Effect of Nutrient Periodicity on Microbial Community Dynamics

Abstract

When microbes are subjected to temporal changes in nutrient availability, growth rate and substrate affinity can contribute to competitive fitness and thereby affect microbial community structure. This hypothesis was tested using planktonic bacterial communities exposed to nutrient additions at 1-, 3-, 7-, or 14-day intervals. Growth rates after nutrient addition were inversely proportional to the pulse interval and declined from 0.5 h ؊1 to 0.15 h ؊1 as the pulse interval increased from 1 to 14 days. The dynamics of community structure were monitored by 16S rRNA gene PCR-denaturing gradient gel electrophoresis. At pulse intervals of more than 1 day, the community composition continued to change over 130 days. Although replicate systems exposed to the same pulse interval were physiologically similar, their community compositions could exhibit as much dissimilarity (Dice similarity coefficients of <0.5) as did systems operated at different intervals. Bacteria were cultivated from the systems to determine if the physiological characteristics of individual members were consistent with the measured performance of the systems. The isolates fell into three bacterial divisions, Bacteroidetes, Proteobacteria, and Actinobacteria. In agreement with community results, bacteria isolated from systems pulsed every day with nutrients had higher growth rates and ectoaminopeptidase specific activities than isolates from systems pulsed every 14 days. However, the latter isolates did not survive starvation longer than those provided with nutrients every day. The present study demonstrates the dynamic nature of microbial communities exposed to even simple and regular environmental discontinuities when a substantial pool of species that can catabolize the limiting substrate is present.In most natural ecosystems microorganisms are likely to experience alternating periods of unrestricted growth with surplus nutrients, nutrient-limited growth, and starvation (6, 35). For example, phototrophs are exposed to light-dark cycles (23), with resulting effects on substrate supply to heterotrophs (1). These nutrient pulses can take place at all scales in nature (36)-over kilometers in coastal marine upwellings (19) and millimeters in laminated microbial mats. For heterotrophic microorganisms, the availability of organic substrates as the carbon and energy source is probably the most significant environmental restriction on growth (24). This is particularly true in unsaturated soil habitats, where nutrient mobility is restricted and surface-attached bacteria may remain dormant for extended periods (6).The interval between nutrient pulses could have substantial effects on microbial community composition and perhaps on microbial community function. When a nutrient pulse recurs, the physiological traits that are selected may be in opposition to those required for the microbes to survive an extended period of starvation. The exposure of a starved community of bacteria to an energy source results in interspecies competition (9) and was predicted to s...

Microbial Communities Are Well Adapted to Disturbances in Energy Input

“…Konopka et al (45) studied 16 replicate microcosms subject to discrete pulses of gelatin every day and every 7 days and observed very dynamic bacterial communities, although they observed greater variability between their replicates than we did. Similar perturbation studies (46, 47) concluded that internal dynamics seemed to dominate and external forcing was not a strong selective pressure, which is consistent with our findings. Analysis of natural marine communities during a phytoplankton bloom also displayed rapid replacement of the dominant organisms and the importance of internal feedbacks in shaping communities (34).…”

Diversity of Bacterial Communities in Container Habitats of Mosquitoes

“…The Proteobacteria were the predominant group in our investigation, accounting for 45 (50%) of 90 sequences, consistent with other investigations reporting high prevalence (20-50%) of Proteobacteria in bacterial communities in aquatic habitats [2,3,18] such as seawater [15,33], decaying salt marsh grass [7], and wastewater [7]. In potable water distribution systems, many bacterial species, including members of the Proteobacteria, Actinobacteria, low-G+C-content gram-positive bacteria, and Cytophaga-Flavobacterium-Bacterioides group, readily adhere to surfaces to form multispecies biofilms [39].…”

Seasonal shifts of the microbial community structure in a winery waste-impacted wetland soil

“…Our findings therefore suggest that even after a very long adaptation period, recurrent changes in the physicochemical conditions at the wetland surface prevent the formation of a stable microbial community. In agreement with this, Carrero-Colón et al (2006) reported that even after 130 days, no stable community structure developed at any pulse interval when an energy source was periodically added to a complex microbial community. We acknowledge that the observed changes might also have been caused by other seasonally varying environmental factors and note that, as always with open 'natural' systems, it can be impossible to incorporate suitable negative controls.…”