Attached and free-living bacteria: Production and polymer hydrolysis during a diatom bloom

Abstract

Abundance, production and extracellular enzymatic activity of free-living and attached bacteria were measured during the development and collapse of a spring bloom in a eutrophic lake. Free-living bacteria accounted for most of the total bacterial production during the first part of the bloom. Their production had a significant positive correlation to chlorophyll (P < .01) and polysaccharide concentration (P < .02) and to potential β-glucosidase and aminopeptidase activity (P < .05), suggesting that algal release of dissolved polymeric compounds provided an important carbon source for bacterial production. As the bloom collapsed, we observed a change in the activity and structure of the microbial community. The mean contribution of attached bacteria to total bacterial production increased from 12% during the first part of the bloom to 26% at the end. Also, the extracellular enzymatic activity of attached bacteria increased as the bloom collapsed and constituted up to 75% of the total hydrolytic activity. An estimated disparity between hydrolytic activity and the corresponding carbon demand of attached bacteria suggested a net release of dissolved organic compounds from organic particles via polymer hydrolysis by attached bacteria.

Fronts at the Surface Ocean Can Shape Distinct Regions of Microbial Activity and Community Assemblages Down to the Bathypelagic Zone: The Azores Front as a Case Study

“…It is also consistent with the general rise in the molar C:N:P ratios of the oceanic DOM pool (Hopkinson and Vallino, 2005) and the decrease in the amino acid:carbohydrate ratio of sinking particulate organic matter (POM) with depth (Haake et al, 1993). Previous experiments have shown that bacteria degrade proteins faster than polysaccharides during decomposition of phytoplankton-derived detritus (Skopintsev, 1981;Middelboe et al, 1995), suggesting that proteinaceous components of sinking POM are more rapidly degraded than the polysaccharide fraction (Smith et al, 1992;Skoog and Benner, 1997). Thus, the relative concentration of polysaccharides in sinking POM would increase with depth, resulting in an intensive supply of polysaccharide-rich material to deeper waters and a decrease in the LAPase:BGase ratio with depth.…”

“…In contrast, α-glucosidase (AGase) and β-glucosidase (BGase) activities are generally lower at surface and south of the front. The leucine aminopeptidase to glucosidases ratios (LAPase:AGase and LAPase:BGase), which are suggested to be indicative of the relative degradation of polysaccharides relative to proteinaceous material (Middelboe et al, 1995), decrease with depth, with a marked shift coinciding with the location of the AF. The reduction with depth of the these ratios is in agreement with a previous study in the subtropical North Atlantic ) that reports a sharp decline in the LAPase:BGase ratio from the epipelagic (0-200 m) down to the bathypelagic (>1,000 m) zone.…”

Microbial activities on Trichodesmium colonies

“…A comparison of the hydrolysis rates of U-and P-glucosides for 7 colonies in 1 1 of water (1.70% h-' for a-glucosides and 4.21 % h-' for P-glucosides) and the glucose turnover of attached and free living bacteria in the same volume (0.28 % h-' and 0.1 1 YO h-', respectively) could demonstrate that only small parts of released substrates were taken up. This phenomenon of a loose connection between hydrolysis of high molecular weight substances and the uptake of low molecular weight substances by particle associated bacteria has also been described by Azam & Smith (1991), Smith et al (1992Smith et al ( , 1995 and Middelboe et al (1995). With respect to free living bacteria, Chrost & Overbeck (1990) found a close coupling between the heterotrophic activity and the activity of P-glucosidase in limnic biotopes.…”

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

“…The different aggregation behaviours of M. aeruginosa in different growth phases were related to the succession of the associated heterotrophic bacterial community during the various growth phases. Some algae-associated bacteria may play a protective role (Armstrong et al, 2001) while others may have an algicidal role (Caiola & Pellegrini, 1984;Middelboe et al, 1995).…”