Comparison of Extracellular Enzyme Activities and Community Composition of Attached and Free-Living Bacteria in Porous Medium Columns

Abstract

Free-living and surface-associated microbial communities in sand-packed columns perfused with groundwater were compared by examination of compositional and functional characteristics. The composition of the microbial communities was assessed by bulk DNA extraction, PCR amplification of 16S ribosomal DNA fragments, separation of these fragments by denaturing gradient gel electrophoresis, and sequence analysis. Community function was assessed by measurement of ␤-glucosidase and aminopeptidase extracellular enzyme activities. Free-living populations in the aqueous phase exhibited a greater diversity of phylotypes than populations associated with the solid phase. The attached bacterial community displayed significantly greater ␤-glucosidase and aminopeptidase enzyme activities per volume of porous medium than those of the free-living community. On a per-cell basis, the attached community had a significantly higher cell-specific aminopeptidase enzyme activity (1.07 ؋ 10 ؊7 nmol cell ؊1 h ؊1 ) than the free-living community (5.02 ؋ 10 ؊8 nmol cell ؊1 h ؊1 ). Conversely, the free-living community had a significantly higher cell-specific ␤-glucosidase activity (1.92 ؋ 10 ؊6 nmol cell ؊1 h ؊1 ) than the surface-associated community (6.08 ؋ 10 ؊7 nmol cell ؊1 h ؊1 ). The compositional and functional differences observed between these two communities may reflect different roles for these distinct but interacting communities in the decomposition of natural organic matter or biodegradation of xenobiotics in aquifers.Functional differences between free-living and particle-or macroaggregate-associated bacteria have been documented in the water columns of aquatic (14, 31, 37) and marine (20,32,35,39,40) environments. Because cell attachment is known to strongly but unpredictably affect cell physiology (29, 41), there has been uncertainty whether these functional differences are due to changes in functional expression or differences in community composition (12,22,32,35). Independent reports of compositional differences in free-living and attached bacteria in marine water columns (1,5,12) and two studies in which aspects of both structure and function of these two communities were measured (10, 35) indicate that compositional differences may be responsible (in part) for the observed functional differences.The current working model in aquatic and marine environments is that attached and unattached bacteria comprise two distinct but interacting communities, shaped by differential access to nutrients and susceptibility to predation (14,20,23,31,32,35,39,40). For example, bacteria attached to particulate matter suspended in water columns display greater extracellular enzyme activity than their free-living counterparts (20,22,31,32,35,39). However, uptake by the attached populations of the products of this extracellular activity appears to be uncoupled from the enzyme activity, creating a supply of usable organic carbon to free-living bacteria in the surrounding water (22,31,39).Differences in rates of polymer hydrolysis, substrate u...

Cross-Ocean Distribution of Rhodobacterales Bacteria as Primary Surface Colonizers in Temperate Coastal Marine Waters

“…Surface colonization may provide many advantages to the colonizers, such as (i) protection from adverse environments and predation, (ii) increasing nutrient availability and metabolic cooperativity, (iii) facilitating new genetic trait exchange and acquisition, (iv) maintaining extracellular enzyme activities, and (v) formation of a higher level of microbial organization (15,23,29,38). Surface-colonizing bacteria play important roles in environmental and geomicrobiological processes, including biomineralization of organic matter, biodegradation of xenobiotic compounds, and biogeochemical cycling of nutrients and other earth elements (7,18,32,40).…”

Gut-associated microbial symbionts of the marsh fiddler crab, Uca pugnax

“…Products of dissolved enzymes are more likely to be lost to the producing cell (Vetter et al 1998) (Huston and Deming 2002;Lehman and O'connell 2002). …”

“…These authors calculated protease and glucosidase activities of attached bacteria and normalized to a percell basis. Using our estimates of total bacterial abundance and Lehman and O'Connell's (2002) per-cell enzyme activities, we estimated total bacterial enzyme activities in both the stomach and hindgut and compared these values with our measurements of total enzyme actitvities for intermolt regular crabs. In the hindgut, total estimated bacterial production was 4.2 times greater than measured protease activity and 44.7 times greater than measured glucosidase activity.…”

“…To assess the potential importance of bacterial contributions to total enzyme activities, we estimated total possible bacterial enzyme production based on literature values (Lehman and O'Connell 2002). These authors calculated protease and glucosidase activities of attached bacteria and normalized to a percell basis.…”

Role and Behavior of Benthic Microbes Able to Degrade Herbicide Atrazine in Naturally Derived Water/sediment Microcosm.

“…In the present study, we attempted to examine from an ecological aspect atrazine biodegradation using simple-scale, naturally derived sediment/water microcosms. Recently, in binary phase environments such as sediment/water, microbial communities both attached and free-living have been recognized to be functionally different 16,21,30) . However, to our knowledge, there have been few reports on such topics dealing with xenobiotic-degrading microbes.…”