Nutrient and Energy Apparent Digestibility of Protein-Based Feed Ingredients and Effect of the Dietary Factors on Growth Performance and Feed Utilization of Sobaity Seabream, Sparidentex hasta.

Two separate feeding trials were undertaken to benchmark a series of commercial diets and determine the nutrient and energy apparent digestibility coefficients of a variety of protein-based feed ingredients when fed to sobaity seabream, Sparidentex hasta. In Experiment 1, triplicate groups of fish (initial body weight: 330.5 ± 2.6 g) were fed with one of three locally available diets containing crude protein (CP) levels ranging from 44 to 46% of dry matter (DM), each with ~12% crude fat. Fish grew at around 3.2 g day-1 with a specific growth rate (SGR) of 0.7% day-1. Both the feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly better in fish fed diets, which contained the highest (46.4%) crude protein level. Overall, the data from these preliminary studies suggest that the best performance by sobaity seabream was obtained with a diet containing 46% crude protein, 20 MJ/kg, and a protein-to-energy ratio of 23 mg/kJ. In Experiment 2, fish with an initial body weight of 319 ± 7 g were held in 11 tanks and fed reference (D1) and test diets (D2-D11) for 7 days before fecal collection. This process was repeated twice in a blocking arrangement to generate three replicates. Each of the ten test diets contained 30% of a test ingredient, with the remaining 70% proportionally identical to the D1 diet. Diet apparent digestibility coefficients (ADCs) were measured, and the diet ADCs were then used to derive the protein and energy ADCs for the individual test ingredients. Ingredient protein ADC ranged between 75.5 and 93.9%, while ingredient energy ADC ranged between 66.8 and 81.2%.

Biosynthetic multitasking facilitates thalassospiramide structural diversity in marine bacteria.

Thalassospiramides A and B are immunosuppressant cyclic lipopeptides first reported from the marine α-proteobacterium Thalassospira sp. CNJ-328. We describe here the discovery and characterization of an extended family of 14 new analogues from four Tistrella and Thalassospira isolates. These potent calpain 1 protease inhibitors belong to six structure classes in which the length and composition of the acylpeptide side chain varies extensively. Genomic sequence analysis of the thalassospiramide-producing microbes revealed related, genus-specific biosynthetic loci encoding hybrid nonribosomal peptide synthetase/polyketide synthases consistent with thalassospiramide assembly. The bioinformatics analysis of the gene clusters suggests that structural diversity, which ranges from the 803.4 Da thalassospiramide C to the 1291.7 Da thalassospiramide F, results from a complex sequence of reactions involving amino acid substrate channeling and enzymatic multimodule skipping and iteration. Preliminary biochemical analysis of the N-terminal nonribosomal peptide synthetase module from the Thalassospira TtcA megasynthase supports a biosynthetic model in which in cis amino acid activation competes with in trans activation to increase the range of amino acid substrates incorporated at the N terminus.

Bacterial biosynthesis and maturation of the didemnin anti-cancer agents.

The anti-neoplastic agent didemnin B from the Caribbean tunicate Trididemnum solidum was the first marine drug to be clinically tested in humans. Because of its limited supply and its complex cyclic depsipeptide structure, considerable challenges were encountered during didemnin B's development that continue to limit aplidine (dehydrodidemnin B), which is currently being evaluated in numerous clinical trials. Herein we show that the didemnins are bacterial products produced by the marine α-proteobacteria Tistrella mobilis and Tistrella bauzanensis via a unique post-assembly line maturation process. Complete genome sequence analysis of the 6,513,401 bp T. mobilis strain KA081020-065 with its five circular replicons revealed the putative didemnin biosynthetic gene cluster (did) on the 1,126,962 bp megaplasmid pTM3. The did locus encodes a 13-module hybrid non-ribosomal peptide synthetase-polyketide synthase enzyme complex organized in a collinear arrangement for the synthesis of the fatty acylglutamine ester derivatives didemnins X and Y rather than didemnin B as first anticipated. Imaging mass spectrometry of T. mobilis bacterial colonies captured the time-dependent extracellular conversion of the didemnin X and Y precursors to didemnin B, in support of an unusual post-synthetase activation mechanism. Significantly, the discovery of the didemnin biosynthetic gene cluster may provide a long-term solution to the supply problem that presently hinders this group of marine natural products and pave the way for the genetic engineering of new didemnin congeners.

Culture-dependent bacteria in commercial fishes: Qualitative assessment and molecular identification using 16S rRNA gene sequencing.

Fish contamination has been extensively investigated along the Saudi coasts, but studies pertaining to bacterial pathogens are scarce. We conducted qualitative assessment and molecular identification of culture-dependent bacteria in 13 fish species from three coastal sites and a local fish market in Jeddah, Saudi Arabia. Bacterial counts of gills, skin, gut and muscle were examined on agar plates of Macconkey's (Mac), Eosin Methylene Blue (EMB) and Thiosulfate Citrate Bile Salts (TCBS) culture media. Bacterial counts significantly differed between species, sources and feeding habits of examined fishes. Mugil cephalus exhibited higher counts on TCBS (all body parts), Mac (gills, muscle and gut) and EMB (gills and muscle). Fishes from Area I had higher bacterial loads, coinciding with those in seawater and sediment from the same site, indicating direct association between habitat conditions and the levels of bacterial contamination. By feeding habit, detritivorous fish harbored higher counts than herbivorous and carnivorous species. Bacterial counts of skin were higher in fish from market than field sites, and positively correlated with other body parts indicating the relation of surface bacterial load on the overall quality of fish. Rahnella aquatilis (Enterobacteriaceae) and Photobacterium damselae (Vibrionaceae) were among the dominant species from fish muscle based on 16S rRNA sequencing. These species are known human pathogens capable of causing foodborne illness with severe antibiotic resistance. Opportunistic pathogens, e.g. Hafnia sp. (Enterobacteriaceae) and Pseudomonas stutzeri (Pseudomonadaceae) also occurred in fish muscle. The inclusion of bacterial contamination in future monitoring efforts is thus crucial.