Prediction, enrichment, and isolation identify a responsive, competitive community of cellulolytic microorganisms from a municipal landfill

Landfills are engineered, heterogeneously contaminated sites containing large reservoirs of paper waste. Cellulose degradation is an important process within landfill microbial ecology, and these anoxic, saturated environments are prime locations for discovery of cellulases that may offer improvements on industrial cellulose degradation efforts. We sampled leachate from three locations within a municipal landfill, a leachate collection cistern, and groundwater from an adjacent aquifer to identify cellulolytic populations and their associated cellulases. Metagenomic sequencing identified wide-spread and taxonomically diverse cellulolytic potential, with a notable scarcity of predicted exocellulases. 16S rRNA amplicon sequencing detected nine landfill microorganisms enriched in a customized leachate medium amended with microcrystalline cellulose or common paper stocks. Paper-enrichment cultures showed three competition dynamics in response to the specific composition (lignin: hemi-cellulose: cellulose) of the different paper stocks. From leachate biomass, four novel cellulolytic bacteria were isolated, including two with the capacity for cellulolysis at industrially-relevant temperatures. None of the isolates demonstrated exocellulase activity, consistent with the metagenome-based predictions. However, there was very little overlap between metagenome-derived predicted cellulolytic organisms, organisms enriched on paper sources, or the isolates, suggesting the landfill cellulolytic community is at low abundance but able to rapidly respond to introduced substrates.

Community development of free-living aquatic nematodes in littoral periphyton communities

The development of an epilithic nematode community and the mode of colonisation was monitored over a 57-day period during spring in a field experiment in the littoral zone of a large oligotrophic lake. Two types of experimental units were used: one type prohibited direct colonisation via active crawling by elevating substrates into the water column and the second type had substrates placed on the lake bottom. Data from the two types of units and from nearby natural hard substrates were compared. The nematodes quickly colonised on the introduced substrates and reached maximum densities of 123 individuals per 10 cm2 after 57 days. Nematode densities on elevated and non-elevated substrates did not differ significantly. The nematode abundance and community structure showed a large initial variation, but became more stable over time and resembled the natural community structure at the end of the experiment. The maximum number of nematode species was reached after 2 weeks of colonisation, with a maximum species number on days 12 and 14 in the experimental units and on day 19 on the surrounding natural hard substrates. The five numerically dominant species, Eumonhystera vulgaris, Chromadorina bioculata, Eumonhystera filiformis, Chromadorina viridis and Daptonema dubium, accounted for most of the variation between the different communities. The results indicate that water-column transport was the main colonisation pathway of epilithic nematodes. The distribution of nematode species points to potential morphological adaptations of some species for persistence on hard substrates.

Colonization of wood substrates by the aquatic xylophage Xylotopus par (Diptera: Chironomidae) and a description of its life history

Xylotopus par populations were monitored in a central Michigan stream during the summer growth period by sampling two types of indigenous logs and four types of introduced wood block "baits." Populations of larvae in the two indigenous logs were very similar over the course of the study with regard to number of individuals, biomass accumulation, developmental rate, and spatial distribution within colonized areas. Populations of larvae in the wood baits followed trends in density and biomass accumulation that differed between wood types. A positive relationship of the parameters with substrate softness was observed. Populations of larvae in the introduced wood baits developed faster than those in indigenous logs, with portions of the bait-inhabiting populations apparently able to complete development during the summer. Populations in indigenous logs normally require a full year for development and the accelerated growth in the "fresh," introduced substrates indicates a plastic phenology that allows X. par to exploit wood of variable quality. A prerequisite for terrestrial decay in determining wood suitability for X. par is also discussed.