Identification of the Maltose transporter of the hyperthermophilic bacterium, Thermotoga maritima.

What is it about?

Thermotoga maritima is an important fermentative and hyperthermophilic bacterium because it produces H2 to levels that approach the biological limit of H2 production. However, lack of a genetic system in this bacterium has been a major obstacle to comprehend the genetic basis of metabolic enzymes and sugar transporters that contribute to a higher amount of H2 formation. Typically, sub-units of ABC transporters are identified due to their contiguous nature within operons however in T. maritima the ATPase subunit (MalK) of the maltose transporter is not within the maltose operon and it is present in three copies (malK1, malK2 and malK3) elsewhere in the genome. For the first time, gene disruption of all three malK was performed individually and the maltose catabolic function was accessed in the malK disruption mutants. Only a disruption of malK3 produced a defect in maltose catabolism that was further repaired with the malK3 wild copy to restore the maltose uptake function. Even though T. maritima possesses three paralogs of MalK only one of them is functional. This suggests that the evolution in the ancient hyperthermophilic bacterium, T. maritima, has made other MalK paralogs non-functional. Our bioinformatic analysis shows that there are multiple paralogous genes in the genome of T. maritima and only genetic dissection can reveal their true function.

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Why is it important?

The unique ability of Thermotoga maritima to produce H2 to levels that approach the biological limit of H2 production makes it an interesting bacterium to comprehend the genetic basis of metabolic genes and sugar transporters. While various methods exist to predict the function of a gene in T. maritima, the presence of multiple copies of a gene and poor annotation further complicates the reliability on the function of a gene. T. maritima possesses the second highest number of transporter genes that belong to the ABC transporters and these transport seems to be the crucial components in H2 synthesis. However, the genetic basis of these transporters has not been studied and prior studies including transcriptomics, in-silico prediction and expression studies in E. coli are the indirect measure to reveal the function of a gene that is present in multiple copies. The described method in this paper has a potential to clarify the role of a gene whose paralogs are present in the genome. Moreover, manipulating the amount of transported maltose through the maltose transporter employing genetic engineering is likely to change the maltose metabolism and the amount of formed H2. The continued use of genetics to investigate gene function in T. maritima will promote the development of this organism as a model hyperthermophile, and specifically for the production of biohydrogen with this species.

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