Growth Rates Of Typical Heterotrophic Bacteria In Pure Cultures And In Marine Ecosystems

As global warming intensifies,it has been urgently need for studying on the microbes in the oceans and their roles in the carbon cycle and climate regulations on the global scale.Marine heterotrophic bacteria are the important part of marine microbiological community and plays crucial roles in matter cycling and energy flow in marine ecosystem.Marine Roseobacter clade is one of the representative groups in the marine heterotrophic bacterial communities and thus the important model organisms on studying the structure and function of the marine bacterial community.The process by which bacteria convert nutrients and organic matter into biomass-particulate organic carbon is bacterial production.Bacterial growth rate is highly correlated with bacterial production,which can reveal the survival strategies of different bacterial groups and their relative contributions to carbon fixation and storage in marine environments.Thus,studies on bacterial growth rate contribute to better understanding the microbial loop,microbial food web and microbial carbon pump,the carbon cycle that microbes mainly involved.However,growth rates of heterotrophic bacterial communities calculated by traditional methods are quite different.Moreover,growth rates of individual taxa in the community can not be accurately determined,the method of which should be further explored.The determinations of the relationship between 16S rRNA:rDNA and growth provide the possibility of using molecular methods to assess the real growth rate of marine heterotrophic bacteria.(1)In order to explore the relationship between the growth rate of heterotrophic bacteria and 16S rRNA:rDNA in the oceans,we chose six Roseobacter strains isolated in the laboratory to determine the relationship between 16S rRNA:rDNA and growth rate in culture.The results indicated that the16S rRNA:rDNA ratio versus growth rate relationships at the individual level varied.At the population level,however,the positive relationships held significantly when the six strains were compared together(R2=0.634,P<0.001).(2)We then applied the 16S rRNA:rDNA versus growth rate relationships measured in culture to estimate growth rates for the Roseobacter clade in environments(surface sediments of Jiulong River,the surface waters and the surface sediments of the Yangtze River,the surface and subsurface waters of the South China Sea and the surface waters of the Western Pacific).In terms of the surface water,growth rates of the Roseobacter clade in the northern South China Sea(0.43±0.57 d-1)are much higher than in the low latitude area of the West Pacific(0.02±0.03 d-1).In terms of the surface costal sediments,growth rates of the Roseobacter clade in Yangtze River(0.29±0.41 d-1)are slightly higher than in Jiulong River(0.23±0.26 d-1).Furthermore,we compared the ratios of the 16S rRNA:rDNA for the Roseobacter clade and the total bacterial community in environment.In most areas of this study(the surface sediments of Jiulong River,the surface and subsurface waters of the South China Sea and the surface waters of the Western Pacific),the 16S rRNA:rDNA of the Roseobacter clade were higher than the bacterial communities.The results indicated that growth rates of the Roseobacter clade might lower than the growth rates of the total bacterial communities.(3)Strain JL30074T was isolated from the 1500m deep portions of Northeastern Indian Ocean(4°30.041r S,95°31.946' E).Based on the morphological,phenotypic and phylogenetic analysis,strain JL30074T(=JCM 31906T=CGMCC 1.16124T)was considered to represent a novel genus and species within the family Rhodospirillaceae,for which the name Secretiobacterium indicum gen.nov.,sp.nov is proposed.