Halimeda bioherms occur as extensive geological structures on the northern Great Barrier Reef (GBR), Australia. We present the most complete, high-resolution spatial mapping of the northern GBR Halimeda bioherms, based on new airborne lidar and multibeam echosounder bathymetry data. Our analysis reveals that bioherm morphology does not conform to the previous model of parallel ridges and troughs, but is far more complex than previously thought. We define and describe three morphological sub-types: reticulate, annulate, and undulate, which are distributed in a cross-shelf pattern of reduced complexity from east to west. The northern GBR bioherms cover an area of 6095 km2, three times larger than the original estimate, exceeding the area and volume of calcium carbonate in the adjacent modern shelf-edge barrier reefs. We have mapped a 1740 km2 bioherm complex north of Raine Island in the Cape York region not previously recorded, extending the northern limit by more than 1° of latitude. Bioherm formation and distribution are controlled by a complex interaction of outer-shelf geometry, regional and local currents, coupled with the morphology and depth of continental slope submarine canyons determining the delivery of cool, nutrient-rich water upwelling through inter-reef passages. Distribution and mapping of Halimeda bioherms in relation to Great Barrier Reef Marine Park Authority bioregion classifications and management zones are inconsistent and currently poorly defined due to a lack of high-resolution data not available until now. These new estimates of bioherm spatial distribution and morphology have implications for understanding the role these geological features play as structurally complex and productive inter-reef habitats, and as calcium carbonate sinks which record a complete history of the Holocene post-glacial marine transgression in the northern GBR.
Six strains of Nocardia asteroides, two strains of N. caviae, and two strains of N. braziliensis were grown in medium supplementted with glycine, lysozyme, D-cycloserine, glycine plus lysozyme, and glycine plus D-cycloserine. It was shown that three strains of N. asteroides, and two strains of N. caviae, readily formed spheroplasts and/or protoplasts when grown in the presence of glycine plus either lysozyme or D-cycloserine. This process was studied by both phase contrast microscopy and electron microscopy. The induced cultures were then plated on hypertonic medium for the isolation of L-forms. It was shown that the organisms differed greatly in their ability to produce spheroplasts and subsequently grew as L-forms or transitional-phase variants. 相似文献
Most of the theory for the evolution of caste specialization in social insects assumes that increased efficiency in worker labor leads to specialization and increased worker efficiency gives colonies with behavioral specialists an advantage. However, there are an increasing number of studies that show that the task specialists within social insect colonies do not have the highest efficiency. Indeed, some studies show that some groups of workers are uniformly better than all other groups at every task. In this note, I adapt the principle of comparative advantage from economics to show that, rather than maximizing the payoff, specialization is advantageous when minimizing opportunity costs. This leads to the prediction that caste specialization should be associated with reduced opportunity costs rather than increased task efficiency. 相似文献
The chemical composition of the cell walls of several L-form revertants derived from Nocardia asteroides 10905 was determined at different stages of growth. It was observed that each L-form revertant had a cell well that differed from that of the parental strain when grown under identical conditions. In some strains the peptidolipid and mycolic acid components were affected the most, whereas in other strains the fatty acid, sugar, and mycolic acid moieties were altered. Shifts in mycolic acid size were prominent, whereas the basic peptidoglycan structure appeared to be affected the least. Both the method used to induce the L-form of N. asteroides 10905 and the length of time these organisms were maintained in the wall-less state affected the degree of cell wall modification during the reversion process. Thus, removal of the cell wall appeared to potentiate and select for mutational alterations within the cell envelope of N. asteroides, and these changes resulted in altered cellular and colonial morphology. 相似文献
Natural products have long served as rich sources of drugs possessing a wide range of pharmacological activities. The discovery
and development of natural product drug candidates is often hampered by the inability to efficiently scale and produce a molecule
of interest, due to inherent qualities of the native producer. Heterologous biosynthesis in an engineering and process-friendly
host emerged as an option to produce complex natural products. Escherichia coli has previously been utilized to produce complex precursors to two popular natural product drugs, erythromycin and paclitaxel.
These two molecules represent two of the largest classes of natural products, polyketides and isoprenoids, respectively. In
this study, we have developed a platform E. coli strain capable of simultaneous production of both product precursors at titers greater than 15 mg l−1. The utilization of a two-phase batch bioreactor allowed for very strong in situ separation (having a partitioning coefficient
of greater than 5,000), which would facilitate downstream purification processes. The system developed here could also be
used in metagenomic studies to screen environmental DNA for natural product discovery and preliminary production experiments. 相似文献
Heterologous natural product biosynthesis has emerged as a strategy to produce medicinal compounds that pose challenges to conventional production routes. Polyketide compounds, an important class of natural products with wide-ranging therapeutic value, have been heterologously produced through Escherichia coli, presenting new opportunities to realize the medicinal potential of polyketide natural products. However, current production levels are often suboptimal when compared to native strain producers or heterologous theoretical yields. This problem provides an excellent opportunity to apply and further develop current metabolic engineering tools. 相似文献