Narasimmalu Rajendran

Distribution of phospholipid ester-linked fatty acid biomarkers for bacteria in the sediment of Ise Bay, Japan

Abstract Surface sediments collected from 40 stations in Ise Bay, which is one of the most polluted bays in Japan, were subjected to phospholipid ester-linked fatty acid (PLFA) analysis. Thirty-five fatty acids were identified in the sediments; they included saturated, unsaturated and branched fatty acids. The major fatty acids included the even-numbered straight chain fatty acid 16:0 (20%), branched chain fatty acids i15:0 (8%) and a15:0 (11%),and monounsaturated fatty acids 16:1d9c (11%) and 18:1d11 (10%). Fatty acids which are common in bacterial membranes were found, and low amounts of longer chain fatty acids were detected in relatively constant amounts in the bay. One of the characteristic features of the PLFA analysis in Ise Bay is the virtual absence of polyunsaturated fatty acids in the sediments, except for 18:2. The PLFA profiles indicate that the microbial community structure is characterized by the absence of polyunsaturated fatty acids typical of microeukaryotes and high proportions of fatty acid biomarkers of prokaryotes in sediments. A wide distribution of aerobic bacteria. Gram-positive bacteria, anaerobic bacteria and sulfate-reducing bacteria in the microbial community structure was indicated by the presence of biomarker fatty acids. Similarity analysis of the PLFA profiles in sediments of all the stations showed that they were similar at the 90% level. The results of Tukeys test showed that a majority of the fatty acids in sediments were not significantly enriched in the bay. The absence of significant variation in the PLFA profiles in sediments revealed that the microbial community structure is similar throughout the bay, and this uniformity was attributed to the reported pollution and eutrophication in Ise Bay. Further, the significant PLFA patterns, with a high proportion of prokaryotic biomarker fatty acids and an absence of microeukaryotic biomarkers, indicate that PLFA analysis could be used as a measure of pollution in sediments.

Comparative description of microbial community structure in surface sediments of eutrophic bays

Comparisons of microbial community structure in sediments of eutrophic areas such as Hiroshima Bay, Etauchi Bay, Osaka Bay and Kojima Lake in Japan were undertaken by analysing the phospholipid fatty acid (PLFA) composition in sediments. In addition, the PLFA composition of aerobic bacteria, anaerobic bacteria and sulphate reducing bacteria (SRB) were analysed to assess their contribution to sedimentary lipid. The monounsaturated PLFA and branched PLFA were predominantly present in aerobic bacteria, and anaerobic bacteria and SRB, respectively. The PLFA composition of sediments showed significant regional differences among the four study areas, indicating the significant difference in microbial community structure. The aerobic prokaryotes and eukaryotes were predominantly present in all the study areas except in Osaka Bay where the gram-positive bacteria and anaerobic bacteria were predominant. The characteristic PLFA of aerobic prokaryotes and eukaryotes were significantly higher in Kojima Lake than other areas whereas the biomarker PLFA of gram-positive bacteria were predominantly present in Osaka Bay than that in other areas. These significant variations in microbial community structure can be attributed to the differences in environmental perturbation.

Assessment of bacterioplankton viability by membrane integrity

Abstract The present paper reports the variability of bacterial viability, assessed by membrane integrity (BacLight probe), observed in the western Seto Inland Sea of Japan. The average concentrations of bacteria (1.54.2×10 6 ml −1 in January and 1.1–1.7×10 6 ml −1 in September) were typical of eutrophic coastal waters. The percentage of viable bacteria were 40.5–80.3% (mean of 59.6%) in September 1996, and 65.2–86.4% (mean of 79.6%) in January 1997. The present investigation shows that: 1 . BacLight provides valuable information for studies in microbial ecology; 2 . lower bacterial viability was not necessarily associated with higher or lower bacterial concentrations, or with a particular water layer; 3 . temperature and concentration of dissolved oxygen might play a role in influencing the viability ratio of bacterioplankton, since higher viability were observed at lower temperature and higher oxygen concentration. Further work is required in order to understand the relationship between bacterial viability and environmental parameters.

The Role of Suspended Oyster Culture on Nitrogen Cycle in Hiroshima Bay

The predominance of bivalves affects the cycle of materials in the coastal ecosystem. In the present study, the role of suspended oyster culture on the nitrogen cycle was demonstrated for the northern Hiroshima Bay. The nitrogen cycle was considered as two systems, (1) the primary production (PP) system and (2) the oyster culture (OC) system. The results show that about 26% of N productivity was supplied to process by cultured oysters in the OC system. This process varies seasonally due to the seasonal variations of PON, physiological activities and biomass of oysters. The N processing rates were found to be high in summer and low in winter. The biodeposition and excretion of N in the OC system are 3.0 and 2.1 ton N d−1, while the natural sedimentation rate and N regeneration in the PP system are 8.3 and 18.0 ton N d−1, which indicates that the PP system is a major system regenerating N in the water column. The release of total dissolved N from the bottom to the water column is about 8.3 ton N d−1. The amount of N harvested as oyster product was about 1.3 ton N d−1, which is about 10% of daily N loading in north Hiroshima Bay. According to the N cycle developed in the present study, the results suggest the significant role of suspended oyster culture on the nitrogen cycle in Hiroshima Bay. In addition, our results indicate that oyster production was efficiently harvested, suggesting that oyster culture could probably be used as a tool to remove N from Hiroshima Bay.

Microbial community Structure Analysis of Euxinic Sediments Using Phospholipid Fatty Acid Biomarkers

Microbial community structure in sediments, as determined by the phospholipid ester-linked fatty acid (PLFA) analysis, collected from Kojima Lake during summer and winter was described with reference to the environmental quality of the lake. A characteristic feature of the study area was the persistence of anoxia in summer and winter in the deeper area, and the sediments were under the reduced condition with high levels of sulfide, chemical oxygen demand, and low values of oxidation-reduction potential. PLFA profiles of the sediment were dominated by the saturated, branched and monounsaturated fatty acids. Small amounts (less than 5% of the total PLFA) of polyunsaturated fatty acids (biomarker fatty acids of microeukaryotes) and long chain fatty acids were detected in sediments. Total PLFA concentrations in sediments were higher in summer than in winter. Microbial community structure in the lake sediments was predominated by the prokaryotes, as evidenced from the larger amounts of bacterial biomarker fatty acids in the range of C10 to C20. The presence of signature fatty acids of sulfate reducing bacteria in sediments was consistent with the high levels of sulfide in the sediment and anoxic condition in the study area. PLFA showed significant differences in PLFA profiles between shallow and deeper areas, indicating the differences in the lipid contributing communities. However, no such a significant difference was observed between summer and winter.

Microbial community structure in sediments of a polluted bay as determined by phospholipid ester-linked fatty acids

Abstract Phospholipid ester-linked fatty acid (PLFA) composition in sediments were determined in order to understand the microbial community structure in a polluted bay. The PLFA pattern in sediments revealed the presence of aerobic and anaerobic bacteria, the composition of which differed among the stations. The community structure in sediments, as characterized by the composition of PLFA showed an absence of polyunsaturated fatty acids, except 18:2, signature fatty acids of microeukaryotes and a greater proportion of bacterial biomarker fatty acids. The results of Tukeys honestly significant difference test showed distinctive differences in the PLFA among the stations and also shifts in the microbial community structure in the bay. The significant patterns of PLFA in sediments with the virtual absence of lipid biomarkers for microeukaryotes and the relatively high proportions of bacterial biomarkers indicate the prokaryotic consortium responsive to organic contamination.

Bioconcentration of endosulfan in different body tissues of estuarine organisms under sublethal exposure.

The organochlorine pesticide endosulfan is applied in the agricultural fields as liquid in India. Investigations have revealed the occurrence and distribution of endosulfan in both biotic and abiotic components of Vellar estuary. The results from static bioassay studies revealed that fishes were more susceptible to the organochlorine pesticides than mollusks. Though the available information on the uptake of endosulfan by the estuarine organisms are limited to whole body tissues, no attempt has been made to find out the extent of uptake of pesticides by the different body tissues of the estuarine organisms. Hence the present study was planned to determine the bioconcentration of endosulfan in different tissues of fishes Mugil cephalus, Mystus gulio, oyster Crassostrea madrasensis and clam Katelysia opima based on the measured concentration of endosulfan in the experimental medium of the continuous flow through system for a period of 10 d.

Bacterial loss and degradation of bacterial membrane in preserved seawater samples

Abstract The present study reports the loss of bacteria in four samples preserved with formaldehyde and stored at 4°C in the dark. The degradation of bacterial membrane was estimated by BacLight probe and related to storage time, bacterial loss and attachment to the bottle surface. The concentration of bacteria decreased sharply in the first week of storage in two out of the four samples. After 3 months of storage, the final concentrations of bacteria were between 30 and 63% of the initial concentration in three out of the four samples. A linear decrease in the ratio of intact bacteria of 6–8% over a 10 day period was observed. The attachment of bacteria onto the bottle surface did not seem to play an important role in bacterial loss. The results of this study suggested that bacteria in seawater samples should be enumerated as soon as possible after sampling, in order to minimise error.

Microbial Biomarker Fatty Acid Composition in Coastal Sediments

沿岸海底堆積物中の微生物現存量と微生物の群集構造を明らかにするために堆積物中のリン脂質の脂肪酸組成を解析した。その結果、33種の脂肪酸が検出され、それらの中には多くの細菌指標性の脂肪酸が含まれていた。微生物現存量は堆積物乾重量1gあたり1.5×10 ～9.3×10 cellsと推定された。微生物バイオマーカー脂肪酸の類似度分析からは微生物の群集構造に対応する4つの異なったクラスターが認められた。沿岸堆積物中のリン脂質脂肪酸中の不飽和脂肪酸と分枝脂肪酸の分析結果から好気性細菌ならびに嫌気性細菌、特に硫酸塩還元細菌の地域的な存在特性が明らかとなった。

Uptake and Release of Particulate Materials by Suspended Oyster Culture in Hiroshima Bay : Results From Raft Study

沿岸域で行われている垂下式カキ養殖による粒状物の取り込みと排出の季節変動を定量的に明らかにするため、1995年10月～1996年8月に広島湾の養殖筏を対象に研究を行った。筏(200m2)の上流と下流の粒状物質(PM)、クロロフィルa(Chl. a)および粒状態有機炭素(POC)・窒素(PON)・リン(PP)を測定した。筏下および対照海域(筏から100m)における沈降物の質量(SM)、炭素(SC)・窒素(SN)・リン(SP)量を測定した。筏に流入する海水の上流側と下流側での粒状物質のC:N:P比に違いはなかったが、それらの濃度には有意な違いが見られた。筏下と対照海域でのSMフラックスは大きく異なっていた。これらのことは、垂下式カキ養殖が物質の取り込みと排出という面で大きな役割を果たしていることを示している。さらに、筏での粒状物質の取り込みと排出の季節変動は大きいことがわかった。すなわち、PM、Chl. a、POC、PON、PPの取り込みは、それぞれ1.1-8.5kg DW raft-1 h-1、0.8-2.8g raft-1 h-1、6.7-43、1.3-7.0、0.09.-0.30g atom raft-1 h-1 であった。広島湾の垂下式カキ養殖による POC と Chl. a の取り込み速度は他の海域の高密度天然カキ礁やイガイ床で報告されている値と同程度である。筏下におけるSM、SC、SPの沈降フラックスは約60-1、400g DW raft-1 h-1、1、4-12、0.1-0.6、0.01-0.06g atom raft-1 h-1であった。この研究の結果は、広島湾において粒状物質の水柱からの取り込みと海底に対する負荷という点で、垂下式カキ養殖が果たしている役割が大きいことを示している。