Bacterial-algal interactions in polysaccharide production

Abstract

ABSTRACT. The effects of phosphate limitation and of the presence of marine bacteria during phosphate limitation on growth and polysaccharide production in the diatom Cylindrotheca fusiformis grown in batch cultures are described in this paper. Growth of C. fusiformis was inhibited under low Pi (inorganic phosphate) conditions, corresponding to an increasing N/P ratio, and higher amounts of polysaccharides were extruded in the medium, in particular during the stationary phase of growth. The presence of bacteria reduced phytoplankton cell density only when the phosphate added corresponded to 1/6 of the initial amount. Even when diatom cell growth was not affected, the presence of bacteria stimulated a higher polysaccharide production. These results are interpreted in the light of the fact that nutrient-stressed phytoplankton cells produced and released a higher amount of polysaccharides and, as bacteria exhibited a better utilization of phosphate than algal cells, their presence accentuated the Pi depletion, resulting in a higher polysaccharide production.

Major inter-annual variations in microbial dynamics in the Gulf of Trieste (northern Adriatic Sea) and their ecosystem implications

“…In the spring of 2000 polysaccharide production by phytoplankton (mostly composed by diatoms) could also have been enhanced due to the increase of P limitation; this is consistent with the findings of several authors (Guerrini et al 1998, Myklelstad 1999, Alcoverro et al 2000, Staats et al 2000) that P-limited diatoms release copious amounts of polysaccharides.…”

Effect of bacteria on growth and biochemical composition of two benthic diatoms Halamphora coffeaeformis and Entomoneis paludosa

“…A competition can occur between the two groups for the use of resources such as inorganic nutrients (nitrate, phosphate), especially under limiting conditions (Guerrini et al, 1998;Joint et al, 2002;Rhee, 1972). Bacteria seem more efficient than microalgae for phosphate assimilation under limiting P-conditions; whereas the inverse occurs when the two organisms are cultured with high concentration of phosphate (Guerrini et al, 1998).…”

Microbial ecology of organic aggregates in aquatic ecosystems

“…Because all experimental studies on the formation of TEP by phytoplankton were carried out with non-axenic cultures and because under in situ conditions phytoplankton are always associated with bacteria, it is possible that bacteria are much more actively involved in the formation of TEP than we assume. Bacteria in the phycosphere may control the production of TEP by algae by reducing the availability of inorganic phosphate to algae, resulting in enhanced rates of algal polysaccharide secretion (Guerrini et al 1998, Grossart 1999. To specifically examine the role of bacteria in forming TEP, comparative experiments with axenic and nonaxenic algae need be carried out.…”

“…Also, bacteria were recently shown to secrete large amounts of TEP and thus may directly control the formation of macroaggregates . (4) Specific bacterial populations colonizing diatoms or living in their phycosphere (Bell & Mitchell 1972) obviously also control phytoplankton growth, mortality and secretion of polysaccharides, and thus may directly control the aggregate formation (Azam 1998, Brussaard & Riegman 1998, Guerrini et al 1998, Grossart 1999.…”