Microbial community composition was examined in two soil types, Anthrosols and adjacent soils, sampled from three locations in the Brazilian Amazon. The Anthrosols, also known as Amazonian dark earths, are highly fertile soils that are a legacy of pre-Columbian settlement. Both Anthrosols and adjacent soils are derived from the same parent material and subject to the same environmental conditions, including rainfall and temperature; however, the Anthrosols contain high levels of charcoal-like black carbon from which they derive their dark color. The Anthrosols typically have higher cation exchange capacity, higher pH, and higher phosphorus and calcium contents. We used culture media prepared from soil extracts to isolate bacteria unique to the two soil types and then sequenced their 16S rRNA genes to determine their phylogenetic placement. Higher numbers of culturable bacteria, by over two orders of magnitude at the deepest sampling depths, were counted in the Anthrosols. Sequences of bacteria isolated on soil extract media yielded five possible new bacterial families. Also, a higher number of families in the bacteria were represented by isolates from the deeper soil depths in the Anthrosols. Higher bacterial populations and a greater diversity of isolates were found in all of the Anthrosols, to a depth of up to 1 m, compared to adjacent soils located within 50-500 m of their associated Anthrosols. Compared to standard culture media, soil extract media revealed diverse soil microbial populations adapted to the unique biochemistry and physiological ecology of these Anthrosols.

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Monsoonal upwelling along south and central west coast of India leads to intense biological productivity. As a consequence of excess organic matter production following upwelling during June-October and low dissolved oxygen in the upwelled waters, denitrification occurs in the near shore waters. Implicitly, these processes ought to bring alterations in microbial communities. Therefore, diversity and community structure of bacteria from subsurface layers of a tropical region experiencing intense seasonal lows of oxygen were analyzed through sequencing of 16S rRNA gene clones. The overall diversity was more during hypoxic period of Fall intermonsoon (FIM, October) compared either to Spring intermonsoon (SIM, March) or summer monsoon (SuM, June) months. As many as 14 lineages of bacterial domains: Gammaproteobacteria (37%), Alphaproteobacteria (21%), Cyanobacteria (20%), Deltaproteobacteria (3%), Firmicutes (3%), Betaproteobacteria (2%), Acidobacteria (2%), Actinobacteria (7%), Marinimicrobia (2%), Bacteroidetes (1%), Verrucomicrobia (1%), Planctomycetes (0.4%), Chloroflexi (0.2%) and Omnitrophica bacterium (0.2%), were recognized from our coastal location. Notably, sequences of Planctomycetes, Chloroflexi and Omnitrophica bacterium were found exclusively during FIM. A generally higher representation of sequences of Betaproteobacteria during SuM and of Actinobacteria and Firmicutes during SIM was discernible. This study is thus useful to recognize that microbial community might undergo strong temporal shifts in the monsoon affected tropical coastal ecosystems. Keywords Tropical coastal ecosystem Á Goa Á Upwelling Á Hypoxia Á Bacterial community Á 16S rDNA clones Á Phylogenetic composition Electronic supplementary material The online version of this article (

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Northeastern Arabian Sea (NEAS) is a recognized region of intense denitrification, with its 200-1200m water column being anoxic. Abundance of bacteria, viral particles as well as bacterial community (BC) were studied in addition to various chemical and other biological parameters from the Arabian Sea Time Series (ASTS) station. Water samples from surface, deep chlorophyll maximum (DCM), 250, 500 and 1000m were collected during Spring intermonsoon (SIM), Fall Intermonsoon (FIM), and Northeast monsoon (NEM) seasons and analyzed for various parameters. Bacterial abundance varied seasonally (P ≤ 0.05), with its highest abundance observed during FIM at all sampling depths. Conversely, seasonal variations in viral abundance were minimal, though a significant correlation between virus and bacterial abundance (r = 0.526, P < 0.05, n=14) was evidenced. Hierarchical clustering of denaturing gradient gel electrophoresis (DGGE) profiles revealed clear patterns of vertical as well as temporal partitioning of BC during all three seasons. In that, BC varied seasonally both in the surface and DCM, whereas in the oxygen minimum zone (OMZ; 250-1000m) it was more or less identical during all three seasons in spite of significant seasonal variation in bacterial abundance, pH and DO level in the OMZ. Following the band-matching, several DGGE bands were excised and sequenced. Phylogenetic analysis of these sequences brought forth Alphaproteobacteria, Gammaproteobacteria, and Cyanobacteria as the dominant bacterial groups at the ASTS location. Linkage tree (LINKTREE) and canonical correspondence analysis (CCA) were performed to decipher the effect of environmental factors on the BC. From these analyses it is inferred that dissolved oxygen (DO) and total organic carbon (TOC) are responsible for vertical separation of BC between the surface and OMZ. Our results suggest seasonal variations in BC occurs in the surface layers with least or minimal temporal differences in the OMZ.