Aerobic Respiration in Lactococcus lactis based on Gene Expression
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Abstract:
The homology of genes coding for respiratory chain and cytochrome oxidase activity of Lactococcus lactis strains that can or cannot undergo aerobic respiration were compared to provide a foundation for determining the necessary conditions for aerobic respiration in Lactococcus lactis. Firstly, growth curves of the two selected strains, KLDS4.0325 and KLDS4.1102, were determined under fermentation and aerobic respiration conditions. Secondly, the genomic DNA of strain KLDS4.1102 was extracted, and its respiratory chain-encoding genes were amplified by polymerase chain reaction (PCR), followed by DNA sequencing. Finally, the sequences of genes coding for the respiratory chain of KLDS4.0325 were downloaded from the GenBank database, the homology of genes coding for the respiratory chain in the two Lactococcus lactis strains was compared by DNAMAN software, and the cytochrome oxidase activities of these two strains were determined. The biomass and pH of KLDS4.0325 undergoing aerobic respiration increased significantly, but KLDS4.1102 presented a consistent growth trend between the two physiological conditions. The homology analysis of the genes coding for respiratory chain of two strains showed that KLDS4.1102 possessed a complete respiratory chain, while cytochrome oxidase activity could not be detected in KLDS4.1102. This finding suggests that KLDS4.1102 cannot undergo respiratory metabolism normally, possibly because some gene cannot be expressed normally, leading to abnormal cytochrome oxidase function.
