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Old 01/04/2016, 07:31 AM   #2509
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Gamma-proteobacteria, including vibrio, are common in marine sediments and often numerically dominant in the top centimeter or two of oxygenated sediments, where most saprophytic activity takes place -- benthic dinos would pretty much have to make friends with them to be benthic. Further, gamma- and epsilon-proteobacteria are the dominant sulfur oxidizing bacteria in marine sediments. Sulfur is the terminal electron receptor of choice for a great many anaerobes, and to give you an idea of how important that is, your preferred terminal electron receptor is oxygen... You breathe oxygen, they breathe sulfur.

Before O2 was made widely available by the evolution of cyanobacteria 2.7 billion years ago, bacteria got by for more than a billion years using other electron receptors like iron and nitrogen, but sulfur, which has five oxidation states ranging from +2 (sulfate) to -2 (sulfide), was the terminal electron receptor of choice for most bacteria, so much so that microbiologists sometimes refer to the ancient, anoxic biosphere as "the sulfur Earth". And much as plants turn CO2 back into O2, something has to close the sulfur cycle and turn sulfide back into sulfate. This happens all by itself if sulfide is exposed to oxygen, and capturing the energy released by the chemical reactions involved is an easy way for bacteria to make a living. Lots of them do it, or at least have the genes for it and can do it if the opportunity presents itself. Back before O2 was around and this ecological niche didn't yet exist, anaerobic sulfur oxidizers evolved to use sulfide as an electron donor and make SO4 using oxygen from CO2, but they're phototrophs and can only do this if there's light available. Sulfide accumulation can be highly problematic for anaerobic communities in deep water because it readily reacts with iron and hydrogen and can cause bacterial ecosystems to grind to a halt by locking up these key electron donors (...the word for this in Science is "euxinia" -- if you like to geek out on this stuff, search Google Scholar for Canfield ocean and "Canfield ocean", and if you're looking for a new apocalypse to worry about, search regular Google for Canfield ocean). Partnering with sulfur oxidizing bacteria seems like a good idea for benthic dinos, as they make a living, and possibly also make food for the dinos, off the waste products of anaerobic and facultatively anaerobic bacteria (sulfide) and the dinos (oxygen).

Partnering with cytophaga, on the other hand, looks downright suicidal for thecate dinoflagellates with cellulose armor like O. lenticularis or O. ovata, as the type species of the genus, Cytophaga hutchinsonii, can subsist on cellulose without any other source of organic carbon. Ostis no doubt have a biochemical trick or two up their sleeves to keep themselves from being eaten, and it may be that in copiotrophic sediments, cytophaga can be "bribed" with labile organic carbon because that's what they need to get at the tough stuff. But there are probably limits to whatever ostis are doing to protect themselves from cytophaga on their bacteria farms, as algicidal bacteria are known to play a key role in ending red tides and other algae blooms, and I've read about symbiotic bacteria turning on algae and actually releasing algicidal chemicals when they detect signs of weakness due to age or viral infection or lack of nutrients... Such highly opportunistic, "Curse your sudden but inevitable betrayal!" type partnerships may be common between algae and bacteria, and this could explain why dino blooms sometimes mysteriously go away when hobbyists decide to leave them alone and let nature take its course.

It's also interesting that cytophaga are apparently dominant in the bacterial community associated with ostis rather than alpha-proteobacteria, which are dominant in the pelagic dino holobiont, or gamma-pros, which are generally dominant among benthic saprophytic communities. I was unable to find any sort of broad-based information that might indicate what a "normal" population of bacteria in marine sediments on a healthy reef should look like, but FWIW I found a breakdown of bacterial DNA in sand from the Great Barrier Reef:

gamma-proteobacteria 29.4%
bacteroidetes/CFB group 20.4%
epsilon-proterobacteria 13.6%
planctomycetaceae 7.7%
alpha-proteobacteria 6.8%
verrucomicrobiaceae 6.8%
cyanobacteria 5.4%
acidobacteriaceae 2.7%

Contrast this diversity with the bacterial community associated with O. lenticularis...

Originally Posted by Bacteria Associated with Toxic Clonal Cultures of the Dinoflagellate Ostreopsis lenticularis
A library consisting of partial 16S rRNA sequences (~500 bp) was constructed from total bacterial DNA extracted from O. lenticularis (clones no. 302 and no. 303). A total of 127 sequences (62 sequences from clone no. 302 and 65 from clone no. 303) were generated and analyzed phylogenetically. ... Based on BLASTN comparisons, these clusters were grouped within two major bacterial clades that included: Proteobacteria (alpha and gamma) and the CFB complex. Previous studies have shown that bacterial communities associated with different toxic dinoflagellates are also restricted to these two bacterial phyla.
This collapse in bacterial biodiversity appears to be real because observations in NSW confirm that alpha-pros, gamma-pros, and Bacteroidetes are associated with dinos, but it could be an artifact of in vitro cultures... There was an experiment with small corals taken from the Red Sea, placed in 2 liter fishbowls, and maintained with water changes every three days, and the bacterial community in the coral mucus shifted to just proteobacteria (alphas, betas, and gammas) and Bacteroidetes/CFBs. As noted above, proteobacteria and bacteroidetes normally dominate marine heterotrophic bacterial communities, and the reason for this is that they share essentially the same biochemical system for quorum sensing. This doesn't mean they can all automatically talk to one another, but because the underlying machinery is the same, it's easy (as these things go) for them to acquire the ability to sense the presence of and even communicate with another species so they can coordinate their actions and cooperate in the organization and defense of the biofilms they live in -- or so they can detect and fight it out with another species competing for the same ecological niche.

Originally Posted by The effect of quorum-sensing blockers on the formation of marine microbial communities and larval attachment
The tested QS blockers caused changes in bacterial density and bacterial community structure... The groups most affected by QS blockers were Alphaproteobacteria, Gammaproteobacteria and the Cytophagales [which in the context of this paper from 2006 means Bacteroidetes]. ...

Although bacteria are unicellular organisms, they can control their growth and population densities. In order to achieve this, bacteria have evolved a regulatory mechanism named quorum sensing (QS) that consists of exuded info-chemicals that activate or de-activate target bacterial genes responsible for cell division and adhesion and, thus, control biofilm formation and composition. Biofilm formation, in turn, can control many processes at surfaces, for example the uptake or release of compounds by host organisms, bacterial virulence for the host, and biocorrosion. The process of QS is based on the production and release of low-molecular-weight signal molecules (often called autoinducers). The extracellular concentration of QS molecules reflects the population density of the producing organism. Bacteria can perceive and react to such signal molecules, allowing the whole cell population to initiate a concerted action once a critical population density has been reached. ...

A genomic database analysis has indicated that such interspecies communication possibly occurs throughout the Eubacteria. The QS-producing bacteria are highly diverse and fall within a large number of species among Alpha-, Beta- and Gammaproteobacteria which are dominant in tropical waters. In contrast to Gram-negative bacteria, Gram-positive bacteria exude peptides as signal molecules. QS signals produced by bacteria may also show transphyletic effects and induce algal spore attachment. ...

Many marine organisms, such as the red alga Delisea pulchra and the bacterium Aeromonas veronii, use QS blockers to control epibiotic biofilm formation. Delisea pulchra produces furanones that interfere with bacterial AHLs [a class of signaling molecules called N-acetyl homoserine lactones] and inhibit the growth of Gram-negative bacteria as well as the settlement of invertebrate larvae. At the same time, it is possible to propose that QS blockers can control larval settlement indirectly by regulating the microbial community structure of biofilms and the density of bacteria...
Remember those vibrio bacteria that make prawns glow in the dark? That's quorum sensing in action. The vibrio don't want to kill the prawns because other bacteria would take over during decomposition, so they've evolved to stop short of that and light up, instead, to make sick animals even easier prey.

Eukaryotes, including prawns, are able to eavesdrop on and participate in the quorum sensing conversations of some bacteria, allowing them to select for and interact with their obligate bacterial symbionts. Current science suggests that obligate symbiotic associations between a specific species of bacteria and a larger host organism like a dinoflagellate or coral polyp or fish or person are rare in the sense that host organisms do not select for their entire microbiome but only a handful of keystone species within it. Other bacteria associated with any particular organism may serve functionally as symbiotes in that they're rendering some biochemically important service for their host, but they can in fact be replaced with other species competing for the same niche. This plasticity in the microbiomes associated with host organisms is adaptive, like corals being able to swap out their zoox for a new symbiodinium species to adapt to warmer water.

The manipulation of specific QS and QQ ("quorum quenching") chemicals by host organisms allows them to establish required relationships with key bacterial symbiotes, and the selection of those particular bacteria is the foundation that defines the overall structure of the hosts' microbiomes -- symbiotes have a good thing going, and they don't want any pathogens to foul things up, so they only tolerate commensal bacteria that won't harm them or their host. There are also other mechanisms hosts use to influence the population of bacteria that grow on and in them, including an organism's immune system, of course, as well as chemical defenses that function within individual cells and tissue types, and structuring the overall mix of organic carbon they exude so as to give a competitive advantage to their preferred bacteria (...mother's milk is structured to do exactly this in the digestive tracts of babies, for example, and formula contains small amounts of exotic sugars in a comparatively ham-fisted effort to imitate this effect). But bacteria reproduce, and thus evolve, so much more quickly than corals and fish and people that these countermeasures would eventually, inevitably be beaten. The host's symbiotic and commensal bacteria are thus the keystone of the whole operation -- especially for reef-building stony corals, which seem to have no innate immune systems ( contrast, extracts of branching and soft corals have been shown to have antibacterial effects).

As a result, when the fishbowl corals were put back where they came from in the Red Sea, instead of being overwhelmed by opportunistic bacteria, their mucus bacteria populations returned to normal and matched other healthy corals in the area. Corals are constantly exposed to bacteria from the water column and the food they capture, and they (and every marine organism) solved the problem of living in bacteria soup by establishing a microbiome that selects for commensal bacteria. In fact, corals seem to be able to selectively attract certain types of bacteria from the water. For example, coral mucus effectively traps picocyanobacteria -- in recent years, scientists have become aware of a vast and diverse population of picoplankton eking out a living in the clear waters of the "nutrient desert" in the open ocean, and corals tap into this invisible nutrient pool by capturing super-tiny cyano that drifts onto reefs. This is apparently another adaptation corals have made to obtain nitrogen in the oligotrophic reef environment.

So if dinos exert selective pressures on the bacterial communities associated with them -- and in fact, that's something I would expect dinos to be particularly good at because, as noted, stealing DNA from bacteria is kinda their thing -- then the obvious question is whether ostis use their toxins or exude some other chemicals to shift the saprophytic bacteria population in the sand to favor cytophaga, or if a bloom begins by taking advantage of conditions that naturally favor the dominance of cytophaga ( does happen in the wild, but not often). From what I can determine, eutrophy generally favors the dominance of gamma-pros and flavobacteria among benthic saprophytes, presumably because flavos are geared towards consuming macromolecules made by green algae. If so, that would be good news for phyto dosers, as adding green phyto would be a selective pressure that wants to tilt the Bacteroidetes population in the sand from cytophaga to flavobacteria, which would not be good news for ostis.

There have been efforts to connect O. ovata blooms to eutrophic conditions, especially since they began to show up along the southern coast of Europe in the Mediterranean and Adriatic Seas -- like hobbyists, scientists generally seem to regard dinos simply as algae and want to tie them to certain nutrient conditions. However, nobody has been successful in identifying conditions that might trigger an ostreopsis bloom, and in fact the idea that osti blooms are associated with elevated nutrient levels was pretty well refuted by the documentation of a major O. ovata bloom in the shallow and generally nutrient-poor waters around a small, isolated, uninhabited group of islands in the equatorial mid-Atlantic.

Originally Posted by Ostreopsis cf. ovata (Dinophyta) bloom in an equatorial island of the Atlantic Ocean
The Archipelago of Saint Paul's Rocks consists of a remote group of ten small islands... Only the biggest island has low vegetation and the area is subjected to severe sea and wind conditions. The area provides shelter for many species of seabirds, fish, crustaceans as well as insects and is important as feeding and reproductive area for various migratory species. The waters in the area are oligotrophic but upwelling events caused by the interaction between oceanic currents and the submarine relief may happen. The region is considered strategic to the development of industrial fisheries, although there are recent reports of negative impacts of this activity (overfishing) in the area. Koening and Oliveira (2009) reported that dinoflagellates represent 82% of the total number of microphytoplankton species in the area and the cyanobacterium Trichodesmium thiebautii is distinguished by its frequency and dominance. ...

In the present study, a bloom of O. ovata is reported in an oceanic area where the only identifiable anthropogenic impact would be apparently the industrial fishing activity. ... As a comparison, along Rio de Janeiro, at the southeastern subtropical Brazilian coast, O. ovata has been found in bloom densities in an area subjected to coastal upwelling, distant from heavy freshwater discharge from rivers and not eutrophic. At other more eutrophic areas, subjected to anthropogenic impacts (such as treated sewage discharge), the species has not been found in bloom densities. ... The question raised is if O. ovata blooms are singular for not being associated to eutrophic conditions, in contrast to most other harmful species.

Moreover, studies with O. cf. ovata laboratory cultures have shown that the species develops aberrant cell shape when grown in full media (L2), what is reverted when cells are transferred to a less concentrated (L2/2) medium. This same pattern was observed in cultures of Ostreopsis siamensis when grown in GSe and f/2 medium. According to those authors, increased nitrate and phosphate concentrations impeded the growth of O. siamensis and caused aberrant cell shape. ...the massive abundance of O. ovata at Saint Paul's Rocks, located 1000 km away off the main continental landmass and not inhabited is, controversially, an indication that eutrophication is possibly not playing a part in stimulating blooms of this species.
Fun science fact: Trichodesmium thiebautii is a common species of diazotrophic cyanobacteria in both the Atlantic and Pacific Oceans that's known to be able to rapidly fix nitrogen. If you have cyano associated with a persistent bloom of O. ovata and access to a microscope, please take a look at your cyano and see if it could be tricho -- this might be an obligate association, or it might be O. ovata recruiting whatever species of cyano was handy.

I found it very interesting that O. ovata took over this isolated reef complex and wondered what Saint Paul's Rocks might have in common with our aquaria...

There isn't a lot of information on the reef ecology of the Archipelago of Saint Peter and Saint Paul, aka Saint Paul's Rocks, because it's one of the smallest and most isolated reefs in the world, being as it is way the hell out in the middle of the Atlantic Ocean. Geologically, the islands are unusual in that they're an exposed high point in the mid-oceanic ridge, and though officially a national park of Brazil, there are no regulations on fishing in the area, and the archipelago is regarded by marine biologists as a "paper park" -- a protected area on paper, but not in fact. The area has been heavily fished since the 1950s, so the local ecology has been trashed to the point where reef sharks are locally extinct (...the word for this in Science is "extirpation", incidentally). That is, the sharks' prey species were fished out, so the sharks starved -- in the 1970s, they were so numerous that scientists reported losing fish they caught for examination to hungry sharks. By the turn of the century, no more reef sharks, just the occasional pelagic specimen wandering in from the open ocean.

I recognize this phenomenon from reading Coral Reefs in the Microbial Seas a few years ago. The same pattern of events has been identified on reefs all over the world: overfishing depletes the population of fish on a reef; released from grazing pressure by the lack of herbivores, algae grows like crazy and takes over the reef; DOC released by algae triggers the growth of pathogenic bacteria that kill reef corals; along the way, sharks disappear because there aren't enough fish around to support a population of apex predators. However, the model does not predict a successional stage in which a dying reef is taken over by benthic dinos... What's so special about this tiny, rocky reef out in the middle of nowhere that 10 years after the sharks died off, 80% of the phyto was dinoflagellates and O. ovata owned the place?

Well, I'm thinking it's copiotrophy -- if eutrophy favors flavos, perhaps copiotrophy favors cytophaga (...or bacteroides, or whatever bacteria ostis are eating). This appears to be consistent with the sole identified environmental impact on Saint Paul's Rocks: "industrial fishing". Large fishing vessels nowadays are floating factories that can process and freeze tons of fish every day. This generates large volumes of waste -- offal, basically, as well as bycatch -- that of course is dumped into the sea. This waste is a food resource for seabirds and, perversely, fish. So the archipelago is probably occasionally contaminated by plumes of proteinaceous waste consisting of uneaten food and fish poo. Sound familiar? Plus, it crossed my mind that waste plumes from factory fishing vessels might be seeding the sands with dino-friendly bacteria in a sort of reverse Montireef Protocol...

And there was something else that jumped out at me:

Originally Posted by Ostreopsis cf. ovata (Dinophyta) bloom in an equatorial island of the Atlantic Ocean
The Saint Paul's Rocks is an oceanic area with a number of endemic species and low functional redundancy relative to coastal sites. As an example, herbivorous fishes such as acanthurids [tangs] and scarids [parrotfish], which are commonly found in tropical reef areas, are functionally absent there. This role is performed by abundant pomacentrids [damsels] and balistids [triggerfish].
The fact that the ecosystem of Saint Paul's Rocks is half-broken due to missing species is also a noteworthy parallel with our tanks (and our tanks will always have this problem, I expect -- no reefer in his right mind would want a bumphead parrotfish even if he had a DT big enough to support one, for example) but it caught my eye that triggerfish were called out as herbivores, as even the algae-eating, reef-safe trigs in the aquarium trade are pretty aggressive predators on small crustaceans like pods and shrimp. If triggerfish are especially abundant in the waters off Saint Paul's Rocks, grazing pressure from them might be holding down the pod population, which in turn would reduce the grazing pressure that should be holding down the dino population. And shrimp and benthic pods are detrivores, so a shortage of them could reduce the efficiency with which the reef sands process detritus -- think of it as the difference between a Shimek-compliant DSB and a DT SSB.

By the time a plume of waste from a factory fishing operation hit the reef, it would be diluted and heavily worked over by bacteria. Whatever settled on the reef would be largely recalcitrant, partially degraded, high molecular weight proteins.

Now have a look at this:

Originally Posted by Google Scholar
Gradients of coastal fish farm effluents and their effect on coral reef microbes
M Garren, S Smriga, F Azam - Environmental microbiology, 2008 - Wiley Online Library
... For example, Cytophaga gene sequences were associated with high-molecular-weight dissolved ... and colleagues (2005), other studies in the region found that benthic sediments near suspended ... libraries of different origin (ie coral, feces or water bacterial communities) (Table 4 ...
Cited by 34 Related articles All 4 versions Cite Save
Emphasis mine. A paper from 2008 is borderline but should be recent enough that the authors are referring to the modern, post-reorganization cytophaga genus, especially given that they're talking about gene sequences. However, that paper is behind a paywall... So close, yet so far!


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