Valorisation of wheat bran to produce natural pigments using selected microorganisms.

Pigments are compounds with highly diverse structures and wide uses, which production is increasing worldwide. An eco-friendly method of bioproduction is to use the ability of some microorganisms to ferment on renewable carbon sources. Wheat bran (WB) is a cheap and abundant lignocellulosic co-product of low recalcitrance to biological conversion. Microbial candidates with theoretical ability to degrade WB were first preselected using specific databases. The microorganisms were Ashbya gossypii (producing riboflavin), Chitinophaga pinensis (producing flexirubin), Chromobacterium vaccinii (violacein) and Gordonia alkanivorans (carotenoids). Growth was shown for each on minimal salt medium supplemented with WB at 5 g.L-1. Activities of the main enzymes consuming WB were measured, showing leucine amino-peptidase (up to 8.45 IU. mL-1) and ß-glucosidase activities (none to 6.44 IU. mL-1). This was coupled to a FTIR (Fourier Transform Infra-Red) study of the WB residues that showed main degradation of the WB protein fraction for C. pinensis, C. vaccinii and G. alkanivorans. Production of the pigments on WB was assessed for all the strains except Ashbya, with values of production reaching up to 1.47 mg.L-1. The polyphasic approach used in this study led to a proof of concept of pigment production from WB as a cheap carbon source.

Metatranscriptomic exploration of microbial functioning in clouds.

Clouds constitute the uppermost layer of the biosphere. They host diverse communities whose functioning remains obscure, although biological activity potentially participates to atmospheric chemical and physical processes. In order to gain information on the metabolic functioning of microbial communities in clouds, we conducted coordinated metagenomics/metatranscriptomics profiling of cloud water microbial communities. Samples were collected from a high altitude atmospheric station in France and examined for biological content after untargeted amplification of nucleic acids. Living microorganisms, essentially bacteria, maintained transcriptional and translational activities and expressed many known complementary physiological responses intended to fight oxidants, osmotic variations and cold. These included activities of oxidant detoxification and regulation, synthesis of osmoprotectants/cryoprotectants, modifications of membranes, iron uptake. Consistently these energy-demanding processes were fueled by central metabolic routes involved in oxidative stress response and redox homeostasis management, such as pentose phosphate and glyoxylate pathways. Elevated binding and transmembrane ion transports demonstrated important interactions between cells and their cloud droplet chemical environments. In addition, polysaccharides, potentially beneficial for survival like exopolysaccharides, biosurfactants and adhesins, were synthesized. Our results support a biological influence on cloud physical and chemical processes, acting notably on the oxidant capacity, iron speciation and availability, amino-acids distribution and carbon and nitrogen fates.