Microplastics – good for marine bacteria, bad for marine ecosystem functioning?

 Plastic pollution in our oceans is an ever looming threat to biodiversity within marine environments. Not only this but it has been found with increasing frequency in shellfish and so it is also becoming an issue for human health. Because of the abundance of plastic in the oceans it is important to understand how plastic interacts with the marine environment.

A study conducted by Galgani et al. in 2018 aimed to look at how polystyrene microplastics interacted with the marine environment and in particular with dissolved organic matter (DOM). Microcosms were set up containing DOM, bacteria and half contained polystyrene microplastics. Dom was measured along with the absorption of chromophoric dissolved organic matter (CDOM) which is a photo-reactive form of DOM; CDOM is produced naturally by marine bacteria by altering pre-existing DOM substrates.

It was found that in the presence of polystyrene microplastics, more CDOM was produced. This may be because the polystyrene acted as a good substrate for the formation of biofilms which would lead to an increase in bacterial activity. However, an increase in CDOM may have negative effects on the upper layers of the water column in oceans as CDOM absorbs light so it may change light conditions. In order to really assess the impacts of marine microplastic pollution pertaining to polystyrene, the effects of increased CDOM should be measured on photosynthetic marine organisms.

 

Galgani, L., Engel, A., Rossi, C., Donati, A., & Loiselle, S. A. (2018). Polystyrene microplastics increase microbial release of marine Chromophoric Dissolved Organic Matter in microcosm experiments. Scientific Reports, 8(1)

Fish guts - the key to preventing disease?

It has long been known that the gut microbiota of fish can greatly affect their susceptibility to certain pathogens. Many aquaculture farms are now opting to use probiotics and prebiotics to boost the gut microbiota of farmed fish to prevent disease rather than using antibiotics which can lead to antibiotic resistance arising within aquaculture systems.

Tran et al. conducted a study in 2018 with the aim of assessing whether there was a difference in the gut microbiota of grass carp (Ctenopharyngodon idellus) infected with an intestinal disease and that of healthy grass carp. These changes in gut microbiota were assessed through NGS-based 16S – rRNA sequencing.

It was found that there was a significant difference in the structures of microbial communities within the guts of healthy and diseased carp with members of the following genera being greatly increased in diseased fish: Dechloromonas, Methylocaldum, Planctomyces, Rhodobacter, Caulobacter, Flavobacterium, and Pseudomonas.

This study manged to shed light on the microbes associated with enteritis in carp which is a common disease found in fish in aquaculture operations that can frequently lead to death so this study has wide ranging implications for the early detection and prevention of this disease in aquaculture. However, quite a small group of fish were sampled, only 16, and the sampling was skewed towards diseased fish so by having more comprehensive and even sampling it may make the results more reliable and the results from the two groups more comparable.

Tran, N. T., Zhang, J., Xiong, F., Wang, G.-T., Li, W.-X., & Wu, S.-G. (2018). Altered gut microbiota associated with intestinal disease in grass carp (Ctenopharyngodon idellus). World Journal of Microbiology and Biotechnology, 34(6)

Absorbed in the search; antimicrobial revelations from marine sponge ecosystems

Strains of bacteria are becoming more resistant to antibiotics; with many scientists warning our drugs could soon become ineffective against even the most basic of infections. On top of this the risk of viral epidemics has been increasing, many solutions are being explored and scientists are looking to marine fungi for potential sources of new antibiotic and antiviral drugs.

Bovio et al (2019) used PCR to identify marine fungi isolated from Atlantic sponge Grantia compressa, OSMAC revealed metabolic diversity in the isolate-Eurotium chevalieri MUT 2316, from which compounds were extracted, isolated, and characterised. Of these, Dihydroauroglaucin was shown to inhibit the replication of influenza A, with another compound-Isodihydroauroglaucin showing antibacterial activity against Escherichia coli ATCC 25922.

This paper is a good first step into looking at alternate sources of antibiotics and antiviral drugs, showing compounds that potentially could be used in the future. However long clinical trials would still be required before any of these compounds are usable. This paper is well written however some of the graphs are convoluted and hard to follow. Future research is needed into these novel compounds and their effects on additional pathogens to the ten presented here.

Bovio, E.; Garzoli, L.; Poli, A.; Luganini, A.; Villa, P.; Musumeci, R.; McCormack, G.P.; Cocuzza, C.E.; Gribaudo, G.; Mehiri, M.; Varese, G.C. Marine Fungi from the Sponge Grantia compressa: Biodiversity, Chemodiversity, and Biotechnological Potential. Mar. Drugs 2019, 17, 220.
https://www.mdpi.com/1660-3397/17/4/220

Are Microplastics Toxic to Microbes?

The effects of microplastics on the marine environment is a globally recognised issue. In this investigation the researchers wanted to test standard endpoints given by International Standard Organization (ISO) protocols. Using concentrations of microplastics well above environmentally relevant concentrations (25mg/L) they showed that there were no growth rate or toxicity effects of microplastics on the bacteria Vibrio fischeri and the diatom Phaeodactylum tricornutum.

Unfortunately, there were some inconsistencies in this investigation that are worth noting. The light to dark periods of the experiment are inconsistent ranging form 12-12h light dark to 16-8h light dark period. The mixing tourniquets and bottle types varied with treatment. These inconstancies and the lack of formatting make this a difficult paper to read. It is also strange that microplastics that are almost the size of or larger than the bacteria or algae used are being considered toxins. It is likely that chemicals on the surface of these plastics are more relevant.

Microplastics may not pose a threat to microbes in the ocean and more sensitive endpoints might need to be made for future investigation as highlighted in the study. I think a different approach to this problem would be more effective.

Gambardella, C., Piazza, V., Albentosa, M., Bebianno, M. J., Cardoso, C., Faimali, M., ... & Sendra, M. (2019). Microplastics do not affect standard ecotoxicological endpoints in marine unicellular organisms. Marine Pollution Bulletin, 143, 140-143.

10,000 marine fungi species waiting to be discovered!

This paper discusses the diversity of marine fungi. In the last 60 years, the number of identified marine fungi species has been multiplied by 5, and species are still being found on various substrata and unexplored habitats (particularly in the tropics). Various guesses on the number of marine fungi species are thought to be a gross underestimate, considering there are still unidentified species, endophytic and cryptic taxa. This review contains several fungal groups that have been poorly surveyed and therefore may be a potential source of more undiscovered marine species. Accounting for the potential sources, the number of marine fungi may in fact exceed 10,000 taxa.

The way that this paper was written made it difficult to comprehend in parts. Some of the sentence structure was hard to follow and other parts seemed to have no flow or direction, making for very wordy sentences that actually don’t say too much. I also found the tables to be a bit confusing, which they could have easily amended by using lined rows. Otherwise, an interesting review on marine fungi diversity and an eye-opening reminder of how little we truly know about marine microbiology.

Reference: Jones, E. (2011). Are there more marine fungi to be described?. Botanica Marina, 54(4).

Does aquaculture turn your stomach? Fish too!

This study focuses on the intestinal microbiota of the fine flounder (Paralichtys adspersus), a flatfish of commercial interest that is native to the Chilean coast. Intestinal microbiota is involved in a wide range of internal processes, such as modulating the immune system and providing nutrition. The societal value of the fine flounder has encouraged the development of aquaculture activities and stock enhancement, making it a species of interest when exploring . Knowledge of microbiota may aid in improving the cultivation of this species and so this study aimed to evaluate the intestinal microbiota community in farmed versus wild fishes.

Contents from the intestines of wild and reared fish were collected and DNA was extracted and then the V3-region of 16S rRNA was PCR amplified and sequenced using the Ion Torrent platform. The compositions of microbiota found in each group of specimens showed important distinctions between reared fish and wild fish. In wild flounder, the most abundant phylum was Proteobacteria which was found in far lower abundances in the reared flounder. Contrastingly, in the reared flounder, the most abundant phylum was Firmicutes, which was much less common in the wild flounder.

A total of four genera were identified between the two conditions and Bacillus and Pseudomonas being highly represented in the reared flounder and Athrobacter and Psychrobacter being highly represented in the wild flounder. These results show that, though in both cases, metabolic pathways indicated that the microbiota compositions found would have beneficial effects for the host, but wild flounder showed more remarkable pathways.

I personally found this paper to be very interesting, perhaps because it feels very current and important. There are mixed opinions on various aspects of aquaculture, such as the ethical treatment of livestock and thus the quality of the product, and the implications to the immediate and extended environment. This paper is one of the only studies I have come across where the actual individual organisms are assessed for the impact of aquaculture rather than looking at the bigger picture, showing that the effects of this type of agricultural practice has impacts on all scales. The only criticism I have is that it tends to get a little repetitive in parts. 

Reference: Ramírez, C. and Romero, J. (2017). Fine Flounder (Paralichthys adspersus) Microbiome Showed Important Differences between Wild and Reared Specimens. Frontiers in Microbiology, 08.

Synechoccocus and Cyanophage control phytoplankton?

This study focuses on unicellular cyanobacteria of the genus Synechococcus and its contribution to primary productivity in the oceans. The main findings support the hypothesis that a virus infection can play a substantial role in determining success of different Synechococcus genotypes and, in extension, seasonal succession.

The study took place in the Gulf of Aqaba, Red Sea, where nutrients levels are low. Here they observed a succession of Synechococcus genotypes over an annual cycle. Restriction fragment length polymorphism analysis of a 4403‐ bp rpoC1 gene fragment showed that there were large changes in genetic diversity. The abundance of co-occurring cyanophage capable of infecting marine Synechococcus was contingent on plaque assays, and their genetic diversity was determined by denaturing gradient gel electrophoresis analysis of a 118‐bp g20 gene fragment.

The results provide evidence that states both abundance and genetic diversity of cyanophage covaried with that of Synechococcus. Using multivariate statistical analyses, this indicated a significant relationship between cyanophage assemblage structure and that of Synechoccocus. These observations ring true to the ideology that cyanophage infection is a major defining factor in picophytoplankton succession.

This paper was very informative but I found that whilst reading it, I was having to research certain terms or methods used in order to understand. Although it is interesting and coherent, I would have appreciated a bit more explanation and descriptions of methods. Contrastingly, the figures were simple and clear which was useful.

Reference: Muhling, M., Fuller, N., Millard, A., Somerfield, P., Marie, D., Wilson, W., Scanlan, D., Post, A., Joint, I. and Mann, N. (2005). Genetic diversity of marine Synechococcus and co-occurring cyanophage communities: evidence for viral control of phytoplankton. Environmental Microbiology, 7(4), pp.499-508.