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BackgroundThe cell growth and ethanol yield of Zymomonas mobilis may be detrimentally affected by salt stress frequently present in some biomass-based fermentation systems, leading to a decrease in the rate of sugar conversion to ethanol or other bioproducts. To address this problem, improving the salt tolerance of Z. mobilis is a desirable way. However, limited progress has been made in development of Z. mobilis with higher salt tolerance for some technical challenges in the past decades. Recently, transposon insertion mutant system has been widely used as a novel genetic tool in many organisms to develop mutant strains. In this study, Tn5-based transposon insertion mutagenesis system firstly used for construction of higher salt tolerance strain in Z. mobilis.ResultsApproximately 200 Z. mobilis ZM4 mutants were generated by using Tn5-based transposon mutagenesis system. The mutant strain ZMT2 with improved salt tolerance phenotype was obtained by screening on RM agar plates with additional 1 % NaCl. Strain ZMT2 was confirmed to exhibit better fermentation performance under NaCl stress than wild type of strain ZM4. The transposon insertion was located in ZMO1122 (himA) by genome walking. Discruption of himA gene showed that himA may play an important role in response to salt tolerance in Z. mobils.ConclusionsThe mutant strain ZMT2 with a transposon insertion in himA gene of the genome showed obviously higher sugar conversion rate to ethonal under up to 2 % NaCl stress than did the wild ZM4 strain. Besides, ZMT2 exhibited shared fermentative capabilities with wild ZM4 strain under no or low NaCl stress. This report firstly showed that himA played a role in responding to NaCl stress. Furthermore, the result indicated that Tn5-based transposon mutagenesis system was a feasible tool not only for genetic engineering in Z. mobilis strain improvement, but also in tapping resistent genes.

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A Gram-staining-positive, spore-forming, strictly anaerobic bacterium, designated strain LAM0A37 T , was isolated from enrichment samples collected from a petroleum reservoir in Shengli oilfield. Cells of strain LAM0A37 T were rod-shaped and motile by peritrichous flagella. The optimal temperature and pH for growth were 40 8C and 7.0-7.5, respectively. The strain did not require NaCl for growth but tolerated up to 3 % (w/v) NaCl. Strain LAM0A37 T was able to utilize glucose, fructose, maltose, xylose, sorbitol, cellobiose, melibiose and melezitose as sole carbon sources. Sulfite was used as an electron acceptor. The main products of glucose fermentation were acetate and CO 2 . The predominant fatty acid was C 16 : 0 (23.6 %). The main polar lipid profile comprised of five glycolipids, six phospholipids and two lipids. No menaquinone was detected. The genomic DNA G+C content was 27.1¡0.2 mol% as determined by the T m method. Analysis of the 16S rRNA gene sequence indicated that the isolate was a member of the genus Terrisporobacter, and was most closely related to Terrisporobacter glycolicus JCM 1401 T and Terrisporobacter mayombei DSM 6539 T with 98.3 % 16S rRNA gene sequence similarity to both. DNA-DNA hybridization values between strain LAM0A37 T and type strains of Terrisporobacter glycolicus and Terrisporobacter mayombei were 45.6¡0.3 % and 38.3¡0.4 %, respectively. Based on phenotypic, phylogenetic and chemotaxonomic characteristics, strain LAM0A37 T is suggested to represent a novel species of the genus Terrisporobacter, for which the name Terrisporobacter petrolearius sp. nov. is proposed. The type strain is LAM0A37 T (5ACCC 00740 T 5JCM 19845 T ).The genus Terrisporobacter belongs to the family Peptostreptococcaceae of the phylum Firmicutes, and was proposed by Gerritsen et al. (2014) during a study which reclassified several species of the genus Clostridium based on phenotypic and genetic considerations. This reclassification included the proposal of the novel genus Terrisporobacter to accommodate Terrisporobacter glycolicus (type species of the genus), previously named Clostridium glycolicum and Terrisporobacter mayombei, previously named Clostridium mayombei. Members of the genus are anaerobic and spore-forming, and cells contain both glycolipids and phospholipids, but phospholipids with free amino groups are absent (Gerritsen et al., 2014). While studying the anaerobic bacterial diversity of samples collected from a petroleum reservoir in Shengli oilfield, Dongying City, China, a Terrisporobacter-like strain, designated LAM0A37 T , was isolated. On the basis of phenotypic, phylogenetic and chemotaxonomic characteristics, the isolate was considered to represent a novel species of the genus Terrisporobacter.Strain LAM0A37 T was isolated from an enriched sample collected from a petroleum reservoir in Shengli oilfield. TSB medium (BD/Difco 211825) was used as the enrichment medium. Serum bottles (100 ml) containing 20 ml TSB medium were autoclaved for 30 min at 121 8C. Oilproduction water (10 %, v/v) fro...