Seasonal co-occurrence patterns of bacteria and eukaryotic phytoplankton and the ecological response in urban aquatic ecosystem

Microorganisms play a key role in aquatic ecosystems.Recent studies show that keystone taxa in microbial community could change the community structure and function.However,most previous studies focus on abundant taxa but neglected low abundant ones.To clarify the seasonal variation of bacterial and microalgal communities and understand their synergistic adaptation to diff erent environmental factors,we studied the bacterial and eukaryotic phytoplankton communities in Fenhe River that runs through Taiyuan City,central China,and their seasonal co-occurrence patterns using 16S and 18S rDNA sequencing.Results indicate that positive interaction of eukaryotic phytoplankton network was more active than negative one except winter,indicating that the cooperation(symbiotic phenomenon in which phytoplankton are interdependent and mutually benefi cial)among them could improve the adaption of microbial community to the local environmental changes and maintain the stability of microbial network.The main genera that identifi ed as keystone taxa in bacterial network were Salinivibrio and Sphingopyxis of Proteobacteria and they could respond to the variation of nitrite and make use of it,while those that identifi ed as keystone taxa in eukaryotic phytoplankton network were Pseudoschroederia and Nannochloris,and they were more susceptible to nitrate and phosphate.Mychonastes and Cryptomonas were closely related to water temperature.However,the loss of the co-occurrence by environmental factor changes aff ected the stability of network structure.This study provided a reference for analyzing relationship between bacteria and eukaryotic phytoplankton and revealing potential importance of keystone taxa in similar ecological domains in carbon,nitrogen,and phosphorus dynamics.

Deciphering microeukaryotic–bacterial co-occurrence networks in coastal aquaculture ponds

Microeukaryotes and bacteria are key drivers of primary productivity and nutrient cycling in aquaculture ecosystems.Although their diversity and composition have been widely investigated in aquaculture systems,the co-occurrence bipartite network between microeukaryotes and bacteria remains poorly understood.This study used the bipartite network analysis of high-throughput sequencing datasets to detect the co-occurrence relationships between microeukaryotes and bacteria in water and sediment from coastal aquaculture ponds.Chlorophyta and fungi were dominant phyla in the microeukaryotic–bacterial bipartite networks in water and sediment,respectively.Chlorophyta also had overrepresented links with bacteria in water.Most microeukaryotes and bacteria were classified as generalists,and tended to have symmetric positive and negative links with bacteria in both water and sediment.However,some microeukaryotes with high density of links showed asymmetric links with bacteria in water.Modularity detection in the bipartite network indicated that four microeukaryotes and twelve uncultured bacteria might be potential keystone taxa among the module connections.Moreover,the microeukaryotic–bacterial bipartite network in sediment harbored significantly more nestedness than that in water.The loss of microeukaryotes and generalists will more likely lead to the collapse of positive co-occurrence relationships between microeukaryotes and bacteria in both water and sediment.This study unveils the topology,dominant taxa,keystone species,and robustness in the microeukaryotic–bacterial bipartite networks in coastal aquaculture ecosystems.These species herein can be applied for further management of ecological services,and such knowledge may also be very useful for the regulation of other eutrophic ecosystems.

Changes of microbiome in response to sugars in a wilt pathogen-infested soil

Sugars are frequently and abundantly found in root exudates,but influence of specific sugars on the fate of soil-borne pathogens,microbiome structure,and particularly microbial interactions are not well understood.A 42-day of microcosm incubation was conducted with two soils:a natural watermelon Fusarium wilt pathogen(i.e.,Fusarium oxysporum f.sp.niveum(FON))-infested soil(Low-FON soil)and the soil further receiving the wilt pathogen inocula(High-FON soil).Both soils were supplemented with four simple sugars before incubation.The results show that,in both soils,FON was enriched by all sugars although co-living with tremendously diverse microbes;and bacterial richness,evenness,and diversity were decreased and bacterial community structure was changed by all sugars.Bacterial richness and evenness were negatively correlated with FON quantity in both Low-FON and High-FON soils,indicating that FON may tend to live in soil with low alpha-diversity.In both Low-FON and High-FON soils,the sugar-spiked networks had more links,higher density,larger modules,and shorter harmonic geodesic distance,suggesting greater potentials for microbial interaction and niche-sharing.The positive links between some of the keystone taxa and FON indicates that these keystone taxa may have promoted FON.This may be one of reasons why FON could proliferate vigorously after sugar supplementation.