Diagnosis of the Diatom Community upon Biofilm Development on Stainless Steels in Natural Freshwater.

Caroline Richard,Smita Mitbavkar,Jessem Landoulsi

doi:10.1155/2017/5052646

Abstract

This paper reports the development of biofilms on stainless steels (SS) upon exposure in a natural freshwater ecosystem for about six months and focuses on the composition of diatom populations. By using environmental scanning electron microscopy (ESEM) technique, we provide a detailed description regarding diatom identification at species level as well as their main characteristics, including type, morphology, ability to form colony, and motility. Results reveal the presence of both prostrate (initial colonizers) and stalked (late colonizers) forms. Pennate diatoms, Cocconeis placentula and Amphora coffeaeformis, and a centric diatom, Melosira varians, are shown to be the abundant forms regardless of the SS type. Pennate diatoms dominate the community and are directly attached to the substratum, whereas the centric form is entangled in the biofilm matrix in a significant number. The dominance of adnate forms suggests that these cells are sturdy and successfully maintaining their population. In situ monitoring of the electrochemical response of immersed materials showed ennoblement of the open circuit potential, which seems to be due to the biogenic production of H2O2, detected in a significant amount within the biofilms. The substantial enrichment of biofilms with diatoms potentially suggests the implication of these microorganisms in the process of ennoblement. A mechanism is proposed in this paper describing the possible interactions of diatom community with SS in the studied ecosystem.

Highlights

Diatoms are microscopic, unicellular, autotrophic algae which are members of the heterokontic group of cells and are responsible for a major portion of the primary productivity, forming the base of the food chain in aquatic ecosystems
Typical environmental scanning electron microscopy (ESEM) micrographs of SS surfaces after about a six-month exposure in the natural river revealed the presence of heterogeneous biofilms (Figure 1)
The enrichment of biofilms with diatom community is obvious in all the micrographs, regardless of the SS type (Figure 1)

Summary

Introduction

Unicellular, autotrophic algae which are members of the heterokontic group of cells and are responsible for a major portion of the primary productivity, forming the base of the food chain in aquatic ecosystems. As centric types do not possess raphes, they are found entangled within the biofilm community Both forms occur as single cells or as colonies in various shapes (filaments, ribbons, fans, zigzags, or even stellate). Within the biofilms, these diatoms play a similar role as their counterparts in the water column forming the base of the benthic food webs.

Results

Discussion

Conclusion