Impact of solid medium composition on the conidiation in Penicillium camemberti

Combined fermentation and ARTP mutagenesis to enhance lipase activity of Penicillium camembertii and its application for high-purity 1,3-diacylglycerol preparation

Penicillium camembertii lipase (PCL) is a glycerol-biased enzyme isolated from P. camembertii, exhibiting high esterification activity. The PCL activity was enhanced by combining fermentation optimization with atmospheric and room temperature plasma (ARTP) mutagenesis. Following multiple rounds of high-throughput screening and serial passages, a genetically stable mutant, P12, was obtained. In shake flask culture, P12 exhibited a lipase activity of 1600 U/g, representing an 800 % increase compared to the wild type (WT), with improved thermostability and methanol stability. Subsequently, P12 was used as a whole-cell biocatalyst to catalyze the esterification of oleic acid with glycerol in a solvent-free system to prepare 1,3-diacylglycerol (1,3-DAG). With an oleic acid /glycerol molar ratio of 4:1, 8 % biocatalyst, and a reaction temperature of 40 °C, the content of 1,3-DAG was 74.7 % after 24 h. These results suggest that the mutant P12 demonstrates considerable potential as a whole-cell biocatalyst for synthesizing high-purity 1,3-DAG.

The Growth and Conidiation of Purpureocillium lavendulum Are Co-Regulated by Nitrogen Sources and Histone H3K14 Acetylation

Plant-parasitic nematodes cause severe economic losses to agriculture. As important biocontrol agents, nematophagous fungi evolved the ability to obtain nitrogen sources from nematodes. However, the impact of nitrogen sources on the growth and development of these fungi is largely unknown. In this study, we aimed to better understand how nitrogen sources could influence vegetative growth and conidiation through epigenetic regulation in the nematophagous fungus, Purpureocillium lavendulum. Through nutrition screening, we found a phenomenon of the fungus, limited colony extension with a large amount of conidia production when cultured on PDA media, can be altered by adding ammonia nitrate. Characterized by site-directed mutagenesis, the histone H3K14 acetylation was found to be involved in the alternation. Furthermore, the acetyltransferase PlGCN5 was responsible for H3K14 acetylation. Knockout of Plgcn5 severely diminished conidiation in P. lavendulum. Chip-seq showed that H3K14ac distributed in conidiation regulating genes, and genes in the MAPK pathway which may be the downstream targets in the regulation. These findings suggest that histone modification and nitrogen sources coordinated lifestyle regulation in P. lavendulum, providing new insight into the mechanism of growth regulation by nutritional signals for the carnivorous fungus.

Conidiation of Penicillium camemberti in submerged liquid cultures is dependent on the nitrogen source

OBJECTIVE

To study the ability of a commercial Penicillium camemberti strain, used for Camembert type cheese ripening, to produce conidia during growth in liquid culture (LC), in media containing different sources of nitrogen as, industrially, conidia are produced by growth at the surface of a solid state culture because conidiation in stirred submerged aerobic LC is not known.

RESULTS

In complex media containing peptic digest of meat, hyphae ends did not differentiate into phialides and conidia. Contrarily, in a synthetic media containing KNO3 as sole nitrogen source, hyphae ends differentiated into phialides producing 0.5 × 10(7) conidia/ml. Conidia produced in LC were 25 % less hydrophobic than conidia produced in solid culture, and this correlates with a seven-times-lower expression of the gene rodA encoding hydrophobin RodA in the mycelium grown in LC.

CONCLUSION

Conidiation of P. camembertii is stimulated in iquid medium containing KNO3 as sole source of nitrogen and therefore opens up opportunities for using liquid medium in commercial productions.

Production of conidia of Penicillium camemberti in liquid medium through microcycles of conidiation

Microcycle conidiation is a survival mechanism of fungi encountering unfavorable conditions. In this phenomenon, asexual spores germinate secondary spores directly without formation of mycelium. As Penicillium camemberti conidia have the ability to produce conidiophores after germination in liquid culture induced by a thermal stress (18 and 30 °C), our work has aimed at producing conidia through this mean. Incubation at 18 and 30 °C increased the swelling of conidia and their proportion thereby producing conidiophores. Our results showed that the microcycle of conidiation can produce 5 × 10(8) conidia ml(-1) after 7 days at 18 °C of culture. The activity of these conidia was checked through culture on a solid medium. Conidia produced by microcycle conidiation formed a normal mycelium on the surface of solid media and 25 % could still germinate after 5 months of storage.

Nutritional requirements for the improvement of growth and sporulation of several strains of Monascus purpureus on solid state cultivation

This paper describes the nutritional requirements for the improvement of growth and sporulation of several strains of Monascus purpureus on solid state cultivation. The findings revealed that glucose enhanced growth of all M. purpureus strains tested but inhibited the sporulation rate. On the other hand, sucrose induced sporulation but inhibited production of cell mass. A combination of glucose and sucrose greatly enhanced sporulation and cell mass production of M. purpureus. Although growth and sporulation rate were related to the ratio of carbon to nitrogen (C/N ratio), the types and concentrations of carbon and nitrogen sources also greatly influenced the growth kinetics. Among the media tested, Hiroi-PDA medium was the most preferred medium for all M. purpureus strains tested for the enhancement of radial growth rate, sporulation, and cell production. Hence, Hiroi-PDA could be suggested as the generic basal medium for the cultivation of M. purpureus. However, individual medium optimization is required for significant enhancement in growth and sporulation of each strain of M. purpureus.

Detection of bacterial endospores in soil by terbium fluorescence

Spore formation is a survival mechanism of microorganisms when facing unfavorable environmental conditions resulting in “dormant” states. We investigated the occurrence of bacterial endospores in soils from various locations including grasslands (pasture, meadow), allotment gardens, and forests, as well as fluvial sediments. Bacterial spores are characterized by their high content of dipicolinic acid (DPA). In the presence of terbium, DPA forms a complex showing a distinctive photoluminescence spectrum. DPA was released from soil by microwaving or autoclaving. The addition of aluminium chloride reduced signal quenching by interfering compounds such as phosphate. The highest spore content (up to 10⁹ spores per gram of dry soil) was found in grassland soils. Spore content is related to soil type, to soil depth, and to soil carbon-to-nitrogen ratio. Our study might provide a basis for the detection of “hot spots” of bacterial spores in soil.

Production of thermotolerant entomopathogenic fungal conidia on millet grain

Thermotolerance of entomopathogenic (insect-killing) fungi should be seriously considered before industrialization. This work describes the feasibility of millet grain as a substrate for production of thermotolerant Beauveria bassiana (Bb) GHA and ERL1170 and Metarhizium anisopliae (Ma) ERL1171 and ERL1540 conidia. First, conidial suspensions of the Bb isolates, produced on millet grain in polyethylene bags, were exposed to five temperatures (43-47 °C) at 15-min intervals for up to 120 min (experiment I). Agar-based quarter-strength (¼) Sabouraud dextrose agar supplemented with yeast extract (SDAY) and whey permeate media served as controls. Millet-grain-based culture was superior in producing the most thermotolerant Bb conidia, followed by whey permeate agar and ¼SDAY-based cultures. Secondly, to compare the thermotolerance of conidia produced at the same conditions, the Bb isolates were then produced on agar-based millet powder medium, with ¼SDAY and whey permeate agar media as controls, and the two Ma isolates were added (experiment II). They were then exposed to the same temperatures as above. More thermotolerant Bb and Ma conidia were produced on millet powder agar than on whey permeate agar and ¼SDAY overall. These results suggest that millet grain can be used as a substrate to produce thermotolerant conidia in a mass production system.

Cloning and expression of genes involved in conidiation and surface properties of Penicillium camemberti grown in liquid and solid cultures

Based on bioinformatic data on model fungi, the rodA and wetA genes encoding, respectively, a RodA hydrophobin protein and the WetA protein involved in conidiation mechanisms, were PCR-cloned and characterized for the first time in Penicillium camemberti. These results, completed by a sequence of the brlA gene (available in GenBank), which encodes a major transcriptional regulator also involved in the conidiation mechanism, were used to compare, by qRT-PCR, the expression of the three genes in liquid and solid cultures in a synthetic medium. While expression of the brlA and wetA genes increased dramatically in both culture conditions after 4 days of growth, expression of the rodA gene increased only with conidiation and in the solid culture, and this expression was correlated with production and secretion of a RodA protein outside the hyphae, which became very hydrophobic. In liquid cultures, no production of RodA occurred in mycelia, which remained hydrophilic, and no conidiation was detected despite formation of swellings at the tips of hyphae. The absence of conidiation in liquid culture correlated with the lack of rodA gene expression, which could be regulated by the medium composition independently of brlA and wetA genes expression.