonate transporter MpsAB as its sole DICS system. IMPORTANCE The discrepancies in the current literature and even in NCBI database, which listed some protein sequences annotated as Staphylococcus aureus carbonic anhydrase (CA), are misleading. One of the existing problems in publicly available sequence databases is the presence of incorrectly annotated genes, especially if they originated from unfinished genomes. Here, we demonstrate that some of these unfinished genomes are of poor quality and should be interpreted with caution. In the present study, we aimed to address these discrepancies and correct the current literature about S. aureus CA, considering the medical relevance of S. aureus. If left unchecked, these misleading studies and wrongly annotated genes might lead to a continual propagation of wrong annotation and, consequently, wrong interpretations and wasted time. In addition, we also show that bicarbonate transporter MpsAB-harboring bacteria are resistant to CA inhibitor, suggesting that pathogens possessing both MpsAB and CA are not treatable with CA inhibitors.