有机碳源和氮源对三角褐指藻生长的影响

研究了8种有机碳源和4种氮源对三角褐指藻(Phaeodactylum tricornutum)生长的影响.结果表明,三角褐指藻具有兼养生长的能力,碳浓度为5mmol/L和50mmol/L时,葡萄糖、果糖、乙酸钠和甘油对其生长有明显的促进作用,乳酸钠和乙醇抑制藻细胞生长,半乳糖和柠檬酸钠对其生长随有机碳浓度而异.甘油、葡萄糖和乙酸钠的适宜浓度范围分别为5 -800mmol/L、100 -400mmol/L和50 -300mmol/L.培养液中分别加入50mmol/L甘油、400mmol/L葡萄糖和150mmol/L乙酸钠,培养第14天,三角褐指藻的最大生物量分别为对照的1.45倍、1.25倍和1.11倍.甘油兼养生长的最优氮源是尿素,适宜浓度范围为0.88-8.8mmol/L.当尿素浓度为4.4mmol/L时,最高生物量可达1.31g/L.     

Oxygen consumption by Metarhizium anisopliae during germination and growth on different carbon sources.

Respirometry was used to monitor the germination and growth of the entomopathogenic deuteromycete Metarhizium anisopliae on media containing carbon sources of different kinds (monosaccharides, polysaccharides, amino acids, and proteins). As also observed in several other species of fungi, M. anisopliae germination was found to be marked by a significant increase in O(2) consumption, which started a few hours before germ tube emergence. The exponential consumption of the carbon source and O(2) coincided with the exponential growth phase of the cultures. QO(2) reached a maximum value during the exponential growth phase and was drastically reduced after the depletion of the exogenous carbon source. Taking glucose as reference, we observed that casein, hydrolyzed casein, and N-acetylglucosamine accelerated germination, reduced the lag phase, and increased the growth rate. This fact demonstrates that the fungus can readily use amino acids and N-acetylglucosamine, which are the monomers of the major constituents of the insect cuticle (proteins and chitin), a property that represents an important physiological adaptation to entomopathogenicity.     

Role of carbon and nitrogen sources in bacterial growth and sporulation

[This corrects the article on p. 131 in vol. 22.].     

Effect of carbon sources upon the mycelial growth of Phytophthora citrophthora

In order to study the effect of carbon originating from different sources on the growth ofP. citrophthora, a modified Christie's formula was used as the basic nutrient medium. Carbon in various forms was then substituted for glucose in equivalent amounts. The fungus grew to a limited extent on glucose as the carbon source, but grew quite well on a maltose medium and less extensively on a sucrose medium. Fungus growth was most profuse on soluble starch, even more so than on potato dextrose and oatmeal medium. No sporangia were found in any of the media.     

Metabolism of various carbon sources by Azospirillum brasilense

Azospirillum brasilense Sp7 and two mutants were examined for 19 carbon metabolism enzymes. The results indicate that this nitrogen fixer uses the Entner-Doudoroff pathway for gluconate dissimilation, lacks a catabolic but has an anabolic Embden-Meyerhof-Parnas hexosephosphate pathway, has amphibolic triosephosphate enzymes, lacks a hexose monophosphate shunt, and has lactate dehydrogenase, malate dehydrogenase, and glycerokinase. The mutants are severely deficient in phosphoglycerate and pyruvate kinase and also have somewhat reduced levels of other carbon enzymes.     

不同无机碳源对粉核油球藻生长的影响

研究了2种无机碳源对粉核油球藻(Pinguiococcus pyrenoidosus CCMP2078)生长的影响。结果表明,适量添加NaHCO₃和通CO₂对P.pyrenoidosus CCMP2078的生长均有促进作用,NaHCO₃的添加方式对该藻的生长具有显著差异。一次性添加和分批添加NaHCO₃的优化浓度分别为5mmoL·L^-1和20mmoL·L^-1,后者对数生长末期的细胞密度、干重和比生长速率均最高,分别为8.93×10⁶cells·mL^-1,0.247g·L^-1和0.225dL^-1。通入CO₂的体积分数为0.5%时,最有利于藻细胞的生长,对数生长末期的细胞密度、干重和比生长率分别为3.83×10⁷cells·mL^-1、0.42g·L^-1和0.212d^-1。     

Utilization of various carbon sources for the growth of waterborne conidial fungi

Four isolates of waterborne conidial fungi (Tetracheatum elegans, Tetracladium marchalianum, Pestalotiopsis submersus and Flagellospora penicillioides) were investigated for their carbon requirement, using eight different carbon sources (viz. glucose, fructose, sucrose, xylose, starch, cellulose, dextrin and lactose). All fungi tested grew sparsely on the basal medium lacking in carbon, which was the control. However these fungi were found to vary in their ability to use the supplied sources of carbon. Glucose and sucrose were found to be suitable sources of carbon for all four fungal isolates, whereas fructose proved good for T. marchalianum and P. submersus. Starch and xylose also supported growth of T. marchalianum, P. submersus and F. penicillioides. Cellulose, a polysaccharide, was a poor source of carbon for the growth of these isolates. Four g/L of glucose was recorded as the most useful concentration that gives the maximum dry weight of selected fungi (262 mg and 400 mg for T. elegans and P. submersus respectively after 15 d).     

Modeling microbial dynamics in heterogeneous environments: growth on soil carbon sources

We have developed a new kinetic model to study how microbial dynamics are affected by the heterogeneity in the physical structure of the environment and by different strategies for hydrolysis of polymeric carbon. The hybrid model represented the dynamics of substrates and enzymes using a continuum representation and the dynamics of the cells were modeled individually. Individual-based biological model allowed us to explicitly simulate microbial diversity, and to model cell physiology as regulated via optimal allocation of cellular resources to enzyme synthesis, control of growth rate by protein synthesis capacity, and shifts to dormancy. This model was developed to study how microbial community functioning is influenced by local environmental conditions in heterogeneous media such as soil and by the functional attributes of individual microbes. Microbial community dynamics were simulated at two spatial scales: micro-pores that resemble 6-20-μm size portions of the soil physical structure and in 111-μm size soil aggregates with a random pore structure. Different strategies for acquisition of carbon from polymeric cellulose were investigated. Bacteria that express membrane-associated hydrolase had different growth and survival dynamics in soil pores than bacteria that release extracellular hydrolases. The kinetic differences suggested different functional niches for these two microbe types in cellulose utilization. Our model predicted an emergent behavior in which co-existence of membrane-associated hydrolase and extracellular hydrolases releasing organisms led to higher cellulose utilization efficiency and reduced stochasticity. Our analysis indicated that their co-existence mutually benefits these organisms, where basal cellulose degradation activity by membrane-associated hydrolase-expressing cells shortened the soluble hydrolase buildup time and, when enzyme buildup allowed for cellulose degradation to be fast enough to sustain exponential growth, all the organisms in the community shared the soluble carbon product and grew together. Although pore geometry affected the kinetics of cellulose degradation, the patterns observed for the bacterial community dynamics in the 6-20 μm-sized micro-pores were relevant to the dynamics in the more complex 111-μm-sized porous soil aggregates, implying that micro-scale studies can be useful approximations to aggregate scale studies when local effects on microbial dynamics are studied. As shown with examples in this study, various functional niches of the bacterial communities can be investigated using complex predictive mathematical models where the role of key environmental aspects such as the heterogeneous three-dimensional structure, functional niches of the community members, and environmental biochemical processes are directly connected to microbial metabolism and maintenance in an integrated model.     

Identification of Streptomyces lividans proteins secreted by the twin-arginine translocation pathway following growth with different carbon sources

Genome-based signal peptide predictions classified Streptomyces coelicolor as the microorganism that secretes the most proteins through the twin-arginine translocation (Tat)-dependent secretion pathway. Availability of a DeltatatC mutant of the closely related strain Streptomyces lividans impaired Tat-dependent protein secretion and enabled identification of many extracellular proteins that are secreted via the Tat pathway. Proteomic techniques were applied to analyze proteins from the supernatants of log-phase cultures. Since the bacterial secretome depends mainly on the carbon sources available during growth, xylose, glucose, chitin, and soil extracts were used. A total of 63 proteins were identified, among which 7 were predicted by the TATscan program, and 20 were not predicted but contained a potential Tat signal motif. Thirteen proteins having no signal sequence could be co-transported by Tat-dependent proteins because the genes that encode these proteins are in close proximity in the genome. Finally, the presence of 23 proteins lacking signal peptides was difficult to explain. More secreted proteins could be identified as Tat substrates in varying carbon sources.