GFAP-positive astrocytes are rare or absent in primary adult human brain tissue cultures

Traditionally, astrocytes are divided into fibrous and protoplasmic types based on their morphologic appearance. Here the cultures were prepared separately from the adult human cortical gray and white matter of brain biopsies. Both cultures differed only in the number of glial fibrillary acidic protein (GFAP)-positive cells. In the gray matter these were absent or rare, whereas in confluent cultures from the white matter they reached 0.1% of all cells. Three main morphologic types of GFAP-positive cells were found in this study: stellate, bipolar and large flat cells. GFAP-positive cells with two or three long processes mimic a neuron-like morphology. We did not find process-bearing cells expressing neuronal markers (MAP-2, NF, and N-CAM). The conflicting reports concerning GFAP immunostaining and the study dealing with the presence of putative neurons in adult human brain cultures are discussed with respect to these findings. The latter classification of astrocytes into type 1 and type 2 is based on immunostaining to A2B5 antigen: type 1 (GFAP+/A2B5−) and type 2 (GFAP+/A2B5+) astrocytes are proposed to be analogous to protoplasmic and fibrous astrocytes, respectively. In adult human brain cultures we found only small amount of A2B5-positive cells. Double immunofluorescence revealed that astroglial cells of similar fibrous or bipolar shape grown on one coverslip were either GFAP+/A2B5+ or GFAP+/A2B5−. On the other hand, the A2B5+/GFAP− immunophenotype was not observed. These results indicate that in general the cell phenotype from adult human brain tissue is not well established when they are in culture.     

Longterm quiescent cells in the aged human subventricular neurogenic system specifically express GFAP‐δ

A main neurogenic niche in the adult human brain is the subventricular zone (SVZ). Recent data suggest that the progenitors that are born in the human SVZ migrate via the rostral migratory stream (RMS) towards the olfactory bulb (OB), similar to what has been observed in other mammals. A subpopulation of astrocytes in the SVZ specifically expresses an assembly‐compromised isoform of the intermediate filament protein glial fibrillary acidic protein (GFAP‐δ). To further define the phenotype of these GFAP‐δ expressing cells and to determine whether these cells are present throughout the human subventricular neurogenic system, we analysed SVZ, RMS and OB sections of 14 aged brain donors (ages 74‐93). GFAP‐δ was expressed in the SVZ along the ventricle, in the RMS and in the OB. The GFAP‐δ cells in the SVZ co‐expressed the neural stem cell (NSC) marker nestin and the cell proliferation markers proliferating cell nuclear antigen (PCNA) and Mcm2. Furthermore, BrdU retention was found in GFAP‐δ positive cells in the SVZ. In the RMS, GFAP‐δ was expressed in the glial net surrounding the neuroblasts. In the OB, GFAP‐δ positive cells co‐expressed PCNA. We also showed that GFAP‐δ cells are present in neurosphere cultures that were derived from SVZ precursors, isolated postmortem from four brain donors (ages 63‐91). Taken together, our findings show that GFAP‐δ is expressed in an astrocytic subpopulation in the SVZ, the RMS and the OB. Importantly, we provide the first evidence that GFAP‐δ is specifically expressed in longterm quiescent cells in the human SVZ, which are reminiscent of NSCs.     

Interstitial Cajal-like cells in human gallbladder

We describe here an interstitial Cajal-like cell type (ICLC) in human gallbladder, resembling the archetypal enteric interstitial cells of Cajal. Gallbladder ICLC were demonstrated in fresh preparations (tissue cryosections) using methylene-blue, and fixed specimens in Epon semi-thin sections stained with toluidine blue or transmission electron microscopy (TEM). The positive diagnosis of gallbladder ICLC was further verified by immunohistochemistry: CD117/c-kit, CD34, and another 16 antigens: vimentin, desmin, nestin, α-smooth muscle actin, NK-1, S-100, PGP-9.5, tau protein, chromogranin A, NSE, GFAP, CD1a, CD62-P, CD68, estrogen and progesterone receptors. Double immunostaining was performed for CD117, CD34 and CD117 and nestin, respectively. In fresh specimens, the spatial density of gallbladder ICLC was 100–110 cells/mm². ICLC mainly appeared beneath the epithelium and in muscularis (about 7%, and ∼5%, respectively). In toto, ICLC represent in gallbladder ∼5.5% of subepithelial cells. TEM showed that diagnostic criteria were fulfilled by ICLC. Moreover, TEM indicated that the main ultrastructural distinctive feature for ICLC, the cell processes, develop into the characteristic shape at a relatively early stage of development. It remains to be established if, in humans, ICLC are involved in gallbladder (dis)functions (e.g. pace-making, secretion (auto-, juxta- and/or paracrine), intercellular signaling, or stone formation). M. E. Hinescu and C. Ardeleanu contributed equally to this study.     

Astrocyte,the star <Emphasis Type="Italic">avatar</Emphasis>: redefined

Until recently, the neuroscience community held the belief that glial cells such as astrocytes and oligodendrocytes functioned solely as “support” cells of the brain. In this role, glial cells simply provide physical support and housekeeping functions for the more important cells of the brain, the neurons. However, this view has changed radically in recent years with the discovery of previously unrecognized and surprising functions for this underappreciated cell type. In the past decade or so, emerging evidence has provided new insights into novel glial cell activities such as control of synapse formation and function, communication, cerebrovascular tone regulation, immune regulation and adult neurogenesis. Such advances in knowledge have effectively elevated the role of the astrocyte to one that is more important than previously realized. This review summarizes the past and present knowledge of glial cell functions that has evolved over the years, and has resulted in a new appreciation of astrocytes and their value in studying the neurobiology of human brain cells and their functions. In this review, we highlight recent advances in the role of glial cells in physiology, pathophysiology and, most importantly, in adult neurogenesis and “stemness”, with special emphasis on astrocytes.     

Improved organogenic capacity of shoot cultures from mature pedunculate oak trees through somatic embryogenesis as rejuvenation technique

Theoretically, complete rejuvenation of mature trees should occur through somatic embryogenesis, however, this has not been extensively studied. The main objective of the present study was to increase the efficiency of in vitro clonal propagation for mature Quercus robur (100–300 years old), by induction of somatic embryogenesis as rejuvenation step prior to establishment of shoot culture through micropropagation of somatic embryo-derived plantlets. Shoot culture lines of “mature” origin were established from epicormic shoots of two centenarian oak genotypes (Sainza and CR-0) and maintained by axillary shoot proliferation. Embryogenic lines were also initiated from epicormic leaf explants of the same genotypes and maintained by secondary somatic embryogenesis. Although the frequency of somatic embryo conversion into plantlets was low in pedunculate oak, shoot culture lines could be established and maintained by axillary branching from several germinated somatic embryos. For each genotype and shoot culture line of the two origins (mature tree and somatic plantlets), shoot multiplication rate and elongation as well as rooting ability parameters were compared. Compared with “mature-origin” shoot cultures and after more than one year propagation in vitro, shoot lines established from somatic plantlets produced a significantly higher proportion of elongated, rootable shoots (from 26.0–31.6 to 36.8–40.5%) with increased rooting ability (from 3.3–45.6% to 23.2–89.8%). In the case of 300-year-old Sainza genotype such a high organogenic capacity was similar to shoot cultures initiated from basal sprouts. Basal sprouts are considered as “mature” material that retains juvenile characteristics compared with epicormic shoots forced from crown branches. Somatic embryogenesis only slightly improved plant regeneration of shoot cultures from basal sprouts, thus validating their use as “juvenile control”. The present results provide evidence that some rejuvenation occurred during the process of somatic embryogenesis and resulted in improved shoot growth and rooting of somatic embryo-derived culture compared with “mature” shoot culture. The results reported in this study might be useful in embryogenic systems with low plant conversion rates. The proposed experimental model might also be useful in finding molecular markers of plant ontogeny.     

Question 9: Prospects for the Construction of Artificial Cells or Protocells

The construction of artificial cells or protocells that are a simplified version of contemporary cells will have implications for both the understanding of the origins of cellular Life and the design of “cell-like” chemical factories. In this short communication, we discuss the progress and remaining issues related to the construction of protocells from metabolic products. We further outline the de novo design of a simple chemical system that mimics the functional properties of a living cell without being composed of molecules of biological origin, thereby addressing issues related to Life’s origins. Presented at: International School of Complexity—4th Course: Basic Questions on the Origins of Life; “Ettore Majorana” Foundation and Centre for Scientific Culture, Erice, Italy, 1–6 October 2006.     

Antigenic components of human glioblastoma multiforme and rat C6 glioma using monoclonal antibodies

With whole U87MG cells used as antigenic stimulant, two clones 1A5G6 and 1D3A3 secreted monoclonal antibodies which gave intense staining in monolayer cultures of the cells as ascertained by indirect immunofluorescence. Antibodies from clone 1A5G6 stained both the cytoplasm and the processes, and that from clone 1D3A3 stained only the cytoplasm and not the processes. 1A5G6 elicited no cross-reactivity towards human fetal and adult brain and lungs, liver, kidney or spleen, mouse neuroblastoma and melanoma, rat C₆ glioma, neuroblastoma X glioma hybrid and normal rat kidney cells. It gave 58–60% cross reactivity with the human neuroblastoma and T-cell leukemia cells. The antigenic comPonent has been identified to be a membrane protein of molecular weight 25–30 kilodaltons by immunoblotting. Using C₆ glioma cells as antigenic stimulant 19 clones which were positive for C₆ glioma cells, but negative for rat liver cells as inferred by indirect immunofluorescence were selected. Antibodies secreted by all these gave positive reaction towards normal rat kidney and fetal rat kidney cells in culture. Distinct identity of these clones were ascertained by discernible staining patterns in indirect immunofluorescence on C₆ glioma cells.     

Expression of nestin,desmin and vimentin in intact and regenerating muscle spindles of rat hind limb skeletal muscles

We describe the expression and distribution patterns of nestin, desmin and vimentin in intact and regenerating muscle spindles of the rat hind limb skeletal muscles. Regeneration was induced by intramuscular isotransplantation of extensor digitorum longus (EDL) or soleus muscles from 15-day-old rats into the EDL muscle of adult female inbred Lewis rats. The host muscles with grafts were excised after 7-, 16-, 21- and 29-day survival and immunohistochemically stained. Nestin expression in intact spindles in host muscles was restricted to Schwann cells of sensory and motor nerves. In transplanted muscles, however, nestin expression was also found in regenerating “spindle fibers”, 7 and 16 days after grafting. From the 21st day onwards, the regenerated spindle fibers were devoid of nestin immunoreactivity. Desmin was detected in spindle fibers at all developmental stages in regenerating as well as in intact spindles. Vimentin was expressed in cells of the outer and inner capsules of all muscle spindles and in newly formed myoblasts and myotubes of regenerating spindles 7 days after grafting. Our results show that the expression pattern of these intermediate filaments in regenerating spindle fibers corresponds to that found in regenerating extrafusal fibers, which supports our earlier suggestion that they resemble small-diameter extrafusal fibers.     

Requirements for maintaining the embryonic state of avian tendon cells in culture

Summary Primary avian tendon cells (PAT) maintain their embryonic state when cultured in medium F-12 with very low serum (0.2%) and ascorbate (50 μg per ml); that is, they retain the potential for devoting 20–30% of their total protein synthesis to collagen. However, if the cells are left at a confluent cell density or are derived from confluent cultures, this potential is irreversibly decreased. This effect, along with poor medium formulations, probably accounts for the “dedifferentiation” process that occurs when fibroblasts are cultured. In contrast, PAT cells kept at subconfluent cell densities retain the ability to synthesize high levels of collagen. The one limitation in obtaining long-term cultures of high collagen-producing tendon cells in the inability of serum at low concentrations to remain a potent mitogen after a few subcultures. The quantitative loss of function has long been considered to be a cell culture artifact; however, we propose that this drop in collagen synthesis is a reflection of the developmental programing of these cells. In separate series of experiments using organ cultures, we show that tendon tissue from the embryo makes over 30% collagen, whereas, “young” tendons make 18% and “older” tendons from the adult make less than 1%. Therefore, a quantitative drop in collagen synthesis would be expected if normal development were to occur in culture. Our data are consistent with the idea that cultures of embryonic tendon cells are triggered to mature by a mechanism that correlates with high cell density. This investigation was supported in part by National Science Foundation Grant PCM 77-14982; in part by the Division of Biomedical and Environmental Research of the Department of Energy under contract W-7405-ENG-48; and by a National Institutes of Health Fellowship IF32 CA 05807-01, from the National Cancer Institute to R. I. S.     

Laminin provides a better substrate than fibronectin for attachment,growth, and differentiation of 1003 embryonal carcinoma cells

Summary Culture of cells in hormonally defined media has allowed (a) the demonstration of physiological responses from cells usually unable to express them in vitro and (b) the study of the effects on growth and differentiation of diffusible factors and attachment factors. The embryonal carcinoma line 1003 forms multidifferentiated tumors in vivo but is unable to differentiate in vitro when grown in serum-containing medium. In a defined medium containing insulin, transferrin, selenium, and fibronectin as attachment factors, 1003 cells grow for several generations and differentiate into neurons and embryonic mesenchyme (Darmon et al., 1981, Dev. Biol. 85: 463–473). In the present work the effects of fibronectin and laminin were compared. In the presence of laminin the cells attached and spread better, grew faster, and could be plated at lower densities. Neurite extension was also better under these conditions and most importantly, it was found that laminin induced an important formation of muscular tissue when the cells had been seeded at low densities. Multinucleated myotubes could be stained with antibodies directed against embryonic muscular myosin. Coating the dishes with polylysine or adding FGF or serum-spreading factor to the medium allowed growth of low-density cultures with fibronectin instead of laminin but muscular differentiation was not detected under these conditions. Addition of fibronectin to laminin-containing medium did not inhibit muscular differentiation. Presented in the symposium on Plant and Animal Physiology in Vitro at the 33rd Annual Meeting of the Tissue Culture Association, San Diego, California, June 6–10, 1982. This research was supported in part by grants from the “Centre National de la Recherche Scientifique” (LA 269), the “Délégation Générale à la Recherche Scientifique et Technique,” the Fondation pour la Recherche Médicale Fran?aise,” the “Institut National de la Santé et de la Recherche Medicale,” the “Ligue Nationale Fran?aise centre le Cancer,” and the “Fondation André Meyer.” This symposium was supported in part by the following organizations: Bellco Glass, Inc., California Branch of the Tissue Culture Association, Collaborative Research, Hana Media, Hybridtech, K C Biological, Inc., and Millipore Corporation.     

成年鼠缺血性脑损伤诱导nestin的表达

应用免疫组化和免疫荧光双标技术结合激光共聚焦扫描显微镜,观察缺血性脑损伤后脑内nestin的表达及其细胞类型。实验观察结果为,再灌后1天,在缺血中心区可见nestin阳性突起;再灌后3天和1周时,除缺血中心区外,周边I、Ⅱ、Ⅲ区均有nestin阳性突起主要与GFAP共存;2周时,nestin阳性突起变粗、变长,并与NSE的共存明显增多。上述研究结果提示,脑缺血可诱导大鼠脑缺血区域表达nestin,该表达可能与神经细胞的修复有关。     

The cancer cell’s “power plants” as promising therapeutic targets: An overview

This introductory article to the review series entitled “The Cancer Cell’s Power Plants as Promising Therapeutic Targets” is written while more than 20 million people suffer from cancer. It summarizes strategies to destroy or prevent cancers by targeting their energy production factories, i.e., “power plants.” All nucleated animal/human cells have two types of power plants, i.e., systems that make the “high energy” compound ATP from ADP and P _i . One type is “glycolysis,” the other the “mitochondria.” In contrast to most normal cells where the mitochondria are the major ATP producers (>90%) in fueling growth, human cancers detected via Positron Emission Tomography (PET) rely on both types of power plants. In such cancers, glycolysis may contribute nearly half the ATP even in the presence of oxygen (“Warburg effect”). Based solely on cell energetics, this presents a challenge to identify curative agents that destroy only cancer cells as they must destroy both of their power plants causing “necrotic cell death” and leave normal cells alone. One such agent, 3-bromopyruvate (3-BrPA), a lactic acid analog, has been shown to inhibit both glycolytic and mitochondrial ATP production in rapidly growing cancers (Ko et al., Cancer Letts., 173, 83–91, 2001), leave normal cells alone, and eradicate advanced cancers (19 of 19) in a rodent model (Ko et al., Biochem. Biophys. Res. Commun., 324, 269–275, 2004). A second approach is to induce only cancer cells to undergo “apoptotic cell death.” Here, mitochondria release cell death inducing factors (e.g., cytochrome c). In a third approach, cancer cells are induced to die by both apoptotic and necrotic events. In summary, much effort is being focused on identifying agents that induce “necrotic,” “apoptotic” or apoptotic plus necrotic cell death only in cancer cells. Regardless how death is inflicted, every cancer cell must die, be it fast or slow.     

Design of bioreactors suitable for plant cell and tissue cultures

Plant cell suspension cultures and hairy roots are potential sources of secondary metabolites and recombinant proteins. In contrast to traditionally grown “whole wild plants” or “whole transgenic plants”, their production in bioreactors guarantees defined controlled process conditions and therefore minimizes or even prevents variations in product yield and quality, which simplifies process validation and product registration. Moreover, bioreactors and their configuration significantly affect cultivation results by accomplishing and controlling the optimum environment for effective cell growth and production of bioactive substances. This review highlights the main design criteria of the most widely used bioreactor types, both for plant cell suspension cultures and for hairy roots, and outlines suitable low-cost disposable bioreactors which have found increasing acceptance over the last 10 years. Plants for human health in the post-genome era, PSE congress 26.8.2007–29.8.2007, Helsinki.     

Adult-type myogenesis of the frog <Emphasis Type="Italic">Xenopus laevis</Emphasis> specifically suppressed by notochord cells but promoted by spinal cord cells in vitro

Larval-to-adult myogenic conversion occurs in the dorsal muscle but not in the tail muscle during Xenopus laevis metamorphosis. To know the mechanism for tail-specific suppression of adult myogenesis, response character was compared between adult myogenic cells (Ad-cells) and larval tail myogenic cells (La-cells) to a Sonic hedgehog (Shh) inhibitor, notochord (Nc) cells, and spinal cord (SC) cells in vitro. Cyclopamine, an Shh inhibitor, suppressed the differentiation of cultured Ad (but not La) cells, suggesting the significance of Shh signaling in promoting adult myogenesis. To test the possibility that Shh-producing axial elements (notochord and spinal cord) regulate adult myogenesis, Ad-cells or La-cells were co-cultured with Nc or SC cells. The results showed that differentiation of Ad-cells were strongly inhibited by Nc cells but promoted by SC cells. If Ad-cells were “separately” co-cultured with Nc cells without direct cell–cell interactions, adult differentiation was not inhibited but rather promoted, suggesting that Nc cells have two roles, one is a short-range suppression and another is a long-range promotion for adult myogenesis. Immunohistochemical analysis showed both notochord and spinal cord express the N-terminal Shh fragment throughout metamorphosis. The “spinal cord-promotion” and long-range effect by Nc cells on adult myogenesis is thus involved in Shh signaling, while the signaling concerning the short-range “Nc suppression” will be determined by future studies. Interestingly, these effects, “Nc suppression” and “SC promotion” were not observed for La-cells. Situation where the spinal cord/notochord cross-sectional ratio is quite larger in tadpole trunk than in the tail seems to contribute to trunk-specific promotion and tail-specific suppression of adult myogenesis during Xenopus metamorphosis.     

Slow modulation of synaptic transmission by brain-derived neurotrophic factor leads to the central sensitization associated with neuropathic pain

Chronic constriction injury (CCI) of the rat sciatic nerve increases the dorsal horn excitability. This “central sensitization” leads to behavioral manifestations analogous to those related to human neuropathic pain. We found, using whole-cell recording from acutely isolated spinal cord slices, that 7-to 10-day-long CCI increases excitatory synaptic drive to putative excitatory “delay”-firing neurons in the substantia gelatinosa but attenuates that to putative inhibitory “tonic”-firing neurons. A defined-medium organotypic culture (DMOTC) system was used to investigate the long-term actions of brain-derived neurotrophic factor (BDNF) as a possible instigator of these changes. When all five neuronal types found in the substantia gelatinosa were considered, BDNF and CCI produced similar patterns, or “footprints,” of changes across the whole population. This pattern was not seen with another putative “pain mediator,” interleukin 1β. Thus, BDNF decreased synaptic drive to “tonic” neurons and increased synaptic drive to “delay” neurons. Actions of BDNF on “delay” neurons were presynaptic and involved increased mEPSC frequency and amplitude without changes in the function of postsynaptic AMPA receptors. By contrast, BDNF exerted both pre-and post-synaptic actions on “ tonic” cells to reduce the mEPSC frequency and amplitude. These differential actions of BDNF on excitatory and inhibitory neurons contributed to a global increase in the dorsal horn network excitability as assessed by the amplitude of depolarization-induced increases in the intracellular [Ca²⁺]. Experiments with the BDNF-binding protein TrkB-d5 provided additional evidence for BDNF as a harbinger of neuropathic pain. Thus, the cellular processes altered by BDNF likely contribute to “central sensitization” and hence to the onset of neuropathic pain. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 315–326, July–October, 2007.     

Transient alterations in cellular permeability in cultured human proximal tubule cells: Implications for transport studies

Summary Primary cultures of human proximal tubule (HPT) cells possess the characteristics of a tight epithelium and retain the characteristics of in vivo renal function. HPT cells from confluent monolayers when grown on collagen-coated polycarbonate inserts in a hormonally defined serum-free medium. However, initial studies of transepithelial transport observed large bidirectional fluxes of the paracellular probe inulin. The present studies were designed to assess the transformation of HPT cell tight junctions to a “leaky” state and subsequent recovery. The apparent transepithelial electrical resistance of HPT cells at confluence was 952.0±70.0 ohms*cm², suggesting a well-developed tight junction-mediated paracellular pathway in this epithelium. However, replacement of the growth media produced an immediate 90% drop in the initial resistance, which was paralleld by an increased flux of inulin and of phenol red. This transient abolition of barrier function spontaneously reestablished over 1–2 h by a process that was dependent on the ionic composition of the added media. Complete recovery of cellular resistance was paralleled by markedly decreased fluxes of inulin and of phenol red. The recovery of cellular barrier function was inhibited by cytochalasin B suggesting an intracellular action, not a physical disruption of the monolayer. These results suggest that the tight junctions in these cells appear to transiently produce a leaky state during removal of the media, but rearrange to a “tight conformation” when incubated in the appropriate media.     

GFAP-Deficient Astrocytes Are Capable of Stellationin VitroWhen Cocultured with Neurons and Exhibit a Reduced Amount of Intermediate Filaments and an Increased Cell Saturation Density

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein predominantly expressed in cells of astroglial origin. To allow for the study of the biological functions of GFAP we have previously generated GFAP-negative mice by gene targeting [Peknyet al.(1995)EMBO J.14, 1590–1598]. Astrocytes in culture, similar to reactive astrocytesin vivo,express three intermediate filament proteins: GFAP, vimentin, and nestin. Using primary astrocyte-enriched cultures from GFAP-negative mice, we now report on the effect of GFAP absence on (i) the synthesis of other intermediate filament proteins in astrocytes, (ii) intermediate filament formation, (iii) astrocyte process formation (stellation) in response to neurons in mixed cerebellar astrocyte/neuron cultures, and (iv) saturation cell densityin vitro.GFAP−/− astrocytes were found to produce both nestin and vimentin. At the ultrastructural level, the amount of intermediate filaments as revealed by transmission electron microscopy was reduced in GFAP−/− astrocytes compared to that in GFAP+/+ astrocytes. GFAP−/− astrocytes retained the ability to form processes in response to neurons in mixed astrocyte/neuron cultures from the cerebellum. GFAP−/− astrocyte-enriched primary cultures exhibited an increased final cell saturation density. The latter leads us to speculate that the loss of GFAP expression observed focally in a proportion of human malignant gliomas may reflect tumor progression toward a more rapidly growing and malignant phenotype.     

Male competition and coalitions in langurs (Presbytis entellus) at Jodhpur,Rajasthan, India

During a 15 month study on free ranging langurs (Presbytis entellus) at Jodhpur, Rajasthan, India, 5 adult male replacements were observed as a result of nontroop male invasions into the home ranges of 3 neighbouring one-male troops comprising 16–28 members each. Jodhpur langurs have no breeding season. Periods of instability during resident male changes lasted 11–119 days. Linear dominance hierarchies could be detected within the 3 main rival male bands of 2, 5, and 28–35 members. The respective alphas drove their allies away after their bands succeeded cooperatively at occupying a troop. During gradual replacements interim residencies alternated with multi-male stages. A large band's alpha may have had better chances to win the competition, since adult and nonadult allies functioned as “buffers” in agonistic encounters. The role of kin selection in structuring the composition of male bands and male coalitional behaviour cannot yet be quantified. Tactical “deceit” of powerful males to cause unrealistic expectations and in this way agonistic engagement of less strong males can be ruled out. “Sneaking copulations” is a proximate advantage for subordinate supporters, since they participated in 61.9% of all sexual interactions. Female promiscuity might reflect a strategy to induce male-male competition and thus select for a strong resident.     

The ecological niche of the consortium “Pelochromatium roseum”

A dense accumulation of the phototrophic consortium “Pelochromatium roseum” in a small, eutrophic, freshwater lake (Dagowsee, Brandenburg, Germany) was investigated. Within the chemocline, the number of epibionts of the consortia represented up to 19% of the total number of bacteria. Per “P. roseum” a mean value of 20 epibionts was determined. Similar to other aquatic habitats, consortia in the Dagowsee were found only at low light intensities (< 7 μmol quanta m^–2 s^–1) and low sulfide concentrations (0–100 μM). In dialysis cultures of “P. roseum”, bacterial cells remained in a stable association only when incubated at light intensities between 5 and 10 μmol quanta m^–2 s^–1. Intact consortia from natural samples had a buoyant density of 1046.8 kg m^–3, which was much higher than that of ambient chemocline water (995.8 kg m^–3). Under environmental conditions and without motility, this density difference would result in rapid sedimentation of consortia toward the lake bottom. Our results indicate that (1) consortia are adapted to a very narrow regime of light intensities and sulfide concentrations, (2) motility and tactic responses must be of ecological significance for the colonization of the free water column of lakes, and (3) phototrophic growth of consortia can be explained only by a cycling of sulfur species in the chemocline, possibly within the consortia themselves. Received: 27 May 1997 / Accepted: 16 September 1997