Shoals Soil Salinity Gradient Effects On The Microbial Community Structure

Mudflat soils with different salt concentrations were collected from Dafeng, Jiangsu Province China. Culturability of bacteria in the soils was examined with different culture schemes. Results showed that natural sea water was necessary as a media supplement for growing bacteria in the soils. cAMP did not show improvement of bacterial culturability. Medium concentration was a key factor affecting the culturability. Prolonged incubation up to 25 days increased number of colony forming unit on plate. Liquid media were better than solid ones in term of growing maximal number of bacteria. By the most probable number method, it was noted that tubes not showing turbidity but showing mucous precipitation were also positive tubes, which can be easily overlooked as negative tubes. Microscopic and sequence examination showed the mucous precipitation consists of mainly small short rod-shaped bacteria (0.6×1.2~2.6μn), with high similarity to Bacillus sp. Optimized culture scheme for the mudflat soils is proposed, which includes 1/10 nutrient broth supplemented with 100% natural sea water, liquid culture, and prolonged incubation up to 25 days. Carbon compounds in the media should be further optimized. To our best knowledge, there has been no information on the changes of sediment microbial communities along a desalinization gradient slowly evolved from intertidal sediment to arable land. And the mudflat is of agricultural importance, so we restrict our study on nitrifying and denitrifying communities. Results showed that the bacterial community structure in the mudflat varies with salinity levels and that the diversity increases with the decrease of salinity levels. Based on the datum, it is estimated that community change from sediment to arable land took roughly 60 years under natural desalinization processes, as the distance between the two sites is 3 km. It means that microbial community changes in response to salinity could be rapid.