The Eco-Evo Mandala: Simplifying Bacterioplankton Complexity into Ecohealth Signatures

The microbiome emits informative signals of biological organization and environmental pressure that aid ecosystem monitoring and prediction. Are the many signals reducible to a habitat-specific portfolio that characterizes ecosystem health? Does an optimally structured microbiome imply a resilient microbiome? To answer these questions, we applied our novel Eco-Evo Mandala to bacterioplankton data from four habitats within the Great Barrier Reef, to explore how patterns in community structure, function and genetics signal habitat-specific organization and departures from theoretical optimality. The Mandala revealed communities departing from optimality in habitat-specific ways, mostly along structural and functional traits related to bacterioplankton abundance and interaction distributions (reflected by ϵ and λ as power law and exponential distribution parameters), which are not linearly associated with each other. River and reef communities were similar in their relatively low abundance and interaction disorganization (low ϵ and λ) due to their protective structured habitats. On the contrary, lagoon and estuarine inshore reefs appeared the most disorganized due to the ocean temperature and biogeochemical stress. Phylogenetic distances (D) were minimally informative in characterizing bacterioplankton organization. However, dominant populations, such as Proteobacteria, Bacteroidetes, and Cyanobacteria, were largely responsible for community patterns, being generalists with a large functional gene repertoire (high D) that increases resilience. The relative balance of these populations was found to be habitat-specific and likely related to systemic environmental stress. The position on the Mandala along the three fundamental traits, as well as fluctuations in this ecological state, conveys information about the microbiome’s health (and likely ecosystem health considering bacteria-based multitrophic dependencies) as divergence from the expected relative optimality. The Eco-Evo Mandala emphasizes how habitat and the microbiome’s interaction network topology are first- and second-order factors for ecosystem health evaluation over taxonomic species richness. Unhealthy microbiome communities and unbalanced microbes are identified not by macroecological indicators but by mapping their impact on the collective proportion and distribution of interactions, which regulates the microbiome’s ecosystem function.

Patterns of Structural and Functional Bacterioplankton Metacommunity along a River under Anthropogenic Pressure

Bacteria, an integral part of aquatic ecosystems, are responsible for the circulation of matter and flow of energy. Since bacterioplankton rapidly responds to any natural and human-induced disturbances in the environment, it can serve as a bioindicator of these changes. Knowing factors that shape the microbial community structure may help the sustainable management of the water environment. However, the identification of environmental signals affecting the structure and function of bacterioplankton is still a challenge. The study analyses the impact of environmental variables on basic microbial parameters, which determines the effectiveness of ecological processes in rivers. Measurements of bacterioplankton abundance (BA) and extracellular enzyme activity (EEA) were based on fluorescent markers. The bacterial community structure was determined by 16S rRNA gene amplicon sequencing (Illumina). The results indicate spatial variation in bacterioplankton abundance. Temporal variation was not significant. Lipase and aminopeptidase had the highest level of activity. EEA was not correlated with bacterial abundance but was significantly correlated with temperature. Moreover, differences in lipase, α-glucosidase and β-glucosidase activity levels between spring and summer were noted. At the same time, the location of sampling site had a significant influence on aminopeptidase activity. The taxonomic analysis of bacterioplankton communities in the Brda River indicated that, although different numbers of OTUs were recorded in the studied river sections, bacterioplankton biodiversity did not change significantly along the river with distance downstream. Anthropogenically modified river sections were characterized by the dominance of Flavobacterium (Bacterioidetes) and hgcl clade (Actinobacteria) taxa, known for their ability to produce extracellular enzymes. PCoA analysis revealed that the sites located in the lower river course (urban area) had the most similar bacterial community structure (β-diversity). The study provides new insight into the changes in microbial communities along the river and emphasizes the potential impact of anthropogenization on these processes.

Interaction among bacterioplankton and macrophytes in shallow lakes with high macrophyte cover

Growth of submerged and emergent macrophytes was studied together with heterotrophic bacterioplankton abundance and production in two Hungarian shallow lakes with dominant macrophyte covers. It was expected that bacterioplankton numbers and activity would have an effect on macrophyte biomass accumulation. Bacterial production and abundance showed a strong seasonal pattern with maximum in the warmest months (July, August). It was found that macrophyte biomass increased with heterotrophic bacterial production and abundance up to 5.6 µg C l− 1 h− 1 and 5.30*106 cells, respectively, while over that value was negatively associated with macrophyte growth. It was also shown that the relationship between heterotrophic bacteria and macrophytes also varied seasonally, showing a multifaceted relationship. It was demonstrated that macrophytes are not only the most significant carbon and energy source for the bacteria in shallow, macrophyte-dominated lakes, but are also competing organisms that could be supressed by excessive bacterial activity. These findings could help better understand the interaction between macrophytes and bacterioplankton, and assist wetland managers in quantifying what may be a primary cause of reed die-back.

MICROBIAL CONTROL OF LIVE/DEAD ZOOPLANKTON RATIO IN SEVASTOPOL BAY

To explain higher fraction of live zooplankton in heavily polluted and eutrophic Sevastopol Bay comparing with cleaner adjacent waters, a hypothesis has been proposed and tested experimentally that more intensive bacteria-driven decomposition of dead organisms in the bay reduced their pool and, as a result, increased the live-to-dead zooplankton ratio. In the experiment, a heat-killed batch culture of the copepod Calanipeda aquaedulcis was used as a substrate for decomposition by natural microbial communities from the waters of different pollution status. Bacterioplankton abundance and in situ decomposition rate of copepod carcasses were shown to be about 3-fold higher in the bay (1.3 × 106 cells ml-1 and 0.13 day-1, respectively) while an approximation of zooplankton non-predatory mortality rates gave equal values for both the sites (about 0.046 day-1). These findings call for revising the ways of interpreting the results of zooplankton viability assays in their relation to water pollution status.