Danilo Giroldo

Release of carbohydrates and proteins by a subtropical strain of Raphidiopsis brookii (cyanobacteria) able to produce saxitoxin at three nitrate concentrations.

Raphidiopsis brookii P. J. Hill (cyanobacteria) was isolated from a small subtropical eutrophic pond (Biguá Pond) located in the grounds of Rio Grande University in the extreme south of Brazil, following a toxic bloom of this species. Growth, saxitoxin production, and release of carbohydrates and protein were monitored at three sodium nitrate concentrations (500, 1,000, and 1,500 μM), from inoculation up to the stationary growth phase. Growth was monitored by determining the biovolume, chl content, and trichome count. Growth was better described in terms of biovolume and chl measurements, because trichome fragmentation was observed to increase at the stationary growth phase. Carbohydrates and proteins were released in small amounts during most of the experiment, with a significant increase during the stationary phase. Extracellular polysaccharides were essentially composed of glucose, galactose, N‐acetyl‐glucosamine, mannose, xylose, rhamnose, arabinose, and fucose. The relative proportions of these units showed no significant variation during growth. Small quantities of extracellular free carbohydrates were also detected, and only fucose was released in significant amounts at the lowest nitrate concentration (500 μM). R. brookii produced both saxitoxin and dc‐saxitoxin, the former at four times the rate of the latter. This was the first study demonstrating saxitoxin production and the release of both carbohydrate and protein by R. brookii.

Microbial degradation of extracellular polysaccharides released by a tropical strain of Staurastrum orbiculare (Zygnematophyceae)

D. Giroldo, A.A.H. Vieira and B.S. Paulsen. 2005. Microbial degradation of extracellular polysaccharides released by a tropical strain of Staurastrum orbiculare (Zygnematophyceae). Phycologia 44: 671–677. The extracellular polysaccharide (EPS) released by a freshwater desmid, Staurastrum orbiculare (Zygnematophyceae), was characterized and their degradation by heterotrophic microbial populations was also evaluated. The EPS was purified by anion exchange column chromatography, the monosaccharide composition was determined by gas chromatography and the linkages of the monosaccharides by gas chromatographic analysis coupled with electron impact mass spectrometry. The EPS was mainly eluted in one weak acid fraction, although a smaller strong acid fraction was also eluted. The two fractions had similar composition and both of them were mainly composed of fucose, glucuronic acid, galactose, galacturonic acid, xylose, glucose, rhamnose and N-acetyl glucosamine. We monitored the entire EPS degradation, and also their components separately, during 35 days using pulse amperometric detection in a high-performance liquid chromatography. Fucose, galactose and especially glucose showed a faster degradation pattern than rhamnose and arabinose, whereas xylose and the total EPS showed an intermediate degradation pattern. The entire EPS was degraded in about 14 days evidencing S. orbiculare EPS as a high quality carbon source to the natural bacterial community of Barra Bonita reservoir.

Limnological characterisation and phytoplankton seasonal variation in a subtropical shallow lake (Guaiba Lake, Brazil): a long-term study

AIM: to provide a long-term limnological characterisation of a subtropical shallow lake in addition to verifying seasonal differences, including phytoplankton variation. METHODS: monthly sampling at sites IP, SJ and MD from 2000 to 2009 to analyse temperature - T; depth - Z; the depth of the euphotic zone - Zeu; Zeu/Z (%); total suspended solids - TSS; dissolved oxygen - DO; pH; electrical conductivity - EC; N-NH3, N-NO2, N-NO3; soluble reactive phosphorus - SRP; chlorophyll a - Chl-a and phytoplankton. RESULTS: low values of Z and Zeu characterised the shallow and turbid conditions of lake and corresponded to the contribution of nano-microflagellates (Chlamydomonas sp., Spermatozopsis sp., Cryptomonas sp. and Rhodomonas sp ) and diatoms (Aulacoseira granulata). Zeu/Z (%), SRP and Chl-a were significantly different at site IP (meso-eutrophic) compared to sites SJ and MD (eutrophic). Phytoplankton density was also significantly higher at sites SJ and MD, and the largest relative contribution of Actinastrum sp., Dictyosphaerium sp., Micractinium sp., Monoraphidium sp., Scenedesmus/Desmodesmus sp. and Euglena sp. corresponded to the most polluted waters at site SJ. The significantly higher T (oC) in summer corresponded to significantly higher Chl-a as well as a greater richness and density of phytoplankton. Cocconeis sp., Gomphonema sp. and Pinnularia sp. (pennated diatoms) were negatively correlated with temperature and were therefore more representative at the three sites in winter. Asterionella formosa was correlated with SRP and vernal blooms were recorded (2000-2001). Planktothrix isothrix and Planktothricoides raciborskii were expressive in the summer/late summer (2004-2005), and were significantly correlated with Chl-a and low SRP in water column. CONCLUSIONS: The study corroborated the sensitivity of phytoplankton in characterising different stages of eutrophication at different sites and corresponding watersheds as well as in characterising different seasons in a shallow lake in the subtropical zone of Brazil.

Efficiency of Neutral Red, Evans Blue and MTT to assess viability of the freshwater microalgae Desmodesmus communis and Pediastrum boryanum

This study assessed the efficacy of three cell viability assays – Methyl‐thiazolyl‐tetrazolium (MTT), Evans Blue, and Neutral Red – for two freshwater microalgae species, Desmodesmus communis and Pediastrum boryanum (Chlorophyceae), in order to find suitable techniques to detect the levels of pollution in water ecosystems. Following exposure to a glyphosate‐based herbicide, our results showed that Evans Blue did not adequately measure cell viability in either species, while MTT and Neutral Red were able to detect decreased cellular viability for both algae in response to herbicide exposure. Overall, however, Neutral Red proved to be more sensitive than MTT for these algae.

New records of bryophytes for the state of Rio Grande do Sul, Brazil

The aim of this study was to complete the species list and disseminate data regarding the diversity of bryophytes in the state of Rio Grande do Sul, Brazil. We registered 51 species of bryophytes (11 mosses and 40 liverworts) as new records for Rio Grande do Sul, of which six represent the second records for Brazil.

CARBOHYDRATE RELEASE BY A SUBTROPICAL STRAIN OF SPONDYLOSIUM PYGMAEUM (ZYGNEMATOPHYCEAE): INFLUENCE OF NITRATE AVAILABILITY AND CULTURE AGING1

This paper describes the influence of nitrate availability on growth and release of dissolved free and combined carbohydrates (DFCHOs and DCCHOs) produced by Spondylosium pygmaeum (Cooke) W. West (Zygnematophyceae). This strain was isolated from a subtropical shallow pond, located at the extreme south of Brazil (Rio Grande, RS). Experiments were carried out in batch culture, comparing two initial nitrate levels (10/100 μM) in the medium. Growth was monitored by direct microscopic cell counts and chl a content. Nitrate consumption was determined by ion chromatography, while the production of extracellular carbohydrates was monitored by the phenol‐sulfuric method. The monosaccharide compositions of DFCHOs and DCCHOs were determined in each growth phase by HPLC with pulse amperometric detection (HPLC‐PAD). At the end of the experiment, the total composition of extracellular polysaccharide (EPS) molecules >12 kDa was determined by gas chromatography. Nitrate availability had no influence on S. pygmaeum cell density at any phase. On the other hand, chl a content decreased after a few days growth when the availability of nitrate was restricted, but continued to rise when nitrate was plentiful. Also, nitrate depletion was faster at 10 μM nitrate. No influence of the growth phase or nitrate availability on the total carbohydrates (TDCHOs) released per cell was observed. Only DCCHOs were released by S. pygmaeum, and the composition varied between growth phases, especially at lower nitrate availability. EPS molecules >12 kDa were composed mainly of xylose, fucose, and galactose, as for other desmids. However, a high N‐acetyl‐glucosamine content was found, uniquely among desmid EPSs.