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Caulobacters are adherent prosthecate bacteria that are members of bacterial biofouling communities in many environments. Investigation of the cell surface carbohydrates produced by two strains of the freshwater Caulobacter crescentus, CB2A and CB15A, revealed a hitherto undetected extracellular polysaccharide (EPS) or capsule. Isolation and characterization of the EPS fractions showed that each strain produced a unique neutral EPS which could not be readily removed from the cell surface by washing. Monosaccharide analysis showed that the main CB2A EPS contained D-glucose, D-gulose, and D-fucose in a ratio of 3:1:1, whereas the CB15A EPS fraction contained D-galactose, D-glucose, D-mannose, and D-fucose in approximately equal amounts. Methylation analysis of the main CB2A EPS showed the presence of terminal glucose and gulose groups, 3-linked fucosyl, and two 3,4-linked glucosyl units, thus confirming the pentasaccharide repeating unit indicated by 'H nuclear magnetic resonance analysis. Similar studies of the CB15A EPS revealed a tetrasaccharide repeating unit consisting of terminal galactose, 4-linked fucosyl, 3-linked glucosyl, and 3,4-linked mannosyl residues. EPS was not detectable by thin-section electron microscopy techniques, including some methods designed to preserve or enhance capsules, nor was the EPS readily detected on the cell surface by scanning electron microscopy when conventional fixation techniques were used; however, a structure consistent with EPS was revealed when samples were prepared by cryofixation and freezesubstitution methods.Caulobacter crescentus is a gram-negative stalk-forming bacterium which is typically found in natural settings attached to surfaces via an adhesive holdfast organelle located at the distal tip of the stalk (33). The strategy for growth and dispersal of cells for this organism involves a cell differentiation process by which a motile dispersal (swarmer) cell is produced. Swarmer cells express a single flagellum, pili, and the holdfast, all of which are located at one cell pole. At a specific time in the life cycle, all the polar features of the swarmer cell except for the holdfast are lost and a stalk develops at the same pole as the swarmer differentiates into a stalked cell (33,34,37). Throughout the entire life cycle, the cell is completely covered with a protein surface array (S layer) distal to the outer membrane, composed of geometrically arranged subunits consisting of a single protein (39,40).We were interested in the surface molecules of caulobacters on the presumption that they all participate in some way in the persistence of caulobacters in microbial biofilm communities. Clearly, the adhesive holdfast has a primary role, being involved with surface attachment, and we have reported initial analyses for the holdfast of freshwater and marine species (28)(29)(30). The organelle appears to be a complex polysaccharide whose composition varies somewhat between species (26,28
For reasons other than the climate, 2020 was an extraordinary year. The COVID-19 pandemic has affected almost all of us, changing the lives of many people around the globe. While the economic disruption associated with COVID-19 led to modest estimated reductions of 6-7% (e.g., le Quere et al. 2020;Friedlingstein et al. 2020; BP Statistical Review of the World Energy 2021) in global anthropogenic carbon dioxide (CO 2 ) emissions, atmospheric CO 2 levels continued to grow rapidly-a reminder of its very long residence time in the atmosphere and the challenge of reducing atmospheric CO 2 . As we show in this chapter, the climate has continued to respond to the resulting warming from these increases in CO 2 and other greenhouse gases such as methane and nitrous oxide, which also experienced record increases in 2020.The year 2020 was one of the three warmest since records began in the mid-to-late 1800s, with global surface temperatures around 0.6°C above the 1981-2010 average, despite the El Niño-Southern Oscillation progressing from neutral to La Niña conditions by August (see section 4b). Lower tropospheric temperatures matched those from 2016, the previous warmest year. Meanwhile, stratospheric temperatures continued to cool as a result of anthropogenic CO 2 increases. Along with the above-average surface temperatures, an unprecedented (since instrumental records began) geographic spread of heat waves and warm spells occurred. Antarctica observed its highest temperature on record (18.3°C) at Esperanza in February. In August, Death Valley, California, reported the highest temperature observed anywhere on Earth since 1931 (preliminary value of 54.4°C).Consequently, many permafrost measurement sites experienced their highest temperatures on record; Northern Hemisphere (NH) snow cover was below the 51-year average and the fourthleast extensive on record. Glaciers in alpine regions experienced their 33rd consecutive year of negative mass balance and 12th year of average losses of more than 500 mm depth. On average, NH lakes froze over 3 days later and thawed 5.5 days earlier than the 1981-2010 average during the 2019/20 winter, which was the third-shortest ice cover season since 1979/80.The atmosphere responded to higher temperatures accordingly by holding more water. Total column water vapor was high relative to the 1981-2010 average, ranging from 0.75 to 1.06 mm over ocean and 0.58 to 0.94 mm over land, but did not reach the record values of 2016. At the surface, specific humidity over oceans was at record high levels (0.23 to 0.41 g kg −1 ) and was well above average over land (0.14 to 0.36 g kg −1 ). Conversely, relative humidity was well below average over land (-1.28 to -0.68 %rh), continuing the long-term declining trend. Precipitation increased compared to 2019, driven largely by land values, but there were few exceptional extreme precipitation events, coupled with below-average cloudiness over most of the land. More lakes showed positive water level anomalies than 2019, and in East Africa, Lake Victoria's level ...
2021, coinciding with a large ozone hole persisting until December (sections 2g4, 6h). The equatorial stratosphere's quasi-biennial oscillation progressed in 2021 as it usually has for more than half a century: downward-propagating easterly and westerly wind regimes and accompanying temperature variations, with a mean periodicity of somewhat more than two years. This regular downward propagation from the upper to lower stratosphere was interrupted in both 2016 and 2020, but more regular evolution appeared to resume at the end of 2020 with an easterly phase propagating downward from the middle stratosphere (https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo.html).
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