Exopolysaccharide and Poly-(beta)-Hydroxybutyrate Coproduction in Two Rhizobium meliloti Strains

Abstract

The effects of different nitrogen and carbon sources on cell growth, pH, and exopolysaccharide (EPS) and poly-␤-hydroxybutyrate (PHB) production by two strains of Rhizobium meliloti (M5N1 and Su47) are reported. Differences in the behavior of glucose-and fructose-grown cells were shown, in particular with the M5N1 strain. Growth in a glucose-containing medium was accompanied by acidification of the culture medium, which leads to cell death. On fructose, acidification was detected only in the medium with a mineral nitrogen supply. A lag phase in EPS production was observed with cells grown with glucose, probably related to an initial extracellular conversion of the carbohydrate into an acid. No lag phase was observed in EPS production from fructose or in PHB synthesis whatever the carbon source. A decrease in PHB content was noticed for both strains under conditions where acidification of media occurred. The extent of production, emphasized by the use of a coproduction index, indicates that the M5N1 strain is a more promising organism than is the Su47 strain for polymer production. Such a strain, put in rich medium (containing yeast extract) supplemented with fructose, accumulated PHB up to 85% of dry cell weight and excreted about 1.5 g of EPS per liter in the medium. Regulation of the coproduction of EPS and PHB by these cells is suggested.

Osmoregulated trehalose‐derived oligosaccharides in Sinorhizobium meliloti

“…LC-ELSD analysis of the hyperosmotic extracts showed the DP3 to DP6 oligosaccharides in all the strains tested, while they were absent in hypoosmolarity. Same experiments in the RC rich medium more commonly used to cultivate S. meliloti species [10] gave the same results.…”

“…The S. meliloti strains used were the wild-type Rm1021 and the mutant Rm10004 (Rm1021, exoA::Tn5, ndvB::Tn5), kindly provided by Prof. G.C. Walker (MIT, Massachusetts), and five other wild-type strains: Rm2011, Rm102F34Sm R , Su47, Rm5000 and M5N1 [8][9][10][11][12]. Cultures were grown at 30°C and 130 rpm in a minimal growth medium (Tris: 25 [3,4,13].…”

“…Cultures were grown at 30°C and 130 rpm in a minimal growth medium (Tris: 25 [3,4,13]. The RC rich medium [10] was also used and its osmolarity (87 mosM) was eventually increased by NaCl at 0.1 M (255 mosM) or 0.4 M (761 mosM). The medium osmolarity was measured with an automatic osmometer (Roebling).…”

Carbohydrate cycling in micro-organisms: what can C-NMR tell us?

“…One exception is the case of bacteria, such as S. meliloti, that synthesise PHB during the stationary phase of growth because the biosynthesis of this polymer requires two NADPH per monomer. In S. meliloti, PHB can accumulate up to 80% of the dry cell weight [90,91], and the requirements for NADPH are elevated. The recycling of carbohydrates may be a way to sustain such high demands.…”

“…Interestingly enough, both PP (NADPH optimisation) and triose-phosphate (hexose-phosphate conservation) were observed in S. meliloti, in situations of sugar excess (sustained acetyl-CoA formation). This seems to provide favourable conditions for the simultaneous and signi¢cant synthesis of both polysaccharides and PHB [90,91]. 5.2.2.3.2.…”