Ehsan Ali

Binding of S-layer homology modules from Clostridium thermocellum SdbA to peptidoglycans.

S-layer homology (SLH) module polypeptides were derived from Clostridium josui xylanase Xyn10A, Clostridium stercorarium xylanase Xyn10B, and Clostridium thermocellum scafoldin dockerin binding protein SdbA as rXyn10A-SLH, rXyn10B-SLH, and rSdbA-SLH, respectively. Their binding specificities were investigated using various cell wall preparations. rXyn10A-SLH and rXyn10B-SLH bound to native peptidoglycan-containing sacculi consisting of peptidoglycan and secondary cell wall polymers (SCWP) prepared from these bacteria but not to hydrofluoric acid-extracted peptidoglycan-containing sacculi (HF-EPCS) lacking SCWP, suggesting that SCWP are responsible for binding with SLH modules. In contrast, rSdbA-SLH interacted with HF-EPCS, suggesting that this polypeptide had an affinity for peptidoglycans but not for SCWP. The affinity of rSdbA-SLH for peptidoglycans was confirmed by a binding assay using a peptidoglycan fraction prepared from Escherichia coli cells. The SLH modules of SdbA must be useful for cell surface engineering in bacteria that do not contain SCWP.

Enhancement of lipase catalyzed-fatty acid methyl esters production from waste activated bleaching earth by nullification of lipase inhibitors

This study sought to identify inhibitory factors of lipase catalyzed-fatty acid methyl esters (FAME) production from waste activated bleaching earth (wABE). During the vegetable oil refinery process, activated bleaching earth (ABE) is used for removing the impure compounds, but adsorbs vegetable oil up to 35-40% as on a weight basis, and then the wABE is discarded as waste material. The impurities were extracted from the wABE with methanol and evaluated by infra-red (IR) spectroscopy, which revealed that some were chlorophyll-plant pigments. The chlorophylls inhibited the lipase during FAME conversion from wABE. The inhibition by a mixture of chlorophyll a and b was found to be competitive. The inhibition of the enzymatic hydrolysis of waste vegetable oil contained in wABE by chlorophyll a alone was competitive, while the inhibition by chlorophyll b alone was non-competitive. Furthermore, the addition of a small amount of alkali nullified this inhibitory effect and accelerated the FAME production rate. When 0.9% KOH (w/w wABE) was added to the transesterification reaction with only 0.05% lipase (w/w wABE), the maximum FAME production rate improved 120-fold, as compared to that without the addition of KOH. The alkali-combined lipase significantly enhanced the FAME production rate from wABE, in spite of the presence of the plant pigments, and even when a lower amount of lipase was used as a catalyst.

Functions of family-22 carbohydrate-binding module in Clostridium thermocellum Xyn10C.

Clostridium thermocellum xylanase Xyn10C (formerly XynC) is a modular enzyme, comprising a family-22 carbohydrate-binding module (CBM), a family-10 catalytic module of the glycoside hydrolases, and a dockerin module responsible for cellulosome assembly consecutively from the N-terminus. To study the functions of the CBM, truncated derivatives of Xyn10C were constructed: a recombinant catalytic module polypeptide (rCM), a family-22 CBM polypeptide (rCBM), and a polypeptide composed of the family-22 CBM and CM (rCBM–CM). The recombinant proteins were characterized by enzyme and binding assays. Although the catalytic activity of rCBM–CM toward insoluble xylan was four times higher than that of rCM toward the same substrate, removal of the CBM did not severely affect catalytic activity toward soluble xylan or β-1,3-1,4-glucan. rCBM showed an affinity for amorphous celluloses and insoluble and soluble xylan in qualitative binding assays. The optimum temperature of rCBM–CM was 80 °C and that of rCM was 60 °C. These results indicate that the family-22 CBM of C. thermocellum Xyn10C not only was responsible for the binding of the enzyme to the substrates, but also contributes to the stability of the CM in the presence of the substrate at high temperatures.

Function of the Family-9 and Family-22 Carbohydrate-Binding Modules in a Modular β-1,3-1,4-Glucanase/Xylanase Derived from Clostridium stercorarium Xyn10B

Clostridium stercorarium Xyn10B having hydrolytic activities on xylan and β-1,3-1,4-gllucan is a modular enzyme composed of two family-22 carbohydrate-binding modules (CBMs), a family-10 catalytic module of the glycoside hydrolases, a family-9 CBM, and two S-layer homologous modules, consecutively from the N-terminus. We investigated the function of family-9 and family-22 CBMs in a modular enzyme by comparing the enzymatic properties of a truncated enzyme composed of two family-22 CBMs and the catalytic module (rCBM22-CM), an enzyme composed of the catalytic module and family-9 CBM (rCM-CBM9), an enzyme composed of two family-22 CBMs, the catalytic module, and family-9 CBM (rCBM22-CM-CBM9), and the catalytic module polypeptide (rCM). Although the addition of family-9 CBM to rCM and rCBM22-CM did not significantly change catalytic activity toward xylan and β-1,3-1,4-glucan, the addition of family-22 CBM to rCM and rCM-CBM9 drastically enhanced catalytic activity toward xylan and especially β-1,3-1,4-glucan. Furthermore, the addition of family-22 CBM to rCM and rCM-CBM9 shifted the optimum temperature from 65 °C to 75 °C, but that of family-9 CBM to rCM and rCBM22-CM did not affect the optimum temperature. These facts suggest that the enzyme properties of Xyn10B were mainly dependent on the presence of the family-22 CBMs but not family-9 CBM.

Electrocoagulation of palm oil mill effluent as wastewater treatment and hydrogen production using electrode aluminum

Palm oil mill effluent (POME) is highly polluting wastewater generated from the palm oil milling process. Palm oil mill effluent was used as an electrolyte without any additive or pretreatment to perform electrocoagulation (EC) using electricity (direct current) ranging from 2 to 4 volts in the presence of aluminum electrodes with a reactor volume of 20 L. The production of hydrogen gas, removal of chemical oxygen demand (COD), and turbidity as a result of electrocoagulation of POME were determined. The results show that EC can reduce the COD and turbidity of POME by 57 and 62%, respectively, in addition to the 42% hydrogen production. Hydrogen production was also helpful to remove the lighter suspended solids toward the surface. The production of Al(OH)XHO at the aluminum electrode (anode) was responsible for the flocculation-coagulation process of suspended solids followed by sedimentation under gravity. The production of hydrogen gas from POME during EC was also compared with hydrogen gas production by electrolysis of tap water at pH 4 and tap water without pH adjustment under the same conditions. The main advantage of this study is to produce hydrogen gas while treating POME with EC to reduce COD and turbidity effectively.

Functions of Family-22 Carbohydrate-Binding Modules in Clostridium josui Xyn10A

Clostridium josui xylanase Xyn10A is a modular enzyme comprising two family-22 carbohydrate-binding modules (CBMs), a family-10 catalytic module (CM), a family-9 CBM, and two S-layer homologous modules, consecutively from the N-terminus. To study the functions of the family-22 CBMs, truncated derivatives of Xyn10A were constructed: a recombinant CM polypeptide (rCM), a family-22 CBM polypeptide (rCBM), and a polypeptide composed of the family-22 CBMs and CM (rCBM-CM). Recombinant proteins were characterized by enzyme and binding assays. rCBM-CM showed the highest activity toward xylan and weak activity toward some polysaccharides such as barley β-glucan and carboxymethyl-cellulose. Although rCBM showed an affinity for insoluble and soluble xylan as well as barley β-glucan and Avicel in qualitative binding assays, removal of the CBMs negligibly affected the catalytic activity and thermostability of the CM.

Growth of Scenedesmus dimorphus in different algal media and pH profile due to secreted metabolites

In this study investigation was made to evaluate the effects of different algal media components to get optimized cell count of Scenedesmus dimorphus . Five different fresh water algal media such as Bold’s Basal Medium (BBM), M4N medium, BG-11 medium, N-8 medium and M-8 medium were used for culturing S. dimorphus in flask culture. A set of environmental factors including light, temperature, air flow rate and nutritional components was standardized to obtain the highest productivity of 0.1406 g/L with specific growth rate of 0.10483/day. This study designates the bold basal medium as advantageous one for S. dimorphus and also reveals that production of metabolites by the same algal strain depends mostly on the nature of constituents of media and might have different influence on the pH. Keywords: Scenedesmus dimorphus , bold basal medium, algal growth African Journal of Biotechnology , Vol 13(16), 1714-1720

Electrocoagulation for Treatment of Industrial Effluents and Hydrogen Production

World has entered into a new era where sustainability is the main factor to encounter the challenges of depletion of our reserves and environmental upsets. Wastewater is not only one of the main causes of irreversible damages to the environmental balances but also contributing to the depletion of fresh water reserves at this planet, generating threats to the next generation. A lot of industrial processes are conducted at the expense of plenty of fresh water which is exhausted as a wastewater, and need to be treated properly to reduce or eradicate the pollutants and achieve the purity level for its reutilization in the industrial process to promote sustainability. A number of wastewater treatment methods are prevailing associated with subsequent advantages and disadvantages. Most commonly wastewater treatments involve biological treatment[1], chemical treatment [2] and Electrocoagulation [3]. Biological and chemical treatments of wastewater are usually associated with the production of green house gases and activated sludge along with some other limitations regarding required area and removal of residual chemicals respectively. On the other hand, Electrocoagulation is an extremely effective wastewater treatment system, removing pollutants and producing hydrogen gas simultaneously as revenue to compensate the operational cost[3]. Electrocoagulation has been documented positively to treat the wastewater from steam cleaners, pressure washers, textile manufacturing, metal platers, meat and poultry processors, commercial laundry, mining operations, municipal sewage system plants and palm oil industrial effluents.