## 1 Introduction  
In order to survive in extreme salty habitat, various labophilic microorganisms have applied two different strategies to maintain osmotic balance. One of the ways is through inorganic salts in the cytosol, which could counterbalance the high extracellular salt concentrations [1, 2]. Another method is to synthesize small organic molecules called compatible solutes (including sugars, polyols, methylamines, betaines, amino acids and their derivatives) as osmotic counterweights, such as _HalodothiNADPH-dependent reaction by L-2, 4-diaminobutyrate:2-oxoglutarate-4-aminotransferase (Asd) were similar to the biosynthetic pathway of amino acids of the aspartate family [13]. The following biosynthesis was carried out by a cascade of three biochemical conversions catalyzed by diaminobutyrate-2-oxoglutarate transaminase (EctB), L-2, 4-diamino-butyrateacetyltransferase (EctA), and L-ectoine synthase (EctC), and finally led to the formation of tetrahydropropylimide, ectoine (Figure 1).  
It was reported that a number of species which carried the _ectABC_ cluster have been shown to synthesize ectoine in salt stress habitat [14; 15]. In recent years, the widely producing and marketing of ectoine used in pharmaceuticals products and cosmetics had led to the increasing commercial demand of this bio-functional compound [16; 17; 18]. In order to satisfy the increasing commercial needs of ectoine, numerous biosynthesis strains for ectoine production have been chosen and built in the past two decades [19; 20; 21]. A bioprocess technique called \"bacterial milking\" was conducted using the halophilic eubacterium _Halomonas elongata_ and employing kinds of biology strategies [22; 23]. However, relatively high purity of ectoine required specific fermentation with more complicated and costly process because of high salt addition and elimination during this bioprocess. To avoid these drawbacks, a series of heterologous expressions of the cluster _ectABC_ in non-halophilic bacterium _E. coli_ had been attempted and the final recombinant _E. coli_ strain BW (pBAD-_ectABC_) could accumulate and secrete 25.1 g/L ectoine by fed-batch fermentation [19]. In another report, utilizing transcriptional balancing, the engineered strain _Corynebacterium glutamic ectABC_P_H has proven to achieve high production of ectoine to a final titer of more than 65 g/L within 56 h [24]. These results suggested that heterologous expression of the ectoine biosynthetic pathway could be an attractive strategy for industrial production of pharmaceutical organic molecules.  
In this study, we designed a synthetic cell factory by recruiting the novel _ectABC_S. salaris_ (see Appendix A) cluster from _Salinicola salarius_ 1A01339, which was isolated from seawater of Indian Ocean and might produce enzymes with desirable characteristics. The _ectABC_S. salaris_ cluster, which had not been reported and studied, was firstly gene-mined from the Genbank Database and then successfully expressed in _E. coli_ BL21(DE3) to obtained the recombinant strain BL-SsEct. We further optimized the condition of ectoine biosynthesis and preformed an efficient whole-cell bioconversion at a lower temperature of 25 \({}^{\circ}\)C. These results provide a promising potentiality for large-scale ectoine production in industrial applications using a more economical and effective bioprocess.