## 5 Conclusions  
In summary, we reported a recombinant _E. coli_ strain BL-SsEct harboring a novel _ectABC\({}_{S.\ salarius}\)_ gene of ectoine biosynthesis from marine organism _S. salarius_. The engineered strain demonstrated a high efficiency in whole-cell biocatalysis of ectoine and led to an extracellular accumulation of 3.28 g/L in the flask using fed-batch culture method. Further bioconversion was performed in the fermentor system, and the total ectoine production of 22.5 g/L with the specific ectoine productivity of 0.94 g/L-h was achieved under the distinctive temperature condition of 25 \({}^{\circ}\)C. It should be noted that the requirement of lower temperature in the bioconversion process made the BL-SsEct more competitive and more capable in commercial and economical production of ectoine. The following are available online at [[https://www.mdpi.com/article/10.3390/app11156873/s1](https://www.mdpi.com/article/10.3390/app11156873/s1)]([https://www.mdpi.com/article/10.3390/app11156873/s1](https://www.mdpi.com/article/10.3390/app11156873/s1)), Figure S1: Multiple sequence alignment of \(\text{EtAcA}_{S.\ salarius}\) with other L-2, 4-diaminobutyric acid acetyltransferases, Figure S2: Multiple sequence alignment of \(\text{EtEtB}_{S.\ salarius}\) with other Diaminobutyrate-2-oxoglutate transaminases, Figure S3: Multiple sequence alignment of \(\text{EtCt}_{S.\ salarius}\) with other L-ectoine synthases, Table S1: The comparation of \(\text{EtAcA}_{S.\ salarius}\) with other EctAs from different microorganisms, Table S2: The comparation of \(\text{EtCt}_{S.\ salarius}\) with other EctBs from different microorganisms, Table S3: The comparation of \(\text{EtCt}_{S.\ salarius}\) with other EctCs from different microorganisms, Figure S4: Phylogenetic tree of diaminobutyrate acetyltransferase (\(\text{EtCa}_{S.\ salarius}\)) from marine bacterium _Salinicola salarius_ 1A01339, Figure S5: Phylogenetic tree of diaminobutyrate-2-oxoglutate transaminase (\(\text{EtCt}_{S.\ salarius}\)) from marine bacterium _Salinicola salarius_ 1A01339, Figure S6: Phylogenetic tree of ectoine synthase (\(\text{EtCt}_{S.\ salarius}\)) from marine bacterium _Salinicola salarius_ 1A01339, Figure S7: The interaction of the substrate within the catalytic centre of \(\text{EtCa}_{S.\ salarius}\), Figure S8: The proposed configuration of active site cavity with key residues in the \(\text{EtCt}_{S.\ salarius}\) module, Figure S9. Crystal modelling views into the catalytic center of the \(\text{EtAcA}_{S.\ salarius}\). Conceptualization, Y.S. and L.L. ; methodology, Y.S., W.P., T.W. ; software, Y.S. ; validation, W.P., T.W. and L.L. ; formal analysis, Y.S., Y.L. ([PERSON]), L.Z. and X.W. ; data curation, Y.L. ([PERSON]), T.W. and L.L. ; writing--original draft preparation, Y.S. ; writing--review and editing, Y.S. and L.L. ; supervision, L.L. All authors have read and agreed to the published version of the manuscript. This work was funded by the Natural Science Research for Colleges and Universities of Anhui Province of China (KJ2020A0066) and Anhui Provincial Key Laboratory of the Conservation and Exploitation Research of Biological Resources. Not applicable. The authors declare no conflict of interest. * [PERSON] et al. (2019) [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] Heterologous Ectoine Production in _Escherichia coli_: Optimization Using Response Surface Methodology. _Int. J. Microbiol._**2019**, _2019_, 1-13. [CrossRef]
* [PERSON] et al. (2014) [PERSON]; [PERSON]; [PERSON] Industrial Production of the Cell Protectant Ectoine: Protection Mechanisms, Processes, and Products. _Curr. Biotech._**2014**, \(3\), 10-25. [CrossRef]
* [PERSON] (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON] Contribution of mechanosensitive channels to osmoadaptation and ectoine excretion in _Halomonas elongata. Extremophiles_**2020**, _24_, 421-432. [CrossRef] [PubMed]
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