Large-scale impact of the 2016 Marine Heatwave on the plankton-associated microbial communities of the Great Barrier Reef (Australia)

Inoviridae prophage and bacterial host dynamics during diversification, succession, and Atlantic invasion of Pacific-native Vibrio parahaemolyticus

IMPORTANCE

An understanding of the processes that contribute to the emergence of pathogens from environmental reservoirs is critical as changing climate precipitates pathogen evolution and population expansion. Phylogeographic analysis of Vibrio parahaemolyticus hosts combined with the analysis of their Inoviridae phage resolved ambiguities of diversification dynamics which preceded successful Atlantic invasion by the epidemiologically predominant ST36 lineage. It has been established experimentally that filamentous phage can limit host recombination, but here, we show that phage loss is linked to rapid bacterial host diversification during epidemic spread in natural ecosystems alluding to a potential role for ubiquitous inoviruses in the adaptability of pathogens. This work paves the way for functional analyses to define the contribution of inoviruses in the evolutionary dynamics of environmentally transmitted pathogens.

The road forward to incorporate seawater microbes in predictive reef monitoring

Marine bacterioplankton underpin the health and function of coral reefs and respond in a rapid and sensitive manner to environmental changes that affect reef ecosystem stability. Numerous meta-omics surveys over recent years have documented persistent associations of opportunistic seawater microbial taxa, and their associated functions, with metrics of environmental stress and poor reef health (e.g. elevated temperature, nutrient loads and macroalgae cover). Through positive feedback mechanisms, disturbance-triggered heterotrophic activity of seawater microbes is hypothesised to drive keystone benthic organisms towards the limit of their resilience and translate into shifts in biogeochemical cycles which influence marine food webs, ultimately affecting entire reef ecosystems. However, despite nearly two decades of work in this space, a major limitation to using seawater microbes in reef monitoring is a lack of a unified and focused approach that would move beyond the indicator discovery phase and towards the development of rapid microbial indicator assays for (near) real-time reef management and decision-making. By reviewing the current state of knowledge, we provide a comprehensive framework (defined as five phases of research and innovation) to catalyse a shift from fundamental to applied research, allowing us to move from descriptive to predictive reef monitoring, and from reactive to proactive reef management.

Algicidal bacteria in phycosphere regulate free-living Symbiodinium fate via triggering oxidative stress and photosynthetic system damage

Free-living Symbiodinium, which forms symbiotic relationships with many marine invertebrates, plays an important role in the vast ocean. Nutrient levels have been shown to significantly impact microbial community structure and regulate algal communities. In this study, the bacterial community structure within the phycosphere of free-living Symbiodinium underwent significant changes in response to nutrient stimulation. Alteromonas exhibited dominance in Zobell 2216E broth nutrient stimulation concomitant with the demise of algal cells. Alteromonas abrolhosensis JY-JZ1, a marine bacterium isolated from the phycosphere of Symbiodinium, demonstrated an algicidal effect on Symbiodinium cells. Optical and scanning electron microscopy revealed that the algal cell membrane structure was disrupted, leading to intracellular leakage. Strain JY-JZ1 exerted its cytotoxicity by producing and secreting bioactive compounds into the supernatant. The marked declines in the chlorophyll a content, photosynthetic efficiency (Fv/Fm) and the electron transport rate (rETR) indicated that the photosynthetic system of Symbiodinium was damaged by JY-JZ1 supernatant. The observed elevation in levels of malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) content suggested that the algal cells experienced oxidative stress. Moreover, the supernatant exhibited remarkable adaptability to temperature and pH. Additionally, it displayed exceptional algicidal efficacy against various harmful algae species. To the best of our knowledge, this study represents the first successful isolation of an algicidal bacterial strain from the phycosphere of free-living Symbiodinium and subsequent investigation into its mechanism for controlling Symbiodinium growth, thereby providing novel insights into algae-bacteria interactions. The remarkable algicidal efficacy exhibited by strain JY-JZ1 against other harmful algae species suggests its significant potential for harmful algal blooms (HABs) control.

Functional and structural responses of plankton communities toward consecutive experimental heatwaves in Mediterranean coastal waters

The frequency of marine heatwaves (HWs) is projected to increase in the Mediterranean Sea over the next decades. An in situ mesocosm experiment was performed in a Mediterranean lagoon for 33 days. Three mesocosms were used as controls following the natural temperature of the lagoon. In three others, two HWs of + 5 °C compared to the controls were applied from experimental day (d) 1 to d5 (HW1) and from d11 to d15 (HW2). High-frequency data of oxygen, chlorophyll-a (chl-a), temperature, salinity and light from sensors immersed in all mesocosms were used to calculate gross primary production (GPP), respiration (R) and phytoplankton growth (µ) and loss (L) rates. Nutrients and phytoplankton community structure from pigments were also analyzed. HW1 significantly increased GPP, R, chl-a, µ and L by 7 to 38%. HW2 shifted the system toward heterotrophy by only enhancing R. Thus, the effects of the first HW resulted in the attenuation of those of a second HW on phytoplankton processes, but not on community respiration, which was strongly regulated by temperature. In addition, natural phytoplankton succession from diatoms to haptophytes was altered by both HWs as cyanobacteria and chlorophytes were favored at the expense of haptophytes. These results indicate that HWs have pronounced effects on Mediterranean plankton communities.

The Evolution of Coral Reef under Changing Climate: A Scientometric Review

In this scientometric review, we employ the Web of Science Core Collection to assess current publications and research trends regarding coral reefs in relation to climate change. Thirty-seven keywords for climate change and seven keywords for coral reefs were used in the analysis of 7743 articles on coral reefs and climate change. The field entered an accelerated uptrend phase in 2016, and it is anticipated that this phase will last for the next 5 to 10 years of research publication and citation. The United States and Australia have produced the greatest number of publications in this field. A cluster (i.e., focused issue) analysis showed that coral bleaching dominated the literature from 2000 to 2010, ocean acidification from 2010 to 2020, and sea-level rise, as well as the central Red Sea (Africa/Asia), in 2021. Three different types of keywords appear in the analysis based on which are the (i) most recent (2021), (ii) most influential (highly cited), and (iii) mostly used (frequently used keywords in the article) in the field. The Great Barrier Reef, which is found in the waters of Australia, is thought to be the subject of current coral reef and climate change research. Interestingly, climate-induced temperature changes in "ocean warming" and "sea surface temperature" are the most recent significant and dominant keywords in the coral reef and climate change area.