Impact of sideways and bottom-up control factors on bacterial community succession over a tidal cycle

Abstract

In aquatic systems, bacterial community succession is a function of top-down and bottom-up factors, but little information exists on ''sideways'' controls, such as bacterial predation by Bdellovibriolike organisms (BLOs), which likely impacts nutrient cycling within the microbial loop and eventual export to higher trophic groups. Here we report transient response of estuarine microbiota and BLO spp. to tidal-associated dissolved organic matter supply in a riverdominated estuary, Apalachicola Bay, Florida. Both dissolved organic carbon and dissolved organic nitrogen concentrations oscillated over the course of the tidal cycle with relatively higher concentrations observed at low tide. Concurrent with the shift in dissolved organic matter (DOM) supply at low tide, a synchronous increase in numbers of bacteria and predatorial BLOs were observed. PCR-restriction fragment length polymorphism of small subunit rDNA, cloning, and sequence analyses revealed distinct shifts such that, at low tide, significantly higher phylotype abundances were observed from ␥-Proteobacteria, ␦-Proteobacteria, Bacteroidetes, and high G؉C Gram-positive bacteria. Conversely, diversity of ␣-Proteobacteria, ␤-Proteobacteria, and ChlamydialesVerrucomicrobia group increased at high tides. To identify metabolically active BLO guilds, tidal microcosms were spiked with six 13 C-labeled bacteria as potential prey and studied using an adaptation of stable isotope probing. At low tide, representative of higher DOM and increased prey but lower salinity, BLO community also shifted such that mesohaline clusters I and VI were more active; with an increased salinity at high tide, halotolerant clusters III, V, and X were predominant. Eventually, 13 C label was identified from higher micropredators, indicating that trophic interactions within the estuarine microbial food web are potentially far more complex than previously thought.Bdellovibrio-like organisms (BLOs) ͉ dissolved organic matter ͉ predator-prey interactions ͉ stable isotope probing ͉ tidal microbiota M arine dissolved organic matter (DOM) is one of the largest active reservoirs of reduced carbon at the earth's surface and, to a large extent, as the primary consumers of this DOM, bacteria control its fate via assimilation and/or remineralization processes (1, 2). The fate of DOM is a also a function of physiologic status and taxonomic composition of the autochthanous microbiota as well as the relative DOM lability supplied to the system, all of which vary both spatially and temporally in response to physiochemical conditions (1, 3, 4). DOM that is assimilated into bacterial biomass is potentially available for trophic transfer via the microbial loop (5) and as such must be accounted for in estimates of marine carbon flux.Bacterial groups that mineralize DOM are taxonomically diverse (2, 3, 6), which is often a function of niche variability (1-3). Specifically, estuarine systems exhibit high spatiotemporal and physiochemical variability, often resulting in short-lived blooms of some bacterial spp....

Prey bacteria shape the community structure of their predators

“…Although the significance of Bacteriovorax community structure and diversity is only beginning to be recognized (Chauhan et al, 2009), in general, biodiversity has been reported to be an important factor in ecosystem function and responses to environmental changes (Bell et al, 2005;Fuhrman, 2009). Regarding services of BALO populations in the environment, diversity is likely an important factor, especially relative to their potential function in controlling and shaping bacterial communities through selective mortality, which may be dependent upon the specific predator OTUs present.…”

Cell-cycle progress in obligate predatory bacteria is dependent upon sequential sensing of prey recognition and prey quality cues

“…BALOs are well distributed in nature, being found in both terrestrial and aquatic ecosystems and possibly in animal (including human) intestines (11,16,17). Because obligate predators cannot replicate in the absence of adequate prey, the structure of BALO populations is under environmental selection (6,7,18), whereas natural selection and arms race may shape predator-prey interactions (19,20). Indeed, BALO isolates possess different prey spectra that are adapted to the prey available in their surroundings (18,21,22).…”

“…However, predation between bacteria, the most abundant cellular living entities on Earth, is poorly understood. The known diversity of predatory bacteria is low (4), and few studies have addressed predation dynamics in natural or man-made environments (5)(6)(7). An important aspect of predatory interactions is prey choice.…”

An aquatic vertebrate can use amino acids from environmental water

“…The DON absorbed by prokaryotes is believed to be transported indirectly to aquatic animals at higher trophic levels via the food chain for use as a nutrient source. This pathway is known as a 'bottom-up cascade', in which DON increases prokaryotic abundance, the abundant prokaryotes are subsequently consumed by protozoa, which are then consumed by zooplankton and so on [5]. In other words, current food-web theory assumes that nutrients flow from DON to aquatic animals via long pathways involving multiple eukaryotic species as intermediary nutrient transporters [6].…”