Diffusion of glutamic acid in relation to growth of Geotrichum candidum and Penicillium camembertii at the surface of a solid medium

Growth of pure cultures of Geotrichum candidum or Penicillium camembertii at the surface of a solid medium was studied. Consumption of nutrients by the microorganisms growing at the surface of the gel induced their diffusion from the core to the rind. Particular attention was paid to the diffusion of glutamic acid, the nitrogen source, in relation to the growth of the microorganism at the surface. The growth kinetic has been described using the Verlhust model. The diffusion coefficient of glutamic acid in sterile culture medium was measured and found to be 0.55 cm² day^?1. With this coefficient and assuming that the glutamic acid consumption was partially linked to growth, the experimental diffusion gradients have been fitted. Good agreement was found between experimental data and the diffusion/reaction model. The glutamic acid diffusion cannot be assumed to limit growth, since noticeable amounts of this substrate always remained at the upper surface of the gel. Copyright © 2004 Society of Chemical Industry     

An unstructured model for the analysis of substrate consumption and product release in relation to biosynthesis and cell maintenance during batch cultures of Geotrichum candidum and Penicillium camembertii

An unstructured model has been developed to predict microbial growth based on carbon or nitrogen substrate consumption, ammonia or carbon dioxide production and proton transfer. The model has been validated for batch cultures of Geotrichum candidum and Penicillium camembertii growing on peptones and peptones + lactate based media. The contributions of the considered kinetics to biosynthesis and cellular maintenance can be deduced from this model. The nitrogen source (peptones) was mainly utilized in biosynthesis: for P camembertii growing on peptones, 86% of the metabolized peptones. G candidum metabolized peptones preferentially to lactate as a carbon source, resulting in lactate utilization by a maintenance mechanism during the stationary state. In contrast, P camembertii, which metabolized fewer amino acids as a carbon source, utilized lactate mainly for biosynthesis (83% of the consumed lactate). Most (up to 71%) of the ammonia released was produced by deamination of amino acids utilized as both carbon and nitrogen sources by growth‐associated metabolism. With peptones, proton transfer resulted from ammonia release, most likely as a result of the growth‐associated mechanism, as supported experimentally (55–58% of the released ammonia for both microorganisms). The contribution of lactate to proton transfer resulted in 76% of protons exchanged by a growth‐associated mechanism during P camembertii growth. For total carbon dioxide production, the contributions of the energy supplies for biosynthesis and cell maintenance were similar; except during P camembertii growth in the presence of lactate (65% of growth‐associated CO₂ production). © 2002 Society of Chemical Industry     

Carbon assimilation and dissimilation during growth of Geotrichum candidum on amino acids and glucose

BACKGROUND: This work examines the metabolic behaviour of amino acids during Geotrichum candidum growth, in the presence of a primary carbon source like glucose. Amino acids were characterized based on their carbon assimilation and dissimilation by G. candidum, in the presence of glucose as the limiting substrate. RESULTS: The first group (Cys, His, Phe, Thr and Trp) was only used as nitrogen sources by G. candidum, with glucose being the carbon and energy source. Glucose repression was shown for the rest of the amino acids, since only after glucose depletion amino acids from the second group (Gly, Lys, Met, Val) were dissimilated for energy supply by oxidation into CO₂, while those from the third group (Ala, Arg, Asp, Glu, Leu, Pro and Ser) were assimilated as carbon sources (and additionally used as nitrogen sources), leading to a diauxic growth. CONCLUSION: This energy‐saving response was not previously shown for the second fungus involved in ripening of soft white cheese—P. camembertii—leading to simultaneous use of some amino acids and glucose as carbon and energy sources, and hence lower growth rates than those recorded during G. candidum growth. Copyright © 2007 Society of Chemical Industry     

柠檬醛对酸腐菌线粒体形态和功能的影响

本研究探讨了柠檬醛对酸腐菌线粒体形态、三磷酸腺苷（adenosine triphosphate,ATP）合成和三羧酸（tricarboxylic acid cycle,TCA）循环的影响。扫描电子显微镜结果显示,柠檬醛处理后,酸腐菌线粒体出现扭曲、坍塌甚至破裂的现象。酸腐菌线粒体结构的破坏导致其胞内ATP流失,胞外ATP含量增加。经最小抑菌浓度和最小杀菌浓度的柠檬醛处理后,酸腐菌TCA循环中柠檬酸合酶、α-酮戊二酸脱氢酶、异柠檬酸脱氢酶、琥珀酸脱氢酶和苹果酸脱氢酶活力以及柠檬酸含量都呈下降趋势。结论：柠檬醛处理影响了酸腐菌线粒体的形态和功能,从而抑制其生长。     

p-茴香醛抑制柑橘酸腐病菌的作用机制

为探讨p-茴香醛对柑橘酸腐病菌的抑制作用和机制,本实验结合体外实验和活体实验测定了p-茴香醛对病原菌的抑制能力,以菌丝体细胞壁、细胞膜和菌丝形态为研究对象,分析了p-茴香醛对病原菌的抑菌机制。结果表明,p-茴香醛能显著抑制柑橘酸腐病菌菌丝体生长,其最低抑菌浓度和最低杀菌浓度（minimum fungicidal concentration,MFC）均为4.48 g/L;果蜡中添加10 MFC p-茴香醛能有效降低柑橘果实酸腐病发病率,接种13 d后发病率仅为30%,显著低于对照的100%（P＜0.05）。进一步研究发现,p-茴香醛诱导胞外碱性磷酸酶活力上升,破坏酸腐病菌菌丝体细胞壁完整性,添加保护剂山梨醇也无法缓解其对病原菌的抑制;碘化丙啶染色实验表明p-茴香醛对病原菌细胞膜造成损伤;通过扫描电子显微镜观察到,p-茴香醛处理的酸腐病菌菌丝呈现褶皱、干瘪、不规则扭曲状。以上结果说明：p-茴香醛能有效抑制柑橘酸腐病菌的生长,并能有效延缓柑橘酸腐病的发病进程,其作用机制可能与p-茴香醛诱导病原菌菌丝体细胞壁和细胞膜损伤有关。     

Lipase ofGeotrichum candidum immobilized on silica gel

Silica gel is a useful support for the lipases ofGeotrichum candidum. Esterification of selected fatty acids and alcohols proceeded to 85–92% conversion in hydrocarbon solvents, and the degree of esterification was increased to 96–98% by adding 4Å molecular sieves at later stages of reaction. The equilibrium ratio of ester to fatty acid (butyl oleate to oleic) was determined for the supported lipase in a number of solvents and ranged from 92∶8 in hexane and isooctane to 16∶84 int-butanol. The essential character of the enzyme seemed unimpaired by deposition onto silica gel as judged by fatty acid selectivity and stereoselectivity.     

清香型白酒生产中白地霉的分离鉴定

从清香型二锅头酿酒车间分离到1株酵母属微生物.经传统形态学分析法结合利用26SrDNA D1/D2区序列对其进行鉴定,鉴定结果为白地霉.该白地霉是酿酒生产中的常见菌种,无酒精发酵力,但能产生良好的清香气味.从其发酵代谢产物中检测出:有机酸4种,酯类20种,醛类8种,醇类15种,芳香族化合物4种,酚类5种,含氮化合物1种.     

Molecular study of Geotrichum strains isolated from Armada cheese

The aim of this work was the genetic characterization at the strain level of 39 presumed Geotrichum candidum isolates isolated throughout the artisanal manufacturing and ripening of Armada cheese and tentatively identified at genus and/or species level by phenotypic characteristics. The molecular identification of the strains included among others the amplification and sequencing of the D1/D2 domains of the 26S rRNA gene. A restriction fragment length polymorphism (RFLP) analysis with the ITS1-5.8S-ITS2 PCR amplicons and a randomly amplified polymorphic DNA (RAPD) analysis with five different primers were carried out. The bands pattern profile obtained through RFLP by enzymatic restriction with HinfI was the same for all the strains studied, which confirmed the classification of the strains at species level. A RAPD-PCR analysis with three different primers was applied to assess the intraspecific diversity, in this way 16 band profiles were obtained for the 39 strains studied by the combined use of primers Ari1 and Omt1. This study contributes to know the occurrence and genotypic biodiversity of G. candidum in Armada cheese.     

解磷微生物的分离筛选及其解磷能力

采用无机磷培养基,从海水、淡水、海水鱼和淡水鱼中分离筛选出六种能降解无机磷的微生物。它们分别是白地霉、大肠杆菌属、链霉素属、黄杆菌属、无色杆菌属、芽孢杆菌。并对其中3株优势菌株白地霉、黄杆菌属和芽孢杆菌所能达到的解磷能力测定分别为:白地霉,51.4%,黄杆菌属,20.0%,芽孢杆菌,24.3%。