Virus Production and Lysate Recycling in Different Sub-basins of the Northern Baltic Sea

In the Gulf of Bothnia, northern Baltic Sea, a large freshwater inflow creates north-southerly gradients in physico-chemical and biological factors across the two sub-basins, the Bothnian Bay (BB) and the Bothnian Sea. In particular, the sub-basins differ in nutrient limitation (nitrogen vs. phosphorus; P). Since viruses are rich in P, and virus production is commonly connected with bacterial abundance and growth, we hypothesized that the role of viral lysis differs between the sub-basins. Thus, we examined virus production and the potential importance of lysate recycling in surface waters along a transect in the Gulf of Bothnia. Surprisingly, virus production and total P were negatively correlated. In the BB, virus production rates were double those elsewhere in the system, although bacterial abundance and production were the lowest. In the BB, virus-mediated cell lysates could account for 70-180% and 100-250% of the bacterial carbon and P demand, respectively, while only 4-15% and 8-21% at the other stations. Low concentrations of dissolved DNA (D-DNA) with a high proportion of encapsulated DNA (viruses) in the BB suggested rapid turnover and high uptake of free DNA. The correlation of D-DNA and total P indicates that D-DNA is a particularly important nutrient source in the P-limited BB. Our study demonstrates large and counterintuitive differences in virus-mediated recycling of carbon and nutrients in two basins of the Gulf of Bothnia, which differ in microbial community composition and nutrient limitation.     

Higher abundance of bacteria than of viruses in deep Mediterranean sediments

The interactions between viral abundance and bacterial density, biomass, and production were investigated along a longitudinal transect consisting of nine deep-sea stations encompassing the entire Mediterranean basin. The numbers of viruses were very low (range, 3.6 x 10(7) to 12.0 x 10(7) viruses g(-1)) and decreased eastward. The virus-to-bacterium ratio was always < 1.0, indicating that the deep-sea sediments of the Mediterranean Sea are the first example of a marine ecosystem not numerically dominated by viruses. The lowest virus numbers were found where the lowest bacterial metabolism and turnover rates and the largest cell size were observed, suggesting that bacterial doubling time might play an important role in benthic virus development.     

THE NORTHEASTERN ALBORAN SEA, AN IMPORTANT BREEDING AND FEEDING GROUND FOR THE LONG-FINNED PILOT WHALE (GLOBICEPHALA MELAS) IN THE MEDITERRANEAN SEA

Little is known about the long-finned pilot whale's population size, structure, distribution, and dynamics in the Western Mediterranean basin. The research region covered since 1992 in southeast Spain, at the edge of the Alboran Sea, is considered an important oceanographic transition zone between the Mediterranean and the Atlantic Ocean. The research ship Toftevaag carried out surveys covering a total of 10,173 nmi (18,840 km) from April to September each year, 1992-1997, all years pooled. Effort for ten-by-ten-mile quadrants was stratified by depth and sea state to ascertain encounter rates. Tracking was used together with photo-identification of animals to analyze home range of groups. Behavior was recorded ad libitum , and underwater video taping was used to analyze specific behavior patterns. One hundred and nine sightings of pilot whales were made. The average group size was 41.4 ± 58.4, ranging from 1 to 350. The average depth at encounters was 848.7 ± 281.2 m ranging from 300 to 1,800 m. Compatison of results for encounter rate and group size with those for other Mediterranean regions, together with site fidelity shown by photo-identification and observations of reproductive behavior, reflect the importance of the Alboran Sea to the species in the Mediterranean.     

Effects of fish farming on microbial enzyme activities and densities: comparison between three Mediterranean sites

AIM: The effects of fish farming on microbial enzyme activities and heterotrophic bacterial density were investigated in three Mediterranean sites before and after the start of mariculture. METHODS AND RESULTS: Microbial activities were measured on water and sediment samples by using fluorogenic substrates specific for leucine aminopeptidase, beta-glucosidase and alkaline phosphatase (AP); bacterial counts were determined by Marine agar plates. SIGNIFICANCE AND IMPACT OF THE STUDY: Comparison of activity and abundance values obtained before and after the experiment showed that fish farming mainly affected the levels of microbial activities; they were significantly enhanced both in water and sediments, reaching an increase of 183.66 times for AP in Castellammare Gulf. After mariculture, no significant variations were recorded in heterotrophic bacterial density in the waters, while significant changes were observed in the sediments. Effects induced appeared to be extended not only to stations in which cages were located, but also to control sites far from the direct influence of fish farming.     

Cloning and characterization of a Pseudomonas aeruginosa gene involved in the negative regulation of phosphate taxis.

Pseudomonas aeruginosa PAO1 exhibited a positive chemotactic response to P(i). The chemotactic response was induced by P(i) limitation. An alkaline phosphatase (AP) constitutive mutant showed a chemotactic response to P(i), regardless of whether the cells were starved for P(i). Sequence analysis and complementation studies showed that the P. aeruginosa phoU gene was involved both in the regulation of AP expression and in the induction of P(i) taxis. However, unlike AP expression, P(i) taxis was not regulated by the phoB gene product.     

Fueling Plankton Production by a Meandering Frontal Jet: A Case Study for the Alboran Sea (Western Mediterranean)

A three dimensional biophysical model was employed to illustrate the biological impacts of a meandering frontal jet, in terms of efficiency and persistency of the autotrophic frontal production, in marginal and semi-enclosed seas. We used the Alboran Sea of the Western Mediterranean as a case study. Here, a frontal jet with a width of 15–20 km, characterized by the relatively low density Atlantic water mass, flows eastward within the upper 100 m as a marked meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of a strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates phytoplankton growth along the jet. Biological production is larger in the western part of the basin and decreases eastwards with the gradual weakening of the jet. The higher production at the subsurface levels suggests that the Alboran Sea is likely more productive than predicted by the satellite chlorophyll data. The Mediterranean water mass away from the jet and the interiors of the western and eastern anticyclonic gyres remain unproductive.     

Enzymatic Activities and Prokaryotic Abundance in Relation to Organic Matter along a West–East Mediterranean Transect (TRANSMED Cruise)

The distribution of extracellular enzymatic activities (EEA) [leucine aminopeptidase (LAP), ?-glucosidase (GLU), alkaline phosphatase (AP)], as well as that of prokaryotic abundance (PA) and biomass (PB), dissolved organic carbon (DOC), particulate organic carbon and particulate total nitrogen (POC, PTN), was determined in the epi-, meso-, and bathypelagic waters of the Mediterranean Sea along a West-East transect and at one Atlantic station located outside the Strait of Gibraltar. This study represents a synoptical evaluation of the microbial metabolism during early summer. Decreasing trends with depth were observed for most of the parameters (PA, PB, AP, DOC, POC, PTN). Significant differences between the western and eastern basins of the Mediterranean Sea were found, displaying higher rates of LAP and GLU and lower C/N ratios more in the eastern than in the western areas. Conversely, in the epipelagic layer, PA and PB were found to be higher in the western than in the eastern basins. PB was significantly related to DOC concentration (all data, n = 145, r = 0.53, P < 0.01), while significant correlations of EEA with POC and PTN were found in the epipelagic layer, indicating an active response of microbial metabolism to organic substrates. Specific enzyme activities normalized to cell abundance pointed out high values of LAP and GLU in the bathypelagic layer, especially in the eastern basin, while cell-specific AP was high in the epi- and bathypelagic zone of the eastern basin indicating a rapid regeneration of inorganic P for both prokaryotes and phytoplankton needs. Low activity and abundance characterized the Atlantic station, while opposite trends of these parameters were observed along the Mediterranean transect, showing the uncoupling between abundance and activity data. In the east Mediterranean Sea, decomposition processes increased probably in response to mesoscale structures which lead to organic matter downwelling.     

Nutrient Utilization Strategies of Algae and Bacteria after the Termination of Nutrient Amendment with Different Phosphorus Dosage: A Mesocosm Case

The impacts of nutrient amendment termination on the growth strategies of algae and bacteria were conducted in experimentally designed mesocosm in which two different phosphorus (P) dosages were treated. The algal community composition did not change greatly in Group A (low phosphorus) and Group B (high phosphorus). In Group A, the secretion of bacterial alkaline phosphatase (AP) after nutrient termination stimulated bacterial phosphorus acquisition, which caused the decrease in algal phosphorus levels, in terms of the increase of bacterial abundance and bacterial production, as well as the decrease in chlorophyll a and particulate organic carbon. The algal collapse resulted in dissolved organic carbon secretion, further fuelling bacterial growth. In Group B, excess phosphorus input urged algae to store phosphorus as poly-phosphate. When phosphorus input ceased, in order to maintain their used high phosphorus demand, algae strengthened to gain phosphorus through the hydrolysis of dissolved organic phosphorus in water column and ploy-phosphate inside the cells by AP, evidenced by high algal alkaline phosphatase activity, algal growth continuation, and bacterial growth decline. These facts indicated that phosphorus content should reduce to a lower level than expected, so that algal bloom can be effectively controlled in eutrophic water bodies.     

Higher Abundance of Bacteria than of Viruses in Deep Mediterranean Sediments

The interactions between viral abundance and bacterial density, biomass, and production were investigated along a longitudinal transect consisting of nine deep-sea stations encompassing the entire Mediterranean basin. The numbers of viruses were very low (range, 3.6 × 10⁷ to 12.0 × 10⁷ viruses g⁻¹) and decreased eastward. The virus-to-bacterium ratio was always < 1.0, indicating that the deep-sea sediments of the Mediterranean Sea are the first example of a marine ecosystem not numerically dominated by viruses. The lowest virus numbers were found where the lowest bacterial metabolism and turnover rates and the largest cell size were observed, suggesting that bacterial doubling time might play an important role in benthic virus development.     

Metazoan parasites on the gills of the skipjack tuna Katsuwonus pelamis (Osteichthyes: Scombridae) from the Alboran Sea (western Mediterranean Sea)

The gills of 31 skipjack tuna Katsuwonus pelamis (L.) caught in the Alboran Sea (western Mediterranean Sea) were examined for metazoan parasites, and the gills of 4 specimens from the Balearic Sea (also western Mediterranean Sea) were analysed for comparative purposes. Nine -species of parasites were found, including 8 didymozoid trematodes (Atalostrophion cf. bio-varium, Didymocylindrus filiformis, Didymocylindrus simplex, Didymocystis reniformis, Didymoproblema fusiforme, Didymozoon longicolle, Koellikeria sp. and Lobatozoum multisacculatum) and 1 caligid copepod (Caligus bonito). Koellikeria sp. and L. multisacculatum were not recorded in the Balearic Sea. Most of the parasites (79.2% of all specimens) were didymozoids. Didymozoon longicolle was the dominant species; A. cf. biovarium, D. simplex, D. fusiforme and L. multisacculatum are reported from the Mediterranean Sea for the first time. No correlation was found between the intensity of infection of any parasite species and host size or sex. Most of the parasites, particularly didymozoids, showed a high site-specificity. Significant differences were found between the parasite assemblages of K. pelamis from the Alboran Sea and from the Atlantic Ocean. D. fusiforme, D. longicolle and L. multisacculatum are suggested as potential tags to follow skipjack tuna migrations between the Atlantic Ocean and Mediterranean Sea.     

Distribution of virus-like Particles in an Oligotrophic Marine Environment (Alboran Sea,Western Mediterranean)

Viruses are abundant in a variety of aquatic environments, often exceeding bacterial abundance by one order of magnitude. In the present study, the spatial distribution of viruses in offshore waters of the Alboran Sea (Western Mediterranean) have been studied to determine the relationships between viruses and host communities in this oligotrophic marine environment. Viral abundance was determined using two methods: (i) epifluorescence light microscopy using the dsDNA binding fluorochrome DAPI, and (ii) direct counts by transmission electron microscopy (TEM). The results obtained were significantly different; the highest viral counts were obtained by mean of TEM analyses. In all the samples tested the number of viruses was exceeded by the bacterial concentrations, with a ratio between viral and bacterial titers varying between 1.4 and 20. VLP (virus-like particle) counts were not significantly correlated (p > 0.001) with chlorophyll a concentration or the abundance of cyanobacteria. However, there was a positive and significant correlation with bacterial abundance (p < 0.001). The analysis of size and morphology of viral particles by TEM and the correlation obtained between the numbers of VLP and bacteria suggest that the majority of the viral particles in the Alboran Sea are bacteriophages. None of the indirect evidence suggested that eukaryotic algae or cyanobacteria were important host organisms in these waters.     

Diversity and structure of pelagic copepod populations in the frontal zone of the eastern Alboran sea

During the oceanographic campaign, ALMOFRONT I (April 24–May 26, 1991) a total of 50 vertical zooplankton hauls was carried out in the Alboran Sea using a triple net. Leg A (18 stations; 18 hauls) described a widely spaced grid in the region of the Atlantic current and some northern eddies, while Leg B (16 stations; 32 hauls, 6 hydrodynamically characterized sites sampled during a two day period) covered a more restricted area in the frontal zone. Ninety-one species of copepods were found in 100 samples collected by either 200 µm or 500 µm mesh size nets, including 32 genera and 26 families. Copepod abundance, structure indexes (species richness, evenness, Shannon species diversity index, standardized for unequal sample counts) and species abundance patterns (as rank-frequency diagrams) are presented and compared among the sites of leg-B. Copepod abundance was found to be the highest in the more productive sites of the Atlantic current. Structure indexes values and the changing shape of rank-frequency diagrams give a coherent view of the ecological succession stages of the copepod community. Juvenile stage (1) develops from the Atlantic divergence zone, left side of the jet. More mature stages (1 and 2) occur on the right side of the jet influenced by cross frontal flow. Both abundance and structure indexes decrease within an anticyclonic gyre south to the current. A situation more influenced by oligotrophic conditions was observed in a Mediterranean anticyclonic gyre north of the current. The importance of lateral displacement and meandering of the Atlantic current across the Alboran Sea to the community structure is discussed.     

Light conditions affect the measurement of oceanic bacterial production via leucine uptake

The effect of irradiance in the range of 400 to 700 nm or photosynthetically active radiation (PAR) on bacterial heterotrophic production estimated by the incorporation of 3H-leucine (referred to herein as Leu) was investigated in the northwestern Mediterranean Sea and in a coastal North Atlantic site, with Leu uptake rates ranging over 3 orders of magnitude. We performed in situ incubations under natural irradiance levels of Mediterranean samples taken from five depths around solar noon and compared them to incubations in the dark. In two of the three stations large differences were found between light and dark uptake rates for the surface most samples, with dark values being on average 133 and 109% higher than in situ ones. Data obtained in coastal North Atlantic waters confirmed that dark enclosure may increase Leu uptake rates more than threefold. To explain these differences, on-board experiments of Leu uptake versus irradiance were performed with Mediterranean samples from depths of 5 and 40 m. Incubations under a gradient of 12 to 1,731 micromol of photons m(-2) x s(-1) evidenced a significant increase in incorporation rates with increasing PAR in most of the experiments, with dark-incubated samples departing from this pattern. These results were not attributed to inhibition of Leu uptake in the light but to enhanced bacterial response when transferred to dark conditions. The ratio of dark to light uptake rates increased as dissolved inorganic nitrogen concentrations decreased, suggesting that bacterial nutrient deficiency was overcome by some process occurring only in the dark bottles.     

RANGE EXTENSION OF CUTLERIA HANCOCKII (CUTLERIALES; PHAEOPHYTA) TO THE SOUTHWESTERN GULF OF CALIFORNIA, MÉXICO

A new method was utilized to study species-specific responses of phytoplankton to phosphorus limitation in a nutrient enrichment experiment. A substrate, ELF, produces a fluorescent precipitate at the sites of alkaline phosphatase (AP), which makes it possible to visually detect phosphorus (P) limitation in individual cells of multiple species. Lake water was incubated in the laboratory to induce nitrogen (N) or P limitation. Initially, little or no ELF labeling was observed for any of the phytoplankton species, indicating a general lack of P limitation. This observation was supported by low bulk AP activity in the initial field samples. During the experiment, several chlorophyte taxa ( Coelastrum , Eudorina , a solitary spiny coccoid) were driven to P limitation, as evidenced by a high percentage of cells displaying ELF labeling when inorganic N was added. Taxa such as Actinastrum and Dictyosphaerium , on the contrary, were never P limited. Little or no ELF was observed in cyanobacterial species, suggesting that P limitation was not achieved in these organisms. Using traditional bulk AP activity, significantly higher levels of AP activity were observed in treatments with inorganic N additions, compared to those with phosphate additions. ELF labeling generally followed the trend of bulk AP, except in species that did not dominate the biomass. Finally, we noted that all species observed were ELF labeled at least on one occasion, except for fragile flagellates which did not withstand the labeling procedure.     

Mammalian intestinal alkaline phosphatase acts as highly active exopolyphosphatase.

Recent results revealed that inorganic polyphosphates (polyP), being energy-rich linear polymers of orthophosphate residues known from bacteria and yeast, also exist in higher eukaryotes. However, the enzymatic basis of their metabolism especially in mammalian cells is still uncertain. Here we demonstrate for the first time that alkaline phosphatase from calf intestine (CIAP) is able to cleave polyP molecules up to a chain length of about 800. The enzyme acts as an exopolyphosphatase degrading polyP in a processive manner. The pH optimum is in the alkaline range. Divalent cations are not required for catalytic activity but inhibit the degradation of polyP. The rate of hydrolysis of short-chain polyP by CIAP is comparable to that of the standard alkaline phosphatase (AP) substrate p-nitrophenyl phosphate. The specific activity of the enzyme decreases with increasing chain length of the polymer both in the alkaline and in the neutral pH range. The K(m) of the enzyme also decreases with increasing chain length. The mammalian tissue non-specific isoform of AP was not able to hydrolyze polyP under the conditions applied while the placental-type AP and the bacterial (Escherichia coli) AP displayed polyP-degrading activity.     

SPECIES‐SPECIFIC RESPONSE IN ALKALINE PHOSPHATASE ACTIVITY OF FRESHWATER PHYTOPLANKTON IN A NUTRIENT ENRICHMENT EXPERIMENT

A new method was utilized to study species‐specific responses of phytoplankton to phosphorus limitation in a nutrient enrichment experiment. A substrate, ELF, produces a fluorescent precipitate at the sites of alkaline phosphatase (AP), which makes it possible to visually detect phosphorus (P) limitation in individual cells of multiple species. Lake water was incubated in the laboratory to induce nitrogen (N) or P limitation. Initially, little or no ELF labeling was observed for any of the phytoplankton species, indicating a general lack of P limitation. This observation was supported by low bulk AP activity in the initial field samples. During the experiment, several chlorophyte taxa (Coelastrum, Eudorina, a solitary spiny coccoid) were driven to P limitation, as evidenced by a high percentage of cells displaying ELF labeling when inorganic N was added. Taxa such as Actinastrum and Dictyosphaerium, on the contrary, were never P limited. Little or no ELF was observed in cyanobacterial species, suggesting that P limitation was not achieved in these organisms. Using traditional bulk AP activity, significantly higher levels of AP activity were observed in treatments with inorganic N additions, compared to those with phosphate additions. ELF labeling generally followed the trend of bulk AP, except in species that did not dominate the biomass. Finally, we noted that all species observed were ELF labeled at least on one occasion, except for fragile flagellates which did not withstand the labeling procedure.     

Is dinitrogen fixation significant in the Levantine Basin,East Mediterranean Sea?

We report N(2) fixation rates measured from two stations monitored monthly off the Mediterranean coast of Israel during 2006 and 2007, and along a transect from Israel to Crete in September 2008. Analyses of time-series data revealed expression of nifH genes from diazotrophs in nifH clusters I and II, including cyanobacterial bloom-formers Trichodesmium and diatom-Richelia intracellularis associations. However, nifH gene abundance and rates of N(2) fixation were very low in all size fractions measured (> 0.7 μm). Volumetric (15) N uptake ranged from below detection (～ 36% of > 300 samples) to a high of 0.3 nmol N l(-1) d(-1) and did not vary distinctly with depth or season. Areal N(2) fixation averaged ～ 1 to 4 μmol N m(-2) d(-1) and contributed only ～ 1% and 2% of new production and ～ 0.25% and 0.5% of primary production for the mixed (winter) and stratified (spring-fall) periods respectively. N(2) fixation rates along the 2008 east-west transect were also extremely low (0-0.04 nmol N l(-1) d(-1), integrated average 2.6 μmol N m(-2) d(-1) ) with 37% of samples below detection and no discernable difference between stations. We demonstrate that diazotrophy and N(2) fixation contribute only a minor amount of new N to the P impoverished eastern Mediterranean Sea.     

Phylogeography of the marine isopod Stenosoma nadejda (Rezig, 1989) in North African Atlantic and western Mediterranean coasts reveals complex differentiation patterns and a new species

The transition zone between the Mediterranean and Atlantic basins has been extensively addressed in phylogeographical studies of marine species. However, biases exist towards the analysis of highly dispersive species, and there is a higher sampling effort in European coasts compared to North Africa. This may be hindering a detailed understanding of the historical and contemporary processes that shaped patterns of population genetic structure in the region. In the present study, we investigated the phylogeographical and phylogenetic patterns of mitochondrial cytochrome c oxidase subunit I sequences from a species with direct development and low dispersal abilities, Stenosoma nadejda (Rezig, 1989). The study area included 13 localities along the Atlantic and Mediterranean North African coasts, as well as the Alboran Sea. A new Stenosoma species, from the coasts of Algeria and Alboran Island, was discovered. For S. nadejda, phylogeographical analyses revealed three distinct clades: one in the Iberian Atlantic plus the Alboran Sea, one in the western Mediterranean, and another in the Atlantic coast of Africa. Haplotypes from the Alboran Island were more related to those from the western Mediterranean coast (east of the Almeria–Oran Front). Given the strong differentiation, it is probable that this species survived in multiple glacial refugia during the Pleistocenic glaciations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 419–431.     

供磷水平和根际效应协同影响含碱性磷酸酶基因细菌群落的网络复杂性和稳定性北大核心

【目的】通过研究长期不同供磷水平下根际、土体土壤中编码碱性磷酸酶基因(alkaline phosphatase gene,phoD)细菌群落特征、网络复杂性、群落的稳定性及其与磷酸酶活性之间的关系,揭示供磷水平和根际效应在调控土壤有机磷矿化中的微生物学机制。【方法】选取华北平原长期施磷的小麦-玉米轮作体系石灰性土壤为基质土壤,开展根箱试验。选取的试验处理包括3个供磷水平,分别是0、50.0、200.0 kg P/hm^(2)(分别表示为P0、P50、P200)。玉米种子播种30 d后,采集玉米的根际土和土体土。采用高通量测序技术分析根际和土体土壤中编码碱性磷酸酶基因(phoD)细菌群落,探究施肥及根际效应对含phoD基因细菌的群落特征、网络特征的影响及其与磷酸酶活性的关系。【结果】随着施磷量的增加,速效磷(available P,AP)和碱性磷酸酶(alkaline phosphatase,ALP)活性在根际、土体土壤中均显著提高,且两者呈显著正相关。phoD基因丰度在P0、P200处理的根际土壤中显著高于土体土壤。含phoD基因细菌群落的α多样性在P50处理下的根际土壤显著高于土体土壤。冗余分析(redundancy analysis,RDA)表明,土壤中AP、有机磷(organic P,Po)和全磷(total P,Pt)是影响微生物群落的主要因素。与不施磷处理(P0)相比,施磷处理(P50、P200)下根际土壤中网络节点数和连接数降低,而土体土壤中网络节点数和连接数增加;同时,施磷处理含phoD基因细菌群落的鲁棒性(robustness)在根际土壤中显著提高,而在土体土壤中显著降低。Mantel检验表明,含phoD基因微生物群落中的优势物种在根际土壤与AP、酸性磷酸酶(acid phosphatase,ACP)、内聚力(cohesion)和网络的鲁棒性显著相关,在土体土壤中无显著性。【结论】供磷水平及根际效应协同影响phoD基因丰度、含phoD基因细菌群落的α多样性、群落结构、优势物种、网络的复杂性及群落的稳定性,进而影响磷酸酶活性,调控了土壤中有机磷的矿化。     

Experimental evidence for interactions between bacterial peptidase and alkaline phosphatase activity in the Baltic Sea

From the observed pattern of aminopeptidase and alkaline phosphatase activities in the Baltic Sea, the question arose whether there is an interaction between the activities of both enzymes. In experiments with 0.8 m filtered seawater, the effects of commercial alkaline phosphatase on bacterial aminopeptidase, the effects of commercial peptidase on bacterial alkaline phosphatase activity (APA), and the effects of proteins, carbohydrates and inorganic nutrients on the activities of both enzymes were investigated.Addition of commercial alkaline phosphatase stimulated bacterial aminopeptidase activity and, similarly, the addition of commercial peptidase increased the APA in bacteria. The proteins, albumin and casein, stimulated aminopeptidase activity and APA simultaneously. Experiments using ammonium and glucose suggested that stimulation of APA by peptidase could be mediated by nitrogen and carbon availability. There were also some indications that stimulation of aminopeptidase activity by alkaline phosphatase functioned by catalysing phosphate release from organic phosphorus compounds.