Spatial stratification of soil bacterial populations in aggregates of diverse soils

Most soil microbial community studies to date have focused on homogenized bulk soil samples. However, it is likely that many important microbial processes occur in spatially segregated microenvironments in the soil leading to a microscale biogeography. This study attempts to localize specific microbial populations to different fractions or compartments within the soil matrix. Microbial populations associated with macroaggregates and inner- versus total-microaggregates of three diverse soils were characterized using culture-independent, molecular methods. Despite their relative paucity in most surveys of soil diversity, representatives of Gemmatimonadetes and Actinobacteria subdivision Rubrobacteridae were found to be highly abundant in inner-microaggregates of most soils analyzed. By contrast, clones affiliated with Acidobacteria were found to be relatively enriched in libraries derived from macroaggregate fractions of nearly all soils, but poorly represented in inner-microaggregate fractions. Based upon analysis of 16S rRNA, active community members within microaggregates of a Georgian Ultisol were comprised largely of Gemmatimonadetes and Rubrobacteridae, while within microaggregates of a Nebraska Mollisol, Rubrobacteridae and Alphaproteobacteria were the predominant active bacterial lineages. This work suggests that microaggregates represent a unique microenvironment that selects for specific microbial lineages across disparate soils.

A novel cyanobacterium exhibiting an elevated tolerance for iron

Studies directed at cyanobacteria inhabiting iron-depositing hot springs may provide insights into the role of both ancient and contemporary cyanobacteria mediated iron transformations. Here we phylogenetically, morphologically and physiologically characterize a novel cyanobacterium isolated from an iron-depositing hot spring. Phylogenetic analyses indicate that the bacterium is a representative of a new genus, exhibiting a maximum 95.2% homology to database sequences. The isolate is a unicellular cyanobacterium with bladder-like cells typically packed as duplexes, or in extracellular polymeric substance covered clumps and small chains without the ability to produce baeocystes. No growth without added combined nitrogen occurred. While requiring relatively large amounts of iron for growth (>40microM), the isolate was shown to facilitate removal of iron from culture media. These results suggest that the isolate may be an important component of an iron-depositing microbial community. The name "Chroogloeocystis siderophila" for this cyanobacterium is proposed.