Lilija Auzina

Influence of growth conditions on hydrophobicity of Lactobacillus acidophilus and Bifidobacterium lactis cells and characteristics by FT-IR spectra

In this study we have found, that the values of cell surface hydrophobicity (CSH) of L. acidophilus LA5 and B. lactis Bb12 cells change in response to varied growth conditions – phase of growth, concentration or type of carbon source, presence of oxygen. An evaluation of FT-IR spectra using cluster and quantitative analyses revealed substantial changes of the chemical composition depending on the CSH level of L. acidophilus LA5 and B. lactis Bb12 cells. Decrease of the carbohydrate level was observed in proportion to the increased CSH values alongside with the elevated protein content of more hydrophobic cells of both cultures. The results of present study could help to specify the appropriate physiological state and environment for L. acidophilus LA5 and B. lactis Bb12 to ensure their probiotic properties.

Production of extracellular fructans by Gluconobacter nephelii P1464

Bacterial extracellular fructans, known as levans, have potential applications in food, pharmaceutical and cosmetic industries and high fructan producing strains could contribute into the cost reduction and more extensive commercial usage of them. An acetic acid bacteria (AAB) isolate P1464 was obtained from the Microbial Strain Collection of Institute of Microbiology and Biotechnology, University of Latvia and identified as Gluconobacter nephelii by DNA‐DNA hybridization and the formation of extracellular fructans by this strain was confirmed. Isolated extracellular fructose polymers were characterized using FT‐IR spectroscopy and the structural features of fructan appeared as similar to the reference sample of bacterial levan. Molecular mass estimates showed that the isolated G. nephelii P1464 fructose polymer has a relatively small molecular weight (Mw 1122·939 ± 153·453 kDa) and a sizeable polydispersity (Mw/Mn = 21·57 ± 1·60), as compared with other AAB, which could promote their physiological activity, including the prebiotic effects. Obtained at different cultivation conditions characteristics of fructan production, including the biotechnological indices such as the productivity (Qp) and yield (Yp/s) ranging from 0·774 to 1·244 g l−1 h and from 0·181 to 0·436 g g−1, respectively, confirmed, that G. nephelii P1464 could be used as promising strain for commercial production of levan.