Lijun Xi

Thermophilic fermentation of acetoin and 2, 3-butanediol by a novel Geobacillus strain

BackgroundAcetoin and 2,3-butanediol are two important biorefinery platform chemicals. They are currently fermented below 40°C using mesophilic strains, but the processes often suffer from bacterial contamination.ResultsThis work reports the isolation and identification of a novel aerobic Geobacillus strain XT15 capable of producing both of these chemicals under elevated temperatures, thus reducing the risk of bacterial contamination. The optimum growth temperature was found to be between 45 and 55°C and the medium initial pH to be 8.0. In addition to glucose, galactose, mannitol, arabionose, and xylose were all acceptable substrates, enabling the potential use of cellulosic biomass as the feedstock. XT15 preferred organic nitrogen sources including corn steep liquor powder, a cheap by-product from corn wet-milling. At 55°C, 7.7 g/L of acetoin and 14.5 g/L of 2,3-butanediol could be obtained using corn steep liquor powder as a nitrogen source. Thirteen volatile products from the cultivation broth of XT15 were identified by gas chromatography–mass spectrometry. Acetoin, 2,3-butanediol, and their derivatives including a novel metabolite 2,3-dihydroxy-3-methylheptan-4-one, accounted for a total of about 96% of all the volatile products. In contrast, organic acids and other products were minor by-products. α-Acetolactate decarboxylase and acetoin:2,6-dichlorophenolindophenol oxidoreductase in XT15, the two key enzymes in acetoin metabolic pathway, were found to be both moderately thermophilic with the identical optimum temperature of 45°C.ConclusionsGeobacillus sp. XT15 is the first naturally occurring thermophile excreting acetoin and/or 2,3-butanediol. This work has demonstrated the attractive prospect of developing it as an industrial strain in the thermophilic fermentation of acetoin and 2,3-butanediol with improved anti-contamination performance. The novel metabolites and enzymes identified in XT15 also indicated its strong promise as a precious biological resource. Thermophilic fermentation also offers great prospect for improving its yields and efficiencies. This remains a core aim for future work.

Thermophilic production of polyhydroxyalkanoates by a novel Aneurinibacillus strain isolated from Gudao oilfield, China

Polyhydroxyalkanoates (PHAs) are usually biosynthesized using mesophilic strains, but the fermentation processes often suffer from bacterial contamination. This work reports the screening of thermophilic bacteria capable of producing PHAs under elevated temperatures to reduce the contamination risk. Strain XH2 was isolated from an oilfield and identified as Aneurinibacillus sp. by morphology, physiological‐biochemical characterization, and 16S rDNA phylogenetic analysis. This strain can produce PHA granules, which was detected by Nile red staining and transmission electron microscopic imaging. At 55 °C, 111.6 mg l−1 of PHA was produced in a fermentation medium containing glucose, peptone, and yeast extract. If peptone was removed from the medium, the yield of PHA would be enhanced by 2.4 times. The main monomers of the PHA product were identified to be 3‐hydroxybutyrate and 3‐hydroxyvalerate with a molar ratio of 17.2:1 by gas chromatography‐mass spectroscopy (GC‐MS) and nuclear magnetic resonance analyses. Two minor homologues, 3‐hydroxyoctanoate, and 3‐hydroxy‐4‐phenylbutanoate, were tentatively identified by GC‐MS as well. This is the first report of thermophilic PHA bacterial producer from the Firmicutes phylum.

Identification of an integron containing the quinolone resistance gene qnrA1 in Shewanella xiamenensis.

This study investigated multidrug resistance in Shewanella xiamenensis isolated from an estuarine water sample in China during 2014. This strain displayed resistance or decreased susceptibility to ampicillin, aztreonam, cefepime, cefotaxime, chloramphenicol, ciprofloxacin, erythromycin, kanamycin and trimethoprim-sulfamethoxazole. The antimicrobial resistance genes aacA3, blaOXA-199, qnrA1 and sul1 were identified by PCR amplification and by sequencing. Pulsed-field gel electrophoresis and DNA hybridization experiments showed that the quinolone resistance gene qnrA1 was chromosomally located. qnrA1 was located in a complex class 1 integron, downstream from an ISCR1, and bracketed by two copies of qacEΔ1-sul1 genes. This integron is similar to In825 with four gene cassettes aacA3, catB11c, dfrA1z and aadA2az. An IS26-mel-mph2-IS26 structure was also detected in the flanking sequences, conferring resistance to macrolides. This is the first identification of the class 1 integron in S. xiamenensis. This is also the first identification of the qnrA1 gene and IS26-mediated macrolide resistance genes in S. xiamenensis. Presence of a variety of resistance genetic determinants in environmental S. xiamenensis suggests the possibility that this species may serve as a potential vehicle of antimicrobial resistance genes in aquatic environments.

Complete genome sequence of the novel thermophilic polyhydroxyalkanoates producer Aneurinibacillus sp. XH2 isolated from Gudao oilfield in China

Aneurinibacillus sp. XH2 (CGMCC 1.15535) was isolated from Gudao oilfield in China. It is able to use simple carbon resources to accumulate Polyhydroxyalkanoates (PHAs) in a thermophilic fashion. Here, we describe the genomic features of this strain. The total genome size of Aneurinibacillus sp. XH2 is 3,664,835bp and contains 3441 coding sequences and 114 tRNAs. The annotated genome sequence of this strain provides the genetic basis for revealing its role as a themophilic PHAs producing bacterium.

Biodegradation of C 5 -C 8 fatty acids and production of aroma volatiles by Myroides sp. ZB35 isolated from activated sludge

In the effluents of a biologically treated wastewater from a heavy oil-refining plant, C5-C8 fatty acids including pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, and 2-methylbutanoic acid are often detected. As these residual fatty acids can cause further air and water pollution, a new Myroides isolate ZB35 from activated sludge was explored to degrade these C5-C8 fatty acids in this study. It was found that the biodegradation process involved a lag phase that became prolonged with increasing acyl chain length when the fatty acids were individually fed to this strain. However, when fed as a mixture, the ones with longer acyl chains were found to become more quickly assimilated. The branched 2-methylbutanoic acid was always the last one to be depleted among the five fatty acids under both conditions. Metabolite analysis revealed one possible origin of short chain fatty acids in the biologically treated wastewater. Aroma volatiles including 2-methylbutyl isovalerate, isoamyl 2-methylbutanoate, isoamyl isovalerate, and 2-methylbutyl 2-methylbutanoate were subsequently identified from ZB35 extracts, linking the source of the fruity odor to these esters excreted by Myroides species. To our best knowledge, this is the first finding of these aroma esters in bacteria. From a biotechnological viewpoint, this study has revealed the potential of Myroides species as a promising source of aroma esters attractive for food and fragrance industries.

Catechol 2,3-dioxygenase from a new phenolic compound degrader Thauera sp. K11: purification and biochemical characterization

Catechol 2,3‐dioxygenase (C23O) from a new phenolic compound degrader Thauera sp. K11 was purified and characterized. The native form of the enzyme was determined as a homotetramer with a molecular weight of 140 kDa, and its isoelectric point was close to 6.4. One iron per enzyme subunit was detected using atom absorption spectroscopy, and the effective size of C23O in its dilute solution (0.2 g L−1, pH 8.0) was 14.5 nm. The optimal pH and temperature were 8.4 and 45 °C, respectively. The addition of Mg2+, Cu2+, Fe2+, and Mn2+ could improve the enzyme activity, while Ag+ was found to be a strong inhibitor. C23O was stable in alkali conditions (pH 7.6–11.0) and thermostable below 50 °C. The final purified C23O had a sheet content of 53%, consistent with the theoretical value. This showed that the purified catechol 2,3‐dioxygenase folded with a reasonable secondary structure.

Pannonibacter carbonis sp. nov., isolated from coal mine water

Two bacterial strains were isolated from coal mine water in China. Isolates were facultatively anaerobic, Gram-stain-negative, rod-shaped, motile by means of a single polar flagellum, and they did not produce bacteriochlorophyll α. Cells grew in tryptic soy broth with 0-5.5 % (w/v) NaCl, at 4-55 °C and pH 3.5-10.5. Isolates were positive for catalase, oxidase, urease, Voges-Proskauer test, gelatin hydrolysis and H2S production. Analysis of 16S rRNA gene sequences indicated that the closest relatives of strains Q4.6T and Q2.11 were the type strains Labrenzia suaedae DSM 22153T (97.4 %), Pannonibacter phragmitetus DSM 14782T (96.9 and 97.0 %) and Pannonibacter indicus DSM 23407T (96.8 %). The genomic average nucleotide identity (ANI) value for Q4.6T and Q2.11 was 100 %; however, this value was less than 77.7 % for the type strains P. phragmitetus and P. indicus, and less than 74.0 % for the type strain L. suaedae. The cellular fatty acid profile of strains Q4.6T and Q2.11 consisted primarily of C18 : 1ω7c. The principal quinone of the isolates was Q-10. The polar lipid profile consisted of diphosphatidyl glycerol, phosphatidyl glycerol, phosphatidyl ethanolamine and phosphatidyl choline. On the basis of phylogenetic analysis, genomic ANI analysis, DNA-DNA hybridization results, as well as phenotypic and chemotaxonomic data, strains Q4.6T and Q2.11 are assigned as a novel species within the genus Pannonibacter. The type strain is Pannonibacter carbonis Q4.6T (=CGMCC 1.15703T=KCTC 52466T).