Flexible habitat choice of pelagic bacteria increases system stability and energy flow through the microbial loop

Abstract

Pelagic bacteria can be classified into free‐living and particle‐attached life modes, which either dwell in the water column or attach to suspended particles. Bacteria with a generalist life style, however, can actively shift between these two habitats. Globally increasing densities of natural and artificial particles enhance habitat heterogeneity, with potential consequences for system stability and trophic transfer through aquatic food webs. To better decipher the dynamics of microbial communities, we investigated the influence of adaptive vs. fixed habitat choice on species coexistence for a simplified bacterial community by analyzing a corresponding food web model, consisting of two specialist bacterial prey species (free and attached), a generalist bacterial prey species with the ability to shift between both habitats, and two protist predators, specialized on either water or particle compartment. For simplicity we assume a shared resource pool, considering particles only for colonization but not as a source for nutrients or carbon, that is, inert particles like microplastics or inorganic sediments. The model predicts coexistence on a cyclic attractor between fixed and flexible bacteria, if the costs for adaptive habitat choice can be balanced by adaptation speed. The presence of adaptive prey dampens predator–prey cycle amplitudes, contributing to system stabilization resulting in higher mean predator biomass compared to specialist prey only. Thus, in pelagic microbial systems, flexible habitat choice at the prey level has important implications for system stability and magnitude of energy flow through the microbial loop.

Differing Escape Responses of the Marine Bacterium Marinobacter adhaerens in the Presence of Planktonic vs. Surface-Associated Protist Grazers

“…In contrast, pelagic protozoa like nanoflagellates can only be ingested by smaller filter feeders (e.g., ciliates), which leads to additional trophic levels in the food chain and hence a less efficient energy and matter flux to higher trophic levels (e.g., [ 29 ]). Therefore behavioral defense mechanisms can have consequences for energy flow to higher trophic levels [ 15 ].…”

“…Such a predator-escape mechanism could be an important advantage compared to habitat specialists, especially under high grazing pressure. Assessing and understanding bacterial defense mechanisms is important, due to their far-reaching ecological implications for the dynamics and composition of the microbial community [ 14 ], as well as for energy transport to higher trophic levels [ 15 ]. Thereby, microbial community composition and dynamics can be influenced by habitat heterogeneity determined by particle load and type.…”

“…Increasing particle concentrations can be expected to increase bacterial abundance and correspondingly lead to an increase in their respective grazers. Theoretical studies suggest that this might benefit generalist bacterial species with the ability to escape from habitats with high predation pressure, with potential consequences also for energy transport through the microbial loop [ 15 ]. To assess the ecological consequences, it is important to perform observational studies on bacterial habitat choice and how it is influenced by predation.…”

“…Findings from this study highlight the importance of habitat heterogeneity in pelagic environments, which can create an opportunity of behavioral escape mechanisms via flexible habitat choice for generalist bacteria. This has potential implications for microbial community composition and consequently for energy transfer through the microbial loop [ 15 ].…”

Extracellular enzyme stoichiometry reveals carbon and nitrogen limitations closely linked to bacterial communities in China’s largest saline lake

“…Moreover, the Tibetan Plateau has the largest inland saline lake in China: Qinghai Lake, which presents a higher level of buried surficial sediment organic carbon than many other large freshwater lakes in China, such as Taihu Lake ( Chen et al, 2021 ). Heterotrophic microorganisms mineralize organic matter to create the trophic base for detrital food webs ( Benstead et al, 2021 ), forming the microbial loop that accounts for a crucial portion of the energy and nutrient flow in most aquatic ecosystems, thus driving global carbon and nutrient cycles ( Cherabier and Ferriere, 2022 ; Villalba et al, 2022 ). Extracellular enzymes are secreted by the microbial assemblage to participate in the decomposition of organic sources and subsequent acquisition of limiting nutrients ( Hill et al, 2006 ).…”