Linkages between bacterial community and extracellular enzyme activities crossing a coastal front

Abstract

Exploring the responses of microbial communities and their functions to marine frontal systems are the foci of marine ecologists. However, most of the existing studies have focused on only microbial communities or their functions. The relationships between microbial communities and their functions across coastal fronts therefore remain unclear. Here we studied a coastal front in the Taiwan Strait during late spring and examined the bacterial community structure, extracellular enzymatic activity (EEA), and their linkages. The results showed that the coastal front strongly delineated zones of bacterial community composition and diversity and functioned as a transitional zone rather than a hotspot between the coastal water and offshore water. Co-occurrence network analysis indicated that the interaction of bacterial communities was much weaker in the frontal zone than in the water masses on both sides. The suggestion was that the highly fluctuating environment in the frontal zone reduced the complexity and stability of the bacterial co-occurrence network. The activities of β-glucosidase (BGA) and leucine aminopeptidase (LAPA) were as high in the frontal zone as in the coastal water and much higher than those in offshore waters. We therefore suggest that, despite obvious shifts in the bacterial community structure in the frontal zone, the bacterial community was able to maintain its ability to hydrolyze organic substrates via functional redundancy. The composition of key microbial assemblies differed among the three water masses, and the relative abundance of module 2 in the frontal zone was positively correlated with BGA and LAPA. The indication was that changing the bacterial assemblage was the mechanism that made it possible for the bacterial community to maintain EEA in the frontal zone. Our results help to improve understanding on how bacterial community-function linkages vary in marine frontal systems.