Microbial pectinolytic enzymes: A review

Extracellular polymeric substances (EPS) produced by microorganisms are a complex mixture of biopolymers primarily consisting of polysaccharides, as well as proteins, nucleic acids, lipids and humic substances. EPS make up the intercellular space of microbial aggregates and form the structure and architecture of the biofilm matrix. The key functions of EPS comprise the mediation of the initial attachment of cells to different substrata and protection against environmental stress and dehydration. The aim of this review is to present a summary of the current status of the research into the role of EPS in bacterial attachment followed by biofilm formation. The latter has a profound impact on an array of biomedical, biotechnology and industrial fields including pharmaceutical and surgical applications, food engineering, bioremediation and biohydrometallurgy. The diverse structural variations of EPS produced by bacteria of different taxonomic lineages, together with examples of biotechnological applications, are discussed. Finally, a range of novel techniques that can be used in studies involving biofilm-specific polysaccharides is discussed.

https://www.mdpi.com/1420-3049/14/7/2535/pdf

Bacterial extracellular polysaccharides involved in biofilm formation.

https://www.cell.com/trends/neurosciences/pdf/S0166-2236(08)00163-X.pdf

Neuronal calcium mishandling and the pathogenesis of Alzheimer's disease.

Phosphatidylserine (PS) is the most abundant negatively charged phospholipid in eukaryotic membranes. PS directs the binding of proteins that bear C2 or gamma-carboxyglutamic domains and contributes to the electrostatic association of polycationic ligands with cellular membranes. Rather than being evenly distributed, PS is found preferentially in the inner leaflet of the plasma membrane and in endocytic membranes. The loss of PS asymmetry is an early indicator of apoptosis and serves as a signal to initiate blood clotting. This review discusses the determinants and functional implications of the subcellular distribution and membrane topology of PS.

The distribution and function of phosphatidylserine in cellular membranes.

Autoimmunity and the Clearance of Dead Cells

The primary genes involved in β-(1,2) cyclic glucan synthesis and transport in Rhizobiaceae and Agrobacteriaceae are chv A, chv B, ndv A, and ndv B. The genes, ndv B and ndv C are involved in β-(1,3) glucan synthesis. The genes, ndvB, ndvC, and ndvD are involved in the synthesis of β-(1,3)-(1,6) cyclic. The genes opgG, H, B, C, D, I, opg HXcv, cgs, and cgm are also responsible for the synthesis of periplasmic glucans in Proteobacteria. In the early stages of polysaccharide synthesis pentose-phosphate and Entner–Doudoroff pathways are involved. The enzymes, cyclic glucan synthase and β-(1,3), β-(1,6)-(1,3), and β-(1,3)-(1,6) glucosyltransferase catalyse the biosynthesis process in the respective glucan synthesis. The β-glucanases are involved in the degradation of glucans.

Mechanism of Cyclic β-Glucan Production

Coffee wastewater contains large amounts of caffeine which affects microflora and seed development to great extent. Although several physio‐chemical methods available for caffeine degradation, they are not preferred for large‐scale treatment. In this study, we optimized induced cell concentration, aeration and agitation rate for maximizing caffeine degradation rate in bioreactor using Uniform design. Maximum caffeine degradation rate of 23·59 mg L−1 h−1 was achieved. The reduction in chemical oxygen demand, biological oxygen demand and total organic carbon removal were found to be 72, 78 and 72% respectively. Mathematical model was developed through regression analysis and predicted maximum caffeine degradation rate of 24·2 mg L−1 h−1 under optimal conditions of 0·35 g L−1 biomass, 395 rev min−1 and 1·62 vvm. Experimental validation at optimum condition resulted in 22 mg L−1 h−1 of caffeine degradation rate. This is the first‐ever bioreactor study showing highest caffeine degradation rate in synthetic coffee wastewater with limited experimental runs.

Optimization by uniform design U8(83) approach for enhanced caffeine degradation in synthetic wastewater in bioreactor

Human alcohol dehydrogenases, specifically ADH1 oxidize primary alcohols to aldehydes in the skin. These aldehydes act as haptens, leading to sensitization. Inhibition of these ADH enzymes may help in combating skin allergies. In the present study, the recombinantly purified stereospecific enzyme from Candida parapsilosis ATCC 7330, Candida parapsilosis Carbonyl Reductase (CpCR) has 23.31 % sequence similarity with human alcohol dehydrogenase ADH1B1. These two enzymes have perfectly overlapping cofactor and zinc binding domains. CpCR was found to oxidize primary alcohols to their corresponding aldehydes. Oxidation of primary alcohols by CpCR was further optimized with cinnamyl alcohol as the model substrate that initially showed a conversion of 56 % ± 0.25, and upon optimization increased to 98.2 % ± 0.23. An increase of 20–50 % in the conversion rate has been observed for various primary alcohols under the optimized reaction conditions. A simple and efficient model was designed for the screening of compounds that inhibit CpCR with the possibility of mitigating the action of skin allergens by inhibiting ADH1. p-Nitrophenylglyoxal (PNG) was found to be a good inhibitor for CpCR which showed inhibitory activity at very low concentration (IC50,100 mM ± 1.27) as compared to the standard inhibitor 4-methyl pyrazole (4MP) (IC50, 400 mM ± 2.05). 

Candida parapsilosis carbonyl reductase as a tool for preliminary screening of inhibitors for alcohol dehydrogenase induced skin sensitization

During the implementation of microbial enhanced oil recovery (MEOR) technique in reservoirs, various reservoir and microbial kinetic parameters play major roles in governing the efficiency of crude oil recovery from hydrocarbon reservoirs. The present study numerically investigates the sensitivity of reservoir porosity, injected microbial species at different temperatures, maximum microbial specific growth rate, Monod saturation constant and yield coefficient on biomass and biosurfactant production and their impacts on microscopic oil displacement efficiency within the reservoir. A black-oil biochemical multi-species reactive transport model in porous media is developed by coupling the kinetic model with the corresponding transport model. The governing equations involve coupled transport of nutrients and microbes by dispersion and convection, growth and decay rates of microbes, chemotaxis, nutrient consumption, and deposition of microbes and nutrients on rock-grain surfaces. Coupled empirical equations are used to estimate biosurfactant production, oil-water interfacial tension reduction, change in viscosity of injection fluid and their impacts on oil mobility and decrease in residual oil saturation within reservoir. Finite difference discretization technique is adopted to solve the governing equations. Results of the present model are found to be numerically stable and match very well, when verified, with the previously published analytical and experimental results. The model results suggest that at very low reservoir porosity (less than 20%), an early breakthrough of nutrients, microbe and biosurfactant leave insignificant concentrations in their respective fronts which are insufficient for the recovery of the trapped oil. Also, increase in porosity beyond 20% causes loss of nutrients, microbes and biosurfactant because they undergo higher dispersion during their transport within reservoir. Further it is observed that the nature of microbes and nutrients used for MEOR application affect biosurfactant production and in turn oil recovery to a large extent. Those microbial species having very less Monod saturation constant values have high affinity towards their substrates. This phenomenon drastically increases the rates of nutrient consumption and production of biomass and biosurfactant within reservoir when suitable substrate compounds are used, irrespective of differences in the yield coefficients of the microbes. The optimized reservoir and microbial kinetic properties increase capillary number above 10−3 which further increases oil mobility towards production well and there is a significant decline in the effective residual oil saturation (less than 5%) within the reservoir. The present study provides an improved understanding of the combined effects of reservoir porosity and microbial kinetic parameters on fundamental MEOR processes which will better characterize the suitability of a MEOR technique in a typical petroleum reservoir. Moreover, the developed numerical model is easier to implement and produces faster results with relatively lower computational cost which helps in making quick decision before applying MEOR processes in the field.

Numerical Modeling on the Influence of Reservoir Porosity and Microbial Kinetics on Enhanced Oil Recovery by Microbial Flooding

Docosahexaenoic acid (DHA) is an essential dietary supplement that is highly coveted due to its benefits for human health. Extensive research has been conducted for the sustainable commercial production of DHA by various strains in thraustochytrid family due to the accumulation of higher lipid content in the cells. The current study is focused on improving DHA production by investigating various key enzymes like glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), and ATP-citrate lyase (ACL) involved in DHA production using Thraustochytrium sp. T01. The growth of this strain was compared in batch and fed-batch mode. The fed-batch yielded better Dry cell weight (40 g L-1), lipid (27.75 g L-1 or 693 mg g-1 of DCW), and DHA contents (11.10 g L-1 or 277 mg g-1 of DCW). G6PDH activity increased 4-fold during the glucose fed-batch, but ME and ACL did not increase significantly. Furthermore, a study was conducted to determine the effects of organic acids (pyruvate and malate) on key enzyme activities. The addition of pyruvate increased the lipid content by 1.35-fold, and ACL activity by 10-fold as compared with control (without added organic acids). Malate addition into the culture media increased DHA content 1.4-fold, and ME activity increased 14-fold compared with control.

Sathyanarayana N. Gummadi

Papers

Mechanism of Cyclic β-Glucan Production

Optimization by uniform design U8(83) approach for enhanced caffeine degradation in synthetic wastewater in bioreactor

Candida parapsilosis carbonyl reductase as a tool for preliminary screening of inhibitors for alcohol dehydrogenase induced skin sensitization

Numerical Modeling on the Influence of Reservoir Porosity and Microbial Kinetics on Enhanced Oil Recovery by Microbial Flooding

Role of key enzymes in the production of docosahexaenoic acid (DHA) by Thraustochytrium sp. T01.