FECAL METHANOGENS AND VERTEBRATE EVOLUTION

It has been assumed that the feeding habits of vertebrates predispose the variety of intestinal differentiations and the composition of the microbial biota living in their intestinal tracts. Consequently, the presence of methanogenic bacteria in the various differentiations of the large intestine and the foregut of herbivorous vertebrates had been attributed primarily to the existence of anaerobic habitats and the availability of carbon dioxide and hydrogen originating from the fermentative microbial digestion of plant-based diets. However, Australian ratites, many murids, and several New World primates lack methanogens, despite their intestinal differentiations and their vegetarian feeding habits. Crocodiles, giant snakes, aardvarks, and ant-eaters on the other hand release significant amounts of methane. A determination of methane emissions by 253 vertebrate species confirmed that competence for intestinal methanogenic bacteria is shared by related species and higher taxa, irrespective of different feeding habits. In “methanogenic” branches of the evolutionary tree, a variety of differentiations of the large intestine evolved and, in some cases, differentiations of the foregut. In contrast, the lack of competence for methanogens in chiropterans/insectivores and carnivores apparently has precluded the evolution of specialized fermenting differentiations of the digestive tract. Our observations reveal that the presence of intestinal methanogenic bacteria is under phylogenetic rather than dietary control: competence for intestinal methanogenic bacteria is a plesiomorphic (primitive-shared) character among reptiles, birds, and mammals. This competence for methanogenic bacteria has been crucial for the evolution of the amniotes.     

Epilithic bacterial and algal colonization in a stream run, riffle, and pool: a test of biomass covariation

Epilithic bacterial and algal biomass were compared among a run, riffle, and pool along an open-canopy section of a third-order, temperate stream. Epilithic biofilms were sampled after 3, 7, 14, 21, 28, and 35 days colonization on unglazed ceramic tiles that were attached to plastic trays (n = 3) placed across each of the three habitats (i.e., run, riffle, pool). The diverse habitats and sampling regime were selected to provide a range in algal biomass so that potential covariation between epilithic bacterial and algal biomass could be assessed. There were significant differences among habitats and among trays within each habitat for both chlorophyll a and AFDM. Chlorophyll a and AFDM increased in the run and pool throughout the colonization period. In the riffle, chlorophyll a and AFDM increased rapidly early in colonization, then decreased. Epilithic bacterial biomass increased rapidly with no significant differences among the three habitats throughout colonization. Further, bacterial biomass did not correlate with either chlorophyll a or AFDM in any of the three habitats or on any of the sampling days. These results suggest that epilithic algal and bacterial biomass may be regulated by independent controls in some stream environments.     

Spatial distribution and seasonal changes in methylmercury concentrations in shallow lakes

The environmental factors governing the distribution and behaviour of total and methylmercury within mercury contaminated shallow lakes, associated with the River Yare, Norfolk, UK, have been assessed in situ through the use of sediment cores. These were analysed for microbial and chemical changes on both a temporal and spatial scale. The distribution of total mercury proved to be site dependent and related to the hydrology, sediment transport dynamics, the degree of sediment disturbance and distance from the contamination source. The core profiles revealed a subsurface peak in total mercury with maximum concentrations residing at depths of 12 and 36 cm, depending upon location, with enrichment extending down to depths in excess of 88 cm. This vertical distribution was deemed to reflect historical emission in the late 1960s and early 1970s rather than post depositional migration effects. The distribution of methylmercury was distinct from that of its inorganic counterpart since it also displayed temporal variability with highest concentrations occurring in the spring and summer. Maximum concentrations also prevailed in the uppermost 12 cm of sediment, with peak loadings at or just below the sediment/water interface and detectable levels being restricted to the upper 36 cm. The temporal and spatial behaviour of methylmercury appeared to reflect variations in redox potential, the availability of the Hg²⁺ ion and the nature of microbial populations.     

Integrated cultivation of salmonids and seaweeds in open systems

Bacterial abundance and production in a vertical profile in Lake Kariba (17dgS), Zimbabwe, were affected by solar irradiance. At the surface, 1.87 × 10⁹ bacteria 1^–1 were found and abundance peaked at 10 m (2.5 × 10⁹ bacteria l^-1), then decreasing with depth. Bacterial reproduction at the surface(0.145 µg C1^–1 h^–1) was nearly four times less than the production at 10 m although bacterial numbers were only 26% less. Thus, bacterial production per cell was lower at the surface than deeper down, suggesting that bacterial production is inhibited at the surface.Bacterial production in GF/F filtered lake water in Whirl Pack bags showed an exponential decrease down to 3 m depth. The inhibition was well in accordance with light extinction in the UV region. Phosphatase activity was low in light exposed bags compared to dark, indicating photolysis of extracellular enzymes, or phototransformation of recalcitrant DOM, which substitutes enzyme activity. Hypolimnetic enzyme activity was less affected by solar light than epilimnetic.     

Resuscitation of Vibrio cholerae O1 strain TSI-4 from a viable but nonculturable state by heat shock

Abstract Vibrio cholerae strain TSI-4 was incubated in an M9 salt solution at 15 °C for more than 100 days. The plate counts showed no viable cells on day 30, but a broth culture from that day showed the growth of bacteria. However, after 35 days the bacteria entered the nonculturable state, based on the assessment of both the plate counts and broth culture. A portion of the culture was heated at 45 °C for 1 min in a water bath and subsequently plated onto a nutrient agar plate. More than 1000 colonies were recovered after this heat-shock treatment. The recovered cells showed the same chromosomal DNA pattern in the restriction map and the same outer membrane protein pattern in SDS-PAGE. Recovery of viable cells by heat-shock was achieved in cultures grown on M9 salt but not from cultures grown in phosphate-buffered saline. This suggests that the presence of NH₄Cl in the M9 salt solution may support the growth of the bacteria in a low nutrient medium, while also playing an important role in resuscitation.     

Bacterial host specificity of Lucinacea endosymbionts: Interspecific variation in 16S rRNA sequences

Abstract Three tropical lucinid clams ( Codakia orbiculata, Codakia pectinella and Lucina nassula ) from a shallow coastal environment have been studied regarding to their thioautotrophic bacterial endosymbionts. The 16S rRNA genes (rDNA) from these three endosymbionts were amplified using PCR. Phylogenetic analysis by distance matrix and parsimony methods always placed the newly examined symbionts within the monophyletic group composed of symbionts of the bivalve superfamily Lucinacea. A same single 16S rRNA sequence was found in C. orbiculata and C. pectinella and was identical to that found in C. orbicularis and Linga pensylvanica , two other lucinids living in the same type of environment. These data indicate that a same symbiont species may be associated with different host species. Lucina nassula hosts a symbiont with a distinct 16S rDNA sequence, but very closely related to the former.     

Halcyon days with Bill Arnold

The circumstances that led to the discovery that plants luminesce after they are illuminated are described, as are other discoveries that would not have been possible were it not for the fortuitous association I had with my dear and most admirable friend, W.A. Arnold, to whom this special issue is dedicated.     

Bacteriochlorophyll organization and energy transfer kinetics in chlorosomes from Chloroflexus aurantiacus depend on the light regime during growth

We have used measurements of fluorescence and circular dichroism (CD) to compare chlorosome-membrane preparations derived from the green filamentous bacterium Chloroflexus aurantiacus grown in continuous culture at two different light-intensities. The cells grown under low light (6 mol m^–2 s^–1) had a higher ratio of bacteriochlorophyll (BChl) c to BChl a than cells grown at a tenfold higher light intensity; the high-light-grown cells had much more carotenoid per bacteriochlorophyll.The anisotropy of the Q_Y band of BChl c was calculated from steady-state fluorescence excitation and emission spectra with polarized light. The results showed that the BChl c in the chlorosomes derived from cells grown under high light has a higher structural order than BChl c in chlorosomes from low-light-grown cells. In the central part of the BChl c fluorescence emission band, the average angles between the transition dipole moments for BChl c molecules and the symmetry axis of the chlorosome rod element were estimated as 25° and 17° in chlorosomes obtained from the low- and high-light-grown cells, respectively.This difference in BChl organization was confirmed by the decay associated spectra of the two samples obtained using picosecond single-photon-counting experiments and global analysis of the fluorescence decays. The shortest decay component obtained, which probably represents energy-transfer from the chlorosome bacteriochlorophylls to the BChl a in the baseplate, was 15 ps in the chlorosomes from high-light-grown cell but only 7 ps in the preparation from low-light grown cells. The CD spectra of the two preparations were very different: chlorosomes from low-light-grown cells had a type II spectrum, while those from high-light-grown cells was of type I (Griebenow et al. (1991) Biochim Biophys Acta 1058: 194–202). The different shapes of the CD spectra confirm the existence of a qualitatively different organization of the BChl c in the two types of chlorosome.Abbreviations BChl bacteriochlorophyll - CD circular dichroism - DAS decay associated spectrum - PMSF phenylmethylsulfonyl fluoride     

The rare occurrence of plant tissue culture contamination by Methylobacterium mesophilicum

A pink-pigmented, facultative methylotrophic (PPFM) bacterium, Methylobacterium mesophilicum, which is found on the leaf surface of most plants, has been reported to be a covert contaminant of tissue cultures initiated from Glycine max (soybean) leaves and seeds by Holland and Polacco (1992). The bacteria can be detected as pink colonies when leaves are pressed or tissue culture homogenates are plated on a medium with methanol as the sole carbon source. Since the presence of contaminating bacteria can confound any biochemical results obtained with such cultures (Holland and Polacco 1992), we wanted to determine the extent of the contamination of our tissue cultures of soybean and other species. No PPFMs were detected in any soybean culture we have, and previous results describing the biochemical characteristics of ureide utilization by one of our soybean suspension cultures (27C) also indicates that PPFM bacteria were not present. Analysis of about 200 other strains of 11 different species maintained in this lab showed that only three of about 160 callus cultures, recently initiated from Datura innoxia leaves, contained PPFMs. The D. innoxia leaves did have PPFMs on their surface but in most cases they did not survive the surface disinfestation and culture regimes. Thus PPFM bacterial contamination should not be a serious problem in most plant tissue cultures.Abbreviations AMS ammonium mineral salts medium - PPFM pink-pigmented facultative methylotrophic bacteria     

Fate of elemental sulfur in an intertidal sediment

Abstract: Sediment from a tidal flat at Wedderwarden, near the mouth of the Weser estuary, northern Germany, was amended with elemental sulfur, and concentrations of metabolic end products were monitored. The production of both sulfate and sulfide was consistent with disproportionation as the most important fate of the added elemental sulfur. A population of bacteria conducting active elemental sulfur disproportionation was also enriched from the sediment. In the enrichments, containing both elemental sulfur and Fe oxides as a sulfide 'scrub', sulfide and sulfate were produced in a ratio of     , somewhat lower than the predicted ratio of     . The mismatch between predicted and observed production ratios is explained by the channelling of electrons into autotrophic or mixotrophic CO₂ fixation rather than sulfide formation. The production of organic carbon, in the correct amount to explain the observed sulfide to sulfate production ratio, was verified by organic carbon analysis. Finally, rates of sulfate reduction were identical in the elemental sulfur amended sediment, and in control sediment with no added sulfur. Hence, the heterotrophic bacterial community was completely unaffected by an active metabolism conducting elemental sulfur disproportionation.