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Applied Microbiology and Biotechnology (v.58, #4)
Myco-protein from Fusarium venenatum: a well-established product for human consumption by M. Wiebe (pp. 421-427).
Fusarium venenatum A3/5 was first chosen for development as a myco-protein in the late 1960s. It was intended as a protein source for humans and after 12 years of intensive testing, F. venenatum A3/5 was approved for sale as food by the Ministry of Agriculture, Fisheries and Food in the United Kingdom in 1984. Today, myco-protein is produced in two 150,000 l pressure-cycle fermenters in a continuous process which outputs around 300 kg biomass/h. The continuous process is typically operated for around 1,000 h. One factor which has limited the length of production runs was the appearance of highly branched mutants in the population. Several factors affect the time of appearance of such mutants and a number of strategies for delaying their appearance have been investigated. After reduction of the RNA content, the fungal biomass is mixed with egg albumin and made into a variety of products. Consumption of these can lead to reduced blood cholesterol and to lower energy intake in a subsequent meal. F. venenatum myco-protein is now used in products available in six European countries and there are plans for it to be sold in France, the United States and Germany.
An update on the use of unconventional substrates for biosurfactant production and their new applications by R. Makkar; S. Cameotra (pp. 428-434).
Biosurfactants are valuable microbial amphiphilic molecules with effective surface-active and biological properties applicable to several industries and processes. Microbes synthesize them, especially during growth on water-immiscible substrates, providing an alternative to chemically prepared conventional surfactants. Because of their structural diversity (i.e., glycolipids, lipopeptides, fatty acids, etc.), low toxicity, and biodegradability, these molecules could be widely used in cosmetic, pharmaceutical, and food processes as emulsifiers, humectants, preservatives, and detergents. Moreover, they are ecologically safe and can be applied in bioremediation and waste treatments. They can be produced from various substrates, mainly renewable resources such as vegetable oils, distillery and dairy wastes, which are economical but have not been reported in detail. In this review, we report advances made in using renewable substrates for biosurfactant production and their newer applications.
Draw-fill batch culture mode for production of xylanases by Cellulomonas flavigena on sugar cane bagasse by J. Vega-Estrada; L. Flores-Cotera; A. Santiago; I. Magaña-Plaza; C. Montes-Horcasitas (pp. 435-438).
Draw-fill culture was evaluated as a method for xylanase production by Cellulomonas flavigena on sugar cane bagasse. Specific xylanase activity and volumetric xylanase activities were measured by harvesting 50%, 55%, 60% and 70% of fermented broth at the end of each subculture. Maximum specific (64 IU mg–1 protein) and volumetric (166 IU ml–1) xylanase activities were obtained by harvesting 50–55% of broth. Values were 3.4 and 3.8 times greater than those obtained in batch cultures carried out under the same conditions. Enzyme productivity of 4.2 IU ml–1 h–1 was significantly greater than that obtained in continuous cultures (2.4 IU ml–1 h–1) (P<0.05).
Purification and characterization of a recombinant β-galactosidase with transgalactosylation activity from Bifidobacterium infantis HL96 by M.-N. Hung; B. Lee (pp. 439-445).
A β-galactosidase isoenzyme, β-GalI, from Bifidobacterium infantis HL96, was expressed in Escherichia coli and purified to homogeneity. The molecular mass of the β-GalI subunit was estimated to be 115 kDa by SDS-PAGE. The enzyme appeared to be a tetramer, with a molecular weight of about 470 kDa by native PAGE. The optimum temperature and pH for o-nitrophenyl-β-D-galactopyranoside (ONPG) and lactose were 60°C, pH 7.5, and 50°C, pH 7.5, respectively. The enzyme was stable over a pH range of 5.0–8.5, and remained active for more than 80 min at pH 7.0, 50°C. The enzyme activity was significantly increased by reducing agents. Maximum activity required the presence of both Na+ and K+, at a concentration of 10 mM. The enzyme was strongly inhibited by p-chloromercuribenzoic acid, divalent metal cations, and Cr3+, and to a lesser extent by EDTA and urea. The hydrolytic activity using lactose as a substrate was significantly inhibited by galactose. The K m and V max values for ONPG and lactose were 2.6 mM, 262 U/mg, and 73.8 mM, 1.28 U/mg, respectively. β-GalI possesses strong transgalactosylation activity. The production rate of galactooligosaccharides from 20% lactose at 30 and 60°C was 120 mg/ml, and this rate increased to 190 mg/ml when 30% lactose was used.
High production of heterologous proteins in Escherichia coli using the thermo-regulated T7 expression system by Y.-P. Chao; W.-S. Law; P. Chen; W.-B. Hung (pp. 446-453).
The exclusive use of isopropyl β-D-thiogalactopyranoside to activate the T7 promoter for protein production has limited the general use of the expression system. We have sought an alternative by constructing a recombinant Escherichia coli strain, BL21 (G2), to carry a chromosomal copy of T7 gene 1 fused to the λPL and λPR tandem promoter. As a result, the recombinant strain harboring the carbamoylase gene from Agrobacterium radiobacter NRRL B11291 was shown to display various levels of protein production in response to different degrees of heat shock. In particular, the system remained inactive at 30°C and exhibited high sensitivity to heat such that a detectable carbamoylase activity could be measured after exposure to 33°C. Moreover, heating in two steps – elevating the temperature from 30°C to 39°C and holding for a brief period, followed by reducing to 37°C – was found to be the most potent method for protein production in this case. Using this approach, the recombinant protein accounted for 20% of total protein content of the cell. These results reveal the advantages of this expression system: responsiveness to thermal modulation and high-level production capability. In an attempt to enhance the total protein yield, a fed-batch fermentation process was carried out to control the cell growth rate by adjusting the substrate inflow. By applying the two-step temperature change, a carbamoylase yield with enzyme activity corresponding to 14,256 units was obtained. This production yield is a 10-fold increase in comparison with that at the batch-fermentation scale and 2,000-fold higher than that achieved at the shake-flask scale. Overall, it illustrates the promise of the newly constructed T7 system based on heat inducibility for industrial scale production of recombinant proteins.
Transformation of the Pseudonocardiaceae Amycolatopsis sp. strain HR167 is highly dependent on the physiological state of the cells by H. Priefert; S. Achterholt; A. Steinbüchel (pp. 454-460).
The Pseudonocardiaceae Amycolatopsis sp. strain HR167 is used in a biotransformation process to produce vanillin from ferulic acid. To make this strain accessible for genetic engineering, a direct mycelium transformation system developed for Amycolatopsis mediterranei [Madon and Hütter (1991) J Bacteriol 173:6325–6331] was applied and optimized for Amycolatopsis sp. strain HR167. The physiological state of the cells had a major influence on the transformation rate. The highest transformation rate of about 7×105 transformants per microgram of DNA was obtained with mycelium harvested 6.5–7.5 h after the culture has reached the stationary growth phase. When cells were harvested outside of this time slot, the transformation rate drastically decreased. The density of the mycelium suspensions used in the transformation mixture and the methylation state of the plasmid DNA used for the transformation were also crucial parameters. With plasmid DNA isolated from Escherichia coli ET12567, transformation rates were 3,500-fold higher than those obtained with DNA isolated from E. coli XL1-Blue.
Constitutive expression of the Trichoderma reesei β-1,4-xylanase gene (xyn2) and the β-1,4-endoglucanase gene (egI) in Aspergillus niger in molasses and defined glucose media by S. Rose; W. van Zyl (pp. 461-468).
The xylanase II (xyn2)- and endoglucanase I (egI)-encoding regions of Trichoderma reesei QM6a were successfully expressed in Aspergillus niger D15 under the transcriptional control of the glyceraldehyde-6-phosphate dehydrogenase (gpd) promoter from A. niger and the glaA terminator of Aspergillus awamori. A stable xyn2 transformant produced β-xylanase activity of 8,000 nkat/ml and 5,000 nkat/ml in shake-flask cultures containing defined or 20% (v/v) molasses medium, respectively. The recombinant Xyn2 enzyme expressed highest activity at pH 5–6 and 50–60 °C and retained more than 75% of its activity after 3 h of incubation at 50 °C. A stable egI transformant produced endo-β-1,4-glucanase activity of 2,300 nkat/ml in shake-flask cultures containing defined media and about half the activity in 20% molasses medium. Maximum endoglucanase activity was obtained at pH 5 and 60 °C. Both Xyn2 and EgI retained >80% activity after incubation at 50 °C for 3 h. The heterologous Xyn2 and EgI represent a significant portion of the total extracellular proteins produced.
Identification and characterization of the AgmR regulator of Pseudomonas putida: role in alcohol utilization by H. Vrionis; A. Daugulis; A. Kropinski (pp. 469-475).
Two-phase partitioning bioreactors (TPPBs) comprise an aqueous phase containing all non-carbon nutrients necessary for microbial growth and a solvent phase containing high concentrations of inhibitory or toxic substrates that partition at sub-inhibitory levels to the aqueous phase in response to cellular demand. This work aimed at eliminating the growth of Pseudomonas putida ATCC 11172 on medium-chain-length (C8–C12) aliphatic alcohols, hence enabling their use as xenobiotic delivery solvents within two-phase partitioning bioreactors. Experiments resulted in the isolation of a mini-Tn5 mutant unable to utilize these alcohols. The mutation, which also eliminated growth on glycerol and ethanol, was identified to be within a homologue of the P. aeruginosa agmR gene, which encodes a response regulator. Enzyme analysis of the agmR::Tn5Km mutant cell extracts revealed a 10-fold decrease in pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase activity. A knockout in a gene (exaA) encoding a PQQ-linked alcohol dehydrogenase slowed but did not eliminate growth on medium-chain-length alcohols or ethanol, suggesting metabolic redundancy within P. putida ATCC 11172. Analysis of P. putida KT2440 genome sequence data indicated the presence of two PQQ-linked alcohol dehydrogenase-encoding genes. The successful elimination of alcohol utilization in the agmR mutant indicates control by AgmR on multiple pathways and presents a useful strain for biotechnological applications requiring alcohol non-utilizing microbial catalysts.
Electrically enhanced ethanol fermentation by Clostridium thermocellum and Saccharomyces cerevisiae by H. Shin; J. Zeikus; M. Jain (pp. 476-481).
Ethanol production by Clostridium thermocellum ATCC 35609 and Saccharomyces cerevisiae ATCC 26603 was improved in an electrochemical bioreactor system. It was increased by 61% with Cl. thermocellum and 12% with S. cerevisiae in the presence of –1.5 V of electric potential. These increases were attributed to high production rates due to regeneration and availability of increased reduced equivalents in the presence of electric potential. The electric current caused considerable shift in the metabolite concentrations on a molar basis in Cl. thermocellum fermentation but less in S. cerevisiae fermentation. Increasing electric potential in Cl. thermocellum fermentation resulted in less acetate and more lactate production. Acetate production was also reduced with increased electric potential in S. cerevisiae fermentation. The high electric potential of –5 V adversely affected the Cl. thermocellum fermentation, but not the S. cerevisiae fermentation even at a high electric potential of -10 V.
Growth of sulfate-reducing bacteria with solid-phase electron acceptors by O. Karnachuk; S. Kurochkina; O. Tuovinen (pp. 482-486).
Hannebachite (CaSO3·0.5H2O), gypsum (CaSO4·2H2O), anglesite (PbSO4), and barite (BaSO4) were tested as electron acceptors for sulfate-reducing bacteria with lactate as the electron donor. Hannebachite and gypsum are commonly associated with flue gas desulfurization products, and anglesite is a weathering product found in lead mines. Barite was included as the most insoluble sulfate. Growth of sulfate-reducing bacteria was monitored by protein and sulfide (dissolved H2S and HS–) measurements. Biogenic sulfide formation occurred with all four solid phases, and protein data confirmed that bacteria grew under these electron acceptor conditions. Sulfide formation from gypsum was almost comparable in rate and quantity to that produced from soluble sulfate salt (Na2SO4); hannebachite reduction to sulfide was not as fast. Anglesite as the electron acceptor was also reduced to sulfide in the solution phase and galena (PbS) was detected in solids retrieved from spent cultures. Barite as the electron acceptor supported the least amount of growth and H2S formation. The results demonstrate that low-solubility crystalline phases can be biologically reactive under reducing conditions. Furthermore, the results demonstrate that galena precipitation through sulfide production by sulfate-reducing bacteria serves as a lead enrichment mechanism, thereby also alleviating the potential toxicity of lead. In view of the role of acidophilic thiobacilli in the oxidation of sulfides, the present work accentuates the role of anaerobic and aerobic microbes in the biogeochemical cycling of solid-phase sulfates and sulfides.
Overproduction of BiP negatively affects the secretion of Aspergillus niger glucose oxidase by the yeast Hansenula polymorpha by M. van der Heide; C. Hollenberg; I. van der Klei; M. Veenhuis (pp. 487-494).
We have cloned the Hansenula polymorpha BIP gene from genomic DNA using a PCR-based strategy. H. polymorpha BIP encodes a protein of 665 amino acids, which shows very high homology to Saccharomyces cerevisiae KAR2p. KAR2p belongs to the Hsp70 family of molecular chaperones and resides in the endoplasmic reticulum (ER)-lumen. H. polymorpha BiP contains a putative N-terminal signal sequence of 30 amino acids together with the conserved –HDEL sequence, the typical ER retention signal, at the extreme C-terminus. We have analysed the effect of BIP overexpression, placing the gene under control of the strong alcohol oxidase promoter (P MOX ), on the secretion of artificially produced Aspergillus niger glucose oxidase (GOX) by H. polymorpha. BiP overproduction did not lead to any growth defects of the cells; at the subcellular level, proliferation of ER-like vesicles was observed. However, artificially enhanced BiP levels strongly affected GOX secretion and led to accumulation of this protein in the ER-like vesicles. This was not simply due to the high BiP overproduction, because it was also observed under conditions of low P MOX induction during growth of cells on glycerol. Vacuolar carboxypeptidase Y was properly sorted to its target organelle in the BiP overproducing strains.
Growth physiology and dimorphism of Mucor circinelloides (syn. racemosus) during submerged batch cultivation by M. McIntyre; J. Breum; J. Arnau; J. Nielsen (pp. 495-502).
Mucor circinelloides is being investigated as a possible host for the production of heterologous proteins. Thus, the environmental conditions defining the physiology and morphology of this dimorphic fungus have been investigated in submerged batch cultivation. The optimal conditions for growth of each form have been defined. Pure cultures of the multi-polar budding yeast form could be obtained under anaerobic conditions (with 70% N2/30% CO2 or 100% N2 as the sparge gas and without aeration). The highest maximum specific growth rate (0.30 h–1) was obtained in anaerobic cultivation; the yield of biomass on glucose (Y sx) was 0.12 (c-mole basis). A high maximum specific growth rate was obtained when the organism grew as the filamentous form under aerobic conditions (0.25 h–1), with a Y sx of 0.24 (c-mole basis). The maximum specific growth rates achieved are comparable to most industrial filamentous fungi under similar growth conditions. High levels of ethanol were observed with all growth conditions. The overriding effector of morphological development was found to be oxygen. In batch cultures it was therefore possible to induce the dimorphic shift by controlling the influent gas atmosphere. A specific growth rate of 0.19 h–1 was maintained during the shift from the yeast to the filamentous form.
Production of volatile compounds by cheese-ripening yeasts: requirement for a methanethiol donor for S-methyl thioacetate synthesis by Kluyveromyces lactis by K. Arfi; H. Spinnler; R. Tache; P. Bonnarme (pp. 503-510).
Five cheese-ripening yeasts (Geotrichum candidum, Saccharomyces cerevisiae, Kluyveromyces lactis, Yarrowia lipolytica and Debaryomyces hansenii) were compared with respect to their ability to generate volatile aroma compounds. K. lactis produced a variety of esters – ethylacetate (EA) being the major one – and relatively limited amounts of volatile sulphur compounds (VSCs). Conversely, G. candidum produced significant amounts of VSCs [with the thioester S-methyl thioacetate (MTA) being the most prevalent] and lower quantities of non-sulphur volatile compounds than K. lactis. We suspect that K. lactis is able to produce and/or accumulate acetyl CoA – a common precursor of MTA and EA – but that it produces limited amounts of methanethiol (MTL); both acetyl CoA and MTL are precursors for MTA synthesis. When supplemented with exogenous MTL, MTA production greatly increased in K. lactis cultures whereas it was unchanged in G. candidum cultures, suggesting that MTL is a limiting factor for MTA synthesis in K. lactis but not in G. candidum. Our results are discussed with respect to L-methionine catabolism.
Controlled transient changes reveal differences in metabolite production in two Candida yeasts by T. Granström; M. Leisola (pp. 511-516).
Physiological responses during growth on xylose and the xylose-degrading pathway of Candida tropicalis and Candida guilliermondii yeasts were investigated. The responses to a linearly decreasing oxygen transfer rate and a simultaneously increasing dilution rate were compared. C. guilliermondii produced acetate but no ethanol, and C. tropicalis ethanol but no acetate under oxygen limitation. Both strains produced glycerol. The D-xylose reductase of C. guilliermondii is exclusively NADPH-dependent, and acetate production regenerated NADPH. The xylose reductase of C. tropicalis has a dual dependency for both NADH and NADPH. It regenerated NAD by producing ethanol. Both strains regenerated NAD by producing glycerol. The effect of intracellular NADH accumulation to xylose uptake and metabolite production was studied by using formate as a cosubstrate. Formate feeding in C. tropicalis triggered the accumulation of glycerol, ethanol and xylitol. Consequently, the specific xylose consumption increased 28% during formate feeding, from 477 to 609 C-mmol/C-mol cell dry-weight (CDW)/h. In C. guilliermondii cultures, formate feeding resulted only in glycerol accumulation. The specific xylose consumption increased 6%, from 301 to 319 C-mmol/C-mol CDW/h, until glycerol started to accumulate.
Metabolic response against sulfur-containing heterocyclic compounds by the lignin-degrading basidiomycete Coriolus versicolor by H. Ichinose; M. Nakamizo; H. Wariishi; H. Tanaka (pp. 517-526).
The fungal conversions of sulfur-containing heterocyclic compounds were investigated using the lignin-degrading basidiomycete Coriolus versicolor. The fungus metabolized a series of sulfur compounds – 25 structurally related thiophene derivatives – via several different pathways. Under primary metabolic conditions, C. versicolor utilized thiophenes, such as 2-hydroxymethyl-, 2-formyl-, and 2-carboxyl-thiophenes, as a nutrient sulfur source for growth; thus, the fungus degraded these compounds more effectively in a non-sulfur-containing medium than in conventional medium. The product analysis revealed that several redox reactions, decarboxylation reactions, and C-S cleavage reactions were involved in the fungal conversion of non-aromatic thiophenes. On the other hand, benzothiophene (BT) and dibenzothiophene (DBT) skeletons were converted to water-soluble products. All the products and metabolic intermediates were more hydrophilic than the starting substrates. These metabolic actions seemed to be a chemical stress response against exogenously added xenobiotics. These metabolic reactions were optimized under ligninolytic conditions, also suggesting the occurrence of a fungal xenobiotic response. Furthermore, the fungus converted a series of BTs and DBTs via several different pathways, which seemed to be controlled by the chemical structure of the substrates. DBT, 4-methylDBT, 4, 6-dimethylDBT, 2-methylBT, and 7-methylBT were immediately oxidized to their S-oxides. BTs and DBTs with the hydroxymethyl substituent were converted to their xylosides without S-oxidation. Those with carboxyl and formyl substituents were reduced to form a hydroxymethyl group, then xylosidated. These observations strongly suggested the involvement of a fungal substrate-recognition and metabolic response mechanism in the metabolism of sulfur-containing heterocyclic compounds by C. versicolor.
Influence of spawn rate and commercial delayed release nutrient levels on Pleurotus cornucopiae (oyster mushroom) yield, size, and time to production by D. Royse (pp. 527-531).
Pleurotus cornucopiae 608 was grown on a mixture of pasteurized cottonseed hulls (75% dry wt), 24% chopped wheat straw, and 1% ground limestone. The substrate was spawned at various levels (1.25%, 2.5%, 3.75%, or 5% wet wt) and not supplemented or supplemented with commercial delayed release nutrient (Campbell's S-41) at various levels (0%, 3%, 6%, 9%, or 12%). Maximum yield (weight of fresh mushrooms harvested at maturity) was obtained at 3.75–5% spawn level and 6% S-41 supplement. As supplement levels exceeded 6%, yields declined significantly. There was a negative correlation (r=–0.81) between spawn rate and days to production. As the spawn rate increased, the number of days to production decreased. By using a spawn rate of 3.75% of the wet substrate wt, it was possible to reduce the time to production by a mean of 9.2 days compared with a spawn rate of 1.25%.
Interactions between photoautotrophic and heterotrophic metabolism in photoheterotrophic cultures of Euglena gracilis by J. Ogbonna; E. Ichige; H. Tanaka (pp. 532-538).
Interactions between photoautotrophic and heterotrophic metabolism in photoheterotrophic culture of Euglena gracilis were studied. Under a low light supply coefficient, these two metabolic activities seem to proceed independently. The cell growth rate in photoheterotrophic culture was about the sum of the growth rates in pure photoautotrophic and heterotrophic cultures. However under a high light supply coefficient, both photoautotrophic and heterotrophic (glucose assimilation) metabolic activities were inhibited, resulting in a low photoheterotrophic growth rate. The photoheterotrophic culture was more sensitive to photoinhibition compared to the pure photoautotrophic culture. Inhibition of glucose assimilation in the photoheterotrophic culture was due to both direct and indirect (through photosynthesis) effects of high light intensity. Cell growth, glucose assimilation and α-tocopherol content of the cells were higher when ambient air was used for aeration than when a mixture of carbon dioxide and air was used. Even when photosynthesis was inhibited by addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea to photoheterotrophic culture, light stimulated α-tocopherol synthesis by E. gracilis.
A lipoxygenase inhibitor from Aspergillus niger by K. Sekhar Rao; S. Divakar; A. Appu Rao; N. Karanth; A. Sattur (pp. 539-542).
A lipoxygenase-1 (LOX-1) inhibitor was isolated from the fermented broth of Aspergillus niger CFTRI 1105. It was purified, using column and preparative thin layer chromatography. 1H NMR and GC-MS examination revealed the structure of the inhibitor to be 2-(2′-methyl, 4′-hydroxyphenyl), 2-(4′′hydroxyphenyl)-propane with a molecular weight of 242 and the molecular formula C16H18O2. This bisphenol-derivative inhibitor shows 50% inhibition of soybean LOX-1 at 0.98 mM concentration. The activity of this inhibitor was compared with commercial bisphenol A and its structural analogues, butylhydroxyanisole and butylhydroxytoluene in an attempt to understand the role of functional groups affecting lipoxygenase activity.
Isolation of an Acinetobacter sp. ST-550 which produces a high level of indigo in a water-organic solvent two-phase system containing high levels of indole by N. Doukyu; T. Nakano; Y. Okuyama; R. Aono (pp. 543-546).
Acinetobacter sp. strain ST-550 was isolated from fumus soil as an efficient indigo producer in the presence of organic solvent. The minimum inhibitory concentration of indole was 0.4 mg/ml for ST-550. ST-550 produced only a small amount of indigo (less than 0.01 µg/ml) when grown in the presence of indole at concentrations of 0.05 to 0.3 mg/ml without any organic solvent. However, ST-550 produced indigo effectively when grown in the presence of a large volume of diphenylmethane and a high level of indole; optimized conditions were 3 ml of a medium containing 0.3 ml diphenylmethane and 2.7 mg indole. Under these conditions, ST-550 produced 0.88 mg indigo (292 µg/ml medium).
Bacillus naphthovorans sp. nov. from oil-contaminated tropical marine sediments and its role in naphthalene biodegradation by W.-Q. Zhuang; J.-H. Tay; A. Maszenan; S. Tay (pp. 547-554).
A Bacillus sp., designated as strain MN-003, was isolated as the dominant cultivatable naphthalene-degrading organism from oil-contaminated tropical marine sediments. Strain MN-003 is strictly aerobic, rod-shaped, Gram-positive, catalase positive, oxidase negative, and forms endospores. Strain MN-003 grew at salinities ranging from 0.28 to 7.00% and temperatures ranging from 15 to 41°C. Phylogenetic analyses reveal that strain MN-003 is most similar to Bacillus sp. VAN14, with a 16S rRNA sequence identity of 97.9%. Based on taxonomic and 16S rRNA data, strain MN-003 was named Bacillus naphthovorans sp. nov. When grown with naphthalene as sole carbon source, strain MN-003 had a maximal specific growth rate (µ max) of 0.32±0.03 h–1, and a half-saturation constant (K s) of 22.3±4.2 µM. A batch study of the tropical marine sediments enriched with naphthalene showed that cells of the Bacillus genus grew to become dominant members of the microbial community. The bacilli comprised 39.5±6.5% of the microbial fraction after 20 days of enrichment.