Ling Ding

Fatty acid biosynthesis in eukaryotic photosynthetic microalgae: Identification of a microsomal delta 12 desaturase in Chlamydomonas reinhardtii

Polyunsaturated fatty acids (PUFAs) are important components of infant and adult nutrition because they serve as structural elements of cell membranes. Fatty acid desaturases are responsible for the insertion of double bonds into pre-formed fatty acid chains in reactions that require oxygen and reducing equivalents. In this study, the genome-wide characterization of the fatty acid desaturases from seven eukaryotic photosynthetic microalgae was undertaken according to the conserved histidine-rich motifs and phylogenetic profiles. Analysis of these genomes provided insight into the origin and evolution of the pathway of fatty acid biosynthesis in eukaryotic plants. In addition, the candidate enzyme from Chlamydomonas reinhardtii with the highest similarity to the microsomal Δ12 desaturase of Chlorella vulgaris was isolated, and its function was verified by heterologous expression in yeast (Saccharomyces cerevisiae).

T-Muurolol Sesquiterpenes from the Marine Streptomyces sp M491 and Revision of the Configuration of Previously Reported Amorphanes

Two new sesquiterpenes, 15-hydroxy-T-muurolol (3d) and 11,15-dihydroxy-T-muurolol (3e), along with the plant cadinenes T-muurolol (3f) and 3alpha-hydroxy-T-muurolol (3g), were isolated from the marine-derived Streptomyces sp. M491. Their absolute configuration was established via NMR spectroscopy and X-ray crystallography of 3-oxo-T-muurolol (3a), which was reisolated from this strain. In addition, the absolute configuration of further sesquiterpenes previously reported from this strain was revised. These products were tested for their cytotoxicity against 37 human tumor cell lines using the MTT method. Only 3d was cytotoxic against a range of human tumor cell lines with a mean IC50 of 6.7 microg/mL.

Isolation, Antimicrobial Activity, and Metabolites of Fungus Cladosporium sp. Associated with Red Alga Porphyra yezoensis

Cladosporium sp. isolate N5 was isolated as a dominant fungus from the healthy conchocelis of Porphyra yezoensis. In the re-infection test, it did not cause any pathogenic symptoms in the alga. Twenty-one cultural conditions were chosen to test its antimicrobial activity in order to obtain the best condition for large-scale fermentation. Phenylacetic acid, p-hydroxyphenylethyl alcohol, and l-ß-phenyllactic acid were isolated from the crude extract as strong antimicrobial compounds and they are the first reported secondary metabolites for the genus Cladosporium. In addition, the Cladosporium sp. produced the reported Porphyrayezoensis growth regulators phenylacetic acid and p-hydroxyphenylacetic acid. No cytotoxicity was found in the brine shrimp lethality test, which indicated that the environmental-friendly Cladosporium sp. could be used as a potential biocontrol agent to protect the alga from pathogens.

Hualyzin, a symmetrical urea derivative isolated from Penicillium herquei isolate GA4

Penicillium herquei isolate GA4 was isolated from the infected Conchocelis of Porphyra yezoensis. A large-scale fermentation using yeast extract sucrose medium and repeated chromatography afforded a new symmetrical urea derivative, hualyzin (1). The structure was determined by detailed NMR spectroscopic investigations and MS fragmentation analysis.

attB site disruption in marine Actinomyces sp. M048 via DNA transformation of a site-specific integration vector.

An efficient conjugation method has been developed for the marine Actinomyces sp. isolate M048 to facilitate the genetic manipulation of the chandrananimycin biosynthesis gene cluster. A φC31‐derived integration vector pIJ8600 containing oriT and attP fragments was introduced into strain M048 by bi‐parental conjugation from Escherichia coli ET12567 to strain M048. Transformation efficiency was (6.38±0.41)×10−5 exconjugants per recipient spore. Analysis of eight exconjugants showed that the plasmid pIJ8600 was stably integrated at a single chromosomal site (attB) of the Actinomyces genome. The DNA sequence of the attB was cloned and shown to be conserved. The results of antimicrobial activity analysis indicated that the insertion of plasmid pIJ8600 seemed to affect the biosynthesis of antibiotics that could strongly inhibit the growth of E. coli and Mucor miehei (Tü284). HPLC–MS analysis of the extracts indicated that disruption of the attB site resulted in the complete abolition of chandrananimycin A–C production, proving the identity of the gene cluster. Instead of chandrananimycins, two bafilomycins were produced through disruption of the attB site from the chromosomal DNA of marine Actinomyces sp. M048.