Links of Extracellular Enzyme Activities, Microbial Metabolism, and Community Composition in the River‐Impacted Coastal Waters

Abstract

Extracellular enzymatic activity (EEA), production, respiration, and composition of the bacterial community were determined along environmental gradients in the river-impacted coastal waters in the South China Sea during summer in order to examine the links of EEA, metabolic activity, and composition of the bacterial community. The initial step of substrate utilization was coupled with metabolic activity of the bacterial community. The activity of leucine aminopeptidase was closely related to the level of phytoplankton biomass, suggesting that leucine-containing compounds primarily resulted from phytoplankton, which was likely partly responsible for the close link between bacterioplankton and phytoplankton in marine environments. A shift from the dominance of leucine aminopeptidase in EEA in eutrophic environments to chitobiases in pristine waters was attributed to bacterial preference for leucine-containing compounds and spatial variability in substrate supply. Spatial pattern of the enzymatic rates along an environmental gradient differed at the community and the cellular level. The enzymatic rates of the bacterial community decreased offshore, which were linked to substrate supply and the bacterial community composition. However, cell-specific enzymatic rates were modulated by not only the bacterial community composition but also the carbon partition between anabolic and catabolic processes as environmental conditions changed, both of which eventually altered bacterial abundance. Functional redundancy of bacterial groups existed despite shifts in the bacterial community composition, suggesting that the bacterial community might maximize their function of hydrolyzing substrates across marine environments. Our findings improved the understanding of the connection of extracellular enzymatic activity, metabolic activity, and community composition of bacterioplankton.

Heterotrophic Bacteria Respond Differently to Increasing Temperature and Dissolved Organic Carbon Sources in Two Tropical Coastal Systems

“…The response of the extracellular enzymatic activities showed similarities and differences between sites, revealing potential changes in microbial organic matter processing as a response to different DOC sources and temperatures. In both the GBR and Red Sea the same order in the responses of the relative enzymatic activity to the altered conditions were found: LAPase > APase > BGase, which is consistent with patterns typically found in marine environments (Baltar et al., 2009, 2017; Lønborg et al., 2019; Nichols & Martin, 2021; Shi et al., 2019). Such relatively higher LAPase activity is commonly linked with the microbial use of organic matter for protein synthesis and increasing supply of leucine containing compounds (Kellogg & Deming, 2014; Piontek et al., 2014; Shi et al., 2019).…”

“…In both the GBR and Red Sea the same order in the responses of the relative enzymatic activity to the altered conditions were found: LAPase > APase > BGase, which is consistent with patterns typically found in marine environments (Baltar et al, 2009(Baltar et al, , 2017Lønborg et al, 2019;Nichols & Martin, 2021;Shi et al, 2019). Such relatively higher LAPase activity is commonly linked with the microbial use of organic matter for protein synthesis and increasing supply of leucine containing compounds (Kellogg & Deming, 2014;Piontek et al, 2014;Shi et al, 2019). The maximum EEA rates were generally lower in the Red Sea than in the GBR, suggesting that the response of EEA to different DOC sources will depend on the ambient microbial communities but also on the composition of the main DOC source (e.g., mangrove and seagrass species).…”

Carbon System Simulation in the Pearl River Estuary, China: Mass Fluxes and Transformations

“…Conceptual framework of the RCA carbon system (RCACS), including the water column and sediment carbon cycles. The POC undergoes hydrolysis into DOC and then DOC remineralization into DIC is supported bySmith et al (1992),Anderson and Tang (2010),Shi et al (2019), andDruon et al (2010).…”

Nutritional Status Regulates Bacteria‐Virus Interactions in the Northern South China Sea

“…Hence, the inshore station (S1) was substrate‐rich and the offshore stations (S2 and S3) were substrate‐low. The river discharge delivered nutrients and triggered phytoplankton growth in the nearshore waters (e.g., S1) (Xu et al., 2018), potentially enhancing the supply of phytoplankton‐derived and high‐molecular‐weight DOC (Kirchman, 2002), which bacteria preferentially utilize (Shi et al., 2019; Xu et al., 2018). The offshore station S2 and S3 located at substrate‐low SCS, where low molecular weight DOC and less bioavailable bacteria and virus‐derived DOC were likely dominated (Dong et al., 2013; Shiah et al., 2022).…”