skip to main content

Explore Research Products in the NSF-PAR

Title: The Functional Significance of Bacterial Predators
ABSTRACT Predation structures food webs, influences energy flow, and alters rates and pathways of nutrient cycling through ecosystems, effects that are well documented for macroscopic predators. In the microbial world, predatory bacteria are common, yet little is known about their rates of growth and roles in energy flows through microbial food webs, in part because these are difficult to quantify. Here, we show that growth and carbon uptake were higher in predatory bacteria compared to nonpredatory bacteria, a finding across 15 sites, synthesizing 82 experiments and over 100,000 taxon-specific measurements of element flow into newly synthesized bacterial DNA. Obligate predatory bacteria grew 36% faster and assimilated carbon at rates 211% higher than nonpredatory bacteria. These differences were less pronounced for facultative predators (6% higher growth rates, 17% higher carbon assimilation rates), though high growth and carbon assimilation rates were observed for some facultative predators, such as members of the genera Lysobacter and Cytophaga , both capable of gliding motility and wolf-pack hunting behavior. Added carbon substrates disproportionately stimulated growth of obligate predators, with responses 63% higher than those of nonpredators for the Bdellovibrionales and 81% higher for the Vampirovibrionales , whereas responses of facultative predators to substrate addition were no different from those of nonpredators. This finding supports the ecological theory that higher productivity increases predator control of lower trophic levels. These findings also indicate that the functional significance of bacterial predators increases with energy flow and that predatory bacteria influence element flow through microbial food webs. IMPORTANCE The word “predator” may conjure images of leopards killing and eating impala on the African savannah or of great white sharks attacking elephant seals off the coast of California. But microorganisms are also predators, including bacteria that kill and eat other bacteria. While predatory bacteria have been found in many environments, it has been challenging to document their importance in nature. This study quantified the growth of predatory and nonpredatory bacteria in soils (and one stream) by tracking isotopically labeled substrates into newly synthesized DNA. Predatory bacteria were more active than nonpredators, and obligate predators, such as Bdellovibrionales and Vampirovibrionales , increased in growth rate in response to added substrates at the base of the food chain, strong evidence of trophic control. This work provides quantitative measures of predator activity and suggests that predatory bacteria—along with protists, nematodes, and phages—are active and important in microbial food webs.  more » « less
Award ID(s):
1636476 1655357 1331940
NSF-PAR ID:
10313768
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; ; ; ; ; ; « less
Editor(s):
Lemon, Katherine P.
Date Published:
Journal Name:
mBio
Volume:
12
Issue:
2
ISSN:
2150-7511
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ( , Ecology)
    Abstract

    In aquatic detrital‐based food webs, research suggests that autotroph‐heterotroph microbial interactions exert bottom‐up controls on energy and nutrient transfer. To address this emerging topic, we investigated microbial responses to nutrient and light treatments duringLiriodendrontulipiferalitter decomposition and fed litter to the caddisfly larvaePycnopsychesp. We measured litter‐associated algal, fungal, and bacterial biomass and production. Microbes were also labeled with14C and33P to trace distinct microbial carbon (C) and phosphorus (P) supportingPycnopsycheassimilation and incorporation (growth). Litter‐associated algal and fungal production rates additively increased with higher nutrient and light availability. Incorporation of microbial P did not differ across diets, except for higher incorporation efficiency of slower‐turnover P on low‐nutrient, shaded litter. On average,Pycnopsycheassimilated fungal C more efficiently than bacterial or algal C, andPycnopsycheincorporated bacterial C more efficiently than algal or fungal C. Due to high litter fungal biomass, fungi supported 89.6–93.1% ofPycnopsycheC growth, compared to 0.2% to 3.6% supported by bacteria or algae. Overall,Pycnopsycheincorporated the most C in high nutrient and shaded litter. Our findings affirm others' regarding autotroph‐heterotroph microbial interactions and extend into the trophic transfer of microbial energy and nutrients through detrital food webs.

     
    more » « less
  2. ; ( , Frontiers in Marine Science)
    Microplastics are ubiquitous contaminants in marine ecosystems worldwide, threatening fisheries production, food safety, and human health. Ingestion of microplastics by fish and large zooplankton has been documented, but there are few studies focusing on single-celled marine predators, including heterotrophic dinoflagellates. In laboratory experiments, the heterotrophic dinoflagellate species Oxyrrhis marina and Gyrodinium sp. readily ingested both algal prey and polystyrene microplastic spheres (2.5–4.5 μm), while Protoperidinium sp. did not ingest microplastics. Compared to algae-only fed dinoflagellates, those that ingested microplastics had growth rates reduced by 25–35% over the course of 5 days. Reduced growth resulted in a 30–50% reduction of secondary production as measured as predator biomass. Ingestion rates of algal prey were also reduced in the microplastic treatments. When given a mixture of microplastics and algal prey, O. marina displayed a higher selectivity for algal prey than Gyrodinium sp. Observations in the coastal ocean showed that phylogenetically diverse taxa ingested microplastic beads, and thus heterotrophic dinoflagellates could contribute to trophic transfer of microplastics to higher trophic levels. The results of this study may suggest that continued increase in microplastic pollution in the ocean could lead to reduced secondary production of heterotrophic protists due to microplastic ingestion, altering the flow of energy and matter in marine microbial food webs. 
    more » « less
  3. ; ; ; ( , Freshwater Biology)
    Abstract

    Pelagic copepods often couple the classical and microbial food webs by feeding on microzooplankton (e.g. ciliates) in oligotrophic aquatic systems, and this consumption can trigger trophic cascades within the microbial food web. Consumption of mixotrophic microzooplankton, which are both autotrophic and heterotrophic within the same individual, is of particular interest because of its influence on carbon transfer efficiency within aquatic food webs.

    In Lake Baikal, Siberia, it is unknown how carbon from a well‐developed microbial food web present during summer stratification moves into higher trophic levels within the classical food web.

    We conducted in situ experiments in August 2015 to test the hypotheses that: (a)  the lake's dominant endemic copepod (Epischura baikalensis), previously assumed to be an herbivore feeding on diatoms, connects the microbial and classical food webs by ingesting ciliates; and (b) this feeding initiates top‐down effects within the microbial food web.

    Our results supported these hypotheses.E. baikalensisindividuals consumed on average 101–161 ciliates per day, obtaining 96%–98% of their ingested carbon from ciliates and the remainder from small diatoms. Clearly,E. baikalensisis omnivorous, and it is probably channelling more primary production from both the microbial food web and the classical food web of Lake Baikal to higher trophic levels than any other pelagic consumer.

    Most ciliates consumed were a mixotrophic oligotrich and such taxa are often abundant in summer in other oligotrophic lakes. Consumption of these mixotrophs is likely to boost substantially the transfer efficiency of biomass to higher trophic levels with potential implications for fish production, but this has seldom been investigated in oligotrophic lakes.

    Feeding ofE. baikalensisinitiated a three‐link predatory cascade which reduced the abundance of ciliates and elevated growth rates of heterotrophic nanoflagellates but did not affect abundance or growth rates of autotrophic picoplankton. This demonstration of a potential trophic cascade in Lake Baikal indicates that investigations at larger spatial–temporal scales are needed to identify the conditions promoting or precluding trophic cascades in this lake.

     
    more » « less
  4. ; ; ; ; ; ( , Ecology)
    Abstract

    Acute resource pulses can have dramatic legacies for organismal growth, but the legacy effects of resource pulses on broader aspects of community structure and ecosystem processes are less understood. Mass emergence of periodical cicadas (Magicicadaspp.) provides an excellent opportunity to shed light on the influence of resource pulses on community and ecosystem dynamics: the adults emerge every 13 or 17 years in vast numbers over much of eastern North America, with a smaller but still significant number becoming incorporated into forest food webs. To study the potential effects of such arthropod resource pulse on primary production and belowground food webs, we added adult cicada bodies to the soil surface surrounding sycamore trees and assessed soil carbon and nitrogen concentrations, plant‐available nutrients, abundance and community composition of soil fauna occupying various trophic levels, decomposition rate of plant litter after 50 and 100 days, and tree performance for 4 years. Contrary to previous studies, we did not find significant cicada effects on tree performance despite observing higher plant‐available nutrient levels on cicada addition plots. Cicada addition did change the community composition of soil nematodes and increased the abundance of bacterial‐ and fungal‐feeding nematodes, while plant feeders, omnivores, and predators were not influenced. Altogether, acute resource pulses from decomposing cicadas propagated belowground to soil microbial‐feeding invertebrates and stimulated nutrient mineralization in the soil, but these effects did not transfer up to affect tree performance. We conclude that, despite their influence on soil food web and processes they carry out, even massive resource pulses from arthropods do not necessarily translate to NPP, supporting the view that ephemeral nutrient pulses can be attenuated relatively quickly despite being relatively large in magnitude.

     
    more » « less
  5. ; ; ; ( , Freshwater Biology)
    Abstract

    Climate change is increasing the frequency, severity, and extent of wildfires and drought in many parts of the world, with numerous repercussions for the physical, chemical, and biological characteristics of streams. However, information on how these perturbations affect top predators and their impacts on lower trophic levels in streams is limited.

    The top aquatic predator in southern California streams is nativeOncorhynchus mykiss, the endangered southern California steelhead trout (trout). To examine relationships among the distribution of trout, environmental factors, and stream invertebrate resources and assemblages, we sampled pools in 25 stream reaches that differed in the presence (nine reaches) or absence (16 reaches) of trout over 12 years, including eight reaches where trout were extirpated during the study period by drought or post‐fire flood disturbances.

    Trout were present in deep pools with high water and habitat quality. Invertebrate communities in trout pools were dominated by a variety of medium‐sized collector–gatherer and shredder invertebrate taxa with non‐seasonal life cycles, whereas tadpoles and large, predatory invertebrates (Odonata, Coleoptera, Hemiptera [OCH]), often with atmospheric breather traits, were more abundant in troutless than trout pools.

    Structural equation modelling of the algal‐based food web indicated a trophic cascade from trout to predatory invertebrates to collector–gatherer taxa and weaker direct negative trout effects on grazers; however, both grazers and collector–gatherers also were positively related to macroalgal biomass. Structural equation modelling also suggested that bottom‐up interactions and abiotic factors drove the detritus‐based food web, with shredder abundance being positively related to leaf litter (coarse particulate organic matter) levels, which, in turn, were positively related to canopy cover and negatively related to flow. These results emphasise the context dependency of trout effects on prey communities and of the relative importance of top‐down versus bottom‐up interactions on food webs, contingent on environmental conditions (flow, light, nutrients, disturbances) and the abundances and traits of component taxa.

    Invertebrate assemblage structure changed from a trout to a troutless configuration within a year or two after trout were lost owing to post‐fire scouring flows or drought. Increases in OCH abundance after trout were lost were much more variable after drought than after fire. The reappearance of trout in one stream resulted in quick, severe reductions in OCH abundance.

    These results indicate that climate‐change induced disturbances can result in the extirpation of a top predator, with cascading repercussions for stream communities and food webs. This study also emphasises the importance of preserving or restoring refuge habitats, such as deep, shaded, perennial, cool stream pools with high habitat and water quality, to prevent the extirpation of sensitive species and preserve native biodiversity during a time of climate change.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email