Microbial dynamics on diatom aggregates in Øresund, Denmark

Abstract

Size, chemical composition, bacteria, flagellate, and ciliate abundance, bacterial production and growth rates as well as community respiration rates were measured on natural diatom aggregates of different sizes collected by SCUBA divers on 5 subsequent days offshore from northern Zealand, Denmark. Aggregate size was highly variable (0.16 to 524 mm 3 ) throughout the sampling period, whereas aggregate (agg.) dry mass (70 to 390 µg agg. ) and organic carbon content (48 to 130 µg agg.-1 ) varied less. The composition of particulate organic amino acids on aggregates was very different from that of total dissolved amino acids in the matrix water of the aggregates. Bacteria, flagellates, and ciliates were 10-to 10 000-fold enriched on aggregates compared to their abundance in the surrounding water. Enrichment factors of bacteria, flagellates, and ciliates decreased significantly with increasing aggregate size. Ciliates showed the highest and flagellates the lowest enrichment on aggregates. Absolute rate of bacterial production was significantly correlated with aggregate size, and it constantly increased on aggregates of similar size throughout the sampling period. Cell-specific production rates were consistently higher for aggregate-associated bacteria than for free-living bacteria, and 3 to 20% of all bacteria were produced on aggregates. High release of dissolved organic matter and bacteria into the surrounding water was indicated by the release of amino acids into the surrounding water and high calculated detachment rates of aggregateassociated bacteria. Marine snow, thus, should be regarded as comprising integral components rather than isolated microenvironments of the pelagic zone. Its nature has important consequences for organic matter cycling from small scales up to the global scale.

Immigration of prokaryotes to local environments enhances remineralization efficiency of sinking particles: a metacommunity model

“…1). Parameters in these processes are based on empirical data: the growth efficiency of prokaryotes (del Giorgio & Cole 2000), mortality of prokaryotes (Strom 2000, Grossart et al 2003, maximum uptake ratio of hydrolyzed carbon (Smith et al 1992), and the supply rate of organic carbon (on the same order as primary production) (Williams 2000) (see Appendix 2 for details).…”

Carboidratos dissolvidos do reservatório de Barra Bonita (Estado de São Paulo, Brasil) e sua relação com as algas fitoplanctônicas abundantes

“…Como constituintes das substâncias húmicas e fúlvicas podem levar a um melhor entendimento dos mecanismos da gênese da matéria orgânica complexa e pela sua susceptibilidade de complexar-se com metais traços, podem controlar a disponibilidade destes no meio aquá-tico (Lombardi & Vieira 2000, Freire-Nordi et al 2005, Gouvêa et al 2005, Nogueira et al 2005. Desde que os polissacarídeos extracelulares podem ser usados como substrato por bactérias (Freire-Nordi & Vieira 1998, Colombo et al 2004, estes componentes podem realizar um importante papel na possível associação específica bactéria/alga (Grossart et al 2003). Também são os principais componentes do carbono orgânico liberado pelas algas e são extremamente variáveis na sua composição monossacarídica e estereo-química.…”

Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation

“…Bacteria densely colonize marine snow (Alldredge et al, 1986) and aggregate-associated microbial processes such as enzyme activities have often been found to be elevated relative to the surrounding water (Smith et al, 1992;Ploug et al, 1999;Grossart et al, 2003Grossart et al, , 2007, making marine snow hotspots for carbon remineralization (Azam and Long, 2001). For instance, in the Baltic Sea, Grossart et al (2003) found 100 to 360 times higher cell-specific protease and β-glucosidase activities, respectively, in aggregates compared to water surrounding the aggregates.…”