Ultrastructure of marine snow. I. Transmission electron microscopy methodology

Abstract

ABSTRACT-Four different approaches to determine the ultrastructure of amorphous aggregates and their principal components are evaluated for t h e~r ability to resolve structural components as small as 1 nm. Based on extensive comparative analysis, the advantages and major drawbacks of the different methods are discussed. Based on experience with marine snow from the Adriatic Sea, it is concluded that only a combination of fixation and preservation treatments ensures optimal ~nterpretation of the results. Specific emphasis is placed on the use of a hydrophilic resin (Nanoplasta) which allows fixation of high]\ hydrated polysaccharide fibrlls In their original configuration and subsequent visualization on a nm scale.

Ultrastructure of marine snow. II. Microbiological considerations

“…As outlined in detail in the companion paper (Leppard et al 1996), 4 different preparatory treatments were used correlatively; this allowed us to delineate the specific artifacts inherent in each of the preparatory treatments. All preparations were performed in 5 replicates and within 10 min after sampling in order to avoid storage artifacts (Perret et al 1991, Leppard 1992.…”

“…The size of the capsule was split in 4 categories: fully developed capsules covered the whole cell surface and were 21 cell diameter; well-developed capsules were >0.5 to I 1 cell diameter or covered more than half of the cell surface; poorly developed capsules consisted of only a few fibrils and/or covered less than half of the cell surface; cells lacking any capsule were also counted. In order to avoid underestimation of the size of the capsular envelope due to extraction artifacts, only glutaraldehyde/rutheniumred-fixed samples (Leppard et al 1996) were examined.…”

“…Samples were taken from various depth layers with rinsed Niskin bott1.e~ as well as by SCUBA divers with hand-made syringes as described in Herndl & Peduzzi (1988). From on board the RV 'Vila Velebita', marine snow from each respective sampling depth was collected as descnbed in d.etai1 in Leppard et al (1996).…”

“…The aim of this study is to elucidate the ultrastructure and natural associations of the marine-snow-associated mlcroorganisms using a newly developed technology (Leppard et al 1996, this issue) to minimize perturbation of the highly hydrated polysaccharide fibrils (see Leppard et a1 1996 for an in-depth description of the methods). Furthermore, specific attention was paid to characterization of the envelope of capsular material of free-living and marine-snow-associated bacteria.…”

INSSECT—an instrumented platform for investigating floc properties close to the seabed

“…The two properties that are most often used to characterize flocs are their size and settling velocity, as these have implications for sedimentological as well as optical studies (Dyer 1989;Hill et al 2001;Mikkelsen 2002). Also of interest is the structure and composition of the flocs as this can influence floc growth (Leppard et al 1996;Milligan and Hill 1998). Due to the fragile nature of flocs, these properties have to be determined in situ.…”