Quantification of the Filterability of Freshwater Bacteria through 0.45, 0.22, and 0.1 μm Pore Size Filters and Shape-Dependent Enrichment of Filterable Bacterial Communities

Abstract

Micro-filtration is a standard process for sterilization in scientific research, medical, and industrial applications, and to remove particles in drinking water or wastewater treatment. It is generally assumed, and confirmed by quantifying filtration efficiency by plating, that filters with a 0.1-0.45 microm pore size can retain bacteria. In contrast to this assumption, we have regularly observed the passage of a significant fraction of natural freshwater bacterial communities through 0.45, 0.22, and 0.1 microm pore size filters. Flow cytometry and a regrowth assay were applied in the present study to quantify and cultivate filterable bacteria. Here we show for the first time a systematic quantification of their filterability, especially their ability to pass through 0.1 microm pore size filters. The filtered bacteria were subsequently able to grow on natural assimilable organic carbon (AOC) with specific growth rates up to 0.47 h(-1). We were able to enrich bacteria communities that pass preferentially through all three pore size filters at significantly increased percentages using successive filtration-regrowth cycles. In all instances, the dominant microbial populations comprised slender spirillum-shaped Hylemonella gracilis strains, suggesting shape-dependent selection during the filtration process. This quantification of the omnipresence of microfilterable bacterial in natural freshwater and their regrowth characteristics demand a change in the sterile filtration practice used in industrial and engineering applications as well as scientific research.

Transformations in DOC along a source to sea continuum; impacts of photo-degradation, biological processes and mixing

“…A number of recent studies have demonstrated that some bacteria are able to pass through commonly used filters sizes (Wang et al 2007;Fedotova et al 2013). For the filter pore size used in this study for Experiment A, 0.45 µm, Wang et al (2007) demonstrated with lake water that on average 50% of total bacterial populations passed through the filter. It seems clear that for Experiment A to have assessed the effects of photo-degradation only, the samples needed to have been filtered through a much smaller pore size to ensure removal of cyanobateria.…”

“…It seems clear that for Experiment A to have assessed the effects of photo-degradation only, the samples needed to have been filtered through a much smaller pore size to ensure removal of cyanobateria. However, even a pore size of 0.1 µm could have allowed some bacteria through (Wang et al 2007), but would likely have excluded a significant part of the total DOC. The DOC increases observed in Experiment A must have been due to the incomplete removal of bacteria and their subsequent reproduction, although the exact mechanism responsible for the increase (exudation through growth or stress) remain unresolved.…”

The respiratory chain is the cell's Achilles' heel during UVA inactivation in Escherichia coli

“…Only slight degradation of pure ATP in bottled water was observed from exposure to UVA light compared to dark controls (,12 %). This degradation (Wang et al, 2007); however, particularly in the initial phase of the experiments, the results were not affected by this slight degradation of ATP (see Methods). The ATP content of E. coli cells showed an initial transient increase to 110 % of the initial value and then dropped massively with increasing UVA fluence (Fig.…”

Dynamics of bacterial abundance and the related environmental factors in large shallow eutrophic Lake Taihu

“…For example, FC was reported to be four times faster and more accurate (<5% standard deviation compared to >10% for EpiM) than EpiM ). Moreover, it is possible to directly count by FC when the concentrations of bacteria are as low as 10 3 -10 4 cells/mL, whereas EpiM requires sample concentration (Wang et al 2007;Hammes et al 2008).…”