Qualitative And Quantitative Study Of Spore-forming Bacteria And Bacterial Endospores In Marine Sediments Of The Western Pacific And Indian Oceans

Recent studies have shown that there are a large number of spore-forming bacteria and their spores in the deep biosphere.Spores are formed when bacteria in the experience extreme environmental conditions.Endospores are a bacterial resistant form with deep dormancy and extremely low metabolic rate used to protect the genetic information and macromlecules.The spores may become vegetative cells once under the right conditions,which play an important role in global biogeochemical cycles.At present,there are few quantitative studies about the number of bacterial spores and their proportion in the deep biosphere.Previous studies have shown that the number of bacterial cells decreases with increasing sediment depth because of increasing temperature and pressure and decreasing energy,whlie the number of spores may increase with increasing depth.For the detection of spores,modern molecular biological methods are not applicable because spores are impermeable.Pyridine dicarboxylic acid(DPA)is a peculiar compound found in bacterial endospores with a proportion between 5% and 15% dry weight of spore,and thus become an ideal spore biomarker.For detecting DPA,a number of different methods have been used the in previous studies,such as fluorescence,Raman spectroscopy,high-performance liquid chromatography(HPLC).However,these methods are either inaccurate or of low sensitivity.In this study we adopted the gas chromatogrphy-mass spectrometry(GC-MS)method to identify and quantify DPA in our samples.High throughput sequencing analysis was carried out to determine bacterial diversity and community structure of the sediments in the seabed sediment of the western Pacific and Indian Oceans,including the distribution of spore-formng bacteria.The proportion of spore-forming bacteria in the Indian Ocean sediment samples was 5.26%.On the other hand,the concentration ofDPA ranged between 0.024 and 2.846 nmol/g.The average number of spores in the Indian Ocean sediment samples was 4.088×106/g,and 0.423×106/g in the western Pacific Ocean.We also isolated and identified a gram-positive bacterium,Bacillus aestuarii DSL-17 T and obtained the number of its spores by staining and counting,which was not much different from the number of spores produced by existing studies.