Biogenic Weathering: Solubilization of Iron from Minerals by Epilithic Freshwater Algae and Cyanobacteria

A sandstone outcrop exposed to freshwater seepage supports a diverse assemblage of photosynthetic microbes. Dominant taxa are two cyanophytes (Oscillatoria sp., Rivularia sp.) and a unicellular green alga (Palmellococcus sp.). Less abundant taxa include a filamentous green alga, Microspora, and the desmid Cosmarium. Biologic activity is evidenced by measured levels of chlorophyll and lipids. Bioassay methods confirm the ability of these microbes to dissolve and metabolize Fe from ferruginous minerals. Chromatographic analysis reveals citric acid as the likely chelating agent; this low molecular weight organic acid is detectable in interstitial fluid in the sandstone, measured as 0.0756 mg/mL. Bioassays using a model organism, Synechoccus elongates strain UTEX 650, show that Fe availability varies among different ferruginous minerals. In decreasing order of Fe availability: magnetite > limonite > biotite > siderite > hematite. Biotite was selected for detailed study because it is the most abundant iron-bearing mineral in the sandstone. SEM images support the microbiologic evidence, showing weathering of biotite compared to relatively undamaged grains of other silicate minerals.

Microbial Biofilm Community Variation in Flowing Habitats: Potential Utility as Bioindicators of Postmortem Submersion Intervals

Biofilms are a ubiquitous formation of microbial communities found on surfaces in aqueous environments. These structures have been investigated as biomonitoring indicators for stream heath, and here were used for the potential use in forensic sciences. Biofilm successional development has been proposed as a method to determine the postmortem submersion interval (PMSI) of remains because there are no standard methods for estimating the PMSI and biofilms are ubiquitous in aquatic habitats. We sought to compare the development of epinecrotic (biofilms on Sus scrofa domesticus carcasses) and epilithic (biofilms on unglazed ceramic tiles) communities in two small streams using bacterial automated ribosomal intergenic spacer analysis. Epinecrotic communities were significantly different from epilithic communities even though environmental factors associated with each stream location also had a significant influence on biofilm structure. All communities at both locations exhibited significant succession suggesting that changing communities throughout time is a general characteristic of stream biofilm communities. The implications resulting from this work are that epinecrotic communities have distinctive shifts at the first and second weeks, and therefore the potential to be used in forensic applications by associating successional changes with submersion time to estimate a PMSI. The influence of environmental factors, however, indicates the lack of a successional pattern with the same organisms and a focus on functional diversity may be more applicable in a forensic context.

Intertidal epilithic bacteria diversity changes along a naturally occurring carbon dioxide and pH gradient

Intertidal epilithic bacteria communities are important components of coastal ecosystems, yet few studies have assessed their diversity and how it may be affected by changing environmental parameters. Submarine CO2 seeps produce localised areas of CO2-enriched seawater with reduced pH levels. We utilised the seawater pH/CO2 gradient at Levante Bay (Italy) to test the hypothesis that epilithic bacteria communities are modified by exposure to seawater with the varying chemical parameters. Biofilms were sampled from three sites exposed to seawater with different pH/CO2 levels and diversity determined using high-throughput sequencing of 16S rRNA genes. Seawater pCO2 concentrations were increased from ambient at site 1 to 621 μatm at site 2 and 1654 μatm site 3, similar to the predicated future oceans beyond 2050 and 2150, respectively. Alpha diversity of total bacteria communities and Cyanobacteria communities was significantly different between sites (anova P < 0.05). Comparison between sites showed that bacteria communities and Cyanobacteria communities were significantly different (anosim P < 0.01; permanova P < 0.01). Proteobacteria, Bacteroidetes and Cyanobacteria dominated all communities; however, there were differences between sites in the relative abundance of specific orders. This study provides the most detailed assessment of intertidal epilithic bacteria diversity and shows that diversity is significantly different along a seawater pH/CO2 gradient. This information supports the evaluation of the impacts of future ocean acidification on coastal marine ecosystems.

Salinity affects compositional traits of epibacterial communities on the brown macroalga Fucus vesiculosus

Epibiotic biofilms have the potential to control major aspects of the biology and ecology of their hosts. Their composition and function may thus be essential for the health of the host. We tested the influence of salinity on the composition of epibacterial communities associated with the brown macroalga Fucus vesiculosus. Algal individuals were incubated at three salinities (5, 19, and 25) for 14 days and nonliving reference substrata (stones) were included in the experiment. Subsequently, the composition of their surface-associated bacterial communities was analyzed by 454 pyrosequencing of 16S rRNA gene sequences. Redundancy analysis revealed that the composition of epiphytic and epilithic communities significantly differed and were both affected by salinity. We found that 5% of 2494 epiphytic operational taxonomic units at 97% sequence similarity were responsible for the observed shifts. Epibacterial α-diversity was significantly lower at salinity 5 but did not differ between substrata. Our results indicate that salinity is an important factor in structuring alga-associated epibacterial communities with respect to composition and/or diversity. Whether direct or indirect mechanisms (via altered biotic interactions) may have been responsible for the observed shifts is discussed.

Records of the Genus Paramerina (Diptera: Chironomidae: Tanypodinae) from Eastern Himalaya and Satpura Hill Regions of India

The pupa and the male imago of Paramerina valida n. sp. and the larva of Paramerina inficia Chaudhuri & Debnath are described and illustrated along with a brief re-description of the adult of P. inficia from the Eastern Himalaya and Satpura hill regions of India. A key to the adult males of the Indian species of the genus Paramerina Fittkau is provided. The notes on ecology of the two species are also provided.