Protoplast fusion between Aspergillus oryzae and Aspergillus niger in relation to their multinuclear nature

Protoplasts of cycloheximide-resistant strains from Aspergillus oryzae IFO 5239 were fused with those of kabicidin-resistant strains from Aspergillus niger IFO 4407. By nuclear staining in conidia, it appeared that all of the fusant conidia had two kinds of nuclei. Small nuclei seemed to be derived from A. oryzae and large nuclei seemed to be derived from A. niger. However, three types of antibiotic resistance were shown among the conidia of fusants. Almost all were kabicidin resistant. Conidia of fusants were multinuclear and had various DNA contents and various sizes. By the comparison with the growth rates of parental strains, the growth rates of A. niger were superior to those of A. oryzae. The inclination in the distribution of antibiotic resistance of fusant conidia seemed to owe more to the differences of growth rates between parental strains than the influence of the multinucleate nature of a parental strain.     

Ecophysiological differences between saprotrophic and clinical strains of the microscopic fungus Aspergillus sydowii (Bainier & Sartory) Thom & Church

A number of ecophysiological differences were shown for saprotrophic and clinical strains of the potentially pathogenic microscopic fungus Aspergillus sydowii. The colony growth rates were determined for four saprotrophic and five clinical fungus strains on Czapek medium within the ranges of temperature (5, 10, 15, 20, 30, 35, 37, 40, 42°C) and humidity (0.8, 0.85, 0.9, 0.95, 099 a_w), as well as on media with other sources of organic matter (Sabouraud medium, Hutchinson medium with cellulose, and water agar). The capacity for growth of A. sydowii strains on a broad spectrum of organic substrates was determined with the EKOLOG method for multisubstrate testing. The clinical and saprotrophic strains of A. sydowii differed in the colony growth rates under the same temperature and humidity combinations, as well as in the capacity for growth on different organic substrates. At decreased water activity (0.90–0.85 a_w), the temperature interval for growth of the saprotrophic strains was narrower (30 ± 2°C) than for the clinical strains (25–30°C). Comparison of growth on different media revealed the highest growth rates of the clinical strains on Sabouraud protein-containing medium. The method of multisubstrate testing showed that the saprotrophic strains grew on sugars better than the clinical ones.     

Algal Bioremediation of Waste Waters from Land-Based Aquaculture Using Ulva: Selecting Target Species and Strains

The optimised reduction of dissolved nutrient loads in aquaculture effluents through bioremediation requires selection of appropriate algal species and strains. The objective of the current study was to identify target species and strains from the macroalgal genus Ulva for bioremediation of land-based aquaculture facilities in Eastern Australia. We surveyed land-based aquaculture facilities and natural coastal environments across three geographic locations in Eastern Australia to determine which species of Ulva occur naturally in this region and conducted growth trials at three temperature treatments on a subset of samples from each location to determine whether local strains had superior performance under local environmental conditions. DNA barcoding using the markers ITS and tufA identified six species of Ulva, with U. ohnoi being the most common blade species and U. sp. 3 the most common filamentous species. Both species occurred at multiple land-based aquaculture facilities in Townsville and Brisbane and multiple strains of each species grew well in culture. Specific growth rates of U. ohnoi and U. sp. 3 were high (over 9% and 15% day⁻¹ respectively) across temperature treatments. Within species, strains of U. ohnoi had higher growth in temperatures corresponding to local conditions, suggesting that strains may be locally adapted. However, across all temperature treatments Townsville strains had the highest growth rates (11.2–20.4% day⁻¹) and Sydney strains had the lowest growth rates (2.5–8.3% day⁻¹). We also found significant differences in growth between strains of U. ohnoi collected from the same geographic location, highlighting the potential to isolate and cultivate fast growing strains. In contrast, there was no clearly identifiable competitive strain of filamentous Ulva, with multiple species and strains having variable performance. The fast growth rates and broad geographical distribution of U. ohnoi make this an ideal species to target for bioremediation activities at land-based aquaculture facilities in Eastern Australia.     

Effect of sodium chloride on growth of heterotrophic marine bacteria

The effect of NaCl on the growth rates and yields of 31 gram-negative, heterotrophic, marine bacteria was determined. The strains used were representative of aerobic genera (Alteromonas, Pseudomonas, Alcaligenes, Bdellovibrio) as well as genera comprised of facultative anaerobes (Beneckea, Photobacterium). Two media were used-the first, a medium designed for the cultivation of marine bacteria and, the second, a medium used for the cultivation of terrestrial strains. These two media differed in the concentrations of divalent cations; the terrestrial medium (TM) contained 2 mM Mg⁺⁺ and 0.55 mM Ca⁺⁺ while the marine medium (MM) contained 50 mM Mg⁺⁺ and 10 mM Ca⁺⁺. The amount of NaCl necessary for optimal growth varied in different strains and was usually considerably higher in TM (100 to 460 mM) than in MM (70 to 300 mM). Many strains which grew in MM and TM had a shorter generation time in the former than in the latter medium. In addition, four strains which grew well in MM usually failed to grow in TM. These results show that higher levels of divalent cations are either essential for growth or stimulate growth rate, indicating that for many marine strains a terrestrial medium modified by the addition of NaCl cannot support optimal growth. Fourteen terrestrial strains of the genera Pseudomonas, Alcaligenes, Acinetobacter, Salmonella, Aeromonas, and Vibrio did not have ionic requirements comparable to those of the marine strains. All of the terrestrial organisms grew in TM without added NaCl (0.068 mM Na⁺ was present as a contaminant). In some terrestrial organisms, growth was stimulated by the addition of NaCl, the highest stimulation being found in Vibrio cholerae. The optimal growth rates and yields for four strains of this species were observed at 2.5 to 5.0 mM NaCl while the growth rates and yields in TM with no added NaCl were 40 to 50% of the optimum.     

Isolation and Characterization of Nisin-Resistant Leuconostoc mesenteroides for Use in Cabbage Fermentations

Leuconostoc mesenteroides strains that are resistant to high levels of nisin (up to 25,000 IU/ml in broth) were isolated. These nisin-resistant mutants were evaluated to determine their potential use as starter culture strains for cabbage fermentations. We found that some L. mesenteroides strains could be adapted to high levels of nisin resistance, while others could not. The nisin resistance trait was found to be stable for at least 35 generations, in the absence of nisin selection, for all mutants tested. The effects of nisin and salt, separately and in combination, on growth kinetics of the nisin-resistant strains were determined. Salt was the most influential factor on the specific growth rates of the mutants, and no synergistic effect between nisin and salt on specific growth rates was observed. The nisin-resistant strains were unimpaired in their ability to rapidly produce normal heterolactic fermentation end products. The use of these L. mesenteroides mutants as starter cultures in combination with nisin may extend the heterolactic phase of cabbage fermentations.     

Intraspecific variation in Gracilaria caudata (Gracilariales,Rhodophyta): growth,pigment content,and photosynthesis

In Brazil, one of the probable reasons for failure in attempts at macroalgal mariculture is the lack of previous studies under controlled conditions. Gracilaria caudata is an important marine red alga which is locally exploited for the production of agar. In this study the aim was to compare in vitro growth rates, pigment content, and photosynthesis in gametophytes and tetrasporophytes of G. caudata from two distinct geographical areas located 2,500 km apart on the Brazilian coast, one in a warmer area closer to the equator (northeastern population), and the other in a colder area closer to the Tropic of Capricorn (southeastern population). Additionally, the artificial ultraviolet B (UVB) radiation effects on strains were evaluated. Under UVB, deleterious effects were observed in all strains. Although the strains from the southeastern population had higher growth rates than those from the northeastern under control condition, the opposite was observed under UVB condition. Under controlled conditions and regardless of the population, growth rates, net photosynthesis, P _max, I _k, and pigment contents were higher in tetrasporophytes than in gametophytes. Consequently, when determining the real potential of a certain phase in cultivation, the tetrasporophyte appears to be the more promising for future experiments along the Brazilian coast. Furthermore, although the growth rate of southeastern strains under control condition was higher, their higher sensitivity to UVB radiation emphasizes the importance of careful selection of the most suitable sites prior to experimental cultivation. The differences in performance between the southeastern and northeastern strains provide support for the hypothesis of their ecotypic differentiation.     

Microbial Control of the Culture of Artemia Juveniles through Preemptive Colonization by Selected Bacterial Strains

The use of juvenile Artemia as feed in aquaculture and in the pet shop industry has been getting more attention during the last decade. In this study, the use of selected bacterial strains to improve the nutritional value of dry food for Artemia juveniles and to obtain control of the associated microbial community was examined. Nine bacterial strains were selected based on their positive effects on survival and/or growth of Artemia juveniles under monoxenic culture conditions, while other strains caused no significant effect, significantly lower rates of survival and/or growth, or even total mortality of the Artemia. The nine selected strains were used to preemptively colonize the culture water of Artemia juveniles. Xenic culture of Artemia under suboptimal conditions yielded better survival and/or growth rates when they were grown in the preemptively colonized culture medium than when grown in autoclaved seawater. The preemptive colonization of the culture water had a drastic influence on the microbial communities that developed in the culture water or that were associated with the Artemia, as determined with Biolog GN community-level physiological profiles. Chemotaxonomical characterization based on fatty acid methyl ester analysis of bacterial isolates recovered from the culture tanks was performed, and a comparison with the initially introduced strains was made. Finally, several modes of action for the beneficial effect of the bacterial strains are proposed.     

Amino acid limited growth of starter cultures in milk

The specific growth rates of several Streptococcus cremoris strains were 10–40% lower in milk than in other growth in media. The growth rates in milk increased when an amino acid mixture or casein was added, whereas, when milk was diluted, the specific growth rate of the streptococci decreased. This decrease could be overcome by bringing the casein concentration in the diluted milk back to the normal value (3%). This indicates that casein-hydrolysis proceeded at a rate too low for the streptococci to reach their potential maximum specific growth rates in milk so that growth in milk is essentially amino acid-limited. This was subsequently demonstrated for S. cremoris by continuous cultivation in media with low casein concentrations. At a low dilution rate casein hydrolysis was fast enough to supply the cells with enough amino acids and lactose was growth-limiting, whereas at higher dilution rates amino acids became growth-limiting. In cultures exponentially growing in milk the concentration of free amino acids was measured to determine which amino acid(s) was(were) absent and could possibly limit growth. A number of essential amino acids (leucine, methionine, glutamate and in some cases phenylalanine) were not detected and addition of these, together, stimulated the growth of S. cremoris in milk. The amino acids leucine and phenylalanine appeared to play a particularly important role in this stimulation. These two are, supposedly, the first amino acids that become limiting during growth in milk. The effect of competition for casein and amino acids by different organisms was studied in continuous cultures. At different dilution rates different strains became dominant in these mixed cultures, suggesting that differences in apparent affinity constants (K_S) for casein, leucine and glutamate existed between the strains.     

Factors Influencing the Chlorine Susceptibility of Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum

The susceptibility of representative strains of Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum (the MAIS group) to chlorine was studied to identify factors related to culture conditions and growth phase that influenced susceptibility. M. avium and M. intracellulare strains were more resistant to chlorine than were strains of M. scrofulaceum. Transparent and unpigmented colony variants were more resistant to chlorine than were their isogenic opaque and pigmented variants (respectively). Depending on growth stage and growth rate, MAIS strains differed in their chlorine susceptibilities. Cells from strains of all three species growing in early log phase at the highest growth rates were more susceptible than cells in log and stationary phase. Rapidly growing cells were more susceptible to chlorine than slowly growing cells. The chlorine susceptibility of M. avium cells grown at 30°C was increased when cells were exposed to chlorine at 40°C compared to susceptibility after exposure at 30°C. Cells of M. avium grown in 6% oxygen were significantly more chlorine susceptible than cells grown in air. Chlorine-resistant MAIS strains were more hydrophobic and resistant to Tween 80, para-nitrobenzoate, hydroxylamine, and nitrite than were the chlorine-sensitive strains.     

Temperature-dependent growth in isolates of Corollospora maritima Werderm. (Ascomycetes) from different geographical regions

The growth rates of five strains of the marine ascomycete Corollospora maritima Werderm., isolated from different geographical regions, show significant differences in their responses to temperature. At 30 °C, strains isolated from warm waters are able to grow at higher rates than cold-water isolates. At 10 °C, strains isolated from cold waters grow at higher rates than warm-water isolates (P < 0.05). A strain isolated from temperate waters shows growth rates intermediate between those of the cold- and warm-water isolates. Strains of C. maritima thus appear to be adapted to grow best near the temperatures at which they are found in nature. It is suggested that the cosmopolitan classification of C. maritima be reexamined, and that the species consists of distinct physiological races which maintain characteristic temperature responses in the laboratory.     

Influence of five spiroplasma strains on growth rate and survival of Galleria mellonella (lepidoptera: Pyralidae) larvae

Infection of Galleria mellonella larvae with five spiroplasma strains caused increased mortality and decreased growth rates of larvae. Reductions in growth rate and survival were related to spiroplasma strain and multiplication rate of the spiroplasma in the larvae. Three strains, considered to be ephiphytic on flowers (23-6, SR-3, PPS1), proved highly pathogenic to G. mellonella larvae, whereas strains known to be pathogenic to plants (SC-27) or honeybees (G-1) had a lesser impact.     

Strains of protoplasts of Entomophthora egressa in spruce budworm larvae

Protoplasts of strain 458 (S458) and strain 521 (S521) of Entomophthora egressa had LD₅₀s of 620 and 8.8 cells/insect, respectively, for sixth-instar spruce budworm larvae. Both protoplast strains exhibited biphasic growth profiles with comparable growth rates in the larval hemocoel. The growth rates of the fungal strains increased as the total hemocyte counts declined. Hemocytopenia was greatest and most rapid in larvae containing S521 protoplasts. Protoplasts of S521 exposed to α-mannosidase and β-N-acetylglucosaminidase were as virulent as the control cells. β-Galactosidase reduced protoplast virulence.     

Relationship Between Catalase and Life Span in Recombinant Inbred Strains of Caenorhabditis elegans

Johnson and Wood constructed recombinant inbred strains of Caenorhabditis elegans with life spans ranging from 10 to 31 days. Using these strains, we have demonstrated previously that hyperoxia and methyl viologen inhibited development at rates inversely correlated with life span. The growth rates of the short-lived recombinant inbred strains were more profoundly inhibited by oxidative stress than were those of the long-lived strains. Here we report a positive correlation between life span and catalase levels in these same strains. Specifically, when compared to short-lived strains at 10 days after fertilization, the long-lived strains possessed higher levels of total enzymatic catalase. Northern blots indicated a similar relationship between life span and clt-1mRNA (the cytosolic catalase). This suggests that at least some of the polygenes that influence life span are also responsible for regulating gene expression of catalase, an important defense component against oxidative stress.     

Initiation and Velocity of Chromosome Replication in Escherichia coli B/r and K-12

The macromolecular composition and a number of parameters affecting chromosome replication were examined over a range of exponential growth rates in two common Escherichia coli strains, B/r and K-12 AB1157. Based on improved measurements of DNA after treatment of exponential cultures with rifampin, the cell mass per chromosomal replication origin (initiation mass) and the time required to replicate the chromosome from origin to terminus (C period) were determined. For these two strains, the initiation mass approached values of 8 × 10⁻¹⁰ and 10 × 10⁻¹⁰ units of optical density (at 460 nm) of culture mass per oriC, respectively, at growth rates above 1 doubling/h (at 37°C). The amount of protein per oriC decreased with increasing growth rate for AB1157 and remained nearly constant for the B/r strain. The C period decreased for both strains in an essentially identical manner from about 70 min at 0.6 doublings/h to about 33 min at 3 doublings/h. From the initiation mass and C period, relative or absolute copy numbers for genes with known map locations can be accurately determined at different growth rates. At growth rates above 2 doublings/h, when chromosomes are highly branched, genes near the origin are about threefold more prevalent than genes near the terminus. At a growth rate of 0.6 doubling/h, this ratio is only about 1.7, which reflects the lower degree of chromosome branching.     

Comparative studies on utilization of fatty acids and hydrocarbons in Nocardia amarae and Rhodococcus spp.

Comparative investigations on the substrate utilization of Nocardia amarae and Rhodococcus spp. (R. rhodochrous and R. erythropolis) were carried out using various fatty acids and paraffinic hydrocarbons. Upon calculation and comparison of their specific growth rates (μ) during the logarithmic phase, it was shown that the lower fatty acids (C2–C5) were utilized preferably and the highest μ value was obtained in octadecane (C18) for all three strains. The initial total organic carbon (TOC) concentration affecting the growth of the 3 strains was investigated, using octadecane as the carbon source. From a comparison of the kinetic parameters of the 3 strains with those obtained in the past studies, it was found that Rhodococcus spp. had higher growth rate and lower affinity for octadecane than N. amarae.     

Strain selection in Gracilaria spp. 2. Selection for high and low temperature resistance in G. verrucosa sporelings

A strain selection procedure using Gracilaria verrucosa gametophytic sporelings was found to be an efficient tool for the improvement of Gracilaria strains. Two strains, C-2 and A-18, which were isolated and grown clonally, showed higher growth rates under high and low temperature conditions, respectively, than the local Gracilaria conferta. Growth rate, photosynthesis and chlorophyll, which were measured under different temperature and photon flux densities, demonstrated an overall advantage of the selected strains over the wild type strains of both G. verrucosa and G. conferta. Growth rates were also generally in positive correlation with the carboxylase activity of Rubisco. The G. verrucosa wild type also had a 40% higher agar content than G. conferta. The selected strains thus showed higher potential for outdoor cultivation than local wild type populations.     

Robust metabolic responses to varied carbon sources in natural and laboratory strains of Saccharomyces cerevisiae

Understanding factors that regulate the metabolism and growth of an organism is of fundamental biologic interest. This study compared the influence of two different carbon substrates, dextrose and galactose, on the metabolic and growth rates of the yeast Saccharomyces cerevisiae. Yeast metabolic and growth rates varied widely depending on the metabolic substrate supplied. The metabolic and growth rates of a yeast strain maintained under long-term laboratory conditions was compared to strain isolated from natural condition when grown on different substrates. Previous studies had determined that there are numerous genetic differences between these two strains. However, the overall metabolic and growth rates of a wild isolate of yeast was very similar to that of a strain that had been maintained under laboratory conditions for many decades. This indicates that, at in least this case, metabolism and growth appear to be well buffered against genetic differences. Metabolic rate and cell number did not co-vary in a simple linear manner. When grown in either dextrose or galactose, both strains showed a growth pattern in which the number of cells continued to increase well after the metabolic rate began a sharp decline. Previous studied have reported that O₂ consumption in S. cerevisiae grown in reduced dextrose levels were elevated compared to higher levels. Low dextrose levels have been proposed to induce caloric restriction and increase life span in yeast. However, there was no evidence that reduced levels of dextrose increased metabolic rates, measured by either O₂ consumption or CO₂ production, in the strains used in this study.     

Highly Invasive Listeria monocytogenes Strains Have Growth and Invasion Advantages in Strain Competition

Multiple Listeria monocytogenes strains can be present in the same food sample; moreover, infection with more than one L. monocytogenes strain can also occur. In this study we investigated the impact of strain competition on the growth and in vitro virulence potential of L. monocytogenes. We identified two strong competitor strains, whose growth was not (or only slightly) influenced by the presence of other strains and two weak competitor strains, which were outcompeted by other strains. Cell contact was essential for growth inhibition. In vitro virulence assays using human intestinal epithelial Caco2 cells showed a correlation between the invasion efficiency and growth inhibition: the strong growth competitor strains showed high invasiveness. Moreover, invasion efficiency of the highly invasive strain was further increased in certain combinations by the presence of a low invasive strain. In all tested combinations, the less invasive strain was outcompeted by the higher invasive strain. Studying the effect of cell contact on in vitro virulence competition revealed a complex pattern in which the observed effects depended only partially on cell-contact suggesting that competition occurs at two different levels: i) during co-cultivation prior to infection, which might influence the expression of virulence factors, and ii) during infection, when bacterial cells compete for the host cell. In conclusion, we show that growth of L. monocytogenes can be inhibited by strains of the same species leading potentially to biased recovery during enrichment procedures. Furthermore, the presence of more than one L. monocytogenes strain in food can lead to increased infection rates due to synergistic effects on the virulence potential.     

Growth rate and carrageenan analyses in four strains of <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales) farmed in the subtropical waters of São Paulo State,Brazil

Growth rate, semi-refined and refined carrageenan yields, 3,6-anhydrogalactose and sulphate contents, and gel strength were investigated in four strains of Kappaphycus alvarezii (brown, green and red tetrasporophytic strains, and one strain derived from tetraspores progeny, called G11) farmed in subtropical waters of São Paulo State, Brazil. All studied strains showed higher growth rates from February to May, decreasing from July to December. The G11 strain exhibited lower growth rates, but had semi-refined and refined carrageenan yields significantly higher than the others and similar to a commercial sample. A negative correlation between growth rate and semi-refined carrageenan yield was verified for all strains. The brown strain had the lowest content of 3,6-anhydrogalactose, while G11 and green strains showed higher values. No clear pattern of variation and no relationship were observed for sulphate and gel strength. However, all strains presented gel strength values near the one obtained from commercial sample. These results show that the carrageenan extracted from brown, green, red, and G11 strains of K. alvarezii cultured in subtropical waters of São Paulo State, Brazil with commercial potentials.     

Effects of Bacterial Host and Dichloromethane Dehalogenase on the Competitiveness of Methylotrophic Bacteria Growing with Dichloromethane

Methylobacterium sp. strain DM4 and Methylophilus sp. strain DM11 can grow with dichloromethane (DCM) as the sole source of carbon and energy by virtue of homologous glutathione-dependent DCM dehalogenases with markedly different kinetic properties (the k_cat values of the enzymes of these strains are 0.6 and 3.3 s⁻¹, respectively, and the K_m values are 9 and 59 μM, respectively). These strains, as well as transconjugant bacteria expressing the DCM dehalogenase gene (dcmA) from DM11 or DM4 on a broad-host-range plasmid in the background of dcmA mutant DM4-2cr, were investigated by growing them under growth-limiting conditions and in the presence of an excess of DCM. The maximal growth rates and maximal levels of dehalogenase for chemostat-adapted bacteria were higher than the maximal growth rates and maximal levels of dehalogenase for batch-grown bacteria. The substrate saturation constant of strain DM4 was much lower than the K_m of its associated dehalogenase, suggesting that this strain is adapted to scavenge low concentrations of DCM. Strains and transconjugants expressing the DCM dehalogenase from strain DM11, on the other hand, had higher growth rates than bacteria expressing the homologous dehalogenase from strain DM4. Competition experiments performed with pairs of DCM-degrading strains revealed that a strain expressing the dehalogenase from DM4 had a selective advantage in continuous culture under substrate-limiting conditions, while strains expressing the DM11 dehalogenase were superior in batch culture when there was an excess of substrate. Only DCM-degrading bacteria with a dcmA gene similar to that from strain DM4, however, were obtained in batch enrichment cultures prepared with activated sludge from sewage treatment plants.