Biodiversity of cyanobacteria and other aquatic microorganisms across a freshwater to brackish water gradient determined by shotgun metagenomic sequencing analysis in the San Francisco Estuary, USA.

Blooms of Microcystis and other harmful cyanobacteria can degrade water quality by producing cyanotoxins or other toxic compounds. The goals of this study were (1) to facilitate understanding of community structure for various aquatic microorganisms in brackish water and freshwater regions with emphasis on cyanobacteria, and (2) to test a hypothesis that Microcystis genotypes that tolerate higher salinity were blooming in brackish water environments during the severe drought, 2014. Shotgun metagenomic analysis revealed that cyanobacteria dominated the brackish water region while bacteria dominated the freshwater region. A group of cyanobacteria (e.g., Aphanizomenon, Microcystis, Planktothrix, Pseudanabaena), bacteria (e.g., Bacillus, Porphyrobacter), and diatoms (Phaeodactylum and Thalassiosira) were abundant in the brackish water region. In contrast, Hassallia (cyanobacteria) and green algae (Nannochloropsis, Chlamydomonas, and Volvox) were abundant in the landward freshwater region. Station variation was also apparent. One landward sampling station located downstream of an urbanized area differed substantially from the other stations in terms of both water chemistry and community structure, with a higher percentage of arthropods, green algae, and eukaryotes. Screening of the Microcystis internal transcribed spacer region revealed six representative genotypes, and two of which were successfully quantified using qPCR (Genotypes I and VI). Both genotypes occurred predominantly in the freshwater region, so the data from this study did not support the hypothesis that salinity tolerant Microcystis genotypes bloomed in the brackish water region in 2014.

Sub-lethal effects of herbicides penoxsulam, imazamox, fluridone and glyphosate on Delta Smelt (Hypomesus transpacificus).

Concerns regarding non-target toxicity of new herbicides used to control invasive aquatic weeds in the San Francisco Estuary led us to compare sub-lethal toxicity of four herbicides (penoxsulam, imazamox, fluridone, and glyphosate) on an endangered fish species Delta Smelt (Hypomesus transpacificus). We measured 17ß-estradiol (E2) and glutathione (GSH) concentrations in liver, and acetylcholinesterase (AChE) activity in brain of female and male fish after 6 h of exposure to each of the four herbicides. Our results indicate that fluridone and glyphosate disrupted the E2 concentration and decreased glutathione concentration in liver, whereas penoxsulam, imazamox, and fluridone inhibited brain AChE activity. E2 concentrations were significantly increased in female and male fish exposed to 0.21 µM of fluridone and in male fish exposed to 0.46, 4.2, and 5300 µM of glyphosate. GSH concentrations decreased in males exposed to fluridone at 2.8 µM and higher, and glyphosate at 4.2 µM. AChE activity was significantly inhibited in both sexes exposed to penoxsulam, imazamox, and fluridone, and more pronounced inhibition was observed in females. The present study demonstrates the potential detrimental effects of these commonly used herbicides on Delta Smelt.