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Background The continuous escalation in wastewater production with declining dependency on conventional resources as a result of rapid urbanization, increasing global water scarcity and growing population have initiated many researchers to look out for efficient means of utilizing wastewater. In this regard, an effectual process economizing approach has been achieved, upon utilizing the discharged wastewater from validamycin A recovery process in fermentation medium as a replacement of costly tap water. Results In this study, wastewater was successfully used as a fermentation medium for the production of validamycin A in plant-scale bioreactor. Moreover, a new strain Streptomyces hygroscopicus K2509 was screened showing a good production capability in this low-cost culture environment and showed maximum validamycin A production and productivity of 21.23 g/L and 0.29 g/L h, respectively. Execution of this study has managed the effective utilization of wastewater by reducing 12.42% production cost per kilogram of validamycin A in an environmental friendly way. Conclusion The novel successful approach for using process wastewater even on being executed in plant-scale bioreactor was proved cost effective. In short, the presented effective way of utilizing wastewater in study will definitely serve as potentially cheap fermentation medium upon replacing tremendously used expensive tap water.

Background Compared with shake flask, bioreactor offers a relatively stable and controllable extracellular environment for cell growth and metabolism. Meanwhile, parallel micro-bioreactor system could well meet the screening flux requirement in the process of high-throughput strain screening. In this study, a self-developed 8-parallel micro-bioreactor system with non-invasive optical biosensors was introduced to substitute the traditional shake flask. Results Optical pH and DO biosensors could be well applied for the process monitoring and controlling in the cultures of commonly used microorganisms through maintaining constant temperature and bioreactor shading treatment. Subsequently, 8-parallel micro-bioreactor system was adopted in the rescreening procedure of high-throughput screening process, and it significantly increased the feasibility of scaling up a cultivating system without any sacrifice on the screening flux. As a result, a designated mutant strain Lactobacillus paracasei S4 was obtained, which presented an improvement of 18.9% on titer value of l-lactic acid. Moreover, the yield also increased from 0.903 ± 0.005 to 0.932 ± 0.013 g/g. Conclusion In this study, the micro-bioreactor system proved to be applicable and effective in the rescreening procedure of high-throughput screening process. The adopted approach provided a robust tool for screening the strain with high l-lactic acid producing performance.

Background In the phase of oxygen limitation during Aspergillus niger fermentation, the cell growth decreased, while the yield of glucoamylase increased continuously and significantly. Explanation on the changes of transcriptome profile during this process may improve our understanding on mechanisms of cell adaption and enzyme production in A. niger. Results The transcriptomic data from 4 time points in oxygen limitation process of a glucoamylase production A. niger strain were analyzed. Hierarchical clustering of all samples showed that the strongest transcriptional response occurred between the early and middle stage of oxygen limitation. 515 differentially expressed genes (DEGs) were identified and were clustered into 12 expression patterns. Continuously down-regulated DEGs were significantly enriched in GO terms of the ribosome, translation, and aminoacyl-tRNA biosynthesis, and continuously up-regulated DEGs were mainly involved in GO terms of fatty acid catabolism, N-acetyltransferase activity, lipase activity, and carboxylesterase activity. Pyruvate kinase and asparagine synthetase which related to the biosynthesis of the main amino acid composition of the enzyme were significantly up-regulated. Sterol-regulatory element-binding proteins (SREBP) transcription factor SrbB was one of the most up-regulated proteins, indicating its important roles in hypoxia fermentation of A. niger. Conclusion Comparative transcriptome data analysis of the fermentation revealed that the overall reduced biosynthesis of translation machine and fatty acid, acceleration of fatty acid catabolism, and increased synthesis of main amino acid compositions of glucoamylase are the key transcriptional changes during the oxygen limitation fermentation process of A. niger.