Interrogation of the cell wall integrity pathway in Aspergillus niger identifies a putative negative regulator of transcription involved in chitin deposition

Microbial Biotechnolog

Rab GDP-dissociation inhibitor gdiA is an essential gene required for cell wall chitin deposition in aspergillus niger

The cell wall is a distinctive feature of filamentous fungi, providing them with structural integrity and protection from both biotic and abiotic factors. Unlike plant cell walls, fungi rely on structurally strong hydrophobic chitin core for mechanical strength together with alpha- and beta-glucans, galactomannans and glycoproteins. Cell wall stress conditions are known to alter the cell wall through the signaling cascade of the cell wall integrity (CWI) pathway and can result in increased cell wall chitin deposition. A previously isolated set of Aspergillus niger cell wall mutants was screened for increased cell wall chitin deposition. UV-mutant RD15.8#16 was found to contain approximately 60% more cell wall chitin than the wild type. In addition to the chitin phenotype, RD15.8#16 exhibits a compact colony morphology and increased sensitivity towards SDS. RD15.8#16 was subjected to classical genetic approach for identification of the underlying causative mutation, using co-segregation analysis and SNP genotyping. Genome sequencing of RD15.8#16 revealed eight SNPs in open reading frames (ORF) which were individually checked for co-segregation with the associated phenotypes, and showed the potential relevance of two genes located on chromosome IV. In situ re-creation of these ORF-located SNPs in a wild type background, using CRISPR/Cas9 genome editing, showed the importance Rab GTPase dissociation inhibitor A (gdiA) for the phenotypes of RD15.8#16. An alteration in the 5′ donor splice site of gdiA reduced pre-mRNA splicing efficiency, causing aberrant cell wall assembly and increased chitin levels, whereas gene disruption attempts showed that a full gene deletion of gdiA is lethal.Plant science

Efficient marker free CRISPR/Cas9 genome editing for functional analysis of gene families in filamentous fungi

Microbial Biotechnolog

Chitin in the fungal cell wall: Towards valorization of spent biomass of Aspergillus niger

Aspergillus niger is an important industrial producer of organic acids and enzymes producing large amounts of spent fungal biomass. In the European Research Area Industrial Biotechnology (ERA-IB) funded project, we effectively aimed to improve the composition of post-fermentation fungal biomass for extraction of the value-added product chitosan as a derivative of cell wall chitin (FunChi). As chitin/chitosan is not encountered in plant or human tissue, it often acts as an elicitor to plant and animal immune responses in order to fight off  possible impending fungal infections. The application of both chitin and chitosan oligomers have been shown to prime plants against infection. This thesis discusses the identification of genes that are important for chitin deposition in the cell wall of A. niger. In addition, the work described here also investigates the genes that facilitate chitin cross-linking to the cell wall. The relevance of all findings are discussed in relation to both the improvement of chitin extraction from post-fermentation biomass and to the integrity of the fungal cell wall. Microbial Biotechnolog

The evolution of no-cost resistance at sub-MIC concentrations of streptomycin in Streptomyces coelicolor

Microbial Biotechnolog

Phytoplankton and pigment patterns across frontal zones in the Atlantic sector of the Southern Ocean

Phytoplankton distribution and concentrations of macronutrients and iron were studied in the Polar Frontal Zone (PFZ) and the eastern Weddell Gyre of the Southern Ocean, during austral autumn. HPLC analysis of algal pigments was combined with microscopy observations to assess algal distribution. Patterns of algal distribution were dictated by the frontal systems. Travelling from north to south, four distinctively different algal communities were observed, the composition of which could be explained by variations in nutrients, light climate and grazing pressure. North of the PFZ, low silicate levels (100 m depth) together with low incident irradiance in autumn were likely limiting algal growth. At the Marginal Ice Zone (MIZ), the phytoplankton community consisted mainly of low numbers of flagellates (Chlorophyceae and haptophytes) and high numbers of microzooplankton, indicating phytoplankton control by grazing. The phytoplankton distribution patterns presented here and the relation with potential growth-controlling factors provides more insight in the mechanisms that control carbon fluxes from the atmosphere into the ocean interior

Deletion of the Aspergillus niger pro-protein processing protease gene kexB results in a pH-dependent morphological transition during submerged cultivations and increases cell wall chitin content

Microbial Biotechnolog

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

The remote waters of the Pacific region of the Southern Ocean are the furthest away from any upstream and upwind continental Fe sources. This prime area for expecting Fe limitation of the plankton ecosystem was studied (March–April 1995) along a north–south transect at ~89°W. At the end of the austral summer the upper wind-mixed layers were in the order of ~100 m deep, thus mixing the algae down into the dimly lit part of the euphotic zone where photosynthesis is severely restricted. The dissolved Fe was found at low concentrations ranging from 0.05 nM near the surface to 0.5 nM in deeper waters. Along the transect (52°S–69°S), the dissolved iron was enhanced in the Polar Front, as well as near the Antarctic continental margin (0.6–1.0 nM). In between, the southern ACC branch was depleted with iron; here the concentrations in surface waters were quite uniform at about 0.21 nM. This is only somewhat lower than the 0.49 nM (October 1992) and 0.31 nM (November 1992) averages in early spring in the southern ACC part of Atlantic 6°W sections. First, the lower ~0.21 nM in March–April 1995 may partly be due to continuation of the seasonal trend where the phytoplankton growth, albeit modest, was removing Fe from the surface waters. Secondly, the 89°W Pacific stations are further downstream continental or seafloor sources than the Atlantic 6°W section. In the latter case, the ACC water had passed through the Drake Passage and also over the Sandwich Plateau. Indeed for Drake Passage, intermediate Fe concentrations have been reported by others. The generally somewhat lower surface water Fe at the ACC and PF at 89°W is consistent with the distance from sources and the late summer. It also would explain the very low abundance of phytoplankton (Chl a) in the region and the conspicuous absence of plankton blooms. In the subAntarctic waters north of the Polar Front there are no diatoms, let alone diatom blooms, due to low availability of silicate. Thus, it appears the biological productivity is suppressed due to iron deficiency, in combination with the severe seasonal effects of wind mixing on the light climate, as well as regional silicate limitation for diatoms.

A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

Plant science