Understanding Of Carbon Metabolism Research Articles

Co-utilization of saccharides in mixtures: Moving toward a new understanding of carbon metabolism in Streptococcus thermophilus

The lactic acid bacterium Streptococcus thermophilus is widely used in food production, notably in yogurt fermentation. It evolved under highly specific ecological conditions, resulting in its ability to efficiently metabolize lactose, the main saccharide in milk. However, when used in sweetened dairy products or plant-based products, S. thermophilus may encounter other saccharides (i.e. alone or in mixtures). To date, the bacterium's metabolic capacities in such contexts have been poorly characterized. Here, we explored saccharide utilization by 39 S. thermophilus strains. Using in silico analysis, we discovered that the identity and structure of saccharide utilization genes are conserved across strains, and we identified six saccharides that might be metabolized. Although underlying genetic variability was low, strains nonetheless displayed differences in growth when supplied with different saccharides: lactose, sucrose, fructose, and glucose.Interestingly, we found that strains preferentially used lactose and sucrose in tandem when given saccharide mixtures. Furthermore, we uncovered some main potential drivers of saccharide metabolism in S. thermophilus. Notably, the sucrose transporter ScrA is also responsible for importing glucose. Overall, this research has yielded useful findings that can help the development of new fermented foods, including plant-based products, in which sucrose may serve as a major carbon source.

The role of intraspecific variation in the ecological and evolutionary success of diatoms in changing environments.

Intraspecific variation in diatoms has been shown to play a key role in species' responses to several important environmental factors such as light, salinity, temperature and nutrients. Furthermore, modelling efforts indicate that this variation within species extends bloom periods, and likely provides sufficient variability in competitive interactions between species under hydrographically variable conditions. The intraspecific variation most likely corresponds to optimal fitness in temporary microhabitats and may help to explain the paradox of the plankton. Here, we examine the implications of intraspecific variation for the ecology and success of diatoms in general and emphasize the potential implications for our understanding of carbon metabolism in these important organisms. Additionally, data from palaeoecological studies have the potential for evaluating genetic variation through past climate changes, going thousands of years back in time. We suggest pathways for future research including the adoption of multiple strains of individual species into studies of diatom carbon metabolism, to refine our understanding of the variation within and between species, and the inclusion of experimental evolution as a tool for understanding potential evolutionary responses of diatom carbon metabolism to climate change.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'.

Functional Characterization of a Hexose Transporter from Root Endophyte Piriformospora indica.

Understanding the mechanism of photosynthate transfer at symbiotic interface by fungal monosaccharide transporter is of substantial importance. The carbohydrate uptake at the apoplast by the fungus is facilitated by PiHXT5 hexose transporter in root endophytic fungus Piriformospora indica. The putative PiHXT5 belongs to MFS superfamily with 12 predicted transmembrane helices. It possess sugar transporter PFAM motif (PF0083) and MFS superfamily domain (PS50850). It contains the signature tags related to glucose transporter GLUT1 of human erythrocyte. PiHXT5 is regulated in response to mutualism as well as glucose concentration. We have functionally characterized PiHXT5 by complementation of hxt-null mutant of Saccharomyces cerevisiae EBY.VW4000. It is involved in transport of multiple sugars ranging from D-glucose, D-fructose, D-xylose, D-mannose, D-galactose with decreasing affinity. The uncoupling experiments indicate that it functions as H+/glucose co-transporter. Further, pH dependence analysis suggests that it functions maximum between pH 5 and 6. The expression of PiHXT5 is dependent on glucose concentration and was found to be expressed at low glucose levels (1 mM) which indicate its role as a high affinity glucose transporter. Our study on this sugar transporter will help in better understanding of carbon metabolism and flow in this agro-friendly fungus.

Identification and characterization of an extracellular acid trehalase from the ectomycorrhizal fungus Amanita muscaria

The non‐reducing disaccharide trehalose is a major storage compound in most fungi. For a better understanding of carbon metabolism in the ectomycorrhizal‐forming basidiomycete Amanita muscaria, trehalase activity was analysed from mycelium growing in liquid culture or on agar plates, and from mycorrhizas. Trehalase activity was found in both the culture medium and in mycelial extracts. The excreted trehalase was purified to apparent homogeneity by anion‐exchange chromatography, gel filtration and preparative gel electrophoresis. The identified enzyme belongs to the group of acid trehalases. The apparent molecular mass of the native enzyme was estimated to be 165 kDa by gel filtration and 135 kDa by SDS–PAGE. Isoelectrofocusing indicated an isoelectric point (pI) of approx. 3.7, which is typical for acid trehalases. The enzyme is highly specific for its substrate trehalose, with an apparent Km of 0.38 mM. Validamycin and sucrose act as competitive inhibitors with Ki values of 45 nM and 15 mM, respectively. The activity of acid trehalase excreted into the growth medium is independent of the carbon source (glucose or trehalose), revealing that the enzyme is not regulated by its substrate trehalose. Nevertheless, fungal hyphae grown in the absence of an external carbon source showed enhanced enzyme excretion. The biochemical characteristics of the trehalase activity measured in the mycelium are in the same range as those determined for the excreted enzyme. The enzyme is localized in the cell wall and its activity is strongly decreased in ectomycorrhizas.