Functional similarity of attached and free-living bacteria during freshwater phytoplankton blooms

Abstract

Phytoplankton blooms were created in freshwater enclosures to study the functional succession and diversification for attached (>10 µm size fraction) and free-living (<10 µm size fraction) assemblages of bacteria. Bacterial dynamics in abundance, production and enzyme activity was monitored by standard methods. The functional diversity with respect to sole carbon source utilization was assessed with Biolog GN plates inoculated with bacteria from the 2 size fractions. Moreover, bacterial isolates were screened for enzyme activity involved in the degradation of carbohydrates, chitin, protein and lipid. As the bloom proceeded, the functional diversity of attached and free-living bacteria appeared to be very similar. Most functional groups present in the free-living bacterial assemblage were also recovered attached to particulate matter. Additionally, the distribution of bacterial isolates with enzyme expression was similar with respect to 6 enzymes (p > 0.07), whereas 3 glucoside-bond cleaving enzymes were more frequent among the free-living isolates (p < 0.02). These results indicate that attached and free-living bacteria were functionally closely related and that their succession tended to converge during the phytoplankton bloom. Hence, bacteria attached to particulate matter are not necessarily functionally distinct and specialized for polymer hydrolysis relative to the free-living assemblage, though they are often anticipated to be different due to their close association with particulate polymers.

Seasonal to hour variation scales in abundance and production of total and particle-attached bacteria in the open NW Mediterranean Sea (0–1000 m)

“…Comparison of microscopic observations before and after sonication showed that our sonication procedure on 0.8 µm filters do not damage the cells and resulted in >95% recovery of particle-attached bacterial cells. In addition, 44 samples analyzed by both methods showed no significant differences (mean=5.9±1.8 and 6.8±1.3×10 5 cells ml −1 by epifluorescence and flow cytometry, respectively) and were closely correlated (R=+0.68, p<0.01, n=44) that confirmed the validity of using sonication before flow cytometric enumerations as shown previously (Riemann and Winding, 2001;Worm et al, 2001).…”

Glycolytic activities in size-fractionated water samples: emphasis on rhamnosidase, arabinosidase and fucosidase activities

“…However, based on the results, it was observed that arabinosidase, fucosidase and rhamnosidase presented lower activity in the attached form than in the free-living form, and free enzymes revealed an important proportion (38-55 %) compared to the former (Table 2). Glucosidases (α-and β-) reached values comparable to other freshwater studies (Worm et al, 2001;Lemarchand et al, 2006). Working with fractionated samples Richardot et al (1999) registered the highest enzymatic activities for glucosidases (α-and β-) in the attached fraction (2-100 µm).…”

“…Conventionally, bacteria associated to marine snow and particulate matter express more enzymatic activities than the surrounding water mainly during phytoplanktonic blooms (Worm et al, 2001). Taking into account the high extracellular enzymatic activity of associated bacteria when compared to free-living bacteria, it may be assumed that this activity would degrade high molecular organic compounds of the aggregate, which would compromise the maintenance of the structure of the aggregates.…”

“…The attached communities can be responsible for up to 75% of the total hydrolytic activity (Middelboe et al, 1995). The data on extracellular glycolytic activities in size-fractionated water samples are generally related to α-and β-glucosidases (Smith et al, 1992;Worm et al, 2001;Zoppini et al, 2005), and, in some cases, galactosidases (Zoppini et al, 2005), while several enzymes that hydrolyze other monosaccharides are omitted. Glucose is, in fact, the most important and abundant monosaccharide present in biopolymers from aquatic environments but galactose, mannose, xylose, arabinose, fucose and rhamnose are also present in approximately the same equimolar concentrations (Sweet and Perdue, 1982;Gremm and Kaplan, 1997;Repeta et al, 2002;Hayakawa, 2004).…”

Untitled

“…Multiple studies have documented the correlation between phytoplankton and bacterial community dynamics, particularly at weekly or more frequent timescales (Worm et al 2001;Kent et al 2004;Newton et al 2006). In our data set, no relationship was found between phytoplankton community composition and BCC at the biweekly timescale (data not shown).…”