Fue estudiada la comunidad bacteriana del Mar Jónico mediante el análisis directo en epifluorescencia (recuentos, morfometría y biovolumen celular) y la determinación del contenido de lipopolisacáridos (LPS). Los microorganismos fueron agrupados en cinco morfotipos: cocos, bacilos, cocobacilos, vibriones y espirilos. La columna de agua se encontró dominada por formas cocoideas (39-73%); las formas bacilares y cocobacilares representaron morfotipos uniformemente distribuidos mientras la presencia de vibriones resultó ser muy variable y los espirilos prácticamente ausentes por debajo de los 100 m de profundidad. Los contenidos de LPS fueron encontrados estrechamente correlacionados con los recuentos celulares (P<0,01; n=88; r=68) y sin relación significativa alguna con los biovolúmenes totales de las muestras. El contenido medio de LPS por ?m3 celular resultó ser de 3,11 (± 1,35) ng en las muestras provenientes de la zona fótica y de 0,96 (± 0,37) ng en las muestras provenientes de la zona afótica. El contenido medio de C por célula calculado a partir del contenido medio de LPS resultó ser de 23 fg C célula-1 siendo similar al calculado a partir del volumen celular (19 fg C célula-1); las biomasas celulares calculadas a partir de ambos parámetros (LPS y volumen celular) resultaron estar significativamente correlacionadas (P<0,01; n=95; r=0,59). Del análisis de nuestros resultados surge que el contenido medio de 20 fg C célula-1 (Lee and Furhman, 1987), utilizado ampliamente en la determinación de la biomasa bacteriana marina, podría ser utilizado en línea de máxima también en el Mar Jónico. No obstante, la amplia variabilidad morfológica-dimensional de las células bacterianas observadas, frecuentemente en una misma columna de agua, cuestionan firmemente el empleo de un único factor de conversión en el estudio de todos los ecosistemas marinos. En consecuencia, resulta esencial el análisis de la biomasa bacteriana en cada ambiente en particular para lograr una visión más precisa de los flujos de los principales bioelementos en el ecosistema.
The abundance, morphotypes and biomass of the bacterial assemblages were investigated in the Ionian Sea by using two different methods: the epifluorescent microscopy technique for enumerating and sizing bacterial cells, and the determination of bacterial lipopolysaccharides (LPS). Five bacterial morphotypes were distinguished: cocci, rods, coccobacilli, vibrios and spirillae. The proportions of cocci were higher than those of other morphotypes at every depth, ranging from 39% to 73%. Both rod-shaped bacteria and coccobacilli were homogenously distributed in the water column, while the proportions of vibrios were rather variable. Spirillae occurred only in surface samples and disappeared below 100 m. The two methodologies were compared: LPS concentrations showed a highly significant correlation with the bacterial numbers (P<0.01; n= 88; r= 0.68), but not with biovolumes, and different ratios between LPS concentrations and bacterial volumes were recorded for the photic and aphotic zones (3.11 ± 1.35 and 0.96 ± 0.37 ng LPS per ?m3 respectively). LPS-derived cell carbon content on average was 23 fg C cell-1, similar to the C amount derived by mean cell biovolume (19 fg C cell-1) and the biomass from two highly correlated methods (P < 0.01; n= 95; r= 0.59). Our results confirm that the widely used factor of 20 fg C cell-1 (Lee and Furhman, 1987) should be plausible for studying the biomass of the natural microbial populations in the study area. Nevertheless, the wide variability of the cell size classes, also along the whole water columns, questions the applicability of a constant conversion factor for all the marine ecosystems. Consequently, locally derived biomass estimates of bacteria are essential in order to obtain an accurate evaluation of the bacterial role in biogeochemical cycles.
Morphology and LPS content for the estimation of marine bacterioplankton biomass in the Ionian Sea.
La Ferla R;Maimone G
2004
Abstract
The abundance, morphotypes and biomass of the bacterial assemblages were investigated in the Ionian Sea by using two different methods: the epifluorescent microscopy technique for enumerating and sizing bacterial cells, and the determination of bacterial lipopolysaccharides (LPS). Five bacterial morphotypes were distinguished: cocci, rods, coccobacilli, vibrios and spirillae. The proportions of cocci were higher than those of other morphotypes at every depth, ranging from 39% to 73%. Both rod-shaped bacteria and coccobacilli were homogenously distributed in the water column, while the proportions of vibrios were rather variable. Spirillae occurred only in surface samples and disappeared below 100 m. The two methodologies were compared: LPS concentrations showed a highly significant correlation with the bacterial numbers (P<0.01; n= 88; r= 0.68), but not with biovolumes, and different ratios between LPS concentrations and bacterial volumes were recorded for the photic and aphotic zones (3.11 ± 1.35 and 0.96 ± 0.37 ng LPS per ?m3 respectively). LPS-derived cell carbon content on average was 23 fg C cell-1, similar to the C amount derived by mean cell biovolume (19 fg C cell-1) and the biomass from two highly correlated methods (P < 0.01; n= 95; r= 0.59). Our results confirm that the widely used factor of 20 fg C cell-1 (Lee and Furhman, 1987) should be plausible for studying the biomass of the natural microbial populations in the study area. Nevertheless, the wide variability of the cell size classes, also along the whole water columns, questions the applicability of a constant conversion factor for all the marine ecosystems. Consequently, locally derived biomass estimates of bacteria are essential in order to obtain an accurate evaluation of the bacterial role in biogeochemical cycles.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
