Carbon metabolism of a novel isolate from Lacticaseibacillus rhamnosus Probio-M9 derived through space mutant

Carbon source is a necessary nutrient for bacterial strain growth. In industrial production, the cost of using different carbon sources varies greatly. Moreover, the complex environment in space may cause metabolic a series of changes in the strain, and this method has been successfully applied in some basic research. To date, space mutagenesis is still limited number of studies, particularly in carbon metabolism of probiotics.

HG-R7970-41 was isolated from bacterium suspension (Probio-M9) after space flight, which can produce capsular polysaccharide after space mutagenesis. Phenotype Microarray (PM) was used to evaluated the metabolism of HG-R7970-41 in 190 single carbon sources. RNA sequencing and total protein identification of two strains revealed their different carbon metabolism mechanisms. PM results demonstrated the metabolism of 10 carbon sources were different between Probio-M9 and HG-R7970-41. Transcriptomic and proteomic analyses revealed that this change in carbon metabolism of HG-R7970-41 mainly related to changes in phosphorylation and the glycolysis pathway. Based on the metabolic mechanism of different carbon sources and related gene cluster analysis, we found that the final metabolic activities of HG-R7970-41 and Probio-M9 were mainly regulated by PTS-specific membrane embedded permease, carbohydrate kinase and two rate-limiting enzymes (phosphofructokinase and pyruvate kinase) in the glycolysis pathway. The expanded culture test also confirmed that HG-R7970-41 had different metabolic characteristics from original strain.

These results suggested that space environment could change carbon metabolism of Probio-M9. The new isolate (HG-R7970-41) showed a different carbon metabolism pattern from the original strain mainly by the regulation of two rate-limiting enzymes.