Antibacterial, antioxidant and cytotoxic activities of extracts from the thermophilic green alga, Cosmarium sp.

Unicellular green algal strains, identified as Cosmarium (Chlorophyta), were isolated from Ain-Echeffa hot spring in north Tunisia. Different extracts (methanol, hexane, acetone, acetone: methanol and water) obtained from both biomass and extracellular polysaccharides (EPS) were evaluated for their antibacterial, antioxidant and cytotoxic activities. First, extracts were tested in vitro for eventual antibacterial activities against a collection of Gram positive and negative bacteria. Most extracts (biomass and EPS) showed significant antibacterial effects, with minimum inhibitory concentrations (MIC) ranging from 28 to 85 µg/ml for biomass and 50 to 150 µg/ml for EPS. Moreover, based on the capacity of each sample to scavenge the ABTS radical cation, we revealed that the EPS aqueous extract presented a moderate antioxidant activity (24.97%). Finally, the toxicity of the biomass extracts was evaluated using the brine shrimp Artemia salina, as test organism. All extracts were identified as non-toxic (LC50 > 400 µg/ml).Key words: Cosmarium, biomass, extracellular polysaccharides (EPS), cytotoxicity, antibacterial, antioxidant

A review on microbial contamination cases in Tunisian coastal marine areas

Microbial pollution in marine environments is one of the critical issues with regard to the sanitary status of recreational activities and seafood harvesting due to a potential contamination by pathogenic microorganisms. This review's objectives were to identify instances of bacterial, viral and protozoan parasite pollution in the Tunisian coastal region and to make recommendations for further research. Fecal indicators such as Escherichia coli and Salmonella spp. were detected in samples of clams and mussels. Vibrionaceae species were also recorded in seawater, sediment, fish and clams in different sites from north to south with the dominance of Vibrio alginolyticus. Bivalve mollusks collected from the Tunisian coast have been revealed to harbor viruses as well as protozoan parasites. Furthermore, the isolation of multidrug-resistant bacterial strains from Tunisian coastlines proves the significant spread and circulation of antibiotic resistance caused by the massive use of antibiotics. In conclusion, we suggest intensive monitoring and cutting-edge wastewater treatment technologies to enhance seawater quality and preserve the biodiversity of aquatic life. Rapid detection techniques for the most important pathogenic microorganisms in seafood and seawater must be also developed to reduce human health risk. HIGHLIGHTS Monitoring the microbial quality of the Tunisian coast environment is crucial.; Wastewater discharge was the main cause of microbial pollution and the spread of multi-resistant strains.; Improvement of wastewater treatment procedure is highly recommended to reduce the pollutant loads to the sea.; More investigations should be conducted especially for viral and parasitic contamination.

First report of Tunisian coastal water contamination by protozoan parasites using mollusk bivalves as biological indicators

In order to establish seawater contamination by emerging protozoan parasites, we used qPCR to molecularly characterize and evaluate the parasitic burden of Giardia duodenalis, Cryptosporidium spp., Toxoplasma gondii, and Cyclospora cayetanensis in 1255 wild bivalve mollusks collected along the Tunisian coasts. T. gondii, G. duodenalis and C. cayetanensis were detected in 6.9% (99% CI = 1.6–12.2%) pools of Ruditapes decussatus. None of the samples were found positive to Cryptosporidium spp.; 6.6% pools of R. decussatus were positive for T. gondii Type I, 1.6% for G. duodenalis assemblage A, and 1.6% for the association T. gondii Type I/C. cayetanensis/G. duodenalis assemblage A. R. decussatus harbored up to 77500 oocysts/sample of T. gondii, up to 395 cysts/sample of G. duodenalis, and 526 oocysts/sample of C. cayetanensis. These results provide the first evidence that the Tunisian coasts are contaminated by zoonotic protozoan parasites that can constitute a direct or indirect risk for human health

Potential to produce brown mussel integrated to a net-cage fish farm in a Mediterranean bay

In this study, we investigated the potential exploitation of the brown mussel Perna perna (Linnaeus, 1758) in an aquaculture farm (Monastir Bay, Mediterranean Sea, Tunisia). The quality of seawater as well as performance indicators such as Condition Index, length, weight, growth and frequency distribution of the mussel were determined over an annual cycle; from July 2017 to August 2018. Interestingly, P. perna has an extended sexual cycle during the year with two main spawning periods, the first in spring and the second in autumn, when suspended matter and Chlorophyll a were at their maximum concentrations in seawater. Spat mussels and young mussels showed significant growth rates from 1 July 2017 to 31 October 2017. Adult mussels exhibited negative allometric growth and a modal size of 41 to 50 mm. Results showed that several potentially toxic microalgae species developed at low densities in this marine zone. By using Solid Phase Adsorption Toxins Tracker (SPATT); lipophilic toxins including Okadaic acid and yessotoxins were detected at low levels in seawater and may be involved in the positive LSTs (lipophilic shellfish toxins) mouse bioassays in P. perna during the autumn. No other toxins such as paralytic shellfish toxins or amnesic shellfish toxins nor pathogenic bacteria or viruses were detected in P. perna. Altogether, our results suggest that finfish farms in Monastir Bay could be suitable sites for farming P. perna