Posts Tagged 'prokaryotes'

Environmental stability impacts the differential sensitivity of marine microbiomes to increases in temperature and acidity

Ambient conditions shape microbiome responses to both short- and long-duration environment changes through processes including physiological acclimation, compositional shifts, and evolution. Thus, we predict that microbial communities inhabiting locations with larger diel, episodic, and annual variability in temperature and pH should be less sensitive to shifts in these climate-change factors. To test this hypothesis, we compared responses of surface ocean microbes from more variable (nearshore) and more constant (offshore) sites to short-term factorial warming (+3 °C) and/or acidification (pH −0.3). In all cases, warming alone significantly altered microbial community composition, while acidification had a minor influence. Compared with nearshore microbes, warmed offshore microbiomes exhibited larger changes in community composition, phylotype abundances, respiration rates, and metatranscriptomes, suggesting increased sensitivity of microbes from the less-variable environment. Moreover, while warming increased respiration rates, offshore metatranscriptomes yielded evidence of thermal stress responses in protein synthesis, heat shock proteins, and regulation. Future oceans with warmer waters may enhance overall metabolic and biogeochemical rates, but they will host altered microbial communities, especially in relatively thermally stable regions of the oceans.

Continue reading ‘Environmental stability impacts the differential sensitivity of marine microbiomes to increases in temperature and acidity’

Microbial ecosystem and anthropogenic impacts

Oceans are the most vulnerable sites for anthropogenic waste from domestic as well as industrial origin. Usually, marine ecosystems are exposed to most anthropogenic stressors ranging from sewage disposal to nuclear waste contaminants. Most recent threats to marine ecosystems are ocean warming and ocean acidification (related to anthropogenic emission of CO2), oil (tarball), and (micro) plastic contamination, which is proved to have a devastating impact on the marine ecosystem. Microbes are abundantly present in marine ecosystems playing essential roles in ecosystem productivity and biogeochemistry. Generally, microbial communities are the initial responders of these stressors. Altered microbial communities in response to these stressors can, in turn, have adverse impact on the marine ecosystem and later on humans. In this review, we highlight the effect of oil pollution, microplastics, and increased CO2 on the marine microbial ecosystem. The information on the impacts of such stressors on microbial communities will be valuable to formulate appropriate remediation approaches for future use.

Continue reading ‘Microbial ecosystem and anthropogenic impacts’

Effects of ocean acidification on Antarctic microbial communities

Antarctic waters are amongst the most vulnerable in the world to ocean acidification due to their cold temperatures, naturally low levels of calcium carbonate and upwelling that brings deep CO2-rich waters to the surface. A meta-analysis demonstrated groups of Antarctic marine biota in waters south of 60!S have a range of tolerances to ocean acidification. Invertebrates and phytoplankton showed negative effects above 500 μatm and 1000 μatm CO2 respectively, while bacteria appear tolerant to elevated CO2. Phytoplankton studied as part of a natural microbial community were found to be more
sensitive than those studied as a single species in culture. This highlights the importance of community and ecosystem level studies, which incorporate the interaction and competition among species and trophic levels, to accurately assess the effects of ocean acidification on the Antarctic ecosystem.

Antarctic marine microbes (comprising phytoplankton, protozoa and bacteria) drive ocean productivity, nutrient cycling and mediate trophodynamics and the biological pump. While they appear vulnerable to changes in ocean chemistry, little is known about the nature and magnitude of their responses to ocean acidification, especially for natural communities. To address this lack of information, a six level, dose-response ocean acidification experiment was conducted in Prydz Bay, East Antarctica, using 650 L incubation tanks (minicosms). The minicosms were filled with Antarctic nearshore water and adjusted to a gradient of carbon dioxide (CO2) from 343 to 1641 μatm. Microscopy
and phylogenetic marker gene sequence analysis found the microbial community
composition altered at CO2 levels above approximately 1000 μatm. The CO2-
induced responses of microeukaryotes (>20 μm) and nanoeukaryotes (2 to 20 μm) were taxon-specific. For diatoms the response of taxa was related to cell size with micro-sized diatoms (>20 μm) increasing in abundance with moderate CO2 (506 to 634 μatm), while above this level their abundance declined. In contrast, nano-size diatoms (<20 μm) tolerated elevated CO2. Like large diatoms, Phaeocystis antarctica increased in abundance between 343 to 634 μatm CO2 but fell at higher levels. 18S and 16S rDNA sequencing showed that picoeukaryotic and prokaryotic composition was unaffected by CO2, despite having higher abundances at CO2 levels !634 μatm. This was likely due to the lower abundance of heterotrophic nanoflagellates at CO2 levels exceeding 953 μatm, which reduced the top-down control of their pico- and nanoplanktonic prey. As a result of the differences in the tolerance of individual taxa/size categories, CO2 caused a
significant change in the microbial community structure to one dominated by nano-sized diatoms, picoeukaryotes and prokaryotes.

Based on the CO2-induced changes in the microbial community, modelling was performed to investigate the future effects of different levels of elevated CO2 on the structure and function of microbial communities in Antarctic coastal systems. These models indicate CO2 levels predicted toward the end of the century under a “business as usual scenario” elicit changes in microbial composition, significantly altering trophodynamic pathways, reducing energy transfer to higher trophic levels and favouring respiration of carbon within the microbial loop. Such responses would alter elemental cycles, jeopardise the productivity that underpins the wealth and diversity of life for which Antarctica is renowned. In addition, it would reduce carbon sequestration in coastal Antarctic waters thereby having a positive feedback on global climate change.

Continue reading ‘Effects of ocean acidification on Antarctic microbial communities’

Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove


•Combined occurrence of hypoxia, acidification and nutrients increased biofilm bacterial diversity and richness

•Elevated nutrients, and depleted oxygen and pH levels resulted in different bacterial community composition

•Higher abundance of Flavobacteriales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales

•Suggests the identities of bacterial groups affected under the ocean trend of pollution, deoxygenation and acidification


Anthropogenic nutrient enrichment results in hypoxia, ocean acidification and elevated nutrients (HOAN) in coastal environments throughout the world. Here, we examined the composition of biofilm bacterial communities from a nutrient-excessive fish farm with low dissolved oxygen (DO) and pH levels using 16S rRNA gene sequencing. HOAN was accompanied by higher bacterial diversity and richness, and resulted in an altered community composition than the control site. HOAN resulted in more Flavobacteriales, Rhizobiales, Epsilonproteobacteria and Vibrionales, but less Oceanospirillales and Alteromonadales. Photobacterium sp. and Vibrio sp. were mostly found to be exclusive to HOAN conditions, suggesting that HOAN could possibly proliferate the presence of these potential pathogens. Our study suggests the complexity of bacterial communities to hypoxia and acidification in response to increased nutrient loads, along with identities of nutrient, oxygen and pH-susceptible bacterial groups that are most likely affected under this ocean trend.

Continue reading ‘Changes in biofilm bacterial communities in response to combined effects of hypoxia, ocean acidification and nutrients from aquaculture activity in Three Fathoms Cove’

External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease

Brown Ring Disease (BRD) is an infection of the Manila clam Ruditapes philippinarum due to the pathogen Vibrio tapetis . During BRD, clams are facing immunodepression and shell biomineralization alteration. In this paper, we studied the role of pH on the growth of the pathogen and formulated hypothesis on the establishment of BRD by V. tapetis .

Methods and Results
In this study, we monitored the evolution of pH during the growth of V. tapetis in a range of pH and temperatures. We also measured the pH of Manila clam hemolymph and extrapallial fluids during infection by V. tapetis . We highlighted that V. tapetis modulates the external pH during its growth, to a value of 7.70. During the development of BRD, V. tapetis also influences extrapallial fluids and hemolymph pH in vitro in the first hours of exposure and in vivo after 3 days of infection.

Our experiments have shown a close interaction between V. tapetis CECT4600, a pathogen of Manila clam that induces BRD, and the pH of different compartments of the animals during infection. These results indicate that that the bacterium, through a direct mechanism or as a consequence of physiological changes encountered in the animal during infection, is able to interfere with the pH of Manila clam fluids. This pH modification might promote the infection process or at least create an imbalance within the animal, that would favor its persistence. This last hypothesis should be tested in future experiment.

Significance and Impact of Study
This study is the first observation of pH modifications in the context of BRD and might orient future research on the fine mechanisms of pH modulation associated to BRD.

Continue reading ‘External pH modulation during the growth of Vibrio tapetis , the etiological agent of Brown Ring Disease’

Subtle bacterioplankton community responses to elevated CO2 and warming in the oligotrophic South Pacific gyre

Bacterioplankton play a critical role in primary production, carbon cycling, and nutrient cycling in the oligotrophic ocean. To investigate the effect of elevated CO2 and warming on the composition and function of bacterioplankton communities in oligotrophic waters, we performed two trace‐metal clean deck board incubation experiments during the New Zealand GEOTRACES transect of the South Pacific gyre (SPG). High‐throughput amplicon sequencing of the 16S rRNA gene revealed that bacterioplankton community composition was distinct between the fringe and ultra‐oligotrophic centre of the SPG and changed consistently in response to elevated CO2 at the ultra‐oligotrophic centre but not at the mesotrophic fringe of the SPG. The combined effects of elevated CO2 and warming resulted in a high degree of heterogeneity between replicate communities. Community‐level protein synthesis rates (3H‐Leucine incorporation) and bacterioplankton abundance were not affected by elevated CO2 alone or in combination with warming at the fringe or ultra‐oligotrophic centre of the SPG. These data suggest bacterioplankton community responses to elevated CO2 may be modulated by nutrient regimes in open ocean ecosystems and highlight the need for further investigation in expanding oligotrophic subtropical gyres.

Continue reading ‘Subtle bacterioplankton community responses to elevated CO2 and warming in the oligotrophic South Pacific gyre’

Responses of intertidal bacterial biofilm communities to increasing pCO2

The effects of ocean acidification on ecosystems remain poorly understood, because it is difficult to simulate the effects of elevated CO2 on entire marine communities. Natural systems enriched in CO2 are being used to help understand the long-term effects of ocean acidification in situ. Here, we compared biofilm bacterial communities on intertidal cobbles/boulders and bedrock along a seawater CO2 gradient off Japan. Samples sequenced for 16S rRNA showed differences in bacterial communities with different pCO2 and between habitat types. In both habitats, bacterial diversity increased in the acidified conditions. Differences in pCO2 were associated with differences in the relative abundance of the dominant phyla. However, despite the differences in community composition, there was no indication that these changes would be significant for nutrient cycling and ecosystem function. As well as direct effects of seawater chemistry on the biofilm, increased microalgal growth and decreased grazing may contribute to the shift in bacterial composition at high CO2, as documented by other studies. Thus, the effects of changes in bacterial community composition due to globally increasing pCO2 levels require further investigation to assess the implications for marine ecosystem function. However, the apparent lack of functional shifts in biofilms along the pCO2 gradient is a reassuring indicator of stability of their ecosystem functions in shallow ocean margins.

Continue reading ‘Responses of intertidal bacterial biofilm communities to increasing pCO2’

Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors


• Comparison of siderophore production by healthy and bleached coral associated microbes.

• Catecholate type of siderophore is mainly produced by coral associated microbes.

• Adapting ability of healthy and bleached coral isolates in changing climate.

• Significant effect of lowering pH and increasing temperature on growths and siderophore production of coral associated bacteria.


Bacteria are known to play a crucial role in coral health but their mechanisms are unclear. Siderophore production could be one of the mechanisms by which they benefit or harm the corals. Bacteria produce siderophore to adapt in harsh conditions, such as nutrient limiting and competing environments such as coral surface. In the present study, siderophore producing ability of microbes associated with healthy and bleached corals is evaluated as both healthy and bleached coral surface provide a different environment concerning nutrients and competitions. Total of 129 siderophore-producing bacteria associated with two healthy (n = 66 isolates) and bleached coral (n = 63) species (Porites spp. and Turbinaria spp.) from the Gulf of Kutch (GoK), Gujarat (India) are screened and compared. No relation between coral health status and siderophore producing ability of microbes is observed (one-way ANOVA, p = 0.67). All the isolates are positive to catecholate type of siderophore which has the strongest affinity for limiting iron. The study also explores the growth and siderophore production behavior of healthy and bleached coral isolates at decreasing pH and temperature rise as they are the important factors that affects the solubility of nutrients and thus, the structure and functioning of the microbes. Isolates from bleached corals showed an increase in growth even at pH 6, whereas the growth of healthy coral isolates reduces at pH 6. Temperature rise is negatively correlated to growth and siderophore production by all isolates except Bacillus sp. PH26. Combined low pH and temperature rise stress, negatively affect growth and siderophore production of coral-associated microbes with Bacillus sp. PH26 as exception. General correlation trend of bacterial growth and siderophore production is positive. The isolates showing exceptional behavior might be possibly beneficial or harmful to the coral health. Thus, growth and siderophore production of microbes under changing climate conditions might be used as preliminary tools to screen beneficial and pathogenic microbes of corals from opportunistic microbes. This screening would reduce the number of possible candidates for in-situ and in-vitro microcosm experiments to understand the role of siderophore producing microbes in coral health. Overall, pH and temperature have a significant impact on coral-associated microbial growth and siderophore production, which ultimately impact the coral health and disease as the microbes form an integral part of coral holobiont. The study laid the foundation for future studies to understand the role of siderophore producing bacteria in coral health in the global climate-changing era.

Continue reading ‘Evaluation of heterotrophic bacteria associated with healthy and bleached corals of Gulf of Kutch, Gujarat, India for siderophore production and their response to climate change factors’

A high biodiversity mitigates the impact of ocean acidification on hard-bottom ecosystems

Biodiversity loss and climate change simultaneously threaten marine ecosystems, yet their interactions remain largely unknown. Ocean acidification severely affects a wide variety of marine organisms and recent studies have predicted major impacts at the pH conditions expected for 2100. However, despite the renowned interdependence between biodiversity and ecosystem functioning, the hypothesis that the species’ response to ocean acidification could differ based on the biodiversity of the natural multispecies assemblages in which they live remains untested. Here, using experimentally controlled conditions, we investigated the impact of acidification on key habitat-forming organisms (including corals, sponges and macroalgae) and associated microbes in hard-bottom assemblages characterised by different biodiversity levels. Our results indicate that, at higher biodiversity, the impact of acidification on otherwise highly vulnerable key organisms can be reduced by 50 to >90%, depending on the species. Here we show that such a positive effect of a higher biodiversity can be associated with higher availability of food resources and healthy microbe-host associations, overall increasing host resistance to acidification, while contrasting harmful outbreaks of opportunistic microbes. Given the climate change scenarios predicted for the future, we conclude that biodiversity conservation of hard-bottom ecosystems is fundamental also for mitigating the impacts of ocean acidification.

Continue reading ‘A high biodiversity mitigates the impact of ocean acidification on hard-bottom ecosystems’

Symbiont community diversity is more variable in corals that respond poorly to stress

Coral reefs are declining globally as climate change and local water quality press environmental conditions beyond the physiological tolerances of holobionts—the collective of the host and its microbial symbionts. To assess the relationship between symbiont composition and holobiont stress tolerance, community diversity metrics were quantified for dinoflagellate endosymbionts (Family: Symbiodiniaceae) from eight Acropora millepora genets that thrived under or responded poorly to various stressors. These eight selected genets represent the upper and lower tails of the response distribution of 40 coral genets that were exposed to four stress treatments (and control conditions) in a 10‐day experiment. Specifically, four ‘best performer’ coral genets were analyzed at the end of the experiment because they survived high temperature, high pCO2, bacterial exposure, or combined stressors, whereas four ‘worst performer’ genets were characterized because they experienced substantial mortality under these stressors. At the end of the experiment, seven of eight coral genets mainly hosted Cladocopium symbionts, whereas the eighth genet was dominated by both Cladocopium and Durusdinium symbionts. Symbiodiniaceae alpha and beta diversity were higher in worst performing genets than in best performing genets. Symbiont communities in worst performers also differed more after stress exposure relative to their controls (based on normalized proportional differences in beta diversity), than did best performers. A generalized joint attribute model estimated the influence of host genet and treatment on Symbiodiniaceae community composition and identified strong associations among particular symbionts and host genet performance, as well as weaker associations with treatment. Although dominant symbiont physiology and function contribute to host performance, these findings emphasize the importance of symbiont community diversity and stochasticity as components of host performance. Our findings also suggest that symbiont community diversity metrics may function as indicators of resilience and have potential applications in diverse disciplines from climate change adaptation to agriculture and medicine.

Continue reading ‘Symbiont community diversity is more variable in corals that respond poorly to stress’

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Ocean acidification in the IPCC AR5 WG II

OUP book