Application of response surface methodology to enhancement of biomass production by Lactobacillus rhamnosus E/N

Response surface methodology (RSM) was employed to study the effects of various medium components on biomass production by Lactobacillus rhamnosus E/N. This strain is commonly used in the pharmaceutical and food industries due to its beneficial effect on the human gut and general health. The best medium composition derived from RSM regression was (in g/l) glucose 15.44, sodium pyruvate 3.92, meat extract 8.0, potassium phosphate 1.88, sodium acetate 4.7, and ammonium citrate 1.88. With this medium composition biomass production was 23 g/l of dry cell weight after 18 h of cultivation in bioreactor conditions, whereas on MRS the yield of biomass was 21 g/l of dry cell weight. The cost of 1 g of biomass obtained on MRS broth was calculated at the level of 0.44 € whereas on the new optimal medium it was 25 percent lower. It may be concluded then, that the new medium, being cheaper than the control MRS allows large scale commercial cultivation of the L. rhamnosus strain. This study is of relevance to food industry because the possibility to obtain high yield of bacterial biomass is necessary step in manufacturing of probiotic food.

The Structure and Metabolic Diversity of Population of Pea Microsymbionts Isolated from Root Nodules.

Aims: The study of strains belonging to local rhizobial population, concerning their diversity in the genetic, metabolic and symbiotic properties, and their prevalence in the microsymbiont population. Methodology: 257 rhizobial isolates recovered from nodules of five pea (Pisum sativum cv. Ramrod) plants grown at one site were classified using PCR-RFLP analysis of 16-23S rRNA ITS. After that, for representative group of 55 strains, 16-23S rRNA ITS region was sequenced, nodA-F region was analyzed by PCR-RFLP and sequencing, metabolic capabilities were studied using Biolog`s and growth tests and symbiotic performance in plant tests were assayed. Results: Individual plants were infected by numerous and diverse strains, however, in the entire sampled population of microsymbionts, only three large clusters of strains could be distinguished on the basis of PCR-RFLP and sequence analyses of 16S-23S rRNA ITS region. Rhizobium strains belonging to different groups varied in plasmid number and the amount of plasmid DNA, utilization of carbon and energy sources, growth on soil extractbased media and the ability for symbiotic plant growth promotion. The most numerous group of the isolates was characterized by the high plasmid DNA content, low number of utilized sugar substrates, and comprised numerous strains with low symbiotic efficiency. Conclusion: Sampled population of pea microsymbionts had its own characteristic structure with clearly distinguishable sub-populations, composed of numerous strains - probably descendants of a few old lineages, which diversified in the lapse of time. These strains are still competing during root nodule colonization, resulting in the symbiosis of individual pea plants with broad spectrum of different Rhizobium strains.