Marine Proteobacteria as a source of natural products: advances in molecular tools and strategies.

Covering: up to 2019Humanity is in dire need for novel medicinal compounds with biological activities ranging from antibiotic to anticancer and anti-dementia effects. Recent developments in genome sequencing and mining have revealed an unappreciated potential for bioactive molecule production in marine Proteobacteria. Also, novel bioactive compounds have been discovered through molecular manipulations of either the original marine host bacteria or in heterologous hosts. Nevertheless, in contrast to the large repertoire of such molecules as predicted by in silico analysis, few marine bioactive compounds have been reported. This review summarizes the recent advances in the study of natural products from marine Proteobacteria. Here we present successful examples on genetic engineering of biosynthetic gene clusters of natural products from marine Proteobacteria. We also discuss the future prospects of discovering novel bioactive molecules via both heterologous production methodology and the development of marine Proteobacteria as new cell factories.

Complex spatial organization and flagellin composition of flagellar propeller from marine magnetotactic ovoid strain MO-1.

Marine magnetotactic ovoid bacterium MO-1 is capable of swimming along the geomagnetic field lines by means of its two sheathed flagellar bundles at a speed up to 300 µm/s. In this study, by using electron microscopy, we showed that, in each bundle, six individual flagella were organized in hexagon with a seventh in the middle. We identified 12 flagellin paralogs and 2 putative flagellins in the genome of MO-1. Among them, 13 were tandemly located on an ~ 17-kb segment while the 14th was on a separated locus. Using reverse transcription PCR and quantitative PCR, we found that all the 14 flagellin or putative flagellin genes were transcribed and that 2 of them were more abundantly expressed than others. A nLC (nanoliquid chromatography)-ESI (electrospray ionization)-MS/MS (mass spectrometry/mass spectrometry) mass spectrometry analysis identified all the 12 flagellin proteins in three glycosylated polypeptide bands resolved by one-dimensional denaturing polyacrylamide gel electrophoresis and 10 of them in 21 spots obtained by means of two-dimensional electrophoresis of flagellar extracts. Most spots contained more than one flagellin, and eight of the ten identified flagellins existed in multiple isoforms. Taken together, these results show unprecedented complexity in the spatial organization and flagellin composition of the flagellar propeller. Such architecture is observed only for ovoid-coccoid, bilophotrichously flagellated magnetotactic bacteria living in marine sediments, suggesting a species and environmental specificity.