Mat Core Research Articles

Photosynthetic and behavioral versatility of the cyanobacterium Oscillatoira boryana in a sulfide-rich microbial mat

The diel pattern of vertical migratory movements and photosynthetic activity of Oscillatoria cf. boryana was monitored periodically in microbial mats of a shallow tepid pond fed by sulfiderich, hot, geothermal spring water in Rotorua, New Zealand. Motile O. boryana formed a conspicuous and predominant population which was spread over the mat surface during darkness and on overcast days (< 50–100 W m−2). Macrophotography has documented that under higher light (100–300 W m −2) much of the population contracted into streaks or patches. During periods of even higher irradiance (>300 W m−2), O. boryarta disap-peared almost entirely from the mat surface to a position of about 1 mm below the surface pellicle of the mat. O2, sulfide, and pH microelectrodes inserted into excised mat cores with dense O. boryana populations were used to make vertical profiles at intervals of 0.1−0.2 mm and also to estimate rates of oxygenic and anoxygenic photosynthesis during rapid light-dark transitions. In addition, attenuation of irraaiance was measured in mats with O. boryana by a spectroradiometer with mini-fiber optic probe. Light-dependent incorporation of [ 14C]-bicarbonate and [14C]-acetate was measured in collected field populations of O. boryana. The combined results led to the conclusion that populations of O. boryarta typically employed sulfide-dependent anoxTgenic photosynthesis in early morning which depleted sulfide locally. As irradiance increased and sulfide concentration fell below about 50 µM within the Oscillatoria population, oxygenic photosynthesis became dominant. [14C]-Bicarbonate incorporation results indicate that sulfide concentrations over 1.0 mM inhibit oxygenic photosynthesis completely. In populations on excised mats, irradiance levels of about 150–200 W m −2 were required for light-enhanced oxidation of sulfide to balance sulfide input from diffusion and local production. Below that surface-irradiance level it is likely that mainly sulfide-dependent anoxygenic photosynthesis of O. boryana occurred. This capability was confirmed for O. boryana by [14C]-photoincorporation and sulfide-microeleetrode experiments. Forced exposure to high irradiance levels (500–700 W m −2) was inhibitory to oxygenic photosynthesis in O. boryana, but these intensities impinging on mats resulted in a downward retreat. The result was a lowered irradiance level for the Oscillatoria but, nevertheless, a high rate of oxygenic photosynthesis. O. boryana is a versatile cyanobacterium that appears to avoid photoinhibitory conditions and to optimize its light intensity for photosynthesis by vertical migrations, using gliding motility and some form of photoresponse. It is also able to photosynthesize at substantial rates over a wide range of sulfide concentrations by shifting between oxygenic and anoxygenic modes or possibly by combining both.

Photosynthetic and behavioral versatility of the cyanobacterium Oscillatoria boryana in a sulfide-rich microbial mat

The diel pattern of vertical migratory movements and photosynthetic activity of Oscillatoria cf. boryana was monitored periodically in microbial mats of a shallow tepid pond fed by sulfiderich, hot, geothermal spring water in Rotorua, New Zealand. Motile O. boryana formed a conspicuous and predominant population which was spread over the mat surface during darkness and on overcast days ( 300 W m−2), O. boryarta disap-peared almost entirely from the mat surface to a position of about 1 mm below the surface pellicle of the mat. O2, sulfide, and pH microelectrodes inserted into excised mat cores with dense O. boryana populations were used to make vertical profiles at intervals of 0.1−0.2 mm and also to estimate rates of oxygenic and anoxygenic photosynthesis during rapid light-dark transitions. In addition, attenuation of irraaiance was measured in mats with O. boryana by a spectroradiometer with mini-fiber optic probe. Light-dependent incorporation of [ 14C]-bicarbonate and [14C]-acetate was measured in collected field populations of O. boryana. The combined results led to the conclusion that populations of O. boryarta typically employed sulfide-dependent anoxTgenic photosynthesis in early morning which depleted sulfide locally. As irradiance increased and sulfide concentration fell below about 50 µM within the Oscillatoria population, oxygenic photosynthesis became dominant. [14C]-Bicarbonate incorporation results indicate that sulfide concentrations over 1.0 mM inhibit oxygenic photosynthesis completely. In populations on excised mats, irradiance levels of about 150–200 W m −2 were required for light-enhanced oxidation of sulfide to balance sulfide input from diffusion and local production. Below that surface-irradiance level it is likely that mainly sulfide-dependent anoxygenic photosynthesis of O. boryana occurred. This capability was confirmed for O. boryana by [14C]-photoincorporation and sulfide-microeleetrode experiments. Forced exposure to high irradiance levels (500–700 W m −2) was inhibitory to oxygenic photosynthesis in O. boryana , but these intensities impinging on mats resulted in a downward retreat. The result was a lowered irradiance level for the Oscillatoria but, nevertheless, a high rate of oxygenic photosynthesis. O. boryana is a versatile cyanobacterium that appears to avoid photoinhibitory conditions and to optimize its light intensity for photosynthesis by vertical migrations, using gliding motility and some form of photoresponse. It is also able to photosynthesize at substantial rates over a wide range of sulfide concentrations by shifting between oxygenic and anoxygenic modes or possibly by combining both.

Thickness swelling and density variation in aspen flakeboards

This paper reports the relationship between thickness swelling and density in labmade aspen flakeboards. The boards were manufactured with several levels of initial mat moisture content and urea resin content. Weight increase and thickness swelling at 12 locations on each board were recorded under specified environmental conditions over a period of 71 days. Each board was then cut into 12 specimens, each containing one of the 12 locations at its center, and density was calculated. No definite relationship was found between thickness swelling and density among the 12 specimens of each board. Our results suggest that high initial moisture content and high resin content can decrease thickness swelling. Variations in mat pressure and core temperature during the press cycle and weight increase at 80 percent relative humidity are discussed.

Discovery and evidence of nitrogen fixation by thermophilic heterotrophs in hot springs

A previously unknown phenomenon, nitrogenase activity at high temperatures by nonphotosynthetic prokaryotes in thermal springs, is reported. This activity was revealed by dark-bottle incubations during cyanobacterial nitrogenase studies in hot springs of Yellowstone National Park. Benthic mat cores from alkaline thermal streams reduced acetylene in the dark from 30° to 60°C. the bacterial activity was distinguished from that of sympatric cyanobacteria by its sensitivity to oxygen (light bottles), heterotrophic response to organic amendments, and distinctive spatial distribution. Field tests for other biotic or abiotic explanations of the activity were negative. Anaerobic enrichment cultures supported the field evidence. Fourteen morphological types of presumptive diazotrophs, including sulfate-reducing and spore-forming rods. have been observed in these cultures.

DISTRIBUTION AND PHYSIOLOGICAL DETERMINANTS OF BLUE‐GREEN ALGAL NITROGEN FIXATION ALONG A THERMOGRADIENT1

ABSTRACTThe capacity of thermal algal‐bacterial mats to fix nitrogen (N2) was examined in an alkaline thermal stream, Rabbit Creek, of Yellowstone National Park. Nitrogenase activity and nitrogen‐fixation rates of mat cores placed in serum bottles and incubated in situ were estimated by the acetylene‐reduction technique. Active nitrogenase was not detected at 60 or 65 C in either the blue‐green algal or bacterial undermat components of the mats. Acetylene was reduced by all mats ≤55 C along the thermogradient; mean fixation estimates for the mats ranged from 7 to 5,028 nmoles N2 fixed · mg Chl a−1· hr−1. Maximum fixation occurred at 35 C in the stream; statistical comparison of mean rates ordered the thermogradient mats according to estimated activities: 35 &gt; 40 &gt; 30 &gt; 50 ≥ 55 ≥ 45 C. Mats (≤40 C) dominated by species of Calothrix accounted for ca. 97% of the total nitrogen fixation observed in the stream; the remaining activity was associated with mats containing Mastigocladus laminosus Cohn. Light intensity significantly affected fixation rates of the Calothrix mats which responded in a linear fashion from 9–100% full sunlight (ca. 1,900 μEin · m−2· sec−1). Calothrix mats from 30 and 40 C had maximum nitrogenase activity at their growth temperature suggesting that nitrogen fixation along the thermogradient was optimally adapted to in situ temperatures.