Co-culture of microalgae, cyanobacteria, and macromycetes for exopolysaccharides production: process preliminary optimization and partial characterization.

In this study, the biomass and exopolysaccharides (EPS) production in co-cultures of microalgae/cyanobacteria and macromycetes was evaluated as a technology for producing new polysaccharides for medical and/or industrial application. Based on biomass and EPS productivity of monocultures, two algae and two fungi were selected and cultured in different co-culture arrangements. The hydrosoluble EPS fractions from mono- and cocultures were characterized by ¹³C NMR spectroscopy and gas chromatography coupled to mass spectrometry and compared. It was found that co-cultures resulted in the production of an EPS different from those produced by monocultures, showing fungal predominance with microalgal/cyanobacterial traces. Co-cultures conditions were screened (temperature, agitation speed, fungal and microalgae inoculation rate, initial pH, illumination rate, and glucose concentration) in order to achieve maximum biomass and EPS production, resulting in an increase of 33 and 61% in exopolysaccharides and biomass productions, respectively (patent pending)

Bacterial RuBisCO Is Required for Efficient Bradyrhizobium/Aeschynomene Symbiosis

Rhizobia and legume plants establish symbiotic associations resulting in the formation of organs specialized in nitrogen fixation. In such organs, termed nodules, bacteria differentiate into bacteroids which convert atmospheric nitrogen and supply the plant with organic nitrogen. As a counterpart, bacteroids receive carbon substrates from the plant. This rather simple model of metabolite exchange underlies symbiosis but does not describe the complexity of bacteroids' central metabolism. A previous study using the tropical symbiotic model Aeschynomene indica/photosynthetic Bradyrhizobium sp. ORS278 suggested a role of the bacterial Calvin cycle during the symbiotic process. Herein we investigated the role of two RuBisCO gene clusters of Bradyrhizobium sp. ORS278 during symbiosis. Using gene reporter fusion strains, we showed that cbbL1 but not the paralogous cbbL2 is expressed during symbiosis. Congruently, CbbL1 was detected in bacteroids by proteome analysis. The importance of CbbL1 for symbiotic nitrogen fixation was proven by a reverse genetic approach. Interestingly, despite its symbiotic nitrogen fixation defect, the cbbL1 mutant was not affected in nitrogen fixation activity under free living state. This study demonstrates a critical role for bacterial RuBisCO during a rhizobia/legume symbiotic interaction

Identification of the Carotenoid Pigment Canthaxanthin from Photosynthetic Bradyrhizobium Strains

Canthaxanthin (4,4(prm1)-diketo-(beta)-carotene) is produced as the major carotenoid pigment by orange- and dark-pink-pigmented bacteriochlorophyll-containing Bradyrhizobium strains isolated from stem nodules of Aeschynomene species. These two new pigmentation groups differ from the well-studied strain BTAi1, which accumulates spirilloxanthin as the sole carotenoid

Marinobacter vinifirmus sp. nov., a moderately halophilic bacterium isolated from a wine-barrel-decalcification wastewater

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Sinorhizobium teranga bv. acaciae ORS1073 and Rhizobium sp. strain ORS1001, two distantly related Acacia-nodulating strains, produce similar Nod factors that are O carbamoylated, N methylated, and mainly sulfated.

We have determined the structures of Nod factors produced by strains representative of Sinorhizobium teranga bv. acaciae and the so-called cluster U from the Rhizobium loti branch, two genetically different symbionts of particular Acacia species. Compounds from both strains were found to be similar, i.e., mainly sulfated, O carbamoylated, and N methylated, indicating a close relationship between host specificity and Nod factor structure, regardless of the taxonomy of the bacterial symbiont

Halomonas olivaria sp. nov., a moderately halophilic bacterium isolated from olive-processing effluents

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