BackgroundThe pure culture of prokaryotes remains essential to elucidating the role of these organisms. Scientists have reasoned that hard to cultivate microorganisms might grow in pure culture if provided with the chemical components of their natural environment. However, most microbial species in the biosphere that would otherwise be “culturable” may fail to grow because of their growth state in nature, such as dormancy. That means even if scientist would provide microorganisms with the natural environment, such dormant microorganisms probably still remain in a dormant state.ResultsWe constructed an enrichment culture system for high-efficiency isolation of uncultured strains from marine sediment. Degree of enrichment analysis, dormant and active taxa calculation, viable but non-culturable bacteria resuscitation analysis, combined with metatranscriptomic and comparative genomic analyses of the interactions between microbial communications during enrichment culture showed that the so-called enrichment method could culture the “uncultured” not only through enriching the abundance of “uncultured,” but also through the resuscitation mechanism. In addition, the enrichment culture was a complicated mixed culture system, which contains the competition, cooperation, or coordination among bacterial communities, compared with pure cultures.ConclusionsConsidering that cultivation techniques must evolve further—from axenic to mixed cultures—for us to fully understand the microbial world, we should redevelop an understanding of the classic enrichment culture method. Enrichment culture methods can be developed and used to construct a model for analyzing mixed cultures and exploring microbial dark matter. This study provides a new train of thought to mining marine microbial dark matter based on mixed cultures.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0613-2) contains supplementary material, which is available to authorized users.

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Altered nitric oxide (NO) biosynthesis is thought to play a role in the initiation and progression of atherosclerosis and may contribute to increased risk seen in other cardiovascular diseases. It is hypothesized that altered NO bioavailability may result from an increase in endogenous NO synthase (NOS) inhibitors, asymmetric dimethly araginine (ADMA), and N(G)-monomethyl arginine, which are normally metabolized by dimethyarginine dimethylamine hydrolase (DDAH). Lipid hydroperoxides and their degradation products are generated during inflammation and oxidative stress and have been implicated in the pathogenesis of cardiovascular disorders. Here, we show that the lipid hydroperoxide degradation product 4-hydroxy-2-nonenal (4-HNE) causes a dose-dependent decrease in NO generation from bovine aortic endothelial cells, accompanied by a decrease in DDAH enzyme activity. The inhibitory effects of 4-HNE (50 microM) on endothelial NO production were partially reversed with L-Arg supplementation (1 mM). Overexpression of human DDAH-1 along with antioxidant supplementation completely restored endothelial NO production following exposure to 4-HNE (50 microM). These results demonstrate a critical role for the endogenous methylarginines in the pathogenesis of endothelial dysfunction. Because lipid hydroperoxides and their degradation products are known to be involved in atherosclerosis, modulation of DDAH and methylarginines may serve as a novel therapeutic target in the treatment of cardiovascular disorders associated with oxidative stress.

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