Diversity and community structure of cyanobacteria and other microbes in recycling irrigation reservoirs

<div><p>Recycling irrigation reservoirs (RIRs) are emerging aquatic environments of global significance to crop production, water conservation and environmental sustainability. This study characterized the diversity and population structure of cyanobacteria and other detected microbes in water samples from eight RIRs and one adjacent runoff-free stream at three ornamental crop nurseries in eastern (VA1 and VA3) and central (VA2) Virginia after cloning and sequencing the 16S rRNA gene targeting cyanobacteria and chloroplast of eukaryotic phytoplankton. VA1 and VA2 utilize a multi-reservoir recycling irrigation system with runoff channeled to a sedimentation reservoir which then overflows into transition and retention reservoirs where water was pumped for irrigation. VA3 has a single sedimentation reservoir which was also used for irrigation. A total of 208 operational taxonomic units (OTU) were identified from clone libraries of the water samples. Among them, 53 OTUs (358 clones) were cyanobacteria comprising at least 12 genera dominated by <i>Synechococcus</i> species; 59 OTUs (387 clones) were eukaryotic phytoplankton including green algae and diatoms; and 96 were other bacteria (111 clones). Overall, cyanobacteria were dominant in sedimentation reservoirs, while eukaryotic phytoplankton and other bacteria were dominant in transition/retention reservoirs and the stream, respectively. These results are direct evidence demonstrating the negative impact of nutrient-rich horticultural runoff, if not contained, on natural water resources. They also help in understanding the dynamics of water quality in RIRs and have practical implications. Although both single- and multi-reservoir recycling irrigation systems reduce the environmental footprint of horticultural production, the former is expected to have more cyanobacterial blooming, and consequently water quality issues, than the latter. Thus, a multi-reservoir recycling irrigation system should be preferred where feasible.</p></div

α-diversity of microbial communities in eight reservoirs and one adjacent stream.

<p><b>A</b>. Rarefaction curves of operational taxonomic units (OTUs) in clone sequences among the reservoirs. <b>B</b>. Inverse Simpson diversity index and number of observed OTUs in the reservoirs.</p

Neighbor joining phylogenetic tree of microbial communities identified from eight reservoirs and one stream surveyed in this study based on 16rDNA amplified with cyanobacteria primers (tree details are shown in S1 Fig).

<p>Cyanobacteria, eukaryotic phytoplankton and other bacteria are marked in blue, green and red, respectively.</p

Recycling irrigation systems with single or multiple reservoirs at three ornamental horticultural nurseries surveyed in this study.

<p>Arrows illustrate water flow in reservoirs.</p

Physical features and environmental variables of eight reservoirs and one adjacent stream surveyed in this study.

<p>Physical features and environmental variables of eight reservoirs and one adjacent stream surveyed in this study.</p

Microbial community composition in eight reservoirs and one adjacent stream.

<p><b>A.</b> Evenness or percentage of clones within groups in each reservoir. <b>B.</b> Richness or the percentage of OTUs within groups in each reservoir. CYA = cyanobacteria, EP = eukaryotic phytoplankton, and OB = other bacteria.</p

Non-metric Multidimensional Scaling (NMDS) ordination of the variation of taxon compositions in the reservoirs and fitted levels of environmental variables.

<p>Direction of the most rapid changes in environmental variables is shown with pointed arrows. The length of the arrows indicates a proportion to the correlation between ordination and environmental variable. Taxa in green, blue and red are eukaryotic phytoplankton, cyanobacteria and other bacteria, respectively. UCC = unclassified cyanobacteria, UCE = unclassified eukaryotic phytoplankton, UCB = unclassified bacteria. Arrow line in purple indicates that the parameter (NO₃) significantly varied and correlates with the ordination configuration (<i>P</i> < 0.1) in permutation tests. Chl = chlorophyll a, DO = dissolved oxygen, EC = electrical conductivity, P = orthophosphate, Tm = temperature, Turb = turbidity.</p

Heat map showing distribution and abundance of 22 dominant OTUs in eight reservoirs and one adjacent stream.

<p>Heat map showing distribution and abundance of 22 dominant OTUs in eight reservoirs and one adjacent stream.</p

Significance of environmental variables in eight reservoirs and an adjacent stream determined with permutation tests in fitted Non-metric Multidimensional Scaling (NMDS) ordination (Stress = 0.0698).

<p>Significance of environmental variables in eight reservoirs and an adjacent stream determined with permutation tests in fitted Non-metric Multidimensional Scaling (NMDS) ordination (Stress = 0.0698).</p

Monitoring Intracellular Redox Potential Changes Using SERS Nanosensors

Redox homeostasis and signaling are critically important in the regulation of cell function. There are significant challenges in quantitatively measuring intracellular redox potentials, and in this paper, we introduce a new approach. Our approach is based on the use of nanosensors which comprise molecules that sense the local redox potential, assembled on a gold nanoshell. Since the Raman spectrum of the sensor molecule changes depending on its oxidation state and since the nanoshell allows a huge enhancement of the Raman spectrum, intracellular potential can be calculated by a simple optical measurement. The nanosensors can be controllably delivered to the cytoplasm, without any toxic effects, allowing redox potential to be monitored in a reversible, non-invasive manner over a previously unattainable potential range encompassing both superphysiological and physiological oxidative stress