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Vast global declines of freshwater and marine fish diversity and population abundance pose serious threats to both ecosystem sustainability and human livelihoods. Environmental DNA (eDNA)-based biomonitoring provides robust, efficient, and cost-effective assessment of species occurrences and population trends in diverse aquatic environments. Thus, it holds great potential for improving conventional surveillance frameworks to facilitate fish conservation and fisheries management. However, the many technical considerations and rapid developments underway in the eDNA arena can overwhelm researchers and practitioners new to the field. Here, we systematically analysed 416 fish eDNA studies to summarize research trends in terms of investigated targets, research aims, and study systems, and reviewed the applications, rationales, methodological considerations, and limitations of eDNA methods with an emphasis on fish and fisheries research. We highlighted how eDNA technology may advance our knowledge of fish behaviour, species distributions, population genetics, community structures, and ecological interactions. We also synthesized the current knowledge of several important methodological concerns, including the qualitative and quantitative power eDNA has to recover fish biodiversity and abundance, and the spatial and temporal representations of eDNA with respect to its sources. To facilitate ecological applications implementing fish eDNA techniques, recent literature was summarized to generate guidelines for effective sampling in lentic, lotic, and marine habitats. Finally, we identified current gaps and limitations, and pointed out newly emerging research avenues for fish eDNA. As methodological optimization and standardization improve, eDNA technology should revolutionize fish monitoring and promote biodiversity conservation and fisheries management that transcends geographic and temporal boundaries. [ABSTRACT FROM AUTHOR]

The heterocyst is a specialized cell for nitrogen fixation in some filamentous cyanobacteria. Here we report that a rubrerythrin (RbrA) from Anabaena sp. PCC 7120 functions as a peroxidase in heterocysts and plays an important role in protection of nitrogenase. The electron donor for RbrA in H2O2 reduction is NADPH and the electron transfer from NADPH to RbrA depends on ferredoxin:NADP+ oxidoreductase. A rbrA mutant (r27) grew much more slowly than the wild type under diazotrophic conditions. Its nitrogenase activity measured in air was only 8% of that measured under anoxic conditions. Staining r27 filaments with 2′,7′-dichlorodihydrofluorescein diacetate indicated that heterocysts had a higher H2O2 concentration than the vegetative cells. The expression of rbrA was controlled by two promoters and the promoter for the smaller transcript was regulated by HetR. Spatial expression of rbrA was studied and the results showed that the transcription is localized predominantly in heterocysts. In a mutant lacking nifH and rbrA, the H2O2 concentration in heterocysts was lower than that in the vegetative cells, suggesting that NifH is involved in H2O2 generation. Our results demonstrate that RbrA is a critical enzyme for H2O2 decomposition and provide evidence that nitrogenase autoprotection is important in heterocysts. [ABSTRACT FROM AUTHOR]

MreB is a bacterial actin that plays important roles in determination of cell shape and chromosome partitioning in Escherichia coli and Caulobacter crescentus. In this study, the mreB from the filamentous cyanobacterium Anabaena sp. PCC 7120 was inactivated. Although the mreB null mutant showed a drastic change in cell shape, its growth rate, cell division and the filament length were unaltered. Thus, MreB in Anabaena maintains cell shape but is not required for chromosome partitioning. The wild type and the mutant had eight and 10 copies of chromosomes per cell respectively. We demonstrated that DNA content in two daughter cells after cell division in both strains was not always identical. The ratios of DNA content in two daughter cells had a Gaussian distribution with a standard deviation much larger than a value expected if the DNA content in two daughter cells were identical, suggesting that chromosome partitioning is a random process. The multiple copies of chromosomes in cyanobacteria are likely required for chromosome random partitioning in cell division. [ABSTRACT FROM AUTHOR]

The interaction between photosystem I (PS I) and flavodoxin from the cyanobacterium Synechococcus sp. PCC 7002 was investigated by covalent cross-linking in the presence of a hydrophilic cross-linker, Nethyl-3-(3-diaminopropylicarbodiimide. Under the experimental conditions employed, five distinct crosslinking products of flavodoxin and PS I subunits are formed. Immunoblot analyses show that these species are the result of cross-linking of flavodoxin to PsaC, PsaD, an unidentified low-molecular-mass PS I polypeptide, and a 15-kDa subunit. The latter has been indirectly identified us tile PsaF subunit. Analysis of the interaction of flavodoxin with PS I from a psaE mutant indicates that the PsaF subunit is required for correct complex formation between flavodoxin and PS I, although this subunit is not directly crosslinked to flavodoxin. In addition, the cross-linking products of PsaD with PsaC and PsaL, and PsaE with PsaF are observed. The covalent complex of flavodoxin and PS I is shown to be fully inhibited with respect to electron transfer to soluble flavodoxin, ferredoxin or ferredoxin:NADP oxidoreductase. [ABSTRACT FROM AUTHOR]