Growth of yeast colonies on solid media

Colonies on nutrient agar of the aerobic yeast Candida utilis show linear increases in diameter and height with time throughout most of the growth cycle. The concentration of glucose in the agar has a negligible effect on radial growth rate although an increase in the glucose concentration prolongs the linear radial growth phase. The rate of increase in height of the colony is proportional to the square root of the initial glucose concentration. A new model that considers both glucose diffusion and oxygen diffusion in the colony is consistent with the observed colony profiles.     

Growth patterns of yeast colonies depending on nutrient supply

Common theories of microbial growth and physiology are formulated exclusively in terms of the isolated microorganisms – especially bacteria. This is, however, an inadmissible simplification because it is obvious that the organization of microbial populations and colonies follows certain general rules. Bacterial colonies are able to generate complex interfacial growth patterns similar to those observed during diffusion-limited growth processes in non-living systems. One reason for these patterns is assumed to be the ability of many bacteria to swarm in an active manner on a substrate surface. Therefore the models of bacterial colony growth incorporate “random walkers”, which move actively in response to a gradient in the concentration of nutrients and communicate with each other by means of a chemotactic feedback. A selected number of yeasts were tested with regard to their colony growth patterns depending on the medium parameters such as nutrient concentration. Growth patterns similar to those which were described in literature for bacteria were also found in these experiments. It concerns in particular growth types like compact growth, fractal growth and dense-branching growth. This result allows a hypothesis to be formulated, that – especially in the case of fractal growth patterns – wandering of cells on a substrate surface may be induced by uncontrolled “swimming” on a thin water film caused by the metabolic activity (e.g. respiration) of the cells on the surface of the agar. Furthermore it was found that an interplay between changes in the individual morphology of yeast cells and the morphology transitions takes place. Such growth patterns are known for Candida sp. which are able to form pseudomycel and blastospores.     

Growth ofThiobacillus ferrooxidans on solid media containing heterotrophic bacteria

Summary the study of the chemolithotrophic bacteriumThiobacillus ferrooxidans, an organism important in mining and metallurgical applications, has always been complicated by the inability to cultivate and enumerate many wild strains on solid agar. Here, we have described a plate-count procedure that uses an acidophilic heterotrophic bacterium to scavenge organic material from normal agar, permitting colony formation of the autotroph without visible evidence of growth of the heterotroph. This technique could enable anyT. ferroxidans isolate, including those that are agar-sensitive, to grow and develop colonies on solid medium.     

Morphological characterisation of yeast colony growth on solid media using image processing

To rapidly determine the effect of environmental factors on yeast growth, a cell counting and colony sizing image analysis method was developed to characterise colony growth on solid media. A digitised microscopic image of the yeast was analysed using the Watershed algorithm for cell number determination and a morphological edge detection for colony size determination. The influence of temperature and physiological stress on yeast growth was then investigated over 12.5 h and data extracted by the image analysis method. © Rapid Science Ltd. 1998     

Growth of yeast Candida utilis in crotonaldehyde containing media

Summary The inhibitory influence of the higher concentration of 20butenal, crotonaldehyde was followed during the batch and long-term continuous fermentation of Candida utilis growing on synthetic ethanol. Most crotonaldehyde is removed from the medium by biotransformation. Crotonaldehyde inhibits the growth, lengthens the lag phase and decreases the biomass yield and the content of crude proteins in the biomass. The yeast C. utilis is capable of growing on media containing very high concentrations of inhibitor in the in-flow during continuous cultivation. Uncharacteristic transport oscillations of the content of crotonaldehyde were observed for which acidic groups on the cell membrane are probably responsible. A sensitive method which is suitable for measuring very low concentration of crotonaldehyde in aqueous solutions is described. Crotonaldehyde acts as an uncompetitive inhibitor with slight mixed type of inhibition. An equation describing the kinetics of inhibition was derived.     

The role of sensitive bacteria in determining the count of phage negative colonies on solid growth media

The purpose of the work was to study how the number of phage negative colonies on a solid growth medium depended on the concentration of a sensitive bacterial strain. For the system of phage lambda and a sensitive E. coli cell, the number of negative colonies was maximal at a concentration of ca. 4 X 10(8) cells/ml.     

Elastic instability in growing yeast colonies

The differential adhesion between cells is believed to be the major driving force behind the formation of tissues. The idea is that an aggregate of cells minimizes the overall adhesive energy between cell surfaces. We demonstrate in a model experimental system that there exist conditions where a slowly growing tissue does not minimize this adhesive energy. A mathematical model demonstrates that the instability of a spherical shape is caused by the competition between elastic and surface energies.     

Analysis of bacterial populations in a grassland soil according to rates of development on solid media

Abstract The process of colony formation by bacteria from grassland soil sampled in April, July and September was simulated by a colony-forming curve (CFC). The CFC was a super-imposition of several component curves (cCFC) given theoretically by the first order reaction (FOR) model [3,6]. The pattern of FOR model curves was not influenced by the time of sampling and four cCFCs were always recognized during an incubation period of 160 h. It was considered that the CFC describes an inherent property of the bacterial population of the field. Bacterial isolates were obtained from colonies produced in each of four cCFCs on agar plates. Isolates corresponding to one cCFC were classified as one group. The bacterial isolates were characterized by morphological and physiological tests and subsequently clustered. Few oligotrophic bacteria were obtained among bacteria which produced visible colonies within 63 h of incubation time. On the other hand, approx. 50% of bacteria which produced v colonies after 63 h were oligotrophic bacteria. The time required for the appearance of the first colony, t _r of the FOR model, was very similar in the isolates belonging to one group. A close linear relationship was observed between t _r value and doubling time of isolates.