Seasonal and Successional Influences on Bacterial Community Composition Exceed That of Protozoan Grazing in River Biofilms

Abstract

The effects of protozoa (heterotrophic flagellates and ciliates) on the morphology and community composition of bacterial biofilms were tested under natural background conditions by applying size fractionation in a river bypass system. Confocal laser scanning microscopy (CLSM) was used to monitor the morphological structure of the biofilm, and fingerprinting methods (single-stranded conformation polymorphism [SSCP] and denaturing gradient gel electrophoresis [DGGE]) were utilized to assess changes in bacterial community composition. Season and internal population dynamics had a greater influence on the bacterial biofilm than the presence of protozoa. Within this general framework, bacterial area coverage and microcolony abundance were nevertheless enhanced by the presence of ciliates (but not by the presence of flagellates). We also found that the richness of bacterial operational taxonomic units was much higher in planktonic founder communities than in the ones establishing the biofilm. Within the first 2 h of colonization of an empty substrate by bacteria, the presence of flagellates additionally altered their biofilm community composition. As the biofilms matured, the number of bacterial operational taxonomic units increased when flagellates were present in high abundances. The additional presence of ciliates tended to at first reduce (days 2 to 7) and later increase (days 14 to 29) bacterial operational taxonomic unit richness. Altogether, the response of the bacterial community to protozoan grazing pressure was small compared to that reported in planktonic studies, but our findings contradict the assumption of a general grazing resistance of bacterial biofilms toward protozoa.

The food web perspective on aquatic biofilms

“…, , Wey et al. ). Via long‐term microscopic observations, predation and even proliferation events can be visualized and quantified (Erken et al.…”

“…4 A promising method for detecting links within biofilm food webs is video microscopy (Boenigk and Arndt 2000a, b). Video microscopy has been adapted for use in flow cells in which complex biofilm communities were established by connecting them to natural water bodies (Norf et al 2007, 2009a, Wey et al 2012. Via long-term microscopic observations, predation and even proliferation events can be visualized and quantified (Erken et al 2012).…”

The ecology and biogeochemistry of stream biofilms

“…Fungi are probably also an important component of stream biofilms but remain poorly studied 15,16 . Ciliates, flagellates, nematodes and even young-instar insects (such as midges) are among the top consumers in stream biofilms 17,18 , and their grazing activity can change the physical structure 19,20 , community composition 21 and carbon cycling of biofilms 22 . Furthermore, viruses have an important role in marine ecosystems 23 ; for example, in bacterial biofilms 24 , bacterial viruses (or phages) can infect cells and regulate the dynamics and diversity of bacterial communities.…”

Biocidal efficacy of monochloramine against planktonic and biofilm-associated Naegleria fowleri cells

“…; Wey et al . ). Even if it is unclear whether the biofilm matrix is a nutriment source for protozoa, it is likely that some EPS matrix will be ingested, even indirectly if embedded cells are grazed on by protozoa (Parry ; Anderson ), and more studies are required to explore this point of view.…”

“…However, biofilms represent favourable protective environment usually described as the play-ground for numbers of micro-organisms, including protozoa. Even if we cannot exclude the presence of cysts, one can argue that our freshwater biofilms were potentially highly productive environments to support protozoan growth given the high density of bacteria (>10 5 cells cm À2 ) and the likely presence of organic deposits and EPS secreted within the biofilms that provide a suitable matrix for amoeba attachment, grazing and growth (Wingender et al 1999;Wey et al 2012). Even if it is unclear whether the biofilm matrix is a nutriment source for protozoa, it is likely that some EPS matrix will be ingested, even indirectly if embedded cells are grazed on by protozoa (Parry 2004;Anderson 2013), and more studies are required to explore this point of view.…”