Degradation Of Carboxymethyl Cellulose Research Articles

High‐strength, ultrastretchable hydrophobic association hydrogel reinforced by tailored modified carboxymethyl cellulose

AbstractA new pathway to construct high‐strength, ultrastretchable hydrogels based on tailored modified carboxymethyl cellulose (TMCMC)and hydrophobic association(HPA) system was investigated. TMCMC was prepared from degradation of carboxymethyl cellulose (CMC)/N,N′‐methylene bisacrylamide (MBA) chemical cross‐linked hydrogels. The residual double bonds of TMCMC, confirmed by 1H‐NMR and FTIR analysis, reacted with acrylamide in HPA to form TMCMC/HPA hydrogels, and the homogeneous and fine spatial network structure of TMCMC/HPA hydrogel could be observed by scanning electron microscopy. Rheological analysis revealed that the coexistence of physical and chemical crosslinking in TMCMC/HPA hydrogels. Further studies showed that TMCMC/HPA hydrogel with MBA content of 0.5 wt% has outstanding mechanical properties, and its fracture stress, elongation and tensile strength reach 1.17 MPa, 3717.05% and 15.68 MJ·m−3, respectively. Moreover, the hydrogel displayed good swelling resistance and stable strain electrical signal response.

Preparation and identification of carboxymethyl cellulose-degrading enzyme candidates for oilfield applications

Carboxymethyl cellulose (CMC) is often used during hydraulic fracturing (fracking) operations as a fluid viscosifier to facilitate proppant delivery. However, the accumulation of residual CMC at fracture faces can result in formation damage, thereby impeding oil and gas recovery. Whereas harsh chemical oxidizers are typically added to disrupt these polymer accumulations, there is now industrial interest in developing clean, biological approaches for the degradation of CMC under fracking conditions. Using a methanogenic culture known to utilize CMC under conditions typically found in oil fields, we developed an efficient method to isolate and purify CMC-degrading enzymes. Initial purification and concentration of cellular components produced an increase in exo-ß-(1,4)-exoglucanase and ß-(1,4)-glucosidase activities by 9-fold and 26-fold, respectively. Partially purified extracts provided substantial degradation of CMC as monitored by viscosity reduction within three hours at 50 °C, an improvement over the untreated cell-free extract which required 48 h to achieve similar viscosity values, outperforming a commercially-available cellulase preparation. Putative cellulases were identified within the isolated enzyme population, with endo-ß-(1,4)-xylanase from Caldicoprobacter faecalis hypothesized to be an important contributor to CMC degradation. This study demonstrates that enzyme technology holds great promise as a viable approach to degrade CMC accumulations under field conditions.

Using biochemical agents to intensify the treatment of highly concentrated drilling wastewater

Introduction. The co-authors have developed a new approach to the treatment of highly concentrated drilling wastewater (DWW). The approach is based on the enzymic degradation of polysaccharides that drilling wastewater contains. The research objective is to perform an experimental evaluation of the ability of this biochemical agent to intensify the process of removal of solid impurities from highly concentrated polysaccharide-containing DWW. Materials and methods. The research was performed using standardized test solutions of polysaccharides (carboxymethyl cellulose (CMC), xanthane gum, guar gum), highly concentrated DWW-containing polysaccharides. The reliability of results is ensured by certified methods of analysis, included into the Federal Register of Measurement Procedures and performed by an accredited laboratory, as well as multiple series of experiments. Results. The ability of the biochemical agents (brewing waste (BW) and an enzymatic agent (EP)) to intensify the process of removal of solid impurities from highly concentrated DWW-containing polysaccharides is identified experimentally. The efficiency of biochemical agents used in the process of treatment is determined. The biological degradation of CMC and guar gum solutions is faster than the natural biological degradation that involves BW. Depolymerization time is detected for CMC and guar gum solutions that contain EP. Conclusions. The co-authors have developed a cheaper and more environmentally friendly alternative to existing solutions. It represents a biological method of solid impurities removal from highly concentrated BWW-containing polysaccharides. The use of brewing waste products (BW) as a source of microorganisms, that trigger the polysaccharide hydrolysis, is theoretically substantiated and experimentally proven as a method of treatment of highly concentrated BWW-containing polysaccharides. The expediency of using biochemical agents (BW and EP in isolation) to accelerate the settling rate of solid components of highly concentrated BWW is proven experimentally.

Properties enhancement of carboxymethyl cellulose with thermo-responsive polymer as solid polymer electrolyte for zinc ion battery

A novel polymer host from carboxymethyl cellulose (CMC)/poly(N-isopropylacrylamide) (PNiPAM) was developed for a high safety solid polymer electrolyte (SPE) in a zinc ion battery. Effects of the PNiPAM loading level in the range of 0–40% by weight ( wt%) on the chemical, mechanical, thermal, and morphological properties of the CMC/PNiPAMx films (where x is the wt% of PNiPAM) were symmetrically investigated. The obtained CMC/PNiPAMx films showed a high compatibility between the polymers. The CMC/PNiPAM20 blend showed the greatest tensile strength and modulus at 37.9 MPa and 2.1 GPa, respectively. Moreover, the thermal degradation of CMC was retarded by the addition of PNiPAM. Scanning electron microscopy images of CMC/PNiPAM20 revealed a porous structure that likely supported Zn2+ movement in the SPEs containing zinc triflate, resulting in the high Zn2+ ion transference number (0.56) and ionic conductivity (1.68 × 10–4 S cm−1). Interestingly, the presence of PNiPAM in the CMC/PNiPAMx blends showed a greater stability during charge–discharge cyclic tests, indicating the ability of PNiPAM to suppress dendrite formation from causing a short circuit. The developed CMC/PNiPAM20 based SPE is a promising material for high ionic conductivity and stability in a Zn ion battery.

Formaldehyde formation during the preparation of dialdehyde carboxymethyl cellulose tanning agent

Formaldehyde was detected in dialdehyde carboxymethyl cellulose (DCMC) tanning agent prepared through periodate oxidation of sodium carboxymethyl cellulose (CMC). Formaldehyde was then introduced into leather through DCMC tanning, which poses a potential risk to human health. The formation mechanism of formaldehyde in DCMC was investigated by composition analysis and intermediate identification of DCMC with different polymerization degrees and sugar unit structures. Formaldehyde was derived from the overoxidation of C-6 on the reducing glucose residue of CMC. Moreover, glucose was produced from the concomitant degradation of CMC during oxidation, and then oxidized to liberate formaldehyde. The low degradation degree and high degree of substitution of CMC reduced the possibility of the formation of reducing glucose residue and glucose during oxidation, thereby resulting in low formaldehyde content in DCMC and DCMC-tanned leather. These findings serve as a foundation for the minimization of formaldehyde in DCMC and the development of ecological tanning approach.

Degradation of carboxymethylcellulose using ultrasound and β-glucanase: Pathways, kinetics and hydrolysates’ properties

In order to provide an efficient way to degrade carboxymethylcellulose (CMC), three pathways were investigated: enzymolysis, combination of ultrasound pretreatment and enzymolysis, and sonoenzymolysis. Effects of these treatments on enzymatic kinetics, degradation kinetics and properties of degraded CMC were investigated. The degradation degree of CMC was increased by 18.90% and 35.73% with ultrasound pretreatment (at an intensity of 24 W/mL for 30 min) and sonoenzymolysis (at an intensity of 9 W/mL for 50 min), compared with that obtained under the traditional enzymolysis. Analysis of kinetics demonstrated that ultrasound, both pretreatment and combined with β-glucanase, could accelerate CMC degradation. Measurements of rheological properties, molecular weight and structures of CMC hydrolysates revealed that ultrasound broke the glycosidic bond of CMC chains without changing its primary structure. The sonoenzymolysis process was the most efficient method to degrade CMC, with potential to provide a way to obtain CMC with lowest molecular weight or viscosity.

Effect of Na+ and Ca2+ on the Thermal Degradation of Carboxymethylcellulose in Air

Carboxymethylcellulose (CMC), including the acid form (CMC-H) and salt forms (CMC-Na, CMC-Ca), were prepared for the survey of thermal degradation and the CMC-H was obtained by acidifying CMC-Na with HCl. An online-coupled thermogravimetric (TG)-FTIR evolved gas analysis instrument was used to identify and monitor the evolution of gaseous products during the thermal degradation of CMC in air. The thermal degradation characteristics of CMC-H and salt forms CMC-Na, CMC-Ca of carboxymethylcellulose were compared to determine the effect of Na+ and Ca2+ counter-ions on CMC thermal degradation in air. From the TG and DTG curves, thermal degradation of the samples occurred in three stages. During the second stage (200–410 °C) major degradation occurred, accompanied by a large weight loss. The 3D FTIR absorbance spectra and Gram-Schmidt curves of the evolved gases were obtained. In compounds CMC-Na and CMC-Ca, the initial degradation temperature is higher, the rate of CMC degradation increases, and the weight loss in the temperature range 200–410 °C decreases. These samples also catalyse the stable intermediate products in the temperature range 410–600 °C.

Influence of homogenisation and the degradation of stabilizer on the stability of acidified milk drinks stabilized by carboxymethylcellulose

The present work deals with the influences of both homogenisation and the degradation of carboxymethylcellulose (CMC) on the stability of two kinds of acidified milk drinks (AMDs), directly acidified milk drinks and yoghurt drinks. The effect of homogenisation pressure for direct acidification process was investigated and evaluated. The experimental results showed that homogenisation was required to achieve a significantly small particle size (0.7 μm in the present work) and to prevent sedimentation and serum separation. However, homogenisation at too high pressures was not beneficial for the stability of the colloidal systems. The occurrence of degradation of CMC during homogenisation weakened the stabilisation effect of CMC. A qualified homogenisation pressure of 20 MPa should be chosen to achieve a good stability when a usually practical pressure range of 0–30 MPa was applied. In addition, the stability of directly acidified milk and yoghurt drinks prepared under the same homogenisation pressure was also investigated. While their stability increased with increasing CMC concentration, the degradation of CMC at low pH during storage gave rise to instability of the final products.

Characterisation of microbial floras and functional gene levels in an anaerobic/aerobic bio-reactor for the degradation of carboxymethyl cellulose

The current study determined the carboxymethyl cellulose (CMC) degradation efficiency, dominant microbial flora, eubacteria and archaebacteria characteristics, and expression levels of genes cel5A, cel6B, and bglC in an anaerobic/aerobic bio-reactor consisting of two-stage UASB (U1 and U2) and two-stage BAF (B1 and B2). The results showed that under three CMC loads, the CMC degradation efficiency of the UASB-BAF system was 91.25%, 80.44%, and 78.73%, respectively. At higher CMC loads, the degradation of cellulose and transformation to cellobiose in U1 was higher, while the transformation to glucose was lower. The results of DGGE and real-time PCR indicated that cellulose degradation bacteria are dominant in U1, cellulose degradation bacteria and cellulose degradation symbiosis bacteria are dominant in B1, and non-cellulose degradation symbiosis bacteria are dominant in both U2 and B2. The rate-limiting enzyme gene of cellulose degradation in U1, B1, and B2 is cel6B, but it is cel5A in U2.

A kinetic study of ultrasonic degradation of carboxymethyl cellulose

AbstractIn this study, the effect of power of ultrasound, temperature, and concentration of carboxymethyl cellulose (CMC) solution on the rate of ultrasonic degradation were investigated, and a kinetic model based on viscometry data was used to calculate the rate constants in different conditions. To investigation of effect of ultrasonic power on the degradation of CMC, the power of ultrasound was increased and observed that the viscosity of the CMC solution was decreased with an increase in the power of ultrasound, but the extent of the degradation in a constant power was found to decrease with an increase in concentration or temperature. The ultrasonic degradation of CMC solutions was carried out at different temperatures to investigate the effect of the temperature on the rate of degradation. The calculated rate constants indicated that the degradation rate of the CMC solutions decreased as the temperature increased. The degraded CMCs were characterized by gel permeation chromatography, and average molecular weights of ultrasonicated CMCs were compared in different reaction conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Comparison of gamma ray and electron beam irradiations on the degradation of carboxymethylcellulose

Carboxymethylcellulose (CMC) is used for a variety of applications due to its superior properties of high viscosity at a low concentration. In this study, the difference between a gamma ray (GR) irradiation from Co-60 and an electron beam (EB) irradiation with 10 MeV Energy on the viscosity change in CMC solution was compared. At the same irradiation doses, the viscosity of the CMC solution was more severely decreased by GR. Electron spin resonance spectroscopy revealed that the radicals in the CMC were more generated by GR, but there was no difference in the Fourier transform infrared spectra of both irradiated CMC solutions. Also, the degree of substitution in CMC was not changed by both irradiation events. From these results, it can be concluded that EB irradiation could better minimize the decrease in the viscosity of the solution with CMC for the sterilization than GR.

Controlling the radiation degradation of carboxymethylcellulose solution

In this study, the effects of an irradiation on the viscosity of the carboxymethylcellulose (CMC) solution were investigated, and the methods to control the degradation of the CMC caused by an irradiation were developed. The viscosity of the CMC solution was decreased with an increase in the irradiation dose, but the extent of the degradation by an irradiation was found to decrease with an increase in the CMC concentration in the solution. The dependency of the irradiation sources showed that an electron beam radiation had degraded the CMC less severely than a gamma ray radiation. An addition of vitamin C as a radical scavenger to the solution was shown to be effective in preventing the decrease of the viscosity of the solution. Also, in the case of an irradiation at −70 °C, the decrease of its viscosity was efficiently inhibited. The degradation of CMC in the solution was confirmed by the molecular weight distribution.

Effect of short-chain acids on the carboxymethylcellulase activity of the ruminal bacteriumRuminococcus albus

The addition of 100-300 mmol/L of acetic, propionic, butyric or lactic acids (short-chain acids), or of acetic, propionic, and butyric acids (volatile fatty acids, VFA) mixtures increased the degradation of carboxymethyl cellulose (CMC) by R. albus (7.5 to 46 and 6 to 39 %, respectively). Differences among individual acids were observed at 300 mmol/L whereas VFA mixtures differed at 100 mmol/L. When assayed at the same concentration, CMCase activity was increased less by NaCl than by the short-chain acids, whereas ethylene glycol decreased the activity. Since osmolarity and/or ionic strength changes in the medium cannot completely account for the observed increases of carboxymethylcellulase (CMCase) activity, it is suggested that the anions of short-chain acids produce changes in the reaction media polarity that contribute to the effects observed. Alterations in the media could also bring about conformational changes in CMCase leading to increased rates of reaction and subsequent increases in CMC degradation. Finally, explanations for the observed phenomena based on the direct effect of the compounds tested on the cellulosome complex, its domains, and/or its component enzymes are proposed.

In vitro ruminal digestibility of oat hay and cellulolytic activity in the presence of increasing concentrations of short-chain acids and glycerol

The effects of acetic, propionic, butyric and lactic acids (short-chain acids), and of glycerol, on the in vitro dry matter digestibility (IVDMD) of oat hay, and on cellulolysis by a protein extract of rumen fluid were studied. The objective was to gain information on the impact of increasing the concentrations of those compounds in the medium on degradative activities carried out by rumen microorganisms. Short-chain acids were assayed as sodium salts and, for all compounds, the concentrations were 50, 100, 200 and 300 mM. The volatile fatty acids (VFA: acetic, propionic and butyric acids) were tested separately or in two mixtures A and B that contained different proportions of each VFA. The IVDMD was assayed according to a modified Tilley & Terry (1963) technique while cellulolysis was assessed by the hydrolysis of carboxymethylcellulose (CMC) in 1-h incubations at 39 °C. Parallel incubations with NaCl were utilized as controls for ionic strength and osmolarity changes in the incubation medium. Increases of 100–300 mM of short-chain acids decreased IVDMD between 7 and 39%. The inhibitions produced by increases of 200 and 300 mM of acetic acid were smaller than those caused by the same concentrations of either butyric or lactic acids. Increases of 100, 200 and 300 mM of glycerol reduced by 8–15% the IVDMD, and the inhibitions produced by increments of 200 and 300 mM of this compound were smaller than the ones elicited by the short-chain acids, with the exception of 200 mM of acetic acid that did not differ. The IVDMD was inhibited by NaCl only when concentrations were increased by 200 (12%) and 300 mM (26%). The degradation of CMC was reduced by 7–20% by 200 and 300 mM increases of the short-chain acids or glycerol, the exception being lactic acid that had no effect. One hundred mM increases of acetic and butyric acids inhibited the CMC degradation by 7 and 9%, respectively, whereas only butyric acid was inhibitory (7%) at 50 mM. Greater concentration increases of both VFA mixtures A and B than of the individual VFA were necessary to inhibit the hydrolysis of CMC. Cellulolytic activity was decreased 6 and 9% by increases of 200 and 300 mM of NaCl, respectively, and these drops of activity were smaller than those obtained with increases in any of the other compounds. Since osmolarity and/or ionic strength changes in the medium cannot completely account for the observed inhibitions of IVDMD and cellulolysis, it is suggested that glycerol and the anions of short-chain acids produce changes in the reaction media polarity that contribute to the inhibitory effects observed. Alterations in the media could also bring about conformational changes in the degradative enzymes leading to reduced rates of reaction and subsequent decreases in IVDMD and cellulolysis. Since most of the effects were observed with concentration increases that were larger than the physiological concentrations in the rumen, it is suggested that the compounds tested have little impact in vivo on the ruminal degradative activities that were evaluated.

Water‐Soluble AmphiphilicO‐(Carboxymethyl)cellulose Derivatives – Synthesis and Properties

AbstractSummary:Water‐soluble, partially hydrophobized derivatives ofO‐(carboxymethyl)cellulose (CMC) were prepared by esterification of CMC in its ‘gel suspension’ form. The classical esterification method (A) using stearoyl chloride/pyridine as well as two unconventional methods based on reaction with mixed anhydrides (B) and transesterification with vinyl laurate (C) respectively, were compared in terms of the structural, molecular and performance properties of the obtained derivatives. The classical esterification and method B yielded water‐soluble simple fatty acid esters, whereas mixed acetic‐fatty acid esters were obtained by method C. In all cases, molecular degradation of CMC was observed.1H and13C NMR spectroscopy of the acetyl‐lauroyl derivatives of CMC with a degree of esterificationDSEof 0.20 indicated a prevalence of the lauroyl groups (DSAc:DSLa = 0.03:0.17). Most of the water‐soluble derivatives exhibited excellent emulsifying efficiency. They represent polysaccharide‐based surfactants with effective anti‐redeposition properties as well as good washing power. Suitable derivatives can be prepared under mild reaction conditions by both unconventional methods which implies that they have potential as substitutes for the expensive and invasive conventional method.Preparation of CMC derivatives.magnified imagePreparation of CMC derivatives.

Ultrasonic depolymerization of aqueous carboxymethylcellulose

Prolonged exposure of solutions of macromolecules to high-energy ultrasonic waves produces a permanent reduction in viscosity. However, the exact mechanism by which degradation occurs is still open to discussion. According to this study hydrodynamic forces played the primary role in degradation process. This study showed that there is an optimal carboxymethylcellulose (CMC) concentration to the most efficient degradation. Ultrasound degraded preferentially large CMC molecules and cleavage took place roughly at the centre of the CMC molecules. Degradation of CMC did not proceed below a certain molecular mass. During ultrasonic degradation the molecular mass distribution narrowed. For any polymer degradation process to become acceptable to industry, it is important to be able to specify the sonication conditions to produce a particular relative molecular mass distribution.

Radiation preparation and swelling behavior of sodium carboxymethyl cellulose hydrogels

Sodium carboxymethyl cellulose (CMC) is a kind of degraded polymer under γ-irradiation. However, in this work, it has been found that CMC crosslinks partially to form hydrogel by radiation technique at more than 20% CMC aqueous solution. The gel fraction increases with the dose. The crosslinking reaction of CMC is promoted in the presence of N 2 or N 2O due to the increase of free radicals on CMC backbone, but gel fraction of CMC hydrogel is not high (<40%). Some important values related to this kind of new CMC hydrogel synthesized under different conditions, such as radiation yield of crosslinking G( x), gelation dose R g, number average molecular weight of network M c were calculated according to the Charlesby–Pinner equation. The results indicated that although crosslinked CMC hydrogel could be prepared by radiation method, the rate of radiation degradation of CMC was faster than that of radiation crosslinking due to the character of CMC itself. Swelling dynamics of CMC hydrogel and its swelling behavior at different conditions, such as acidic, basic, inorganic salt as well as temperature were also investigated. Strong acidity, strong basicity, small amount of inorganic salts and lower temperature can reduce swelling ratio.

Determination of the degree of polymerisation of carboxymethyl cellulose by size exclusion chromatography

A size exclusion chromatographic (SEC) system was developed in order to investigate the molecular weight distribution of depolymerisation products obtained by enzymatic degradation of carboxymethyl cellulose (CMC). The SEC system, which relies on a Superose 12 HR 10/30 column and an eluent containing sodium hydroxide (0.05 M), enabled an effective separation of CMC fragments. Cellulase was used for the degradation of CMC. Degradation was followed as a function of incubation time and cellulase dosage by viscosity measurements. The CMC hydrolysates separated by SEC were detected as total organic carbon (TOC) and reducing sugars. The degree of polymerisation (DP) of the hydrolysates was then determined by dividing the number of anhydroglucose units by the reducing sugar concentrations. The DP of the CMC fragments obtained after enzymatic hydrolysis ranged from 100 to 1, compared with a DP v of 170 for untreated CMC samples. The results obtained for a series of CMC fragments agreed with the DP values of standards of known molecular weight. The method is an absolute method; no external calibration was needed to calibrate the Superose 12 HR 10/30 column.

The use of capillary viscometry, reducing end-group analysis, and size exclusion chromatography combined with multi-angle laser light scattering to characterize endo-1,4-β- d-glucanases on carboxymethylcellulose: a comparative evaluation of the three methods

Three methods were used to characterize seven purified endo-1,4-β- d-glucanases derived from different microbial sources ( Trichoderma reesei, Thermomonospora fusca, and Acidothermus cellulolyticus) on carboxymethylcellulose (CMC). The methods included capillary viscometry, reducing end-group analysis, and high performance size exclusion chromatography combined with multi-angle laser light scattering (HPSEC-MALLS). The investigation was performed with the objective of comparative evaluation of the different methods for characterizing endoglucanases, particularly in relation to their endo- and exomode of action. The measurement of the initial rate of reducing end-group formation using disodium 2,2′-bicinchoninate (BCA) was found to be the most accurate method for determination of endoglucanase activity. The BCA method was highly sensitive, simple to perform, and directly gave the number of bonds broken, thus allowing for expression of endoglucanase activity in international units (μmol of β-1,4-glucosidic bonds hydrolyzed in 1 min during the initial period of hydrolysis). The viscometric method was simple to perform and highly sensitive for the internal bonds cleaved, but did not account for the hydrolysis of CMC near the chain end, and thus only allowed for expression of endoglucanase activity in arbitrary viscometric units. The HPSEC-MALLS technique provided the number-average molecular weight ( M n) of CMC, thus allowing the quantification of the number of the bonds broken during degradation of CMC; however, reproducibility of the method was low, especially for the high-molecular weight fragments of CMC at the beginning of hydrolysis. As hydrolysis proceeded to the more advanced stages, the HPSEC-MALLS method gave an overestimated (compared to the reducing end-group analysis) values for M n, probably due to insufficient sensitivity of the light-scattering detector for the low-molecular weight products of CMC degradation. The combined use of the three methods allowed characterization of endoglucanases according to their selectivity for hydrolysis of internal bonds within a CMC molecule which was expressed as the ratio of the initial rate of viscosity decrease to the initial rate of glucosidic bonds broken. This ratio was found to be unique for each endoglucanase, and, therefore, no universal equation could be established for all endoglucanases for conversion of arbitrary viscometric units to international units of activity.

Characterization of Rhizobium leguminosarum exopolysaccharide glycanases that are secreted via a type I exporter and have a novel heptapeptide repeat motif.

The prsDE genes encode a type I protein secretion system required for the secretion of the nodulation protein NodO and at least three other proteins from Rhizobium leguminosarum bv. viciae. At least one of these proteins was predicted to be a glycanase involved in processing of bacterial exopolysaccharide (EPS). Two strongly homologous genes (plyA and plyB) were identified as encoding secreted proteins with polysaccharide degradation activity. Both PlyA and PlyB degrade EPS and carboxymethyl cellulose (CMC), and these extracellular activities are absent in a prsD (protein secretion) mutant. The plyA gene is upstream of prsD but appears to be expressed at a very low level (if at all) in cultured bacteria. A plyB::Tn5 mutant has a very large reduction in degradation of EPS and CMC. Cultures of plyB mutants contained an increased ratio of EPS repeat units to reducing ends, indicating that the EPS was present in a longer-chain form, and this correlated with a significant increase in culture viscosity. Thus, PlyB may play a role in processing of EPS. Analysis of the symbiotic properties of a plyA plyB double mutant revealed that these genes are not required for symbiotic nitrogen fixation and that nodulation was not significantly affected. PlyA and PlyB are similar to bacterial and fungal polysaccharide lyases; they contain 10 copies of what we propose as a novel heptapeptide repeat motif that may constitute a fold similar to that found in the family of extracellular pectate lyases. PlyA and PlyB lack the Ca2+-binding RTX nonapeptide repeat motifs usually found in proteins secreted via type I systems. We propose that PlyA and PlyB are members of a new family of proteins secreted via type I secretion systems and that they are involved in processing of EPS.