Aquaculture is the fastest growing industry for food production in the world. Much research has focused on how to manage issues in aquaculture both economically and sustainably – one of these problems is disease control. Heavy use of antibiotics has caused the worldwide issues of: antibiotic resistance, environmental toxicity, aquatic pollution, and high-cost implications. Accordingly, there has been recent investigation into safer and more natural options of biological control – here enter the fungi! In previous studies, both marine fungi and sponges have been highlighted for their antimicrobial activity against fish pathogenic bacteria. Sponges hold a rich diversity of bioactive fungi in their tissues. Sponge-associated fungi produce unique bioactive secondary metabolites and many host-specific toxins. The study by Özkaya et al. (2017) investigated antibacterial activities of fungal isolates, that are associated with sponges, against some commonly occurring pathogens in aquaculture.
The study focused on four of the most well-known fish pathogenic bacteria that cause disease in aquaculture: Vibrio anguillarum, Yersinia ruckeri, Lactococcus garvieae, and Vagococcus salmonarum. V. anguillarum is the most common cause of disease outbreaks for fish and shellfish, causing vibriosis. Y. ruckeri is the agent responsible for the disease yersinoisis – it has caused major economic loss to the salmonid farming industry. L. garvieae is a major problem for a wide range of wild and cultured fish species – both marine and freshwater. Finally, V. salmoninarum is the cause of coldwater streptococcosis; this is an emerging disease for rainbow trout in the European Union which can cause up to 50% broodstock mortality.
The study investigated 70 strains of marine fungi, isolated from sponges, and used ethyl acetate extracts to screen against the four previously named pathogenic bacteria. Antibacterial assays were performed using the agar diffusion method. Authors also used the co-culture technique to test the production rates of novel bioactive (antibacterial) metabolites – they tested each fungal strain combined with a mixture of all target bacteria.
Results showed that a total of sixteen fungal isolates had antibacterial activity against at least one pathogen – all these isolates showed antimicrobial activity against V. salmoninarium. Additionally, three isolates had a strong inhibition of growth against all the tested pathogens, including Penicillum canescens and Aspergillus iizukae. P. canescens was the most active against all bacteria collectively, with an inhibition zone of >13mm. Whereas fungi A. iizukae had the strongest activity in the screening of mono-culture against L. garviae and V. Salmoninarum, with an inhibition zone of 30 – 35mm, respectively. The co-culture experiments found an induction of bioactivity in two isolates. A. iizukae gained broad-spectrum activity with high efficiency against test pathogens when fermented in co-culture conditions.
The study shows that fungi as a use of antibiotics is extremely promising. The antimicrobial activity of fungi varies greatly between differing properties such as: fungal strains, species of targeted pathogen, sponge host species, habitat salinity, seasonal variations, and an array of chemical and bio-physical parameters (there’s quite a lot of varying factors! But this is expected). The study also found that competition between fungi species was also an important factor – the production of secondary metabolites may initiate a defence or attack reaction by stimulating toxin synthesis. Further research is still required to find out the most effective conditions for the use of fungi for antibacterial control, but the benefits appear worth-while.
Overall, marine fungal metabolites can be a great alternative to commercially banned antibiotics. Marine fungi appear to be a potential source of eco-friendly and non-costly disease control against fish pathogenic bacteria in aquaculture.
Study of reference:
Özkaya, F.C., Peker, Z., Camas, M., Sazak Camas, A. and Altunok, M., 2017. Marine Fungi Against Aquaculture Pathogens and Induction of the Activity via Co‐Culture. CLEAN–Soil, Air, Water, 45(8), p.1700238.
This is a fascinating subject, and it's certainly good to see some promising results! This topic is certainly going to receive a lot of interest in the coming years, as antibiotic resistance becomes an even more pressing issue. I think it's also a good way of making fungal biology more relatable to the general public as well, bringing to light the prospects of them being useful to us, and so more engaging to the layperson.
ReplyDeleteI recently blogged about a fungal metabolites paper too, and some of the ideas presented in your blog were very interesting to compare to the paper I read. Especially with quite a different method used, both studies showed promise. https://2015-mbio322.blogspot.com/2019/01/new-year-new-prospects-for-bioactive.html
I wonder, are the sponges and their associated fungi likely to have been exposed to these pathogens in this quantity before? Presumably they'd be present in the environment, but in no where near the quantity as the aquaculture environment where they are an issue. So then perhaps with the co-culture, the metabolites produced against the pathogens would change over time as exposure is increased, becoming more or less effective in their antibacterial properties. This would be interesting to study: maybe it could lead to even more useful bioactive compounds.
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ReplyDeleteThis subject is trully intriguing! Antibiotic resistance is an expanding issue, as aquacultures continue to grow. There has also been some recent research done on the antibacterial activity of marine (micro)algae.
ReplyDeleteI think Caitlin made some fair points about the possible reactions of fungi to a pathogen exposure this high and also their potential adaptivity in a co-culture. I could also imagine that the antibacterial activity of fungi is species-specific, so probably different types of fungi would be needed for the various fish pathogens. It could also be really interesting to see a study done on a co-culture of fungi and algae with antimicrobial activity, and see if them co-habiting has synergistic or antagonistic effects.