Increase and limits of growth yields for heterotrophic microorganisms

Substrates for heterotrophic growth of microorganisms are more or less energy-limited. In order to improve the growth yields phenotypic and genetic measures come into consideration. By means of the auxiliary substrate concept the carbon metabolism determined carbon conversion efficiency of about 75% for C₂ compounds (i.e. non-glycolytic, gluconeogenetic substrates) and about 85%, respectively, for C₃ or glycolytic substrates can be attained experimentally. With methylotrophic microorganisms the growth yield might approach to this limit if the methanol oxidizing methanol dehydrogenase (bacteria) and methanol oxidase (yeasts) are replaced by an NAD⁺-linked dehydrogenase. Due to an increase in the overall P/O quotient up to the maximum this limit cannot be reached.     

Quantum thermodynamics approach to phosphorylation and heterotrophic growth yields

A model of cell growth is presented which is based on the double postulates of quantized loss of energy during phosphorylation and reversible biosynthesis of cell structure. An immediate consequence of the postulates is the identical value for the energy efficiency of the phosphorylation and for that of the whole growth process. Another consequence is the relationship between the energy level of the biomass and the phosphorylation potential as embodied in the equation: EO = gamma'M X EATP, where EO is the heat of transfer of a pair of electrons to oxygen, EATP, the molar heat of hydrolysis of ATP, and gamma'M, the degree of reduction of the biomass, gamma M being constant and equal to 5. The model predicts five levels of growth yields corresponding to five permissible values for the P/O ratio (r = 0, 1, 2, 3, and 4). Any growth process would be characterized by a set of two integers N and lambda; N is the maximal P/O ratio prescribed by the energy content of the substrate as compared with that of the biomass, and lambda the number of further downward quantum jumps of the P/O ratio resulting from the adversity of the growth condition (N - lambda = r). Under full aerobiosis, one has 0 less than or equal to lambda less than or equal to N less than or equal to 3. When growth is limited only by the energy content of the substrate (lambda = 0), the time-independent dispersion of N, owing to substrate-level phosphorylations and (or) dephosphorylations, leads to effective values which are higher than the nominal ones for the yield per mole of oxygen and the heat of transfer of a pair of electrons. Under adverse conditions (lambda greater than 0), the apparent variations of the yields and the P/O ratio in function of the growth rate are shown to be an effect of the random dispersion of lambda and of the existence of a maximal rate of substrate consumption. Statistical evidence for the macroscopic quantum effect in heterotrophic growth is presented.     

Genetic variability in growth rates of marine dinoflagellates

The growth rates of thirty clones of Prorocentrum micans, twenty-two clones of Gonyaulax excavata and fifteen clones of Scrippsiella trochoidea, isolated from eight different water samples were measured under two environmental conditions. There was significant genetic variability in growth rates between clones. The amount of genetic variability between clones ranged from 10–27% (coefficient of variation) in Prorocentrum micans, 31–52% in Gonyaulax excavata and 11–20% in Scrippsiella trochoidea. Unlike Gonyaulax excavata and Scrippsiella trochoidea many different Prorocentrum micans clones had identical growth rates.Supported by Spanish CAICYT, grant num. 2409/83.     

Grazing impact of heterotrophic dinoflagellates and ciliates on common red-tide euglenophyte Eutreptiella gymnastica in Masan Bay, Korea

The euglenophyte Eutreptiella gymnastica is a common red tide causative species. However, there have been no studies on the grazing impact of heterotrophic protists on this species. To investigate the grazing impact of heterotrophic protists on E. gymnastica, we measured daily the abundances of E. gymnastica and co-occurring potential heterotrophic protistan grazers in Masan Bay, Korea, in August 2004 when an E. gymnastica red tide occurred. In addition, we tested whether the common heterotrophic dinoflagellates Gyrodinium dominans, Oxyrrhis marina, Pfiesteria piscicida, Polykrikos kofoidii, Protoperidinium bipes, and Stoeckeria algicida and the naked ciliates Strobilidium sp. (30–40 μm in cell length) and Strombidinopsis sp. (70–100 μm in cell length) were able to feed on E. gymnastica. We also measured their growth and ingestion rates on E. gymnastica as a function of prey concentration. Finally, we calculated the grazing coefficients by combining field data on the abundance of the heterotrophic dinoflagellate and ciliate grazers and co-occurring E. gymnastica with laboratory data on ingestion rates obtained in this study. The maximum abundance of E. gymnastica in Masan Bay in August, 2004 was 7575 cells ml⁻¹, while those of Gyrodinium spp., P. kofoidii, P. bipes, the naked ciliates (≤50 μm in cell length), and naked ciliates (>50 μm in cell length) were 50, 9, 58, 32, and 3 cells ml⁻¹, respectively. The maximum growth rate of G. dominans on E. gymnastica (1.13 d⁻¹) was higher than that of O. marina (0.81 d⁻¹) or P. bipes (0.77 d⁻¹). However, E. gymnastica did not support positive growth of P. kofoidii, Strobilidium sp., and Strombidinopsis sp. (−0.04 ∼ −2.8 d⁻¹). The maximum ingestion rates of G. dominans, P. kofoidii, P. bipes, O. marina, and Strobilidium sp. on E. gymnastica (2.1–2.7 ng C predator⁻¹ d⁻¹) were similar, but they were much lower than that of Strombidinopsis sp. (156 ng C predator⁻¹ d⁻¹). The calculated grazing coefficients for P. bipes, small heterotrophic Gyrodinium spp. (25–35 μm in cell length), naked ciliates (≤50 μm in cell length), P. kofoidii, and naked ciliates (>50 μm in cell length) on E. gymnastica were up to 0.77, 0.61, 0.22, 0.07 and 0.03 d⁻¹, respectively (i.e., up to 54%, 46%, 20%, 7%, and 3% of E. gymnastica populations were removed by the population of each of these heterotrophic protistan grazers in 1 d, respectively). The results of the present study suggest that P. bipes, small heterotrophic Gyrodinium spp., and naked ciliates (≤50 μm in cell length) sometimes have considerable potential grazing impact on the populations of E. gymnastica.     

Feeding and grazing impact by small marine heterotrophic dinoflagellates on heterotrophic bacteria

ABSTRACT. We investigated the feeding of the small heterotrophic dinoflagellates (HTDs) Oxyrrhis marina , Gyrodinium cf. guttula , Gyrodinium sp., Pfiesteria piscicida , and Protoperidinium bipes on marine heterotrophic bacteria. To investigate whether they are able to feed on bacteria, we observed the protoplasm of target heterotrophic dinoflagellate cells under an epifluorescence microscope and transmission electron microscope. In addition, we measured ingestion rates of the dominant heterotrophic dinoflagellate, Gyrodinium spp., on natural populations of marine bacteria (mostly heterotrophic bacteria) in Masan Bay, Korea in 2006–2007. Furthermore, we measured the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria as a function of bacterial concentration under laboratory conditions. All HTDs tested were able to feed on a single bacterium. Oxyrrhis marina and Gyrodinium spp. intercepted and then ingested a single bacterial cell in feeding currents that were generated by the flagella of the predators. During the field experiments, the ingestion rates and grazing coefficients of Gyrodinium spp. on natural populations of bacteria were 14–61 bacteria/dinoflagellate/h and 0.003–0.972 day⁻¹, respectively. With increasing prey concentration, the ingestion rates of O. marina , G . cf. guttula , and P. piscicida on bacteria increased rapidly at prey concentrations of ca 0.7–2.2 × 10⁶ cells/ml, but increased only slowly or became saturated at higher prey concentrations. The maximum ingestion rate of O. marina on bacteria was much higher than those of G . cf. guttula and P. piscicida . Bacteria alone supported the growth of O. marina . The results of the present study suggest that some HTDs may sometimes have a considerable grazing impact on populations of marine bacteria, and that bacteria may be important prey.     

Fine scale spatial correlations between planktonic ciliates and dinoflagellates

Fine scale spatial distributions of planktonic ciliates whichprey on dinoflagellates were investigated in a small estuary.The horizontal distributions of Favella sp., Balanion sp. andStrobilidium sp. were positively correlated with the patchydistribution of dinoflagellates. The vertical distribution ofFavella was positively corrdated with the distribution of dinoflagellates.Throughout the diel cycle, the vertical distribution of Faveilawas similar to the vertical distribution of dinoflagellates.We speculate that behavioral responses are responsible for theassociation of diliates with their prey in the water column.Vertically coincident ciliate and algal populations should respondsimilarly to turbulent mixing and water displacement causedby wind stress, bathymetry, or frontal convergences. This wouldresult in horizontal patches in which the ciliates and algaeremain associated. This fine scale spatial coupling betweenciliates and their prey should result in higher ciliate growthrates and greater impact of ciliate grazing on phytoplanktonpopulations than would be predicted from average ciliate oralgal densities. Coincident patches of algae and ciliates mayalso provide higher food concentrations for larger grazers whichcan use both resources. ^{Contribution No. 5532, W.H.O.I.}     

Low temperature constrains growth rates but not short-term ingestion rates of Antarctic ciliates

Low environmental temperature is a major factor affecting the feeding activities, growth rates, and growth efficiencies of metazooplankton, but these features are poorly characterized for most protistan species. Laboratory experiments were conducted to examine the growth and ingestion rates of cultured herbivorous Antarctic ciliates. Three ciliates fed several algal species individually at 0 °C exhibited uniformly low growth rates (<0.26 day^?1), but the algae varied substantially in their ability to support ciliate growth. Specific ingestion rate (prey biomass consumed per unit ciliate biomass per unit time) was strongly affected by ciliate physiological state (starved vs. actively growing). Starved cells ingested many more prey than cells in balanced growth during short-term (minutes-to-hours) experiment but did not grow faster, indicating temperature compensation of ingestion rate but not growth rate. Field experiments were also conducted in the Ross Sea, Antarctica, to characterize the feeding rates of ciliates in natural plankton assemblages. Specific ingestion rates of two dominant ciliates were an order of magnitude lower than rates reported for temperate ciliates, but estimated rates were strongly affected by prey abundance. Our data indicate that short-term ingestion rates of Antarctic ciliates were not constrained by low environmental temperature although overall growth rates were, indicating the need for caution when designing experiments to measure the ingestion rates of these species at low environmental temperature. We present evidence that artifacts arising from estimating ingestion in short-term experiments may lead to errors in estimating feeding impact and growth efficiencies that are particularly large for polar protists.     

Application of the size-fractionation method to simultaneous estimation of clearance rates by heterotrophic flagellates and ciliates of pico- and nanophytoplankton

To estimate the clearance rates of pico- and nanophytoplankton by heterotrophic nanoflagellates (HNF) and ciliates, the size-fractionation method was employed in combination with a multiple regression analysis. Apparent growth rate of a specific phytoplankton group was decomposed into three terms, net growth rate, grazing rates by HNF and those by ciliates, and the grazing rates were interpreted as a linear function of average cell concentrations of HNF and ciliates. We produced a set of subsamples from a water sample by size-fractionation using three different pore sizes. By measuring phytoplankton and protozoan cell concentrations, apparent growth rate of a specific phytoplankton group was regressed against the average cell concentrations of HNF and ciliates to obtain the net growth rate of the phytoplankton group and the average clearance rates by these two protozoan groups. The estimated values were within the range of those previously reported for cultured and natural protozoan, which supported the feasibility of the present method. The estimated values also suggested that picophytoplankton abundance in Otsuchi Bay in spring is controlled mainly by HNF through active grazing. The present study rediscovered the utility of the size-fractionation method as a method to estimate the clearance rates of different protozoan groups from natural assemblages in a single experiment.     

Effects of ingesting mercury-containing bacteria on mercury tolerance and growth rates of ciliates

The ciliateUronema nigricans was found to acquire tolerance to mercury after being fed mercury-laden bacteria followed by exposure of washed suspensions of these ciliates to various concentrations of mercury in solution. Significant differences in percent mortality were observed for ciliates fed mercury-laden bacteria compared with control suspensions fed mercury-free bacteria. The phenomenon of acquired mercury tolerance was demonstrated within a single generation time. Ciliates fed mercury-free bacteria and subsequently exposed to increasing levels of mercury in solution showed an elevated tolerance to concentrations which, on initial testing, resulted in mortality of 83% of the ciliate population. The effect of ingesting mercury-laden bacteria on growth rate ofUronema was examined, and results showed no significant differences in growth rates of both 3- and 14-day-old cultures of protozoa that had been fed mercury-laden and mercury-free bacteria under controlled conditions.     

Grazing by ciliates and heterotrophic nanoflagellates on picocyanobacteria in Lago Maggiore, Italy

During the oligotrophication of Lago Maggiore, picocyanobacteria(Pcy) increased in abundance and production. In their bimodal,seasonal cycle, the spring peak was due almost exclusively tosingle cells of Pcy, whereas in late-summer/autumn the varietyof morpho-types increased and larger Aphanothece-like rods appeared.Rates of Pcy cell removal by heterotrophic nanoflagellates andciliates were measured by using fluorescently labelled Pcy (FLC)in four experiments performed during the Pcy population shiftfrom small cocci to larger rods. The ciliate community appearedto be composed mainly of oligotrichs in the first two experiments,and subsequently of scuticociliates; heterotrophic nanoflagellatesdecreased in number from May to September, and there was a sizeshift which might reflect species composition change. Peritrichsemerged as the most efficient Pcy grazers. For the other ciliategroups we observed higher individual ingestion rates duringthe spring experiments than during those performed in late summer/autumn.The heterotrophic nanoflagellates ingested from 0.5 to3 Pcyh^-1 while ciliates ingested from 18 to 80 Pcy h^-1. The grazingimpact of the heterotrophic nanoflagellate community rangedfrom 1.9 x 10³ to 8 x 10³ Pcy ml^-1 h^-1, whereas the ciliatecommunity ingestion rate was one order of magnitude lower (0.2x 10³–0.4 x 10³ Pcy ml^-1 h^-1). A significant inverse correlationbetween Pcy size and the clearance rate of heterotrophic nanoflagellatesand ciliates was found. Our results indicate that protozoa areless efficient in cell uptake when the Pcy are composed of largercells. In Lago Maggiore, the carbon flux from Pcy to protozoadecreased from 29.8 to 10.2 µg C l^-1 day^-1 (May and Septemberrespectively). A tentative balance on an annual basis suggeststhat around 80% of the carbon produced by Pcy is taken up byprotozoa and channelled to metazooplankton.     

Comparative growth rates and oxygen consumption in young Galliformes

The high correlation between growth rate and adult body weight has been much more thoroughly documented for altricial birds than for precocial species. This paper gathers data from the literature for precocial Galliformes and also reports new growth data on six galliform species for analysis. The onset of homeothermic ability is investigated in Galliformes over a range of body size. The results confirm that (1) large species' chicks grow at a slower rate than those of smaller species, and (2) larger species' chicks can thermoregulate earlier than smaller species' chicks under cold stress situations. Published embryonic body weights are also analysed to determine when growth rate differences appear in the development of precocial species. No interspecific differences appeared in the relative growth rates of embryos, and therefore species body size does not appear to influence growth rate before hatching.     

Simultaneous utilization of heterotrophic substrates by Hansenula polymorpha MH30 results in enhanced growth rates

Summary The maximum specific growth rate (_max) of Hansenula polymorpha MH30 on xylose as the sole source of carbon and energy is 0.175 h^–1, on methanol 0.21 h^–1, on glycerol 0.27 h^–1 and on glucose 0.61 h^–1. On mixtures of xylose plus methanol, xylose plus glycerol, xylose plus glucose and glycerol plus glucose H. polymorpha MH30 grows faster: 0.36 h^–1, 0.37 h^–1, 0.47 h^–1 and 0.52 h^–1, respectively. Attempts have been made to explain these somewhat surprising results, especially the fact that the growth rates on xylose plus methanol and xylose plus glycerol exceed the specific growth rates of these on even the faster partner in the mixture. Offprint requests to: W. Babel     

Specific growth rates of heterotrophic plankton organisms in a eutrophic lake during a spring bloom

The in situ growth of the dominating pelagic organisms at severaltrophic levels was investigated during a spring bloom characterizedby well-mixed cold water. The study includes primary productionand the carbon flow through the nano-, micro- and mesozooplanktonpopulations based on population dynamics and specific growthrates. The phytoplankton biomass and production were totallydominated by small algae <20 µm. of which {small tilde}5%were <3µm. potentially a food source for the nano-and microzooplankton. The mean carbon-specific primary productionwas 0.15 day^–1 and was regulated solely by light. Themean volume-based specific growth rate of bacterioplankton wasmodest. 0.1 day^–1. and probably controlled by the lowtemperature. The volume-based specific growth rates of heterotrophicnanoflagellates. ciliates. rotifers and copepods were 0.35.0.13. 0.16 and 0.03 day^–1, respectively. The observedgrowth of the heterotrophic plankton was generally not foodlimited, but was controlled by temperature. The stable temperatureduring the experiment therefore allows a cross-taxonomic comparisonof specific growth rates. The b exponent in the allometric relationship(G = aV^th) between volume-specific growth rate (G) and individualbody size (V) was –0.15 ± 0.03 for all filtratingzooplankton. indicating an in situ scaling not far from thephysiological principles onginally demonstrated for laboratorypopulations.     

Respiration rates in heterotrophic,free-living protozoa

Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight^0.75 and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.     

Comparative aspects of basic chromatin proteins in dinoflagellates

Previous work on histone-like proteins in dinoflagellates is summarized, together with some new data to give an overview of basic proteins in these algae. The first two dinoflagellates studied were both found to contain one major acid-soluble protein that migrated to the same position in acidic-urea gels. When several other genera were studied however, it became apparent that the histone-like proteins from different dinoflagellates were similar but not identical. In view of the great diversity of living dinoflagellates it is speculated that further differences in dinoflagellate basic chromatin proteins will be revealed. Electrophoretic data from the eukaryotic (endosymbiont) nucleus of Peridinium balticum showed the presence of five major components. It is speculated that two of these proteins represent an H1-like doublet and two others correspond to the highly conserved histones H3 and H4. The fifth component is a new histone that may substitute for H2A and H2B in the nucleosome. Because histones and nucleosomes are present in all higher organisms but completely lacking in procaryotes, studies on basic proteins in dinoflagellates will provides insights into the evolution of histones and eucaryotic chromatin organization.     

Succession of heterotrophic and mixotrophic dinoflagellates as well as autotrophic microplankton in the harbour of Alexandria, Egypt

In the Eastern Harbour of Alexandria, three trophic categoriesof microplankton, heterotrophic dinoflagellates (HTD), mixotrophicdinoflagellates (MTD) and obligately autotrophic microplankton(OA) were studied in terms of species richness, numerical standingcrop, biovolume and carbon biomass during the summer of 1999.Although represented by a small number of species, MTD provedto be the most important trophic category, contributing morethan half the standing crop and the carbon biomass. Almost allblooms were dominated by the MTD species Prorocentrum minimumand Scrippsiella trochoidea. The HTD and the OA were richerin species but lower in biomass. Mixotrophic and autotrophiccells < 30 µm contributed 98% of the respective biomass,while 90% of the heterotrophic biomass was contributed by cells> 50 µm.     

Macroevolutionary analyses of ciliates associated with hosts support high diversification rates

Ciliophora is a phylum that is comprised of extremely diverse microorganisms with regard to their morphology and ecology. They may be found in various environments, as free-living organisms or associated with metazoans. Such associations range from relationships with low metabolic dependence such as epibiosis, to more intimate relationships such as mutualism and parasitism. We know that symbiotic relationships occur along the whole phylogeny of the group, however, little is known about their evolution. Theoretical studies show that there are two routes for the development of parasitism, yet few authors have investigated the evolution of these characteristics using molecular tools. In the present study, we inferred a wide dated molecular phylogeny, based on the 18S rDNA gene, for the entire Ciliophora phylum, mapped life habits throughout the evolutionary time, and evaluated whether symbiotic relationships were linked to the variation in diversification rates and to the mode of evolution of ciliates. Our results showed that the last common ancestor for Ciliophora was likely a free-living organism, and that parasitism is a recent adaptation in ciliates, emerging more than once and independently via two distinct routes: (i) a free-living ciliate evolved into a mutualistic organism and, later, into a parasitic organism, and (ii) a free-living ciliate evolved directly into a parasitic organism. Furthermore, we have found a significant increase in the diversification rate of parasitic and mutualistic ciliates compared with their free-living conspecifics. The evolutionary success in different lineages of symbiont ciliates may be associated with many factors including type and colonization placement on their host, as well as physical and physiological conditions made available by the hosts.