Investigation of protein secretion and secretion stress in Ashbya gossypii

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 β-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.

Metagenomics revealed the phase-related characteristics during rapid development of halotolerant aerobic granular sludge

Efforts to produce aerobic granular sludge (AGS) for high-efficient and stable nutrient removal in high saline wastewaters have gained much attention recently. This study was undertaken to describe the phase-related characteristics of the rapid formation of glucose-fed salt-tolerant AGS (SAGS) generated from common municipal activated sludge using metagenomic approaches. The time needed for SAGS formation is about 11 days in a multi-ion matrix salinity of 3%. There were three distinct developmental phases during sludge maturation which were designated: I) the salinity adaptation phase (days 1-2), II) the particle-size transition phase (days 3-5) and III) the maturation and steady-state phase (days 6-11), respectively. Genome-based analysis revealed that during the phase I, members of the genus Mangrovibacter, which has the potential to secrete extracellular polymeric substances (EPS), dominated during the formation of initial SAGS aggregates. During phase II, fungi of the class Saccharomycetes, in particular the genus Geotrichum, became dominant and provided a matrix for bacterial attachment. This mutualistic interaction supported the rapid development and maintenance of mature SAGS. This work characterizes a robust approach for the rapid development of SAGS for efficient saline sewage treatment and provides unique insight into the granulation mechanism occurring during the development process.

Changes in morphogenesis and carotenogenesis to influence polygalacturonase secretion in Aspergillus carbonarius mutant

Mycelial morphogenesis and the production of fungal secretory proteins are still largely unknown. A mutant strain of Aspergillus carbonarius UV-10046 produced abundant polygalacturonase (PG) along with partially saturated canthaxanthin (PSC) at low pH conditions. In the present study, the relationship between PG secretion and PSC biosynthesis was studied using carotenogenic inhibitors and SDS-PAGE electrophoresis. Also the correlation between morphogenesis and PG secretion was investigated by analysing through microscopic studies. From the results, it was observed that secretion of PG was positively influenced by the PSC biosynthesis. The results also showed that the mutant with hairy mycelial structure resulted in higher PG activity when compared to the wild type that lacks hyper branching. From the results, it was confirmed that a mutation might have occurred in the isoprenoid pathway that has helped mutant for survival at acidic conditions. Further, an alteration in the morphogenesis and hyper branching development caused over secretion of PG enzyme in the mutant.

New biotechnological applications for Ashbya gossypii: Challenges and perspectives

The filamentous fungus Ashbya gossypii has long been considered a paradigm of the White Biotechnology in what concerns riboflavin production. Its industrial relevance led to the development of a significant molecular and in silico modeling toolbox for its manipulation. This, together with the increasing knowledge of its genome and metabolism has helped designing effective metabolic engineering strategies for optimizing riboflavin production, but also for developing new A. gossypii strains for novel biotechnological applications, such as production of recombinant proteins, single cell oils (SCOs), and flavour compounds. With the recent availability of its genome-scale metabolic model, the exploration of the full biotechnological potential of A. gossypii is now in the spotlight. Here, we will discuss some of the challenges that these emerging A. gossypii applications still need to overcome to become economically attractive and will present future perspectives for these and other possible biotechnological applications for A. gossypii.

The filamentous fungus Ashbya gossypii as a competitive industrial inosine producer

Inosine is a nucleoside with growing biotechnological interest due to its recently attributed beneficial health effects and as a convenient precursor of the umami flavor. At present, most of the industrial inosine production relies on bacterial fermentations. In this work, we have metabolically engineered the filamentous fungus Ashbya gossypii to obtain strains able to excrete high amounts of inosine to the culture medium. We report that the disruption of only two key genes of the purine biosynthetic pathway efficiently redirect the metabolic flux, increasing 200-fold the excretion of inosine with respect to the wild type, up to 2.2 g/L. These results allow us to propose A. gossypii as a convenient candidate for large-scale nucleoside production, especially in view of the several advantages that Ashbya has with respect to the bacterial systems used at present for the industrial production of this food additive. Biotechnol. Bioeng. 2016;113: 2060-2063. © 2016 Wiley Periodicals, Inc.