Eutrophication Makes Toxic Cyanobacteria More Toxic

Nodularia spumigena are a planktonic bacteria and are also diazotrophic, meaning that these bacteria have specialised heterocyst’s for independent nitrogen fixation and can grow and bloom sometimes quite aggressively without the need for further sources of nitrogen. N.spumigena are known for their toxicity due to cacogenic effects whereby it causes inhibition of protein phosphates and in turn severely damages the liver tissue. It is these cyanobacteria in particular that have been of recent study by the University of Gothenburg, who found that these bacteria are favoring raised eutrophic levels that are currently occurring in the Baltic sea, this is thought that it may be occurring through an error in waste water management.

Waste water treatment  error is key to the eutrophication with in the seas as its allowing for a build up of phosphorus particles and lowering levels of nitrogen, two key factors allowing the toxic N.spumigena to thrive. Steps are needed  to be taken in order to manipulate these contaminants to reach  safer levels, as over fertilization of these harmful  bacteria will continue. The article from the university of Gothenburg suggests that there is different views on what is causing the blooms and that it has been suggested that it could be caused by either eutrophication,  the excess of nutrients in the water driven their by man in the forms of domestic and industrial waste, or merely natural effects such as rainfall and river run off, but other scientist believe it is a process that has been occurring for many years and is part of a natural cycle.

Either way I believe that the article demonstrates that higher levels of nutrients within the water column, whether it be human driven or a natural occurrence, are causing significant problems with greater knock on effects, which if monitored closely can reduce such abundant blooms from such toxic bacteria as N. Spumigena. With greater knowledge of these natural pollutants science can help to reduce such problems as the nodularin toxins.

University of Gothenburg. "Eutrophication makes toxic cyanobacteria more toxic." ScienceDaily, 9 Dec. 2010. Web. 10 Oct. 2012.

Distribution of Roseobacter RCA and SAR11 lineages in the North Sea and characteristics of an abundant RCA isolate

The SAR11 clade and roseobacter clade are the two most abundant clades in the marine environment, with almost 25% falling into the SAR11 clade and slightly less falling into the roseobacter clade (Munn, 2012).With quantities this high they must a large impact on their ecosystems, therefore research into them is highly important.

Researchers can begin to understand the effect they have by understanding the needs for these species to survive, in terms of nutrients, temperature etc. Currently not much is known in this field currently. Giebel et al (2010)  investigated the context of environmental and biological properties of the North sea and compared them to the abundance of roseobacter RCA and SAR11 linages. The properties they measured included biogeochemical and microbial parameters: concentrations of chlorophyll a and phaeopigments, suspended particulate matter, particulate organic matter and particulate organic carbon. They also determined the rates of bacterial production and turnover rates of dissolved free amino acids.

Roseobacter clade affiliated abundance was positively correlated with phaeopigments, chlorophyll a, dissolved and particulate organic carbon, turnover rates of dissolved free amino acids, temperature, and negatively correlated with salinity. The last finding is interesting considering previous papers written: members of the Roseobacter clade do not occur in freshwater, demonstrating either a salt requirement or tolerance  (Buchan et al, 2005). This finding seems to suggest that high salt levels are actually detrimental to the bacteria.

This contradiction could mean that Buchan et al’s theory is false, or it could demonstrate the difficulty in describing such a large group. Buchan et al commented on the clade in general, whereas Giebel et al investigated specifically the RCA linage. It is possible that this linage has a lower optimum level of salt, and others have a higher optimum. 

Results from this study were gained using a dilution method, which is more accurate than culturing on agar plates (Munn, 2012). It consisted of diluting samples followed by 109 days incubation at 15oC, before performing PCR. As this study carried out experiments rather than just posing a theory, this is a more reliable conclusion than Buchan et al stated.

The fact that Roseobacter clade is so large could mean that it is impossible to describe the physiological properties of all species under this genus as the same, therefore it is expected that research will provide varying results depending on the specific species analysed. Although, a phylogenetic group contains similar genetic information, and members of the same group should act in a similar way. This highlights a problem with the classification system and the difficulty in describing organisms.
Another interesting finding was  that the SAR11 clade and the Roseobacter group seem to exhibit contrasting lifestyles. This has links to ecology in that it demonstrates how two organisms occupy completely different niches and still be extremely successful.

Future research should focus more a single or limited operational taxonomic units of the roseabacter clade in order to make clear comparisons and understand how variation occurs within the group. It is possible that members that have been described under this title should be reclassified.

Giebel HA, Kalhoefer D, Lemke A, Thole S, Gahl-Janssen R, Simon M, Brinkhoff T (2010) Distribution of Roseobacter RCA and SAR11 lineages in the North Sea and characteristics of an abundant RCA isolate, ISME J 5: 8-19

http://www.nature.com/ismej/journal/v5/n1/full/ismej201087a.html

Evidence from the Vibrio's as to the effects that ocean warming has on the prokaryotic community:

With the ever present threat of global warming happening as we speak (and an expectation that ocean temperatures will increase by a few degrees during this century) it is of interest to everyone in the biological community as to what the effect of this climate change will have on organisms from the largest mammals to the smallest microbes. This study looked at microbes, the vibrio genus to be specific, the reason this is significant is due to the fact that most of todays diseases and illnesses are down to bacteria and prokaryotes so it will be interesting to see what is going to happen with them in this current climate, will illnesses due to vibrio's increase or decrease?

There is some published material regarding the effect that long term warming of the oceans has on eukaryotic organisms, but there is nothing looking at prokaryotes and the effect on their diversity and abundance, the possible reasons for this are due to the fact that in many peoples eyes prokaryotes due to the fact they belong to a lower trophic level are less sensitive to environmental change and therefore arent studied as much.

Vezzulli et al (2012) performed the first published study looking at prokaryotes and their reaction to this ocean temperature increase, the study lasted 44 years, from 1961 to 2005, during this time using a CPR (continuous plankton recorder) 55 samples were collected from 2 areas located off the Rhine & Humber estuaries in the North Sea, the outer limit of these sites being within 50 nautical miles from the North Sea coast. The way the recorder works is by collecting phyto and zooplankton and any other prokaryotes that get caught in its 270 micrometre mesh which collects everything from seven metres and above (so collects from the surface layer as the recorder is dragged behind any commercial waterborne vessel), these collections then can be analysed in numerous ways back in laboratories. One type of analysis that was done was the PCR and then pyrosequencing which gave the genomes and overall identity of the prokaryotes collected.  All of the collections were done in August of the years they were collected.

The results from this study showed that with this increase in sea temperature during the last half century, there has also been a dramatic increase in the abundance of Vibrio bacteria. This includes the well known and studied Vibrio Cholerae. With this increase in abundance there was also a noticeable increase in dominance of the whole genus. This observed increase in temperature explained 45% of the vibrio's variance, with environmental variables explaining the rest. With this increase in abundance there was also a noted increase in diseases related to bathing in these waters. So it was concluded that with this increase in temperature there is an increase in the vibrio genus and their diseases.

I reviewed this article because it is one of a kind, as there is barely any information on prokaryotic alterations in recent years and it will hopefully provide a back bone for this type of study and eventually cause more studies to be done in the future.

Source:

Luigi Vezzulli et al. (2012) - Long Term Effects of ocean warming on the prokaryotic community: evidence from the vibrios.

The energy–diversity relationship of complex bacterial communities in Arctic deep-sea sediments

Several explanations have been proposed for the relationship between diversity and bio available energy, for example, effects of population size, competition and evolutionary, environmental or resource heterogeneity. However, scientists have only just begun to understand the relationship between abundance, diversity and biomass in complex microbial communities. With the advancement of technology, the fingerprinting methods needed to determine the relationships in complex bacterial communities have been discovered. Unscrambling the relationships between environmental conditions, organism diversity and ecosystem functions will help us understand the effects of global change.

Continental slopes are one of the best places to study productivity-diversity relationships as there are relatively defined variations in energy availability with water depth. Communities living in the benthic zone depend on the sedimentation of phytodetritus from the productive surface waters; however the detritus flux decreases with increasing water depth. Phytodetritus flux to the deep sea affects the abundance, biomass and biodiversity of benthic organisms. The input of phytodetritus to deep-sea sediments influences bacterial biomass and activity, though it has not been shown that energy availability at the seafloor and bacterial diversity patterns have been linked.

This is first study that has tested the bacterial energy-diversity relationships for complex natural communities in the Arctic seafloor on a defined, regional scale. Depths were chosen to cover a range of phytodetritus fluxes, and representing mesotrophic to olgiotrophic deep-sea setting.

Community structure and functions were shown to be highly related to each other and with energy availability. These structures and functions include enzymatic activity, oxygen consumption and carbon remineralisation rates. In oligotrophic regions, bacterial richness increased with an increasing sediment pigment content, which means a positive energy-diversity relationship is present. However, richness plateaued when mesotrophic sites were included; meaning that bacterial communities and other benthic fauna may be structured by similar mechanisms. Dominant bacterial taxa showed positive or negative relationships with phtodetritus input. Individual taxa had very different responses to changes in pytodetritus input. This also suggests that various ecological strategies among bacterial groups along the energy gradient. With regards to the environment, it was found that any environmental changes affecting primary productivity and particle export will cause changes in the bacterial community structure and function in the Arctic. This could affect key processes such as carbon cycling.  

The authors in this report have successfully identified an energy-diversity relationship of complex bacterial communities in Arctic deep-sea sediment. This study also offers an ecological baseline against which ecosystem shifts can be assessed in the future.

Christina Bienhold, Antje Boetius and Alban Ramette

The ISME Journal (2012) 6, 724–732; doi:10.1038/ismej.2011.140; published online 10 November 2011

http://www.nature.com/ismej/journal/v6/n4/full/ismej2011140a.html

Cytometric analysis identifying phytoplankton based on their size and chlorophyll ratios

This analysis technique of flow cytometry, in the past, has been used in immunology. The difficulty in the process was the need for the cells to remain in suspension in aqueous solution. The application of flow cytometry to marine phytoplankton requires little effort due to their natural abundance and suspension in water. The process requires a volume of sampled sea water which is then passed down a small tube where it flows past a beam of light from a diode-pumped solid state laser. This process does not kill any cells as the data is gathered from quantifying both the light fluoresced and scattered by the plankton. The detection of the scattered light provides the size of the microbe, the fluorescence detecting the number and ratios of different pigments of chlorophyll.

To do this accurately for marine phytoplankton they modified the analysis to cope with the large range of plankton size (0.3µm to 100µm) while improving the resolution. The extra modifications include; reducing the amount of initial light while increasing the magnification of the detection system, introducing extra lenses which the light pass through (one for focusing the light, another angled to reduce background noise), and finally using multiple detectors.

To distinguish between populations of phytoplankton within a sample, the fluorescence is measured at two different wavelengths which are then plotted on a bivariate plot. Distinct patches of fluorescence can then be identified as separate populations. A high discrimination between species is obtained due to the unique ratios of pigments like carotenoids, chlorophyll a and b.

The authors illustrate how adaptable the technique is by including data obtained by aerobic anoxygenic phototrophs using bacteriochlorophyll. They also point out the use of the technique in detecting quantities of calcification in coccolithophores, demonstrating the wide variety of ways in which flow cytometry can be used in the marine environment. They also point out this could also be a used as a starting point to further genomic analyses like FISH.

Using flow cytometry could also have the potential to build an accurate picture of the dynamic between photosynthetically active species throughout a year. The limitation to the technique is in the acquisition of a ‘bank of information’ to infer species on the bivariate plots.

Petersen TW., Harrison CB., Horner DN., van den Engh G. (2012) Flow cytometric characterization of marine microbes. Methods. 57 (3), 350-358.

Bacteriovorax VS Vibrio: Predator-prey interactions at the microscopic scale

The importance of predator-prey interactions is well established for most macroscopic organisms; however, only a few studies have looked at the influence that bacterial prey has on the community structure of its predator. The most studied bacterial obligate predators are the Bdellovibrio and like organisms (BALOs), which include several bacterial genera. BALOs prey on many gram negative bacteria, serving as both a food source and a growth and multiplication chamber. 

This study focused on the predator Bacteriovorax, a group of BALOs ubiquitous in the salt-water environment. In fact, Chen et al. wanted to investigate how the community structure of Bacteriovorax varies in response to two different preys, Vibrio vulnificus and Vibrio parahaemolyticus. Laboratory microcosms, containing water samples from different locations and a suspension of either V. vulnificus or V. parahaemolyticus, were used to monitor the prey abundance and the Bacteriovorax composition. However, since Bacteriovorax require the presence of their prey to be able to grow and to be cultured, techniques involving pure cultures cannot be used. Instead, the comparative analysis of 16 rRNA sequences has been found useful in the identification and detection of specific Bacteriovorax phylogenetic clusters or operational taxonomic units (OTUs). 

In each case the addition of prey resulted in a thousand fold increase of Bacteriovorax. However, the predator composition varied significantly depending on the prey present in the sample: the predominant Bacteriovorax OTU’s in the V. vulnificus sample were Cluster IX and X, whereas no single OTU dominated in the V. parahaemolyticus sample, where a high diversity of OTUs was observed. These results were narrowed down in a further experiment, where prey abundance (V. vulnificus or V. parahaemolyticus) was monitored in presence of either Cluster IX or Cluster IV Bacteriovorax. Chen et al. showed that Cluster IX preyed on both species, whereas predation of Cluster IV was found significantly higher for V. parahaemolyticus than for V. vulnificus. It was deduced that Cluster IX has the properties of a specialist as exclusive efficient predator on V. vulnificus as well as acting as generalist for having similar feeding efficiency on other prey such as V. parahaemolyticus, which overall makes Cluster IX qualify as versatilist. 

Chen et al. have showed successfully that predator-prey interactions and the resulting selective pressures shape community structure and diversity even at a microbial scale. Furthermore, they propose that more studies should aim to characterise the predatory patterns (specialist, generalist, versatilist) of bacterial predator for “a greater comprehension and appreciation for the diversity of predation among all organisms”.  However, although I appreciate that this study is one of the first in this field, I question the applicability of their findings in the natural environment, where the presence of numerous different prey species, physical parameters such as temperature and light availability, and predation on BALOs themselves will most certainly limit the predictability of ecosystem changes considerably. Therefor further research, notably with a wider range of prey species, is necessary to get a more general picture of the predatory patterns in Bacteriovorax.

Chen, H., Athar, R., Zheng, G., Williams, H.N., 2011. Prey bacteria shape the community structure of their predators. The ISME journal, 5(8), pp.1314–1322.
Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3146273/pdf/ismej20114a.pdf

Response of microbial communities to the Deepwater Horizon oil spill

Oil spills occur naturally and frequently in the Gulf of Mexico, but never on the scale of the 2010 Deepwater Horizon oil spill which released approximately 4.9 million barrels of oil into the ocean over a period in the region of 3 months with an oil plume at a depth of ~1000-1300m. This deep sea oil plume contained gaseous as well as non-gaseous components including saturated hydrocarbons, aromatic hydrocarbons and polar compounds. The composition of the microbial communities found at the site of the plume has previously been studied, but there was no information about which microorganisms were active or which functional genes were expressed in the plume. Mason et al. (2012) aimed to determine this by analysing sequenced total RNA metatranscriptomically and the functional gene repertoire from metagenomic samples. One proximal sample (1.5km from the wellhead) and one distal sample (11km from the wellhead) were taken as well as one uncontaminated sample from plume depth (40km from the wellhead), in which no hydrocarbons were detected, at the end of May 2010.

Plume samples had a lower microbial diversity with a dominance of Oceanospirillales not seen in the uncontaminated sample (>60% and 5% respectively, when analyzed metagenomically). This bloom of Oceanospirillales coincided with an increase in bacterial cell densities by 2 orders of magnitude. Further to this, it was found that dominant members of the community were also active, with a relative abundance of transcripts of 46% in the proximal site and 69% in the distal site.

Hydrocarbon degradation genes were found to have a higher abundance in the plume and the entire pathway for degradation of n-alkanes as well as the nearly complete pathway for cyclohexane degradation were both present and abundant in the plume samples, which suggests that the plume was enriched with communities with the capacity for degradation of alkanes. This was likely carried out anaerobically as oxygen was not significantly depleted inside of the plume. Comparison with other studies shows a shift in the natural microbial community composition over time with a succession of bacteria from a community dominated by Oceanospirillales to domination by Colwellia and Cycloclasticus and eventually to methylotrophic bacteria.  Genes for chemotaxis proteins, flagella, pili and signal transduction were also found, providing evidence that bacterial cells may have been actively attracted to and interacting with the oil plume and this may explain how the shifts in community structure occurred.

I believe that the authors have successfully confirmed the views portrayed by many other scientists and studies in demonstrating that the bacteria naturally present in the oceans play an important role in the cleanup of large scale oil spills. This has been proven previously however this study took the approach of looking at the active organisms and gene transcripts rather than the process itself.

Mason, O., Hazen, T., Borglin, S., Chain, P., Dubinsky, P., Fortney, J., Han, J. et al. (2012) Metagenome, metatranscriptome and single-cell sequencing reveal microbial response to Deepwater Horizon oil spill. The ISME Journal. 6, 1715-1727
http://www.nature.com/ismej/journal/v6/n9/pdf/ismej201259a.pdf