Rhamnose and hydrolysis of MUF-α-L- rhamnopyranoside coupled with producers of rhamnose-rich extracellular polysaccharides in a hypereutrophic reservoir

Abstract

, representing 28% of total dissolved neutral carbohydrates (TDnC) on average. Rhamnose concentration was linearly correlated with TDnC concentration and with the abundance of Microcystis aeruginosa, which releases a rhamnose-rich extracellular polysaccharide (EPS). This correlation was slightly stronger when the cell densities of Aulacoseira granulata, Cryptomonas tetrapyrenoidosa and Anabaena spiroides, also rhamnose-rich EPS producers, were included. The enzymatic activity on methylumbelliferyl (MUF)-α-L-rhamnopyranoside (EARh) ranged from 0 to 57.8 nmol MUF l −1 h −1. Glucose concentrations were found to vary from 0 to 4.15 µmol l −1 (27.5% of TDnC), and the enzymatic activity on MUF-β-D-glucopyranoside (EAGl) ranged from 7.4 to 116.9 nmol MUF l −1 h −1. Variation of EARh in time was directly correlated with the density of M. aeruginosa, and with rhamnose concentration in TDnC, while EAGl activity was correlated with density of M. aeruginosa only for variation with depth. Analysis of rhamnose, glucose, TDnC, EARh, EAGl, and bacterial density at each depth individually provided evidence that EPS released was employed as bacterial substrates, despite the permanent presence of TDnC from surface to bottom, owing to its constant production. These results also showed strong evidence that both enzymes were induced by EPS. Our results strongly suggest that the predominant phytoplankton species, known producers of rhamnose and glucose-rich EPS, α-Lrhamnosidase(s) activity and rhamnose concentration in the Barra Bonita Reservoir were coupled.

Host-Specificity and Dynamics in Bacterial Communities Associated with Bloom-Forming Freshwater Phytoplankton

“…granulata (Ehrenberg) Simonsen (BB001), were isolated from the hypereutrophic Barra Bonita Reservoir in São Paulo State, Brazil, where they form frequent blooms [27], [28]. The isolates were made axenic and maintained in the culture collection of the Botany Department at the Federal University of São Carlos (World Data Center for Microorganisms No.…”

Characterization and photodegradation of dissolved organic matter (DOM) from a tropical lake and its dominant primary producer, the cyanobacteria Microcystis aeruginosa

“…Microcystis-DOM is highly biolabile (Bittar et al, 2015), which implies high biological alteration and turnover rates in the environment (Vieira et al, 2013). Other sources of DOM also exist for Barra Bonita.…”

“…Due to water column stability and Microcystis buoyancy regulation capability, phytoplankton blooms dominated by this species typically remain at the water surface for days to weeks. Given that bacterial abundance and activity tend to be low at the water surface (Vieira et al, 2013), and that phytoplankton release of DOM is generally greater during daylight hours (Kaplan and Bott, 1982), UVB degradation of Microcystis-derived DOM could be a significant mechanism of DOM removal and transformation at the surface of the reservoir. Photodegradation of DOM is considered an important process of C cycling in temperate lakes, including those where the autochthonous DOM component is equally or more dominant relative to terrigenous sources (Bertilsson and Tranvik, 2000;Kellerman et al, 2014;Minor et al, 2012), and this study extends the potential relevance of this process into tropical lakes.…”

“…High tolerance to light stress, buoyancy regulation and low edibility are competitive advantages of M. aeruginosa (Brookes and Granf, 2001;Kluijver et al, 2012;Liu et al, 2004), which, combined with warm temperatures and light-and nutrient-replete conditions, lead to dominance of this species in the Barra Bonita Reservoir throughout the year (Dellamano-Oliveira et al 2008). Consequently, M. aeruginosa is an important source of autochthonous DOM in the reservoir during both wet and dry seasons (Dellamano-Oliveira et al, 2008;Vieira et al, 2013).…”

“…The catchment area is predominantly agricultural, interspersed with small industrial and urban areas. Watershed runoff is also the cause of high inflows of inorganic N and P, mainly of agricultural origin (Tundisi et al, 2008), which favors phytoplankton growth and release of DOM (Vieira et al, 2013;Welch and Lindell, 1992).…”