Zhaopu Liu

Draft Genome Sequence of the Marine Bacterium Streptomyces griseoaurantiacus M045, Which Produces Novel Manumycin-Type Antibiotics with a pABA Core Component

Streptomyces griseoaurantiacus M045, isolated from marine sediment, produces manumycin and chinikomycin antibiotics. Here we present a high-quality draft genome sequence of S. griseoaurantiacus M045, the first marine Streptomyces species to be sequenced and annotated. The genome encodes several gene clusters for biosynthesis of secondary metabolites and has provided insight into genomic islands linking secondary metabolism to functional adaptation in marine S. griseoaurantiacus M045.

Purification and characterization of a novel marine Arthrobacter oxydans KQ11 dextranase.

Dextranases can hydrolyze dextran deposits and have been used in the sugar industry. Microbial strains which produce dextranases for industrial use are chiefly molds, which present safety issues, and dextranase production from them is impractically long. Thus, marine bacteria to produce dextranases may overcome these problems. Crude dextranase was purified by a combination of ammonium sulfate fractionation and ion-exchange chromatography, and then the enzyme was characterized. The enzyme was 66.2 kDa with an optimal temperature of 50°C and a pH of 7. The enzyme had greater than 60% activity at 60°C for 1h. Moreover, 10mM Co(2+) enhanced dextranase activity (196%), whereas Ni(2+) and Fe(3+) negatively affected activity. 0.02% xylitol and 1% alcohol enhanced activity (132.25% and 110.37%, respectively) whereas 0.05% SDS inhibited activity (14.07%). The thickness of S. mutans and mixed-species oral biofilm decreased from 54,340 nm to 36,670 nm and from 64,260 nm to 43,320 nm, respectively.

Purification and characterization of iron-cofactored superoxide dismutase from Enteromorpha linza

A superoxide dismutase was purified from Enteromorpha linza using a simple and safe procedure, which comprised phosphate buffer extraction, ammonium sulphate precipitation, ion exchange chromatography on Q-sepharose column, and gel filtration chromatography on Superdex 200 10/300GL. The E. linza superoxide dismutase (ElSOD) was purified 103.6-fold, and a yield of 19.1% and a specific activity of 1 750 U/mg protein were obtained. The SDS-PAGE exhibited ElSOD a single band near 23 kDa and the gel filtration study showed ElSOD’s molecular weight is near 46 kDa in nondenatured condition, indicating it’s a homodimeric protein. El SOD is an iron-cofactored superoxide dismutase (Fe-SOD) because it was inhibited by hydrogen peroxide, insensitive to potassium cyanide. The optimal temperature for its maximal enzyme activity was 35°C, and it still had 29.8% relative activity at 0°C, then ElSOD can be classified as a cold-adapted enzyme. ElSOD was stable when temperature was below 40°C or the pH was within the range of 5–10. The first 11 N-terminal amino acids of ElSOD were ALELKAPPYEL, comparison of its N-terminal sequence with other Fe-SOD N-terminal sequences at the same position suggests it is possibly a chloroplastic Fe-SOD.

Transcriptomic analysis of Synechocystis sp PCC6803 under low-temperature stress

In this study, cDNA microarrays were developed from 3569 mRNA reads to analyze the expression profiles of the transcriptomes of Synechocystis sp. PCC6803 under low temperature (LT) stress. Among the genes on the cDNA microarrays, 899 LT-affected genes exhibited a 1.5-fold (or greater) difference in expression compared with the genes from normal unstressed Synechocystis sp. PCC6803. Of the differentially expressed genes, 353 were up-regulated and 246 were down-regulated. The results showed that genes involved in photosynthesis were activated at LT (10°C), including genes for photosystem I, photosystem II, photosynthetic electron transport, and cytochrome b6/f complex. Moreover, desB, one of four genes that encode the fatty acid desaturases, was also induced by LT. However, the LT conditions to some degree enhanced the transcription of some genes. In addition, LT (10°C) may reduce cellular motility by regulating the transcription of spkA (sll1575), a serine/threonine protein kinase. The results reported in this study may contribute to a better understanding of the responses of the Synechocystis cell to LT, including pathways involved in photosynthesis and repair.

Improving stability of a novel dextran-degrading enzyme from marine Arthrobacter oxydans KQ11.

Dextranases can hydrolyze dextran, so they are used in the sugar industry to mitigate the milling problems associated with dextran contamination. Few studies have been carried out on the storage stability of dextranase, let alone the dextranase of Arthrobacter oxydans KQ11 isolated from sea mud samples. This study improved the storage stability of dextranase from marine A. oxydans KQ11 by adding enzymatic protective reagents (stabilizer and antiseptic). Initially, the conditions (55 °C and 30 min) for maintaining 50% dextranase activity were obtained. Then, the best stabilizers of dextranase were obtained, namely, glycerol (16%), sodium acetate (18%) and sodium citrate (20%). Results showed that p-hydroxybenzoic acid compound sodium acetate (0.05%), D-sodium isoascorbiate (0.03%), and potassium sorbate (0.05%) were the best antiseptics. Subsequent validation experiment showed that dextranase with enzymatic protective reagents maintained 70.8% and 28.96% activities at the 13th week at 25 and 37 °C, respectively.

Cloning and Expression of a Cytosolic HSP90 Gene in Chlorella vulgaris

Heat shock protein 90 (HSP90), a highly conserved molecular chaperone, plays essential roles in folding, keeping structural integrity, and regulating the subset of cytosolic proteins. We cloned the cDNA of Chlorella vulgaris HSP90 (named CvHSP90) by combining homology cloning with rapid amplification of cDNA ends (RACE). Sequence analysis indicated that CvHSP90 is a cytosolic member of the HSP90 family. Quantitative RT-PCR was applied to determine the expression level of messenger RNA (mRNA) in CvHSP90 under different stress conditions. C. vulgaris was kept in different temperatures (5–45°C) for 1 h. The mRNA expression level of CvHSP90 increased with temperature from 5 to 10°C, went further from 35 to 40°C, and reached the maximum at 40°C. On the other hand, for C. vulgaris kept at 35°C for different durations, the mRNA expression level of CvHSP90 increased gradually and reached the peak at 7 h and then declined progressively. In addition, the expression level of CvHSP90 at 40 or 45 in salinity (‰) was almost fourfold of that at 25 in salinity (‰) for 2 h. Therefore, CvHSP90 may be a potential biomarker to monitor environment changes.

Inhibitory activity of an extract from a marine bacterium Halomonas sp. HSB07 against the red-tide microalga Gymnodinium sp. (Pyrrophyta)

In recent years, red tides occurred frequently in coastal areas worldwide. Various methods based on the use of clay, copper sulfate, and bacteria have been successful in controlling red tides to some extent. As a new defensive agent, marine microorganisms are important sources of compounds with potent inhibitory bioactivities against red-tide microalgae, such as Gymnodinium sp. (Pyrrophyta). In this study, we isolated a marine bacterium, HSB07, from seawater collected from Hongsha Bay, Sanya, South China Sea. Based on its 16S rRNA gene sequence and biochemical characteristics, the isolated strain HSB07 was identified as a member of the genus Halomonas. A crude ethyl acetate extract of strain HSB07 showed moderate inhibition activity against Gymnodinium sp. in a bioactive prescreening experiment. The extract was further separated into fractions A, B, and C by silica gel column chromatography. Fractions B and C showed strong inhibition activities against Gymnodinium. This is the first report of inhibitory activity of secondary metabolites of a Halomonas bacterium against a red-tide-causing microalga.