Microbial Community Structure of Leaf-Cutter Ant Fungus Gardens and Refuse Dumps

BACKGROUND: Leaf-cutter ants use fresh plant material to grow a mutualistic fungus that serves as the ants' primary food source. Within fungus gardens, various plant compounds are metabolized and transformed into nutrients suitable for ant consumption. This symbiotic association produces a large amount of refuse consisting primarily of partly degraded plant material. A leaf-cutter ant colony is thus divided into two spatially and chemically distinct environments that together represent a plant biomass degradation gradient. Little is known about the microbial community structure in gardens and dumps or variation between lab and field colonies. METHODOLOGY/PRINCIPAL FINDINGS: Using microbial membrane lipid analysis and a variety of community metrics, we assessed and compared the microbiota of fungus gardens and refuse dumps from both laboratory-maintained and field-collected colonies. We found that gardens contained a diverse and consistent community of microbes, dominated by Gram-negative bacteria, particularly gamma-Proteobacteria and Bacteroidetes. These findings were consistent across lab and field gardens, as well as host ant taxa. In contrast, dumps were enriched for Gram-positive and anaerobic bacteria. Broad-scale clustering analyses revealed that community relatedness between samples reflected system component (gardens/dumps) rather than colony source (lab/field). At finer scales samples clustered according to colony source. CONCLUSIONS/SIGNIFICANCE: Here we report the first comparative analysis of the microbiota from leaf-cutter ant colonies. Our work reveals the presence of two distinct communities: one in the fungus garden and the other in the refuse dump. Though we find some effect of colony source on community structure, our data indicate the presence of consistently associated microbes within gardens and dumps. Substrate composition and system component appear to be the most important factor in structuring the microbial communities. These results thus suggest that resident communities are shaped by the plant degradation gradient created by ant behavior, specifically their fungiculture and waste management

Integrating microbial ecology into ecosystem models: challenges and priorities

Microbial communities can potentially mediate feedbacks between global change and ecosystem function, owing to their sensitivity to environmental change and their control over critical biogeochemical processes. Numerous ecosystem models have been developed to predict global change effects, but most do not consider microbial mechanisms in detail. In this idea paper, we examine the extent to which incorporation of microbial ecology into ecosystem models improves predictions of carbon (C) dynamics under warming, changes in precipitation regime, and anthropogenic nitrogen (N) enrichment. We focus on three cases in which this approach might be especially valuable: temporal dynamics in microbial responses to environmental change, variation in ecological function within microbial communities, and N effects on microbial activity. Four microbially-based models have addressed these scenarios. In each case, predictions of the microbial-based models differ—sometimes substantially—from comparable conventional models. However, validation and parameterization of model performance is challenging. We recommend that the development of microbial-based models must occur in conjunction with the development of theoretical frameworks that predict the temporal responses of microbial communities, the phylogenetic distribution of microbial functions, and the response of microbes to N enrichment

The PULSE Vision & Change Rubrics, Version 1.0: A Valid and Equitable Tool to Measure Transformation of Life Sciences Departments at All Institution Types

The PULSE Vision & Change Rubrics, version 1.0, assess life sciences departments’ progress toward implementation of the principles of the Vision and Change report. This paper reports on the development of the rubrics, their validation, and their reliability in measuring departmental change aligned with the Vision and Change recommendations. The rubrics assess 66 different criteria across five areas: Curriculum Alignment, Assessment, Faculty Practice/Faculty Support, Infrastructure, and Climate for Change. The results from this work demonstrate the rubrics can be used to evaluate departmental transformation equitably across institution types and represent baseline data about the adoption of the Vision and Change recommendations by life sciences programs across the United States. While all institution types have made progress, liberal arts institutions are farther along in implementing these recommendations. Generally, institutions earned the highest scores on the Curriculum Alignment rubric and the lowest scores on the Assessment rubric. The results of this study clearly indicate that the Vision & Change Rubrics, version 1.0, are valid and equitable and can track long-term progress of the transformation of life sciences departments. In addition, four of the five rubrics have broad applicability and can be used to evaluate departmental transformation by other science, technology, engineering, and mathematics disciplines

Getting Them Engaged: Activating Learning in the Classroom

Presentation for the Symposium for Teaching and Learning Excellence, University of Wisconsin-Madison, 26 February 2009.In this session, we will explore the concept of active learning in our classrooms. Rather than focus on academic or scholarly definitions, we will think pragmatically about the idea of first creating an engaged classroom as a way to activate learning. Participants will be challenged to consider what does an engaged learner look or act like? Are our lectures as active as we think they are? How can we transform them from passive to active? Participants will  generate one or two things to try in their own classrooms

Plenary: Here Be Dragons: Building Bridges and Lowering Barriers to Learning in the College Classroom

Presentation for the Symposium for Teaching and Learning Excellence, University of Wisconsin-Madison, 26 February 2009

The Impact of Long-Term Nitrogen Addition on Microbial Community Composition in Three Hawaiian Forest Soils

We evaluated the microbial communities in three Hawaiian forest soils along a natural fertility gradient and compared their distinct responses to long-term nitrogen (N) additions. The sites studied have the same elevation, climate, and dominant vegetation, but vary in age of development, and thus in soil nutrient availability and nutrient limitation to plant growth. Fertilized plots at each site have received 100 kg ha year-1 N addition for at least 8 years. Soil parameters, water content, pH, and ammonium and nitrate availability differed by site, but not between control and N-addition treatments within a site at the time of sampling. Microbial biomass also varied by site, but was not affected by N addition. In contrast, microbial community composition (measured by phospholipid analysis) varied among sites and between control and N-addition plots within a site. These data suggest that microbial community composition responds to N addition even when plant net primary productivity is limited by nutrients other than N. This may have implications for the behavior of forests impacted by atmospheric N deposition that are considered to be “nitrogen saturated,” yet still retain N in the soil

Do they or don't they? A synthesis of microbial response to environmental change

Background/Question/Methods
Microbial communities have long been thought to possess infinite plasticity, yet evidence in recent years increasingly indicates compositional resistance to change.
While this discovery may largely be due to the changing nature of soil biological research – with its move beyond single-season and single-factor experiments, it nevertheless highlights a critical area in current ecosystem studies and soil microbial ecology. Do they or don't they change? When? Under what circumstances? And does it matter?

Results/Conclusions
In this talk I review microbial community compositional shifts. First I address general microbial response to change – as individuals through their physiological stress responses and as communities through sorting and succession. I will highlight what we don’t know (e.g. microbial community ecology), as well as show data demonstrating what we do know about the surprising resistance of microbial communities to change some times, but not others. Second, I will explore the potential importance of temporal scale and acute versus chronic change in impacting microbial communities. Finally I will question whether ultimately it matters at all anyway.

*The audio track for talks in this symposium may be obtained at the following web address:*

*https://sites.google.com/site/esa2010symposium13audiocontent/esa2010-symposium13-audio-content

Effects of condensed tannins in conifer leaves on the composition and activity of the soil microbial community in a tropical montane forest

[Background and aims]Condensed tannins, a dominant class of plant secondary metabolites, play potentially important roles in plant-soil feedbacks by influencing the soil microbial community. Effects of condensed tannins on the soil microbial community and activity were examined by a short-term tannin-addition experiment under field and laboratory conditions. [Methods]Condensed tannins were extracted from the leaves of a dominant conifer (Dacrydium gracilis) in a tropical montane forest on Mt. Kinabalu, Borneo. The extracted tannins were added to soils beneath the conifer and a dominant broadleaf (Lithocarpus clementianus) to evaluate the dependence of the response to tannin addition on the initial composition of the soil microbial community. [Results]Enzyme activities in the field tannin-addition treatment were lower than in the deionized-water treatment. Carbon and nitrogen mineralization were also inhibited by tannin-addition. The fungi-to-bacteria ratio after tannin-addition was higher compared with the distilled-water treatment in the laboratory experiment. [Conclusions]Based on our results, we suggest that the higher concentration of condensed tannins in the leaf tissues of Dacrydium than in those of Lithocarpus is a factor influencing the microbial community and activity. This may have influences on subsequent plant performance, which induces plant-soil feedback processes that can control dynamics of the tropical montane forest ecosystem