Abstract
An artificial microbial community consisted of Ketogulonicigenium vulgare and Bacillus megaterium has been used in industry to produce 2-keto-gulonic acid (2-KGA), the precursor of vitamin C. During the mix culture fermentation process, sporulation and cell lysis of B. megaterium can be observed. In order to investigate how these phenomena correlate with 2-KGA production, and to explore how two species interact with each other during the fermentation process, an integrated time-series proteomic and metabolomic analysis was applied to the system. The study quantitatively identified approximate 100 metabolites and 258 proteins. Principal Component Analysis of all the metabolites identified showed that glutamic acid, 5-oxo-proline, L-sorbose, 2-KGA, 2, 6-dipicolinic acid and tyrosine were potential biomarkers to distinguish the different time-series samples. Interestingly, most of these metabolites were closely correlated with the sporulation process of B. megaterium. Together with several sporulation-relevant proteins identified, the results pointed to the possibility that Bacillus sporulation process might be important part of the microbial interaction. After sporulation, cell lysis of B. megaterium was observed in the co-culture system. The proteomic results showed that proteins combating against intracellular reactive oxygen stress (ROS), and proteins involved in pentose phosphate pathway, L-sorbose pathway, tricarboxylic acid cycle and amino acids metabolism were up-regulated when the cell lysis of B. megaterium occurred. The cell lysis might supply purine substrates needed for K. vulgare growth. These discoveries showed B. megaterium provided key elements necessary for K. vulgare to grow better and produce more 2-KGA. The study represents the first attempt to decipher 2-KGA-producing microbial communities using quantitative systems biology analysis.
Highlights
Microbial communities play essential roles in nature, making the most contributions to the earth’s species diversity and being of great importance to various environmental, medical, and biotechnological applications [1,2]
Based on the different colony morphologies for K. vulgare and B. megaterium, cell growths rates of these two species were evaluated by counting their colony forming units (CFUs) one milliliter of fermentation broth
The analysis and interpretation of the quantification data showed that B. megaterium helped K. vulgare growth probably by providing a better living environment and supplying essential substances such as substrates for purine nucleotides synthesis
Summary
Microbial communities play essential roles in nature, making the most contributions to the earth’s species diversity and being of great importance to various environmental, medical, and biotechnological applications [1,2]. Much research in the past decades has focused on characterizing compositions and functionality of various microbial communities. Towards these goals, many technological methods have been developed and applied, including 16s-rRNA sequencing for community composition analysis [4,5]; stable isotope probing technologies for linking microbial community function to phylogeny [6]; meta-genomics and meta-transcriptomics for capturing global view of genetic diversity and gene expression of communities [7]. A new research field, metabolomics which measures intracellular metabolites, advanced rapidly, with the potentials to bridge the gap between genetype and phenotype [10]
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