Mitigating risks and maximizing sustainability of treated wastewater reuse for irrigation.

Scarcity of freshwater for agriculture has led to increased utilization of treated wastewater (TWW), establishing it as a significant and reliable source of irrigation water. However, years of research indicate that if not managed adequately, TWW may deleteriously affect soil functioning and plant productivity, and pose a hazard to human and environmental health. This review leverages the experience of researchers, stakeholders, and policymakers from Israel, the United-States, and Europe to present a holistic, multidisciplinary perspective on maximizing the benefits from municipal TWW use for irrigation. We specifically draw on the extensive knowledge gained in Israel, a world leader in agricultural TWW implementation. The first two sections of the work set the foundation for understanding current challenges involved with the use of TWW, detailing known and emerging agronomic and environmental issues (such as salinity and phytotoxicity) and public health risks (such as contaminants of emerging concern and pathogens). The work then presents solutions to address these challenges, including technological and agronomic management-based solutions as well as source control policies. The concluding section presents suggestions for the path forward, emphasizing the importance of improving links between research and policy, and better outreach to the public and agricultural practitioners. We use this platform as a call for action, to form a global harmonized data system that will centralize scientific findings on agronomic, environmental and public health effects of TWW irrigation. Insights from such global collaboration will help to mitigate risks, and facilitate more sustainable use of TWW for food production in the future.

Antibacterial activity of Pseudoalteromonas in the coral holobiont.

Corals harbor diverse and abundant prokaryotic populations. Bacterial communities residing in the coral mucus layer may be either pathogenic or symbiotic. Some species may produce antibiotics as a method of controlling populations of competing microbial species. The present study characterizes cultivable Pseudoalteromonas sp. isolated from the mucus layer of different coral species from the northern Gulf of Eilat, Red Sea, Israel. Six mucus-associated Pseudoalteromonas spp. obtained from different coral species were screened for antibacterial activity against 23 tester strains. Five of the six Pseudoalteromonas strains demonstrated extracellular antibacterial activity against Gram-positive-but not Gram-negative-tester strains. Active substances secreted into the cell-free supernatant are heat-tolerant and inhibit growth of Bacillus cereus, Staphylococcus aureus, and of ten endogenous Gram-positive marine bacteria isolated from corals. The Pseudoalteromonas spp. isolated from Red sea corals aligned in a phylogenetic tree with previously isolated Pseudoalteromonas spp. of marine origin that demonstrated antimicrobial activity. These results suggest that coral mucus-associated Pseudoalteromonas may play a protective role in the coral holobiont's defense against potential Gram-positive coral pathogens.

Characterization of quorum sensing signals in coral-associated bacteria.

Marine environment habitats, such as the coral mucus layer, are abundant in nutrients and rich with diverse populations of microorganisms. Since interactions among microorganisms found in coral mucus can be either mutualistic or competitive, understanding quorum sensing-based acyl homoserine lactone (AHL) language may shed light on the interaction between coral-associated microbial communities in the native host. More than 100 bacterial isolates obtained from different coral species were screened for their ability to produce AHL. When screening the isolated coral bacteria for AHL induction activity using the reporter strains Escherichia coli K802NR-pSB1075 and Agrobacterium tumefaciens KYC55, we found that approximately 30% of the isolates tested positive. Thin layer chromatography separation of supernatant extracts revealed different AHL profiles, with detection of at least one active compound in the supernatant of those bacterial extracts being able to induce AHL activity in the two different bioreporter strains. The active extract of bacterial isolate 3AT 1-10-4 was subjected to further analysis by preparative thin layer chromatography and liquid chromatography tandem mass spectrometry. One of the compounds was found to correspond with N-(3-hydroxydecanoyl)-L-homoserine lactone. 16S rRNA gene sequencing of the isolates with positive AHL activity affiliated them with the Vibrio genus. Understanding the ecological role of AHL in the coral environment and its regulatory circuits in the coral holobiont-associated microbial community will further expand our knowledge of such interactions.

Shewanella corallii sp. nov., a marine bacterium isolated from a Red Sea coral.

A marine bacterial strain, designated fav-2-10-05(T), was isolated from the mucus layer of a coral of the genus Favia, collected from the coral reef in the Gulf of Eilat, Israel (29.5 ° N 34.9 ° E). On the basis of 16S rRNA gene sequence comparisons, strain fav-2-10-05(T) was affiliated with the family Shewanellaceae. The closest relatives of strain fav-2-10-05(T) were Shewanella marisflavi SW-117(T) (96.0 % 16S rRNA gene sequence similarity) and Shewanella haliotis DW-1(T) (95.9 %). Strain fav-2-10-05(T) was Gram-negative, rod-shaped and motile by means of a single polar flagellum and formed yellow-brownish colonies within 2 days of incubation at 26°C. Strain fav-2-10-05(T) demonstrated antibacterial activity against indicator strains and grew in the presence of 0.5-8.0 % (w/v) NaCl and at 10-37°C. The major fatty acids were C17:1ω8c (21.6 %), iso-C15:0 (18.6 %), C15:0 (9.1 %) and iso-C13:0 (8.9 %). The DNA G+C content was 49.1 mol%. The phylogenetic and phenotypic analyses of strain fav-2-10-05(T) suggested that it belongs to a novel species of the genus Shewanella, for which the name Shewanella corallii sp. nov. is proposed. The type strain is fav-2-10-05(T) (=LMG 24563(T) =DSM 21332(T)).

Coral mucus-associated bacteria: a possible first line of defense.

Interactions among microorganisms found in coral mucus can be either symbiotic or competitive. It has been hypothesized that microbial communities found on the surface of coral play a role in coral holobiont defense, possibly through production of antimicrobial substances. Selected microorganisms isolated from the mucus layer of a number of coral species were grown using agar-plating techniques. Screening for antimicrobial substances was performed using overlay and drop techniques, employing several indicator microorganisms. Between 25% and 70% of cultivable mucus-associated bacteria from scleractinian corals demonstrated bioactivity. Higher percentages of activity were evident in mucus-associated cultivable bacteria from massive and solitary corals, as compared with bacteria from branching or soft corals. Isolates related to the genera Vibrio and Pseudoalteromonas demonstrated high activity against both Gram-positive and Gram-negative bacteria. Gram-positive bacteria (Bacillus, Planomicrobium) demonstrated lower levels of activity, primarily against other Gram-positive bacteria. In some cases, inhibitory effects were confined to the cell fraction, suggesting the involvement of a cell-bound molecule, sensitive to temperature and most likely proteinaceous in nature. These results demonstrate the existence of microorganisms with antimicrobial activity on the coral surface, possibly acting as a first line of defense to protect the coral host against pathogens.