Decomposition of dissolved organic matter released by an isolate of Microcystis aeruginosa and morphological profile of the associated bacterial community

Abstract

This study concerns the kinetics of bacterial degradation of two fractions (molecular mass) of dissolved organic matter (DOM) released by Microcystis aeruginosa. Barra Bonita Reservoir (SP, Brazil) conditions were simulated in the laboratory using the associated local bacterial community. The extent of degradation was quantified as the amount of organic carbon transferred from each DOM fraction (< 3 kDa and 3-30 kDa) to bacteria. The variation of bacteria morphotypes associated with the decomposition of each fraction was observed. To find the degradation rate constants (kT), the time profiles of the total, dissolved and particulate organic carbon concentrations were fitted to a first-order kinetic model. These rate constants were higher for the 3-30 kDa fraction than for the lighter fraction. Only in the latter fraction the formation of refractory dissolved organic carbon (DOCR) compounds could be detected and its rate of mass loss was low. The higher bacterial density was reached at 24 and 48 hours for small and higher fractions, respectively. In the first 48 hours of decomposition of both fractions, there was an early predominance of bacillus, succeeded by coccobacillus, vibrios and coccus, and from day 5 to 27, the bacterial density declined and there was greater evenness among the morphotypes. Both fractions of DOM were consumed rapidly, corroborating the hypothesis that DOM is readily available in the environment. This also suggests that the bacterial community in the inocula readily uses the labile part of the DOM, until this community is able to metabolise efficiently the remaining of DOM not degraded in the first moment. Given that M. aeruginosa blooms recur throughout the year in some eutrophic reservoirs, there is a constant supply of the same DOM which could maintain a consortium of bacterial morphotypes adapted to consuming this substrate.

Release of ecologically relevant metabolites by the cyanobacterium Synechococcus elongatus CCMP 1631

“…Phytoplankton-derived DOM is used as an energy source and for growth by microbial communities (Moreira et al, 2011;Nelson and Carlson, 2012), particularly heterotrophic bacteria (Cole et al, 1982;Kaiser and Benner, 2008). Further, the composition of phytoplankton exudates influences microbial community structure over spatial and temporal gradients (Cottrell and Kirchman, 2000;Nelson and Carlson, 2012;Landa et al, 2013).…”

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria)

“…The consumption of a large quantity of phytoplankton-originated DOC within the first days of experiment demonstrated its high availability to bacterial utilization. Similar patterns of degradation, with a rapid phase followed by a slower step where also analyzed in experiments by Chen and Wangersky (1996) and Moreira et al (2011).…”

“…We adjusted the results from organic carbon and nitrogen consumption to a kinetic model of first degree proposed for the degradation of DOM released by Microcystis (Moreira et al, 2011). DOM degradation was assumed to happen according to three competitive processes.…”

Organic Matter in the Contemporary Ocean

“…Finally, the development of rapid genomic screening techniques for monitoring changes in cell metabolism through transcription of ribonucleic acids (RNA) has stimulated a new generation of organic nutrient amendment experiments that serve to inform on DOC metabolism as well as provide information on DOC composition (McCarren et al, 2010;Moreira et al, 2011;Mou et al, 2008). One of the most intriguing questions with regard to DOC cycling is the accumulation of semilabile dissolved polysaccharides in the upper ocean (Hansell, 2002;Hansell and Carlson, 2001;Hansell et al, 2009).…”