Zhen-Xing Xu

Marinifilum albidiflavum sp. nov., isolated from coastal sediment

A novel Gram-stain-negative, facultatively anaerobic, filamentous, and yellowish-white-pigmented marine bacterium, designated strain FB208T, was isolated from marine sediment obtained off the coastal area of Weihai, China. Cells of strain FB208T were filamentous during exponential growth, fragmented to rods in the stationary growth phase and became spherical in aged cultures. It grew optimally at 33 °C, at pH 7.0-7.5 and in the presence of 2.0-3.0 % (w/v) NaCl. Based on the 16S rRNA gene sequence, strain FB208T was found to be closely related to Marinifilum flexuosum DSM 21950T (96.9 % similarity) and Marinifilum fragile JCM 15579T (96.4 %), with less than 90.0 % sequence similarity to other genera of the class Bacteroidia. Phylogenetic analysis, also based on 16S rRNA gene sequences, placed strain FB208T in the genus Marinifilum, family Marinifilaceae. The predominant isoprenoid quinone of strain FB208T was identified as menaquinone MK-7. The main cellular fatty acids were iso-C15 : 0, iso-C17 : 0 3-OH and iso-C17 : 1ω9c, and the major polar lipids were an unidentified lipid and aminophospholipid. The G+C content of the genomic DNA was 43.8 mol%. Based on these phylogenetic and phenotypic data, strain FB208T represents a novel species of the genus Marinifilum, for which the name Marinifilum albidiflavum sp. nov. is proposed. The type strain is FB208T (=KCTC 42591T=MCCC 1H00113T).

Removing Bacillus subtilis from fermentation broth using alumina nanoparticles

In this study, an efficient separation technology using Al2O3 nanoparticles (NPs) was developed for removing Bacillus subtilis from fermentation broth. The dosage of alumina nanoparticles used for separating B. subtilis increased during the culture process and remained stable in the stationary phase of the culture process. The pH of the culture-broth was also investigated for its effects on flocculation efficiency, and showed an acidic pH could enhance the flocculation efficiency. The attachment mechanisms of Al2O3 NPs to the B. subtilis surface were investigated, and the zeta potential analysis showed that Al2O3 NPs could attach to B. subtilis via electrostatic attachment. Finally, the metabolite content and the antibacterial effect of the fermentation supernatants were detected and did not significantly differ between alumina nanoparticle separation and centrifugation separation. Together, these results indicate a great potential for a highly efficient and economical method for removing B. subtilis from fermentation broth using alumina nanoparticles.

Physiological and transcriptomic analyses reveal mechanistic insight into the adaption of marine Bacillus subtilis C01 to alumina nanoparticles.

An increasing number of studies have investigated the effects of nanoparticles (NPs) on microbial systems; however, few existing reports have focused on the defense mechanisms of bacteria against NPs. Whether secondary metabolism biosynthesis is a response to NP stress and contributes to the adaption of bacteria to NPs is unclear. Here, a significant induction in the surfactin production and biofilm formation were detected by adding Al2O3 NPs to the B. subtilis fermentation broth. Physiological analysis showed that Al2O3 NP stress could also affect the cell and colony morphogenesis and inhibit the motility and sporulation. Exogenously adding commercial surfactin restored the swarming motility. Additionally, a suite of toxicity assays analyzing membrane damage, cellular ROS generation, electron transport activity and membrane potential was used to determine the molecular mechanisms of toxicity of Al2O3 NPs. Furthermore, whole transcriptomic analysis was used to elucidate the mechanisms of B. subtilis adaption to Al2O3 NPs. These results revealed several mechanisms by which marine B. subtilis C01 adapt to Al2O3 NPs. Additionally, this study broadens the applications of nanomaterials and describes the important effects on secondary metabolism and multicellularity regulation by using Al2O3 NPs or other nano-products.

Colwellia agarivorans sp. nov., an agar-digesting marine bacterium isolated from coastal seawater

A novel Gram-stain-negative, facultatively anaerobic, yellowish and agar-digesting marine bacterium, designated strain QM50T, was isolated from coastal seawater in an aquaculture site near Qingdao, China. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the isolate represented a member of the genus Colwellia and exhibited the highest sequence similarity (97.4 %) to Colwellia aestuarii SMK-10T. Average nucleotide identity (ANI) values based on draft genome sequences between strain QM50T and C. aestuarii KCTC 12480T showed a relatedness of 72.0 % (ANIb) and 85.1 % (ANIm). Cells of strain QM50T were approximately 0.3-0.6×0.8-2.5 µm in size and motile by means of a polar flagellum. Growth occurred in the presence of 1.0-6.0 % (w/v) NaCl (optimum, 2.0-3.0 %), at pH 6.5-8.5 (optimum, pH 7.0) and at 4-37 °C (optimum, 28-30 °C). Strain QM50T was found to contain ubiquinone 8 (Q-8) as the predominant ubiquinone and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH), C16 : 0 and C17 : 1ω8c as the main cellular fatty acids. Phosphatidylethanolamine and phosphatidylglycerol were found to be major polar lipids. The DNA G+C content of strain QM50T was determined to be 35.7 mol%. On the basis of phylogenetic and phenotypic data, strain QM50T represents a novel species of the genus Colwellia, for which the name Colwellia agarivorans sp. nov. is proposed. The type strain is QM50T (=KCTC 52273T=MCCC 1H00143T).

Tenacibaculum agarivorans sp. nov., an agar-degrading bacterium isolated from marine alga Porphyra yezoensis Ueda

A novel Gram-stain-negative, aerobic, rod-shaped, non-flagellated and agar-digesting marine bacterium, designated as HZ1T, was isolated from the marine alga Porphyra yezoensis Ueda (AST58-103) collected from the coastal area of Weihai, PR China. Phylogenetic analysis based on 16S rRNA gene sequences placed HZ1T in the genus Tenacibaculum, and it formed a distinct clade in the phylogenetic tree with the type strains of Tenacibaculum amylolyticum and Tenacibaculum skagerrakense, with 97.0 % and 96.7 % 16S rRNA gene sequence similarities, respectively. The DNA G+C content of the isolate was 31.8 mol%. HZ1T contained MK-6 as the predominant menaquinone and iso-C15 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), iso-C17 : 0 3-OH and iso-C15 : 1G as the major fatty acids. The major polar lipids were phosphatidylethanolamine, four unidentified lipids and five unidentified aminolipids. On the basis of the results of the phylogenetic analysis and phenotypic properties, it is concluded that HZ1T represents a novel species of the genus Tenacibaculum, for which the name Tenacibaculumagarivorans sp. nov. is proposed. The type strain is HZ1T (=MCCC 1H00174T=KCTC 52476T).

Jeotgalibacillus proteolyticus sp. nov., a protease-producing bacterium isolated from ocean sediments

A Gram-stain-positive, rod-shaped bacterial strain, 22-7T, was isolated from ocean sediment of Laizhou Bay, China, and was characterized by using a polyphasic approach. Optimal growth was observed at 33 °C on a 2216E agar plate of pH 7.5 and with 2 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences identified it as a member of the genus Jeotgalibacillus, most similar to Jeotgalibacillus campisalis SF-57T (98.7 % similarity), Jeotgalibacillus marinus DSM 1297T (98.2 %) and Jeotgalibacillus soli P9T (97.1 %). Average nucleotide identity values and digital DNA-DNA hybridization values were less than 74.2 and 18.1 %, respectively, between strain 22-7T and the type strains of closely related species. The major polar lipids were aminophospholipid, phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol; the major fatty acids (>10 %) were anteiso-C15 : 0 and iso-C15 : 0; and the major menaquinone was MK-7. The peptidoglycan type of the cell wall was A1α linked through l-lysine as the diamino acid. Combined data from phenotypic, chemotaxonomic and genotypic characterizations demonstrated that strain 22-7T represents a novel Jeotgalibacillus species, for which the name Jeotgalibacillus proteolyticus sp. nov. is proposed. The type strain is 22-7T(=MCCC 1H00228T=KCTC 33930T).

Salegentibacter sediminis sp. nov., a marine bacterium of the family Flavobacteriaceae isolated from coastal sediment

A Gram-stain-negative, aerobic, non-motile, rod-shaped (0.2-0.3×0.8-1.4 µm) and yellow-pigmented bacterium, designated K5023T, was isolated from marine sediment obtained off the coast of Weihai, China. Strain K5023T was found to grow at 16-37 °C (optimum, 33 °C), at pH 6.5-8.0 (optimum, 7.0-7.5) and in the presence of 1-10 % (w/v) NaCl (optimum, 5 %). Cells were oxidase-positive and catalase-negative. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain K5023T is a member of the genus Salegentibacter and exhibited the hightest sequence similarity to Salegentibacter flavus DSM 22702T (97.0 %). Menaquinone-6 (MK-6) was detected as the major respiratory quinone. The dominant cellular fatty acids were iso-C15 : 0 and anteiso-C15 : 0. The DNA G+C content of strain K5023T was 40.1 mol%. The polar lipids included one phosphatidylethanolamine, three phospholipids and four unidentified lipids. Based on the phylogenetic and phenotypic characteristics, strain K5023T is considered to represent a novel species of the genus Salegentibacter, for which the name Salegentibacter sediminis sp. nov. is proposed. The type strain is K5023T (=KCTC 52477T=MCCC 1H00173T).

Geofilum rhodophaeum sp. nov., isolated from coastal sediment

A novel Gram-stain-negative, facultatively anaerobic, filamentous and rose-brown pigmented bacterium, designated strain HF401T, was isolated from marine sediment off the coast of Weihai, China. The isolate grew at temperatures between 4 and 45 °C (optimal growth at 33 °C), at pH 6.5-8.5 (optimal growth at pH 7.5) and with 0.5-6.0 % (w/v) NaCl (optimal growth at 3.0 %). The predominant menaquinone was menaquinone 7 (MK-7). The G+C content of the genomic DNA was 50.8 mol% (from high-performance liquid chromatography). The major fatty acids were iso-C15 : 0, C16:0, anteiso-C15 : 0 and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2OH). The major polar lipids were phosphatidylethanolamine, phospholipid and an unidentified lipid. Phylogenetic analysis of 16S rRNA gene sequences indicated that strain HF401T formed a distinct branch with Geofilum rubicundum JCM 15548T in the family Marinilabiliaceae. The most closely related strains of strain HF401T were Natronoflexuspectinivorans AP1T (96.2 % 16S rRNA gene sequence similarity), G. rubicundum JCM 15548T (96.2 %) and Alkalitaleasaponilacus SC/BZ-SP2T (96.0 %). Average nucleotide identity (ANI) values between strain HF401T and G. rubicundum JCM 15548T showed a relatedness of 71.3 % (ANIb) and 86.0 % (ANIm). The percentage of conserved proteins (POCP) value between strain HF401T and G. rubicundum JCM 15548T was 61.2 %. Based on polyphasic analysis, especially the phylogenetic relationships and the higher POCP value, strain HF401T is considered to represent a novel species in the genus Geofilum, for which the name Geofilum rhodophaeum sp. nov. is proposed. The type strain of Geofilum rhodophaeum is HF401T (KCTC 42595T=MCCC 1H00119T).