## 1 Introduction  
Textile dyes comprise a large class of chemicals with highly comprehensive components, diverse origins and extensive applications and they constitute the main source of pollution in sewage discharge from the textile and printing industry. In China and Southeast Asia, contamination caused by various textile dyes from untreated industrial effluents is a serious environmental threat, as a variety of textile dyes are toxic or cross-coupled to toxic components that are relatively recalcitrant to degradation due to their complicated molecular structure [1; 2]. Even a small amount of trace dye in water can seriously affect the transparency and gas solubility of the water [3]. Remediation of dye contamination often involves chemical, physical and various biological processes [4; 5]. Over the past decade, intensive efforts have been made to develop effective bioprocesses for the treatment of dyes in wastewater effluents or other environments [2; 6]. Of the various available biological decolorizers, the macromolecular polymer chitosan (CTS) has particular appeal due to its relatively high natural dye biosorption efficiency and its ease of transformation into biocomposites through physicochemical modification, which leads to efficient decolorization of various dyes [7; 8; 9]. CTS is a natural poly-amino glucosamine polymer that is widely distributed in the exoskeleton of various crustaceans, in the exo- and endocuticle of insects and in the cell wall of fungi, where it functions as an integral component as well as a mechanically strong supporting scaffold material for these organisms; moreover, CTS has been recognized as one of the most plentiful renewable organic resources worldwide [10; 11]. The distinctive biological properties of CTS, particularly its biocompatibility, biodegradability, environmental friendliness and regenerability, as well as its relative permeability and cost-effectiveness, indicate its potential for applications in a variety of industrial fields, such as biochemical engineering, wastewater remediation, food processing [12; 13], bone tissue engineering and other therapeutic applications [14; 15]. In addition to biosorption, enzymatic biodegradation provides another promising approach to the decolorization of wastewater dyes [16]. Among various degrading enzymes such as phenoxidases, lacases and tyrosinases, microbial lacases are being increasingly investigated as an effective and environmentally friendly means of treating industrial phenolic substrates [17]. Lacases (benzenediol:dioxygen oxidoreductaseases, EC1.10S.3.2) are a large group of multi-copper enzymes that are involved in different biological processes of organisms, such as lignifications in plants; morphogenesis, pathogenesis and detoxification in fungi; cuticle osteosis; and resistance to heave metals, chlorides, ultraviolet (UV) radiation and H\({}_{2}\)O\({}_{2}\) in bacteria, among others [16; 18; 19]. Many previous investigations have demonstrated the ability of microbial lacases to oxidatively degrade a broad range of organic compounds, particularly aromatic substrates [20; 21; 22], including industrial or wastewater dyes [17; 23; 24]. In a similar approach, we developed a _Pseudomonas_ cell surface display system to efficiently decolorize the anthraquinone dye Acid Green 25 and diazo dye Acid Red 18 [25] in which a mutated bacterial lacase (WlacD) [26] was projected onto the surface of target cells, enabling fast and goal-oriented decolorization on the cell surface. This system has proven advantages over freely suspended lacase and bacterial cells alone, including the elimination of mass transfer limitation, minimization of dye toxicity to living cells and particularly, promotion of the reaction rate. However, one technical drawback remained in this system: its inability to be applied in large-scale or continuous processes, as high loading of this type of biomass, which is composed of cells, will become clogged under continuous-flow conditions in a reactor.