Study on community structure of microbial consortium for the degradation of viscose fiber wastewater
© The Author(s) 2017
Received: 3 May 2017
Accepted: 30 June 2017
Published: 10 July 2017
Enrichment culture was applied to obtain microbial consortium from activated sludge samples collected from biodegradation system, a chemical fiber plant in Hebei Province, China. Bacterial composition and community dynamic variation were assessed employing denaturing gradient gel electrophoresis fingerprinting technology based on amplified 16S rRNA genes in the entire process of enrichment culture for viscose fiber wastewater.
Four bacteria named as VF01, VF02, VF03, and VF04 were isolated from the microbial consortium adopting the spray-plate method. The DNA bands of these four bacteria were corresponded to the predominant DNA bands in the electrophoresis pattern. VF01, VF02, VF03, and VF04 were phylogenetically closed to Bacillus licheniformis, Bacillus subtilis, Paracoccus tibetensis, and Pseudomonas sp. by sequence analysis, respectively. The degradation effects for CODCr of single isolated strain, mixed strains, and microbial consortium (VF) originally screened from viscose fiber wastewater were determined. The degradation ability was as follows: microbial consortium (VF) > mixed strains > single isolated strain. Microbial consortium (VF) showed the optimum degradation rate of CODCr of 87% on 14th day. Degradation of pollutants sped up by bio-augmentation of four strains. The molecular weight distribution of organic matter showed that viscose fiber wastewater contained a certain amount of large molecular organic matter, which could be decomposed into smaller molecular substances by microbial consortium (VF).
The microbial consortium (VF) obtained from enrichment culture exhibited great potential for CODCr degradation. The screened strains had bio-augmentation functions and the addition of a mixture of four bacteria could speed up the degradation rate of pollutants.
Viscose fiber exhibits good physical, mechanical, and servicing qualities, and its status is next to polyester in chemical fiber industry (Lin 2000). Nowadays, a huge volume of wastewater has been produced in chemical industry which is responsible for serious environmental problems. Viscose fiber wastewater contains acid and alkaline wastewater. Acid wastewater is characterized by foul-smelling, high zinc ion concentration, high temperature, high salinity, sulfide, complex composition, and toxic substances. Alkaline wastewater is characterized by caustic soda and cellulose with low polymerization degree (Liang et al. 2009; Wang et al. 2013). The contaminants, as cellulose and lignin, in the wastewater are hard to be biodegraded and cause serious environment pollution, therefore it is very difficult to effectively deal with industrial wastewater (Kang and Yi 2005). These are the main reasons why the viscose fiber production has been kept stagnated over the past 20 years. Thus, it is of great social and environmental benefits to develop wastewater treatment technology.
The mixed wastewater of viscose fiber is mainly used in the industrial degradation. A large number of cellulose precipitate was formed after acid and alkaline wastewater were mixed (pH = 2–3) in the industrial degradation. At the same time, sulfide is turned into hydrogen sulfide and carbon disulfide in recycling (Liang et al. 2009). Zinc ions are turned into zinc hydroxide precipitation when the pH value was 8–9. Several physical and chemical methods have been used to treat wastewater and improve the degradation efficiency of CODCr (Hamaguchi et al. 2013; Kang et al. 2012). However, the cost is too high and the equipment covers a large area. In contrast, biological processes are the most environmental friendly and economical (Miao et al. 2009). However, no microorganism has been reported that can directly degrade viscose fiber wastewater, due to the complex composition of viscose fiber wastewater, most of which are cellulose, lignin, organic pollutants, and other large molecular substances (Liang et al. 2009; Vikman et al. 2002). It has been observed that few microorganisms can degrade macromolecular substance under high salinity condition (Kanaly and Harayama 2000).
Previous studies indicated that small molecular substances could be degraded by individual strain or single species (Kanaly and Harayama 2000; Head and Oleszkiewicz 2004). In contrast, large molecular substances should be degraded by diverse species of microorganisms, because the degradation could not be completed by individual type and the cooperation of diverse species is necessary (Kanaly et al. 2000). To study the degradation of viscose fiber wastewater by microorganisms, organic matter is converted through a range of metabolic reactions by assembling of microorganisms in wastewater environment.
It is possible to describe bacterial diversity in real environment by combining molecular biology technology based on 16S rRNA gene analysis and culture-dependent approaches as there have been a number of advances in microbial ecology. PCR–DGGE is a useful and powerful tool for describing the structure changes of microbial community in complex wastewater environments and enrichment cultures. PCR–DGGE has been widely used to identify the bacterial composition of different ecological niches, as these approaches are able to detect microorganisms which are not detected by culture-based methods (Muyzer and Smalla 1998; Brito et al. 2006). Molecular biology technology has contributed to further conduct the studies involving microbial composition, phylogeny, and metabolic mechanism during the whole wastewater treatment process (Al-Thukair et al. 2007; Widada et al. 2002).
The purpose of this paper was to (1) apply the viscose fiber wastewater enrichment strategy to establish viscose fiber wastewater degrading communities to enhance biodegradation of viscose fiber wastewater; (2) analyze the structure changes of bacterial community in viscose fiber wastewater by PCR–DGGE; (3) detect the biodegradability of bacterial consortium gathered from viscose fiber wastewater.
Results and discussion
DGGE analysis of community structure
DGGE analysis of mixed culture
Bands 1, 2, 7, VF 01, VF 02, VF 03, and VF 04 were excised from gels following by identification of strains and analysis of phylogeny based on the 16S rRNA sequence (Figs. 1, 2). Bands 1, 2, and 7 were identified to be Pseudomonas sp. (191 bp, 99% identical), Pseudomonas sp. (201 bp, 99% identical), and Bacillus sp. (203 bp, 100% identical), respectively. Bands VF 01, VF 02, VF 03, and VF 04 were identified to be Bacillus licheniformis (1451 bp, 100% identical), Bacillus subtilis (1437 bp, 100% identical), Paracoccus tibetensis (1378 bp, 98% identical), and Pseudomonas sp. (1459 bp, 100% identical), respectively.
VF03 was 98% identical with P. tibetensis sp., which is a kind of denitrification bacteria and can be separated from the wastewater plant. P. tibetensis sp. is mainly used in sewage treatment, such as landscape water treatment, urban river governance, especially aquaculture wastewater treatment.
VF04 was 99% identical with the Pseudomonas sp., which is widely distributed in the nature and has the ability to metabolize a series of compounds, such as polycyclic aromatic hydrocarbons, toluene, cyanide, carbazole, simple aromatic compounds, organic solvent in organic compounds, and chlorinated hydrocarbons (Reineke 1998).
Degradation rate of CODCr
Bacillus sp. can cooperate with Pseudomonas sp. to degrade the large molecules substances in viscose fiber wastewater, such as cellulose and lignin, etc. (Tuomela et al. 2000; Kumar et al. 2001). The mechanism of synergistic degradation has been clear now (Wilson 2004). The interaction of fungi, bacteria, and the microbial community contributed to the complete degradation of large molecules (Hernández et al. 2001), but the degradation of single Bacillus sp. or single Pseudomonas sp. on cellulose, lignin, and other large molecules was limited.
After operation for 14 days, the mixed strains degraded 45.4% of CODCr, which was far below than 87% removal efficiency of consortium (VF), due to that the number and types of microorganisms in the consortium (VF) are more than that of mixture. In contrast, the degradation rate of the mixture and consortium (VF) is faster than that of consortium (VF) from the 1st to 8th day. After 8th day, the degradation rate of the mixture and the consortium (VF) was same with that of consortium (VF), indicating that partial large molecules could be degraded into small molecules by the mixture, such as cellulose and lignin, etc. The addition of the mixture in the consortium (VF) can improve the degradation effect on pollutants. Bacillus sp. and Pseudomonas sp. had bio-augmentation function and could enhance the degradation effect of viscose wastewater.
Dissolved organic matters (DOM) size distribution in viscose fiber wastewater
Microbial degradation rate sped up by bio-augmentation of four strains by comparing the distribution of molecular weight. The organic compounds in wastewater were accelerated into small molecules by bio-augmentation of four strains. The proportion of the large molecular organic matter in wastewater became less and less, e.g., the percentage of 100-30 kDa changed from 3.6 to 0.85% and the percentage of 30-10 kDa changed from 4 to 0.25%. However, the fraction of small molecule organic matter became more and more, e.g., the percentage of <1 kDa changed from 66.1 to 92.27%. The molecular weight distribution of DOM in sewage not only reflected the characteristics of organic matter but also closely related to the degradation efficiency for wastewater (Chang et al. 2000).
Bio-augmentation utilizes microorganisms as bio-degraders to purify sewage in nature and bioreactors to remove contaminants (Chong et al. 1997; El Fantroussi and Agathos 2005; Head and Oleszkiewicz 2004; Reberto et al. 2003). Bio-augmentation is efficient in degrading target pollutants and removing the refractory organics involved in wastewater by inoculating strains. Previous studies indicated that bio-augmentation was feasible for the treatment of waste streams produced from pharmaceutical factories, coke plants, pulp mills, dye, and other industries (Saravanane et al. 2001; Park et al. 2008; Wang et al. 2002; Yu and Mohn 2001; Chen et al. 2006).
The microbial consortium for wastewater degradation was enriched from samples of viscose fiber wastewater collected from a chemical fiber plant in Hebei, China. The method of PCR–DGGE was employed to investigate the changes in microbial community structure and helped us to determine the predominant species for CODCr biodegradation throughout the enrichment process. Consortium (VF) exhibited great potential in CODCr removal and the degradation rate of CODCr reached 87% until 14th day, indicating that enrichment culture as an isolation method was both feasible and effective. Four strains had biological reinforcement functions and the addition of a mixture of four bacteria could speed up the degradation rate of pollutants and the application of these species to bio-augmentation fields would assist in observing their catabolic behavior in highly polluted environments.
Enrichment and cultivation were carried out in modified LB medium (Tryptone 5 g/L, yeast extract 1 g/L, NaCl 3 g/L, agar 1.5 g/L, pH 7.2–7.4).
Sampling, enrichment, and isolation of the viscose fiber wastewater degraders
The characteristics of viscose wastewater sample
Activated sludge samples (2.0 g) were cultured in 250 mL Tri-flask with 100 mL LB media at 30 °C and 150 rpm for 2 days. Hereafter, this culture of 10 mL was shifted to another flask of 250 mL. The amount of viscose fiber wastewater was gradually increased until all wastewater was used as a microbial growth substrate at 10 days. The acclimation time for enrichment culture lasted for 40 days.
Bacteria were screened from the consortium by tenfold series dilution method. Morphologically distinct individual colonies were further purified on LB agar plates.
DNA samples preparation
DNA was respectively extracted from the isolated strains and the enrichment cultures, i.e., the first day of enrichment culture sample, the 10th day of enrichment culture sample, the 20th day of enrichment culture sample, the 30th day of enrichment culture sample, the 40th day of enrichment culture sample following the manufacturer’s protocol (Qiagen, Valencia, CA, USA). The integrity of DNA was detected by agarose gel electrophoresis.
Amplification of DNA and DGGE analysis
The variable region V3 of the 16S rRNA gene was amplified employing primers 341F (5′-CCT ACG GGA GGC AGC AG-3′) with a 40-bp GC clamp at 5′ end (CGC CCG CGC GCG CGG CGG GCG GGG CGG GGG CAC GGG GGG) and 518R (5′-ATT ACC GCG GCT GCT GG-3′) (Watanabe et al. 2001).
Cycling conditions for 16S rRNA gene amplification were as follows: initial denaturation at 94 °C for 5 min, 30 cycles each involved denaturation at 94 °C for 1 min; anneal at 55 °C for 1 min, extended at 72 °C for 1 min; and another extension at 72 °C for 10 min. 5 μL of PCR products was analyzed by electrophoresis on 2% agarose gel in 1× TAE buffer (20 mM Tris–HCl, 10 mM glacial acetic acid, 0.5 mM EDTA, pH 8.0) at 120 V for 30 min.
Samples of PCR products were loaded onto 8% (w/v) polyacrylamide gel within 30–60% denaturing gradient (100% denaturant consisted of 7 M urea and 40% deionized formamide). The electrophoresis was run in 1× TAE buffer for 10 h, (100 V, 60 °C) in Universal Mutation Detection System apparatus (Bio-Rad, Dcode, USA). Finally, the gels were stained with ethidium bromide solution of 0.1% (v/v) (1× TAE) for 15 min, rinsed in distilled water for 20 min, and then were scanned in a Gel Doc XR documentation system (Bio-Rad).
Identification of strains and analysis of phylogeny
Pieces of DGGE bands were excised from polyacrylamide gel with sharp blade and then were, respectively, transferred to a new 2.0 mL Eppendorf tubes with 50 μL of sterilized ultra-pure water and incubated at 4 °C for a night to accelerate the diffusion of DNA out of the gel bands. The centrifugation was conducted at 10,000g for 6 min to obtain supernatant from above DNA solution. 1 μL supernatant was used as amplified template with a set of primer 341F and 518R with no GC clamp. Amplified products were further analyzed by the technique of denaturing gradient gel electrophoresis to confirm that they were successfully isolated.
Bacterial 16S rRNA genes were amplified employing primers 27F (5′V-AGA GTT TGA TCC TGGCTC AG-3′) and 1492R (5′-GGC TACCTT GTT ACG ACT T-3′) (Ikenaga et al. 2002). The amplification procedure was as follows: preliminary at 94 °C for 4 min; 30 cycles of 94 °C for 1 min, 55 °C for 1 min, 72 °C for 2 min, and a final extension at 72 °C for 10 min.
The amplified products were purified from agarose gel and bound with a pMD18-T vector and then transformed into Escherichia coli DH5 and the recombinant clones with a 1.5 kb insert were sent to be sequenced by sequencing company. All generated sequences were compared with nucleotide sequences of known sequences listed in GenBank databases (http://www.ncbi.nlm.nih.gov/) using BLAST (Basic Local Alignment Search Tool).The phylogenetic tree was constructed according to maximum-likelihood analysis implemented in MEGA6 software.
Biodegradation of contaminants
Enrichment culture processes were monitored periodically to isolate the strains capable of removing CODCr in viscose fiber wastewater. Isolated strains presenting clear colonial morphology on LB agar culture medium were further purified and incubated in LB culture media of 200 mL at 30 °C. The cells were harvested by centrifugation at 12,000 rpm for 10 min when the optical density (600 nm) reached at 0.6, pellets were washed with sterile 0.85% NaCl (w/v) twice and then inoculated into conical flasks containing 300 mL of viscose fiber wastewater and placing on a rotary shaker (180 rpm) at 30 °C. The mixture of isolates, the consortium labeled VF, and the mixture with the consortium were added into viscose fiber wastewater under the same conditions. The culture flask containing 300 mL of wastewater without bacterial consortium (VF) was as control experiment. Flasks of the isolates, mixture, the consortium, and the control were taken out from the rotary shaker on the 0th, 2nd, 4th, 6th, 8th, 10th, 12th, and 14th days. The analysis of CODCr content in each sample was carried out with Microwave digestion COD analyzer (DRB-200).
The isolation of dissolved organic matters (DOM)
The corresponding molecular weight cut-off range of each fraction
Molecular weight range
The quantity of dissolved organic carbon (DOC) corresponding to each size fraction of DOM after filtered with different pore-size UF membranes was calculated from DOC concentration and corresponding volume.
The ultrafilter is Amicon 8200 type ultrafiltration cup which was produced by the United States Millipore, having an effective volume of 180 mL, effective film area of 28.7 cm2, maximum withstand pressure of 0.53 MPa, built-in magnetic stirring Pressure-driven high-purity nitrogen (Qiao et al. 2007).
The pH value was measured by a pH meter (METTLER TOLEDO, FE20K). The content of BOD5 was measured by incubation method. The content of total nitrogen (TN) and total phosphorus (TP) were analyzed using alkaline potassium persulfate digestion-UV spectrophotometer and molybdenum blue spectrophotometric (Carranzo 2012). Dissolved organic carbon (DOC) in water samples were measured using UV-per-sulfate technique and infrared carbon dioxide analyzer (Phoenix 8000), and calibrated with potassium hydrogen phthalate.
CZ, SR, and YX designed the experiment. CQ and KR analyzed the data. CQ and KR performed most of experiments in PCR–DGGE section. CQ, KR, HX, and HB wrote the manuscript. All authors read and approved the final manuscript.
The authors duly acknowledge the Laboratory of Industrial Fermentation Microbiology, (Ministry of Education), Tianjin University of Science & Technology, Tianjin Academy of Environmental Sciences, and CNOOC Ener Tech Beijing Research Institute of Engineering & Technology for Safety & Environmental Protection.
The authors declare that they have no competing interests.
Availability of data and materials
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The authors approved the consent for publishing the manuscript.
Ethics approval and consent to participate
All the authors have read and agreed the ethics for publishing the manuscript.
This work was financially supported by the National Natural Science Foundation of China (NSFC 51178311) and Natural Science Foundation of Tianjin (13ZCZDSF00700, 16JCTPJC46100).
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