ABSTRACT
Microbial exopolysaccharides (EPS) are considered as natural bio-thickeners abundantly used in dairy and fermented food industries for quality improvement. In fermentation based dairy industries, researchers are seeking their attention on substitution of artificial food stabilizers with naturals by exploring EPS, especially for improving the rheology of fermented food products. Lactic acid bacteria (LAB) being a starter player for fermented food products are believed to be as one of the best natural producers of EPS. These EPS are basically sugar residues, secreted by microbes in their surrounding environment but their in-vitro production is not economical due to the media and processing costs involved. The process of production is also complex due to the involvement of various enzymes and regulatory proteins. With modernization in dairy sector, our understanding towards EPS needs improvement. The review focuses on a brief explanation on the behavior and functionality of EPS from lactic acid bacteria.
ABSTRACT
Iron mediated regulation of growth and siderophore production has been studied in a diazotrophic cyanobacterium Anabaena cylindrica. Iron-starved cells of A. cylindrica exhibited reduced growth (30%) when the cells were growing under N2-fixing conditions. In contrast, N03-, NO2-, NH4' and urea grown cells exhibited almost 50% reduction in their growth in the absence of iron as compared to their respective counterparts cultured in the presence of iron. However, at 60 microM of iron, A. cylindrica cells exhibited almost equal growth regardless of the nitrogen source available. Siderophore production in A. cylindrica was started after day 2nd of the cell growth and attained its optimal level on day 5th when the cells were at their mid-log phase. No siderophore production was, however, recorded on day 2nd at all the concentrations of iron tested. The production of siderophore in A. cylindrica further increased with increase in iron concentration and attained its optimum level on day 5th at 60 microM iron. A. cylindrica cells took at least 3 days for initiation of siderophore production and produced about 60% siderophore on day 5th even under iron-starved condition. A. cylindrica produced dihydroxamate type of siderophore.
Subject(s)
Anabaena cylindrica/drug effects , Cyanobacteria/drug effects , Iron/pharmacology , Nitrogen/pharmacology , Nitrogen Fixation , Siderophores/biosynthesisABSTRACT
Iron induced changes in growth, N2-fixation, CO2 fixation and photosynthetic activity were studied in a diazotrophic cyanobacterium Anabaena PCC 7120. Iron at 50 microM concentration supported the maximum growth, heterocyst frequency, CO2 fixation, photosystem I (PS I), photosystem II (PS II) and nitrogenase activities in the organism. Higher concentration of iron inhibited these processes. Chl a and PS II activities were more sensitive to iron than the protein and PS I activity.